Schematic for the QRM-180 Version 3.41

 I finally found a jpeg of the schematic for the QRM-180.. here it is:

                 SB-220/221 CONTROL BOARD                               V03

Heath started selling kits in 1947 and the HeathKits were a wonderful way to get equipment that would otherwise have been too expensive to own.  And the kits were easy and fun to build.  The compromise was that HeathKit often had to omit some less-than-vital features to keep it simple enough to build and to keep the costs down.  For those products that have are still useful today, there is a long list of upgrades, improvements and suggestions in magazines and on the internet.

In 1972 Heath was already building a very popular array of amateur radio equipment. The SB-220 was perhaps their best, and most enduring piece of ham radio gear.  It was later superseded by the functionally identical but prettier, HW-2200.  The AG6YJ Control Board combines a number of the popular SB-220 upgrades on a single pc board and does a bit to clean up the underside of the amp as well.  I like to think that this is the way that the Heath engineers would have done it, given the budget.

Adds Soft Start
The board adds a “soft start” to the power circuit to gradually power up the amp.  Sure, the 3-500 tubes are instant on (and the filament transformer does its bit to limit starting current) but the other components still take a hit on power up.  The later, HL-2200 version of the SB-220 is known to regularly burn up the (now unobtainable) primary power switch.  And the capacitors take a pretty solid hit on power up; the series string sometimes exposing one or two to a momentary over-voltage.  The HV transformer also experiences an effective short circuit until the capacitor bank begins to charge up (and an upgraded Cap bank adds to the load).  The fix consists of a simple power resistor in series with the input power with a timer relay to bypass it after a second or two.
24VDC Power
The original HeathKit design cleverly avoided the need for any low voltage control circuitry.  That was fine, at least until you want to add a feature or two.  The new control board includes a 24VDC isolated power supply to provide power for new relays, meter LEDs, and the rest of the control circuitry.
Fan Speed Control
As many have pointed out, the fan in the SB-220 is actually not bad.  With a little maintenance, the fan will do a good job and last forever.  Don’t be tempted to put in a modern design ‘muffin’ fan.  They will not work as well in this application.  The stock fan is sometimes needlessly noisy however, so the new control board adds a temperature sensor and control circuitry to let the fan run at a slow speed until heavy use (and a rise in temperature) requires the high speed mode.  When things cool down the fan slows to quiet mode.
120/240 Selector
The SB-220 is designed to operate from either 240V or 120V.  It is a nice feature.  240V is generally preferable, but on a good 120V circuit the amp will run just fine as long as you don’t try to exceed the limits.  An error in the original design however, could inadvertently burn both transformers (with impressive smoke and fanfare) if just one of them lost a primary winding (or the terminal just came loose).  Heath issued a service notice to fix this by removing wires from the terminal strip and using a wire nut to attach them.  It added considerable confusion when someone new went to switch voltages.  The new control board isolates both transformers and provides a simple connector to switch between voltages.  Simply align the plug to the left for 240 and right for 120.
Soft Key
The SB-220 was originally intended to work with the tube transmitters of the day.  To connect the amp to a modern, solid state, transceiver the PTT input of the SB-220 had to be modified in some way to avoid exposing the radio to destructive high voltage and current.  The new control board circuitry limits the input voltage to 5V and just a few milliamps to ground will engage the antenna relay ( “Soft Key”).
Antenna Relay
A subtle but significant improvement is the addition of a small relay to separately manage the bias for the transmit tubes.  It allows the use of a simpler (and quieter) DPDT relay for antenna switching instead of the original high voltage 3PDT.  The new relay operates on 24V since it is now available.  If at some time you wish to change to vacuum relays (which are usually 26V but work fine on 24V), no other complex circuitry is needed.

The circuits for the soft start, the soft key, and the fan control, are nearly identical.  This makes understanding/ servicing the circuitry simpler and keeps the component variety to a minimum.  All of the components are standard thru-hole types; no surface mount devices to provide needless frustration to the assembly.  There are bypass capacitors all along the power path, as well as capacitors across the relays to ensure that RF is not a problem.

Unfortunately I made a couple of errors in the board layout, requiring a few jumpers on the rear of the board.  I will fix them if I do another layout but in all likely-hood I will add other, similar errors.  The jumpers may already be installed on the board for you but if not, the rework instructions are on the last page.

ASSEMBLY
Start by sorting the components and setting up a work area where the bits an pieces are not going to get lost.  A good soldering station is a must, as well as good hand tools, a multimeter, and probably a magnifying glass of some sort.  Install small parts first and gradually work up in size.  It will leave the most room for fingers as you progress.  As much as possible, leave components (resistors, diodes, and especially transistors) a little above the board.  Things will be cooler and easier to repair if the need arises.

[ ] Before doing anything to the board, it is a good idea to inspect the chassis of your SB-220.  You will want to drill a couple of mounting holes for the new board.  Use the board as a template to mark the location of the holes.  There are 5 mounting pads on the board, two of which should line up with two screws already under the HV transformer (since they are flat-heads you might have to insert a large dia washer to get them to tighten).  You don’t need to provide all 5 mountings but try to get at least 3.  Be careful not to drill into something valuable on the far side.  The included spacers are just long enough that the board should be above the one interfering mounting bolt of the HV transformer.  Reverse that bolt if it appears too close (although the PC board is clear in that area). 

[ ] Then, following the layout diagram, install all of the small resistors. 

[ ] Install the diodes.  There are three black (1N4007) diodes and two 5v zeners.  Make sure that you get the polarity bands correctly installed.

[ ] Install the capacitors.  Only the 4.7uF and the filter cap are polarized. Leave out C4, it is not needed.

[ ] Install the three LEDs.  DC pwr is green, Soft Start is yellow, Fan=Fast is blue, Xmit=on is red.

[ ] Install the 3 relays. Add the rework jumpers for K1 if you intend to use it to short out the 100K bias resistor.

[ ] Install the 6 transistors.  The Q5 and Q6 power transistors are placed so that the metal side is down.  Q3 is placed so that the metal side is facing the power supply.  (plastic side nearest the Qnumber in all cases)

[ ] Install the connectors.  Note that the Temp Sensor 2pin white connector is offset toward the edge of the board unless a screw type connector is supplied.

[ ] Install the trim pot and any remaining parts other than C10 or R9.

[ ] The power supply is held in place by 4 plastic, press-in rivets.  First, inspect the Power supply carefully and trim all leads on the back as short as possible.  Then put the rivets through the holes in the corners of the Power Supply, then put a white plastic spacer on each.  Press the rivets (and the Power supply) in place onto the main board, 24V input to the left.

[ ] Wire the 24V connector from the power supply to the main board.  Route the wires through the small hole, and solder the wires to the rear of the board.  Red positive.  Blk ground.

[ ] Stop assembly here for now.  C10, R9, and the power to the 24DC supply will be installed after testing.

TESTING
If you have a 24V bench supply you can use that to power the board for testing.  Otherwise, you can make a temporary power cable to plug the board’s supply into 120v(or 240v).  Use the Red and Yellow wires of the three pin connector temporarily connected (and insulated) to a power cord.

The three control functions of the board use nearly identical circuits.  In all three circuits an NPN power transistor is used to drive a relay by pulling one side of the relay to ground when the base of the transistor sees current from the pullup resistor.  A 2N7000 FET drives the power transistor by holding the transistor’s base to ground until the gate of the FET goes above a couple of volts.  Note that the voltage at the base (1) of the power transistor doesn’t change much, what matters is the current through the emitter junction.  A feedback resistor provides just a little positive reinforcement to give the circuit a little hysteresis (snap action) to avoid any relay chatter (not needed on soft key). If a function doesn’t seem to be working correctly, check all components in that area for value and placement.  If you have trouble, checking the voltage at the gate (2) of the FET will tell you the most about how the circuitry is working.

With 24V connected, you should be able to check the function of each of the three circuits:

Soft Start
The green LED should be steady on.  The soft start LED should also be on.  Each time power is applied the soft start LED should come on a half-second or so after the DC Pwr LED. (The power supply also takes a second to produce power so it will add a second to the delay)  You should also hear Relay K2 click each time.  In case of problems, you can check Test Point 5 with a voltmeter.  It should be high when voltage is first applied and then drop quickly.  If not, a backwards cap (C3) or nearby component is likely your problem.
Soft Key
With power applied, you should be able to short PTT to ground and turn on the red (Xmit=On) LED.  Relay K1 should also close.  If you measure the PTT input with a voltmeter it should read about 5V. 
Temperature Control
Plug in the temperature sensor to J5.  Apply power and adjust RV1 temp adj trim pot in both directions until the blue LED (Fan=Fast) goes on and off.  Adjust the pot until the LED just goes off.  Hold the sensor in your hand (or against your forehead), the LED should eventually go on.  Relay K3 should also click on.  Now adjust the pot until the LED just goes out.  It is now “calibrated” so that the fan will speed up if the temperature goes above about 100 deg F (38C).  It will be a bit higher if you have the flu.  If you have trouble, TP3 should read around 5V and TP4 should go up and down between 0 and a couple of volts with the adjustment of RV1.
Capacitor Selection
As a separate test from the control board, temporarily wire your cooling fan in series with one of the large capacitors provided and a power cord.  Plug it into 120V (not 240v) and observe the speed.  If you want faster you can try a larger value or temporarily put two capacitors in parallel.  Be careful, the caps can hold a large charge after power is removed (short the plug when unplugged).  When you have a satisfactory speed (quiet with decent air flow) install the capacitor(s) into the control board.  Keep the overall height of the board below the highest point of the 24V supply.   Don’t forget to install the AC power connector for the 24V supply.

INSTALLATION IN THE CHASSIS
If all is good so far, take this opportunity to clean up the power wiring to the circuitry around the breakers so that the board fits comfortably, then you can mount the board in the chassis using 3/8” (9mm) spacers.  Use at least 3.  And  double check using a straight edge that nothing protrudes below the bottom of the chassis.

[ ] The most tedious part of installation is probably connecting the power transformers to the green voltage-select connector.  Take it slow, start with the easiest one and land one wire at a time.  Use ferrules if you have them and the crimping tool, if not, tin the wires with a little solder before putting them into the screw connector J3.  Only put one wire in each location.  Refer to both the schematic and the wiring diagram.  At least one of the transformer leads is destined to be short.  Extend it with a similar color if possible and cover the connection with good heatshrink.  Use at least 16awg wire for all of the power wiring.  A good source of wire is to strip the jacket from old computer power cables.    There are two places where 4 wires are spliced together.  You can  best accomplish this by removing about a 1/4” (6mm) of insulation in the middle length of two wires and then twisting one over the other and soldering.  Cover the 4-wire junction with one or two layers of good heatshrink. 

[ ] If you are replacing the transmit relay with a new 24V one (recommended) you should wire one side of the coil to +24V and the other to the ‘Xmit Relay’ terminal on J1.  The rest of the relay is wired like the original except that only two poles are needed.  The bias can be wired using the relay on the control board assuming the rework has been done.  [To use the original relay, K1 can be used if ‘X’ is jumpered to ground and the original relay connected to ‘Bias’.  The third set of contacts on the original relay then will switch a bias resistor.]

[ ] The Bias terminal on the control board (J1) goes to the center tap of the filament transformer.  Pin 5 (X TRA) goes to the zener voltage on the Diode board (pad #E).

[ ] The power switch wiring simply goes from the two terminals on the power switch to J2 (AC power in) on the control board.  This would be a good place to use 14awg wire if you have it.

[ ]  Install R9 above the board and touching the aluminum chassis corner support.  This will dissipate any excess heat and will do minimal damage if something fails and the resistor overheats. 

[ ]  The fan simply wires to the ‘Fan’ connector.  The temperature sensor can be mounted where you like, but drilling a 7mm hole in the RF enclosure above the HV transformer and inserting the sensor through a grommet is a good location.  (Keep the wires out of the RF area)

[ ]  You can use the 24V to power LED lamps for the meters if desired.  Probably putting the LEDs in series and inserting a suitable current limiting resistor.

[ ]  As with any work on HV, be extra careful when applying power.  Use a variac if available.  It’s a good idea to disconnect the HV lead from the transformer (Red/Yel) to the Cap Bank and temporarily insulate it (well) while you test the power selection wiring.

Rework Instructions  SB-220 Control Board V 2.1

This error was my mis-guided attempt to do something clever with the small relay K1. It didn’t work.  The best use of the relay is to assist in setting the bias for the transmit tubes.  If the filament center tap is connected to the 5v Zener reference through a 100K resistor, the tubes will find their own bias level when idle.  In transmit one must simply short the 100K resistor (a method proposed by Richard AG6K and others).  K1 does this nicely.  Before you begin the rework install K1, R3, J1, and J6

[_]  1  On the back of the board, cut the trace going from one end of the 100K resistor to the upper left pin of K1.

[_]  2  Connect a jumper from pin 2 (Bias) of J1 to the lower right pin of K1.

[_]  3  Connect a jumper from pin 5 (X) of J1 to the right hand side of the 100K and on to the lower left pin of K1.












There was also an error (senior moment) in connecting the 120V for the fan to accomplish speed control:

[_]  4  On the component side of the board, cut the large trace going to pins 3&4 of J4.  Cut this trace close to the pins of J4.  Then install J4.

[_]  5  Add a jumper from pin 7 or 8 of J4 to pin 1 (the square one) of J6 to connect it where it should have gone.






SB-220 Control bd BOM        

SB-200/1 & HL-2200 Replacement Capacitor Bank v02

First… This amplifier has potentially lethal voltages present. Regardless of your background, if you are not afraid of high voltage you should not be doing this. Get help from someone who knows what they are doing and is afraid.

Heath engineers originally designed the amplifier’s capacitor bank with what was available at the time. It was a good design, and the voltage doubler approach has been the standard in high voltage supplies for years. However the engineers were faced with using 8, metal cased electrolytics that posed a significant shock hazard, as well as being difficult to put in kit form. Their solution to put them in the plastic sandwich enclosure worked but also restricted ventilation. (electrolytic capacitors maintain their rating and last longer if kept cooler). Those old can electrolytic caps also varied widely in value, especially over time.

I received the new boards for the capacitor bank, and finished the design for the sheetmetal that holds it in place.  I had to spend nearly a thousand bucks at a sheet metal fab house but I have lots now.  Will hopefully get that back by selling them through ebay.  It will put some new life into a bunch of aging amps.  Wish I could install one in myself.

The board came out nice.  It sits sideways from the old cap bank.  (that is why the new sheet metal)  Today we have capacitors available that are not only more stable, they are smaller, and at least to some degree, individually insulated so the plastic insulators were a waste. The original caps were 200uF so 8 in series created a filter capacitor with a value of 25uF. This new board can support caps in the 200-600uF range giving a filter value up to 75uF. This doesn’t increase the total power available, but does significantly increase the instantaneous power available, and of course improves filtering.

The value of the ‘bleeder resistors’ selected by HeathKit was low (30K) to quickly bleed off the charge in the interest of safety. However it did result in a great deal of unwanted heat which was waste of power and shortens the life of the capacitors. Most upgrade projects today change the resistors to around 100K and rely on good judgment to stay away from the high voltage until it has bled down. Using larger value caps makes the selection of bleeder resistors more interesting. The larger caps mean that the high voltage will be present for as much as three times as long! The included resistors were selected to optimize the power supply and reduce heat. (they also serve to equalize the voltages across the capacitors but a higher value still serves this purpose on the newer caps) If you are concerned that a more rapid bleed down is necessary for safety, feel free to add lower value resistors (or put similar values in parallel). In any event, wait until the meter reads zero, and then another 5 minutes before accessing the chassis (meters are known to fail). Even then, ground the HV before touching anything!

Notes on the SB-220 HV board by AG6YJ

Background:

The combination of being retired and being a ham leads to a lot of tinkering. And as the owner of a Heathkit SB-220 which for some reason was aging more rapidly than myself, I set out to do a rebuild. The internet is full of advice, some good, some bad, and some absurd, so I selected a reasonable subset of information and did a respectable job of rebuilding it and getting it back on the air.

But along the way the tinkering spirit led me to lay out a couple of PCBs to clean up some of my work. So when the boards eventually came in, the chassis went back on the bench and went through another revision. And like so often happens, I realized that the boards could be a little better and set out to design another set.

Well, when you order printed circuit boards, you don’t get just one. Generally I get several dozen so if I am lucky enough to have a useful design, I can have spares to give a few to friends.

In any case, this time I elected to sell a few on eBay to further support my otherwise frivolous tinkering. There is no intent here to compete with the other boards (W7RY and others), they do a good job and provide a reliable source for much needed replacement parts.

I did use this board to upgrade 3 different amps.  Two SB-220s and one HL-2200.  Of course along the way I did a lot of other upgrading.

This is the dis-assembled version of the HL-2200.  One of the 220s is behind it.  I decided to re-do the capacitor bank as well.  Boards are on the way.  I also added a fan speed control to the 220.  Used a controller from ebay.  It works fine but is a little kludgey...

The HV diode board:  (this is from the kit that I put on Ebay)

For the most part, the diode rectifier board is a drop in replacement for the original board in the HeathKit SB-220/221.

However, it has a number of additional features not included on the original.

• Connectors to allow the front panel to be removed or extended during service. The original pads are still present and can be used if connectors to the front panel are not desired.
• A fuse and a 5w resistor in series with the high voltage to minimize damage in the event of a tube failure.
• A string of 1N5408 diodes for the voltage doubler (larger than the originals)
• A filter cap across the high voltage output.
• Diode protection for the plate meter.
• A string of 1N4007 diodes to replace the original Zener, including capacitors to filter the voltage.
• A string of 2meg resistors to divide the high voltage for the voltmeter.
• A limiting resistor to provide the current for LEDs on the panel meters if you decide to do that.

To use the connectors to allow the front panel to be removed, you must add a few new wires to the board. The Relative Power wire must first go to the board so that it can go through the connector to the front panel. Similarly, you also have to route the lamp voltage through the board. Being able to remove and protect the front panel is worth the extra effort.

If you elect to replace the original #47 lamps in the meters with the provided Led arrays you will have to come up with the appropriate dc voltage. The arrays are a string of Leds totaling nearly 12v, so to operate from the original filament voltage of 5vac you will need some sort of voltage multiplier.

One method is to build a voltage quadrupler (about 28vdc). A 150-200 ohm resistor on the board is about right in this case if the two arrays are placed in series.  Use 200uf to 500uf 16V caps and 1N4004 diodes or better.

It is fairly easy to put this little circuit on the front panel using a terminal strip.

Hexbeam antenna project

In this case, I was browsing the Internet for better antenna options and kept running across articles expounding the virtues of the “Hexbeam Antenna” and thinking, “Yeah, I could do that” so off I went.

Like many others, I thought I might be able to get by with materials laying about the house or readily available in my small town stores. After trying numerous versions of PVC pipe and fiberglass rods, I wisely decided that the fiberglass tubes suggested would be the better options. So swallowing the little bit of pride available, I ordered the kit of tubing (plus an extra piece of 3/4” , more on that later).

Whilst waiting for the tubing to arrive I set out to collect whatever else I could locate about the house. The aluminum plate was the first treasure found. It was just a piece of 5mm painted aluminum that fortunately seemed to good to turn in for scrap in the past. It took about an hour with the bandsaw and hand drill to convert my former scrap aluminum to a nice, 6-sided, base plate. I drilled the holes for the U-bolts since I had also found a box of nice stainless ones that had been ordered from China via Ebay for another antenna project. The center hub was still a missing piece so that was left blank.

I thought that I had plenty of stainless hose clamps, but a quick inventory revealed that while I did have a bunch, the hexbeam was going to require many more. OK, fine. But going to the local hardware was going to quickly burn through the budget...so back to Ebay. Lucky me, I found a US vendor selling quantities of 20 all-stainless clamps for two bits each. That works.

Still no hubs, but while I was on an XYL errand in my rural village I wandered into the local pool supply store. I don’t have a pool but it was close to the farm supply where I was sent to procure dog food. As I was leaving, I spotted an old pool ladder behind the store. Can’t resist a closer look... yeah, I like junk. The little aluminum feet at the bottom of the ladder might just make the sought after hubs. $5 made me and the pool guy both happy. I got them both, thinking that one top and one bottom of the antenna base plate might be a good idea.

My table saw (a makeshift work surface) was now covered with a small pile of potential hexbeam antenna components. One lucky find was a spool of really nice black Dyneema rope. The stuff is ridiculously strong and UV resistant. There were also a few spools of 14AWG THNN wire in various colors. I had in mind that I would use some epoxy glue at some point so I set out to locate what I might have, and to see what sort of spray paint I might have that would still come out of the can.

In the middle of the search, the UPS truck pulls up the driveway with the precious fiberglass tube kit. Nothing to do now but get to work.

The hose clamps haven’t arrived as yet so I thought I would try out my original plan A. That is, rather than slitting and clamping the sections of tubing together, I would mix a bit of epoxy and glue each joint. The found epoxy was the fast setting JB weld. It is easy to use and plenty strong. I built one arm complete to evaluate the process. Satisfied, I assembled the two smaller tubes of each arm and after they cured for 20min, added the 1” tube. Lastly, I cut the extra piece of 3/4” into 6 equal pieces and glued them flush into the open end of the 1” end of each of the arms. The thinking here is to make the ends a bit stronger to resist being crushed by the U-bolts.

The next morning there was nothing to do but to assemble the beast. I tried working on the ground but my back was having no part of that. A recycle bin was the only work table in sight, so be it.

The arms went on the base in minutes producing a satisfyingly large representation of my efforts so far. “Hmmm, what should be the next step” and: “Oh S**t”, the center post! I had thought about it but somehow neglected to build it. Narrowly avoiding another trip the the local hardware store, an hour of searching produced the 1” square aluminum extrusion that I had briefly envisioned for the post.

There are thankfully good instructions on various websites that suggest ways to build a center post. I drilled holes at the suggested locations and fabricated 6 sets of PTFE shoulder washers. I wanted a copper center conductor but all I could dig up was a bit of bare 12awg wire. Guess that will work… so I laid the post on the bench (tablesaw), stuck the shoulder washers in the outside, and poked in some #8 brass bolts. It took a little blue tape to hold everything in place. The copper wire then soldered fairly nicely in the slotted heads of the brass bolts. It took a bit of fiddling to get the ground bolts in place but the big holes for the shoulder washers made it possible. It was surprisingly easy to then shove the wire/bolt assembly down the end of the tube and pull the bolts through the holes. Installing the SO-239 connector on the side of the top was a bit more of an effort but having done that I covered the open top with a bit of scrap aluminum and some silicone.

Finally, now back to the assembly. The post was a bit small for the pool ladder flange, but wrapping it in a bit of scrap aluminum solved that little issue and it tightened up nicely with the flange set screw.

I cut 6 eleven foot (plus about 2”) pieces of the wonderful Dyneema line and crimped/epoxied ring lugs on one end and made loops on the other. Using a flame to cut the line left a nice little ball on the end that further strengthened the crimp connection. The loops were also made with crimps of copper tubing and a bit of epoxy. And all joints covered with heat shrink just to make them look nice (like anyone would ever see them).

And like the above, I made another 6 eleven foot lines with loops on both ends to go between the arms.

It took maybe 20 minutes to string the whole thing together. And 10 minutes of that was searching for one of the line that was inadvertently sling shotted into the weeds when I lost my grip on the end.

Time to stand back and admire the new umbrella frame that now occupied most of my driveway. It was like a really big “cat’s cradle”. A real thing of beauty. I had a 4 foot piece of fiberglass post that was part of a military field antenna mast so I put that into service as the bottom post, primarily because it was a perfect fit to the pool ladder flange. The XYL was not so amused at this point so I busied myself with making the wire elements.

I was now practiced in using the Dyneema line so I used that as the spacer between the active elements and the reflector wires. Bending the 12 gage wire into a hook, tinning it, and then laying in the line (with a little ball on the end) in the crux of the hook was perfect. Smashing the hook tight, adding a dab of epoxy, and then covering with adhesive lined heatshrink, made for a super strong but very slim connection.

It took the rest of the day to create all six band wire antenna elements. This is probably the most time-consuming activity of the whole project. So it was the next morning before I could begin stringing the enormous spider web that was the current object of my wife’s complaints (her car was going nowhere until this thing was somewhere else).

I had tested a couple of methods for securing the wires to the arms using the suggested hose clamps, and settled upon using a bit of aluminum strap under the clamp, and about 2 inches of irrigation tubing around the wire. The 20 meter loop went on first, where I quickly discovered that it was annoyingly in the way as I worked on the rest. So the 6 meter went on next and worked outward from there. It really looks like the Internet pictures now.

It took a few hours with my budget antenna analyzer to correct a couple of lengths and get everything tightened up. I couldn’t resist hooking up the radio and made one contact on 20m even though the antenna was still sitting at only 4 feet above ground. That done, I managed to get

the whole thing moved from the driveway, greatly improving the odds that I would remain married.

I emptied out 4 cans of miscellaneous spray paint that I thought might prolong the life of the fiberglass and wires in the harsh California sun. To complete the antenna I constructed a quick balun consisting of a 7 turn coil of coax wound neatly inside of a piece of plastic sewer pipe.

I had a week to admire my creation and to rebuild an old Yaesu 450 rotor (another blog) before my son was able to come to the house so that we could attempt to install the giant umbrella on my homemade tower.

Getting a 22 foot diameter spider web to the top of a tower is no small task. It is not particularly heavy, something around 25 lbs, but it is difficult to find a place to grab the wiggly thing. We managed to sort of slide it up one of the tower guy wires by pulling it with a rope: my son at the t

op of the tower, me at the bottom. There were a couple of iffy moments and then finally my son had it in hand and poked it home in the newly rebuilt rotor. Some clean up of the various cables on the tower and we were able to crank the tower to it’s full height of 41 feet.

Just luck I’m sure, but upon reflection, this project had far fewer mistakes and retries that just about anything I can remember doing. It is hard to say what it cost considering all of the material that was in the various junk boxes but the outlay for new stuff was under $200. As for performance, the hex pretty much lives up to the hype. I have two dipoles and a skyloop for antennas in addition to the new hexbeam. The hex is much better at rejecting local noise (from the neighbors solar panels I think) and being directional has really helped in catching the attention of some fairly distant DX stations. It also catches the attention of the neighbors but no complaints as yet. It would have been nice if it could have covered 40 meters, but that would never have made it to the top of the tower.

Many thanks to those whose contributions to the websites make projects like this one possible.

A simple coax switch...

Sooner or later every ham station will need a way to switch coax connections. There are plenty of commercial switches out there, MFJ offers a decent one that is easy to find. And you can always spend an afternoon collecting the parts and assembling your own. However, both options wind up being a little expensive when all you need is a switch to temporarily evaluate a new radio or some array of antennas.

Wanting another switch, I searched ebay and ran across a 3 position switch made by Workman. It claims 1000W, which I didn’t believe but it was only $12, something I could afford to lose when packing up after a field day. I remember the Workman brand from the 1970's. They mostly had tools and accessories for the TV repairman but also a few reasonably priced items for the hobbyist. I bought three of the switches and they arrived in the predicted 8 days by China post.

As a test the switch, was put in place between my radio and a 20m dipole on position 1 and a 40m dipole on position 2. Sadly, there was a noticeable decrease in signal and without re-tuning, the SWR was also worse. The MFJ switch didn’t exhibit either problem.

So, what's up? It is just a stupid switch. Popped the back cover (two screws) and surprise, it is packed with wires!! WTF! You would expect one wire from each connector to the switch and not much else. It is a cheap switch so you would expect the grounding rely on the screws to the case.

A little closer look and it seems that someone decided that the grounds should also be switched. It makes no sense because they are all tied together anyway! Whoever sent the order to the manufacturer probably wasn’t all too clear on the actual requirements. The good news is that the switch itself is a reasonably good one, and the SO-259 connectors look fine.

Ok fine. Grab a soldering iron and pull out all of the wires other than the four wires from the center of each connector. And even those were un-soldered from the switch.

That's better, now put the four wires back on the switch (on this particular switch I elected to put the input on the side with 3 connectors, your choice). Keep the lengths as short as practical.

Now the grounds. An ohmmeter suggests that the connections are pretty good between the case and the connectors but it looks more accidental than intentional. So, we could use some of that left over wire to tie each connector shell together, or try something better. I happened to have a bit of copper foil so it took a few minutes with a large soldering gun to tack it to each connector and to the steel box after scratching off the paint (good paint BTW). Some bits of copper clad PC board will also work

In this case I had to re-label some the switch positions, but otherwise it looks like the original. A quick test and it now behaves as well as the MFJ version at least under the above conditions. I didn't bother to test it on 2m, but it is probably only useful for HF.

Conclusion: You cant beat this as an option for an occasional use switch. The parts are worth more than the purchase price and it takes barely 20 minutes to do the rework. In spite of the nice statement on the label, this is not the switch to use if you are running more than a couple hundred watts, but it is great for field days and they make welcome gifts for your ham buddies.

QRM-180

QRM-180

Yet another Noise Reduction

 System

Another fun project

 

Background:

Unless you live far out in the countryside you likely have your share of interference from TVs, LED lamps, power lines, computers, solar panels, etc. There are a number of QRM solutions available today, and even a few kits, so, not happy with my noise situation, I have purchased or built any of the versions I could find that looked promising. A common theme (popular since the days of vacuum tube TVs) is to use a second antenna (used to collect a suitable sample of the noise), invert that signal and add it back to the main signal. It sounds simple but like most things, putting it into practice requires some effort.

The good news is that they can be reasonably effective. Don’t expect miracles but one of these can get rid of just enough noise to make them worth having. I own several of the commercial versions, including the MFJ-1026, and ANC-4, as well as the X-phase kit from Russia. They all work well enough, with some subtle differences. The ANC-4 seems the easiest to operate, and is arguably the better made, the MFJ has a useful preamp on the noise line. The X-Phase is pretty basic, but with some additional components is still useful. These units are designed with amateur radio transceivers in mind, but it will work equally well on receiver only applications. Again, they can do a good job canceling a nearby noise source, but not atmospheric noise. There are a lot of reviews on line as well as a bunch of Youtube videos that give some useful information.

The QRM-180 came about because the commercial units actually worked and I couldn’t resist trying to make one myself, so after a lot of iterations on several breadboards, I spent the time to lay out a decent PCB so that I could put a separate one on each of my three transceivers. The board (with ground-plane top and bottom) is much better than my breadboard and managed to fix some of the shortcomings (my subjective opinion) of the commercial units. The circuitry is not all that original, it is a combination of what I deemed to be the best of the existing designs. The board is all through-hole components which makes it much, much easier than surface mount to build by hand and also makes it serviceable in the future.

The case is a compromise between being roomy enough for old, fumble-fingered assembly and not so big as to take up valuable space next to the transceiver. It sits comfortably on top of most external speakers, or on top of the transceiver itself. It is thick aluminum so it is well shielded and heavy enough not to slide about during use.

To minimize confusion, all of the connectors on the rear panel are different. And rather than another SO259 connector, the transceiver is connected with a fixed pigtail/PL259 that should comfortably reach the back of the transceiver.

Power requirement is 12V to 13.8V. The included wall wart will work (it is a switching type and potentially generates noise, but I haven’t been able to detect it) or any other good 12V source. Most transceivers have a 12V output that could be utilized, but you should have at least 400ma available to power the QRM-180. Check your transceiver manual first.

Function:

The circuit is much like the others. A separate noise antenna gathers what is hoped to be a good sample of the offending noise without a lot of your coveted DX signal. That sample is run through a broad band amplifier before being inverted by transformer T1 and fed to a phase shifter. I tried a number of schemes for phase adjustment, and this one is not only the simplest, it introduced less distortion. Two J310 FETs then act to buffer and combine the two basic signals.

The combined signal is then buffered by Q4 and sent to the receiver through a relay. In transmit mode, the relays serve to isolate the device and allow the transceiver to be connected directly to it’s antenna. The relay is large enough to handle 200w, but make sure that you put the QRM-180 between your transceiver and your linear if you use one. It would probably be toast if you try to install it following the amp. The PTT (really just the transmit line not the actual PTT from the mike) input grounds the gate of Q2 which in turn turns on Q4 the power tab transistor. This not only energizes the relays, it supplies power to the rest of the circuitry. The relays energize on PTT low so that the default state is safe (circuitry bypassed) when the power is off.

Like the MFJ-1026 there are fuses and protection diodes on the inputs (although MFJ appears to have defeated some of them, likely to minimize service calls). In spite of some suggestions on the Internet, don’t remove them. They are useful and do not degrade the performance at all (unless they are blown, duh). The pi filters are a little debatable but for the bands where the QRM-180 is useful they are a good thing. I have tried the MFJ-1026 with and without, no difference. If you own the MFJ and want to improve it, add an LNA.

The provided amplifier for the noise antenna is a commercially available pre-amp (LNA) that provides a nice flat, low distortion 30dB of gain that can be adjusted down using RV1. In very rare cases where the noise is very large and the noise antenna is also large, the LNA may not be required and could be bypassed.

The QRM-180 does have transmit-detect circuitry to disable the relays to try and protect things if the PTT is not connected when you transmit (C17 coupling some RF and eventually turning on Q1). Like the other devices with this type of circuitry, it barely works. It is pretty good with AM but anything else is intermittent at best and will quickly blow a fuse. You have to connect the control wire from the transceiver.

Setup:

Start by checking the manual on your transceiver. On any transceiver built in the last 25 years there should be a connection on the back of the transceiver designated for operation of a linear amp. Look for something labeled TX GND, PTT or similar. If you are lucky it is a separate dedicated connector. That is probably what you want to connect to the PTT input of the QRM-180. But check it first: operate the transceiver while monitoring that output with a voltmeter. It may be just relay contacts to ground so if you read no voltage, try measuring continuity. Whatever the case, it must go to ground when in transmit mode. Depending on your transceiver, you may have to obtain a suitable connector to reach this signal.

If your transceiver has a built in tuner, check the output when the tuner operates. The tuner should also pull this output to ground when it transmits. (while it is possible to use the actual PTT line, the same one that comes from the microphone, if you have a built in tuner you will have problems since that line doesn’t generally change when you tune).

At the worst, you may have to install a small relay to provide the low-on-transmit signal. Check the Internet for instructions on how to connect your transceiver to a linear amplifier, the connection is the same.

Operation:

The trick to success is to get just enough of the noise signal to match the level of the noise component on the primary signal path. The kind of noise will dictate the requirements, but generally you will need an antenna and some time to experiment with settings at different times. Don’t expect to reduce atmospheric noise-- you cant. But for a specific noise source you should expect a significant if not complete reduction. Be sure to read the reviews and manuals of the other devices (all available on-line) to get the full picture.

Step one in deciding upon the noise antenna is to see if you can characterize the noise. What time of day is it present, is it near or far, where in the band is it strongest? If you have multiple antennas, is the noise the same on each? Try to tune it in. Start on an easy band, say 20 or 40M. And connect something to the noise antenna (an old TV antenna is great if you have one). Some people swear by a long piece of wire laying on the floor. If that works, the noise is probably in the shack, and should be fixed with some grounding and ferrite beads not a phase inverter.

• The GAIN knob is just that, you are trying to find a level that just matches the noise so that the result is zeroish. It is not to find the best listening level. Use the radio knobs to do that.
• The PHASE knobs jointly adjust the phase of the noise signal. You should adjust each for a minimum. Unfortunately they also mess with the level, so you have to go back and forth a bit between all three.
• The NOISE Attenuator control is rarely used and is on the rear panel. When the LNA is installed it is used to get the noise signal in a range that can be matched by the GAIN control. Without the LNA it will probably just be set to max. It will depend on the size, type, and location of the noise antennas, as well as the strength of the noise source.

Start adjustment by turning the gain down a little on the transceiver, if it has a preamp turn it off (with the gain of the QRM-180 it is unlikely that you will need it). Turn on the QRM-180 and turn it’s gain to about half, then adjust each of the two phase controls for minimum noise. Keep adjusting things until the noise seems to be minimized. If the LNA is installed, start with the Noise Level control set to about 70%.

You have to use your receiver controls as well as the controls on the QRM-180 to get the best results. The signal will likely be different than what you are used to. Try with and without the transceiver’s notch filter, NB, and different width settings. It will take a lot of practice to get things right quickly. I have solar panel noise (from the neighbor’s inverter) that can be killed completely in 3-4 seconds of knob tweaking. Changing frequency within a band should require minimal readjustment.

Try with and without the QRM-180 frequently to be sure that you are helping things. Try to ignore the level change and listen just for the change in the noise component. Use the transceiver volume control to match the levels for comparison. Again, you cant escape atmospheric noise, focus on the specific noise source.

For different bands you may get better results with a different antenna (I don’t understand why but try it). You should run coax from the back of the QRM-180 to the noise antenna, but pretty much anything will work. RG-59, RG-174, or whatever, it doesn’t need or want to be 50ohm. Try a short dipole (I have one in the attic), or rain gutter, or a fence,... you never know what will resonate with your particular noise problem. Going vertical is a good option. Remember you are trying to receive just the offending noise, not the HF signal. If you can set up an antenna with some gain, great, point it at the source. When you have established a decent reduction, note the knob settings. It will be pretty repeatable for the same conditions on the same band. A word of caution, whatever you choose, don’t go with a big noise antenna that is too near to the one you are transmitting on. The noise antenna could easily pick up enough RF to blow the fuse on the noise antenna line.

 PCB assembly

You will need some basic tools: soldering iron with a smallish tip, your favorite solder, sharp flush cutters to trim leads, screwdrivers, and if you are not 13 years old, a good magnifying lens.  A volt-ohmmeter will likely come in handy.  Begin by sorting out the parts so as not to loose anything, get some good light, and a place to work comfortably for a couple of hours.  Complete assembly is probably a two evening job; there are a lot of parts.

It is generally best and easiest to install the smallest parts first, and gradually work up in size.  Put in about half a dozen parts then solder them.  Then trim the leads and put in the next group.  Checking them off of the BOM as you go will save time in the long run.  Don’t worry if you have parts left over, there are a few extra parts in the kit (J310, fuses, some extra diodes, the occasional extra resistor, I don’t count so good).

Caution:  there are THREE significant errors on the PCB… 
1- the collector and emitter of Q4 ore switched, follow the instructions to correctly cross the legs. 
2- the silkscreen for diode D19 is incorrect, it must be installed opposite from what is shown. 
3- C2 is a polarized capacitor but there is no plus sign on the silkscreen. 

4- I forgot that you will want to add R15 to the backside of the board... 

These errors will be corrected on the next layout, but other, similar errors will be inserted at that time.

1) Install the Zener Diode D7 first, this will keep it from being confused with the switching diodes.  As with all the diodes (other than D19 which is marked wrong), watch the polarity and match the band with the silkscreen image.

2) Install the 1N4005 black rectifier diodes.  Put D19 in backward, and install the rest of the diodes.

3) The resistors are next, but don’t install R1!, it is not needed.  And you might want to save R9 for later since it mounts vertically and makes the board a little difficult to work with for now.  Save the potentiometers until later for the same reason.

4) Install the inductors, there are two different values and they can be difficult to tell apart.

5) The capacitors are next, just save C3 and C4 until later.  Only C2,C3 and C4 are polarized, the rest can go in either way.  C2 is inserted with the negative end nearest D6.

6) Now is actually a good time to install the connectors.  You can use some judgment here if you like. There are screw type connectors in the kit that work well but some people would prefer to solder the antenna and transceiver wires directly to the board.  Your choice.  Don’t put a connector in the S1 position, you will solder wires here later for the power switch.  Using the supplied connectors on J2 and J3 is a good idea.

7) Take a break from soldering and wind the transformer.  Wind 10 turns of the enameled wire, and then three turns of the white insulated wire.  The wires can exit the ends or sides of the core, it doesn’t much matter.  Just make sure that when it goes on the board the enameled wires terminate on the C7 side.  After, you will want to trim the wires to about the right length to fit the board (not too short).  The white wire can be stripped with a good pair of strippers.  The enameled wire must be prepped by scraping the ends with a razor blade or sandpaper, then tin the ends to make sure that all of the enamel has been removed.  Double stick tape will hold the core in place on the board.

8) No transistors yet, but all of the larger parts can go in now.   Don’t forget to install R9.  Solder in the controls and the relays.  Note that RV1 is a 1K pot.  The others are 5K.

9) The power jack should be wired with about 6 inches of wire.  Wind 3 or 4 turns of the power wire through the ferrite ring.  The power switch can be connected directly to the board with about 2 inches of wire.  The RCA jack also needs about 2 ½ inches of wire to get to its board connector.

10) OK, Q4, the large power tab transistor….  The board design evolved a bit and somewhere along the line the footprint for this transistor got messed up.  The base pin is correct but the collector and emitter got swapped (sorry about that).  With a little leg twisting, however, the transistor will still fit nicely.  See picture.

11) Install Q3, Q5, and Q6.  You can use in-line sockets if you like but I tend to think that they cause more trouble than they are worth.  Q5 runs warm so install the provided heat-sink.

12) Install Q1, and Q2.   D8, the two color LED can also go in, shortest leg goes into the square pad.  Don’t cut the legs, instead install the LED as high as possible.  It will be bent to fit the front panel later. 

13) Assemble the small PCB by installing two diodes, the fuse, and the connector as shown.  Then attach about 5 inches of coax.  See pix.

14) The 1megohm resistor was originally omitted, but should probably be installed to establish a DC reference for the gate of Q5.  It can be easily tack soldered to the back of the board from one side of RV2 to ground.



You could test the board at this point but it is actually pretty easy to access and remove from the case so I recommend testing after the case is assembled and the board installed.

Case Assembly

1) It is easier to label the back panel before the connectors are installed. You should trim the provided label strip to a length that doesn’t interfere with the mounting screws and put it across the top back.

2) Install the connectors on the back panel nice and tight.  The anodizing on the panel is pretty tough so with a bit a bare copper wire, tie all the ground lugs together as insurance that they are all really grounded.

3) Add the bit of fiberglass shaft to the shaft of RV1.  Use the adhesive lined heat shrink provided.  This will allow this control to be adjusted from the back panel.  If you are lucky, I will have done this for you.

4) Insure that the board controls fit nicely in the front panel but don’t put it on just yet.  With another bit of copper wire, connect the cases of the GAIN, PHASE A, and PHASE B, controls to ground.  Tack the wire to the top of each control and to the small ground plane pads to the extreme left and right.  It doesn't hurt to also ground RV1 in the same manner but you will have to sand the case a bit to get it to take solder.

IMPORTANT-- make sure that all the leads are all trimmed close on the bottom of the board..  long leads will short to the case and cause lots of grief.

5) Slide the board into the one of the housing halves and after fussing with the LED to align it with it’s mounting ring, go ahead and put nuts on the controls and a couple of screws to hold the front panel to the  housing.  You may notice that the front panel is labeled on both sides, DON’T PANIC.  I considered for a short while that it might make sense for the unit to sit vertically.  It didn't.  Just put the horizontal layout to the front.

6) Install the rear panel and hook up everything other than the Noise antenna connections.  With the knobs facing front, the connectors on the rear of the board always have the ground pin to the right, active pin to the left.  Put the rubber feet on the bottom.

7) The transceiver cable goes through a tight grommet, but even so it would be a good idea to put a bit of your favorite glue on the cable to hold it firmly in place.

8) The LNA board simply sits above the main board held in place by a 90 degree SMA coupler to it’s input.  Power is provided by tack soldering two wires on the main board near poor little Q4.  (ground and the collector of Q4)

9) The input to the LNA comes from the rear panel (the BNC connector) through the small red PCB. 

Trouble shooting.
CAUTION: If the transceiver is connected, there is a possibility of high voltage and RF exposure. 
BE CAREFUL!  Turn RF power down on your radio and take care not to transmit.

It is fairly robust circuit so you should not experience any problems if you managed to get all the parts in the right holes and in the proper orientation.  But don’t panic if you do have an issue.  Should something not function, check the schematic for that area and recheck the parts related to that function.  It is surprisingly easy to mis-read a component’s value.  There are a few extra parts included with the kit in case you need them (extra fuses, a J310, etc.)   Start with getting the relays to click when the PTT is grounded.  When that works, you know that the power is right. 

Make sure that the LNA in not in backwards, same for all of the transistors, and the transformer.

If you still have signal problems, try connecting to the receiver but without the antennas.  Use a small probe or bit of wire to touch various points along the signal path.  Just your body as a signal source will introduce plenty of static to locate a fault.   If you can mess with the knobs and get a null in background noise, it is working properly.  You just need to get the best noise antenna and get good at fussing with the knobs.

All else fails, email me and I will try to help.      rob@ag6yj.com