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 two PHASE knobs jointly adjust the phase of the noise signal. You should adjust each for a minimum. Unfortunately they also mess a little 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. If you find that it works best with the attenuator below half way, try reducing the gain by plugging the LNA into the 9V power source, or consider removing it completely.
The DELAY ADJ is inside on the pcb. This screwdriver adjustable trimpot is used to adjust the delay time of the relays after transmit. It is not critical if you just use AM or SSB, the time can be fairly long without being annoying. CW will require a shorter time and a little more fine tuning.
ASSEMBLY of the PCBs:
This kit may not be as challenging as building a HeathKit color TV, but it will still require a bit of time and skill. If you have not built an electronic kit for a while, you should probably practice with a simple DIY kit of some sort from eBay. Before you start the ‘180 assembly, thoroughly study the schematic and understand the function of each part of the circuit, it will be a help in construction and operation. Review the instructions and be certain that you can identify all of the components. 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 at a time. Complete assembly is probably a two evening job; there are a lot of parts.
You will need some basic tools: soldering iron (about 40W) with a smallish tip, your favorite solder, sharp flush cutters to trim leads, screwdrivers, needle nose pliers, and if you are not 13 years old, a good magnifying lens. A volt-ohmmeter, even a cheap one is pretty much a necessity (Harbor Freight has several for $10 or less, as does eBay).
You will notice that when soldering, that the ground plane is quick to dissipate the heat on grounded pads so you will have to stay on those pads a bit longer to get good flow to the top of the board. 3-4 seconds is usually about right.
It is generally best and easiest to install the smallest parts first, and gradually work up in size. Don’t stress about getting the components close to the board. It may look nice if they are all flat and neat, but keeping them a little above the board would make any rework easier and generally improve air flow. This is especially true of all the small transistors. Refer to the board layout drawing and install 6-7 parts at a time, 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 often a few extra parts in the kit (I don’t count so good, but I try hard to never be short).
When the board is complete, you can clean the backside with a little rubbing alcohol and an old toothbrush to remove the flux from soldering. Check to see that all leads are trimmed enough so that they will not short to the case. Check especially those along the edge of the board.
MAIN PCB ASSEMBLY:
[_] 1) It’s a good idea to install the Zener Diode D7 first, this will keep it from being confused with the 1N4148 diodes which look almost identical. Then install the 1N4005 black rectifier diodes (D1 & D18). Now you can put in the three 1N4148 switching diodes (D2, D13, D19). As with all the diodes, watch the polarity and match the band with the silkscreen image.
[_] 2) Install the two full wave bridges, they are in the 4 pin dip packages. Note the + and – location on the board layout drawing.
[_] 3) Install the inductors, be careful, there are two different values and they can be difficult to tell apart. They look like resistors, but will measure nearly zero resistance on your ohmmeter.
[_] 4) The resistors are next. R9 and R7 will run warm in operation so mount them about 1/8” (3mm) or so above the board. Save the potentiometers until later since they are large and get in the way. Some resistors have 4 value bands (1%) and some have 3 bands. It didn’t matter but the 1% types were supplied when available.
[_] 5) Install the capacitors, just save C3 until later. Only C2 and C3 are polarized, the rest can go in either way. Each is marked with a very small 3 digit value code.
[_] 6) Now is actually a good time to install the board connectors. The pre-wired cables should be oriented correctly: The 4 pin cable should wind up with the RED wire in the square pad. The two-pin cables should also be inserted so that the RED wire goes to the square pad. The green connector and the SMA connector may require a little more heat.
[_] 7) Take a break from soldering and wind the transformer. Wind 10 turns of the enameled wire, and then three turns of the 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. Trim the wires to about the right length to fit the board (not too short). The insulated 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 before soldering. Double stick tape will hold the core in place on the board.
[_] 8) Install Q2,Q3, Q5, Q6. Leave out Q1 and U2 until after testing. Leave all the transistors well above the board, it will make removing them possible if that ever becomes necessary. On Q5, install the provided heat-sink before you solder it in.
[_] 9) Install Q4, the large PNP power tab transistor. The metal side of the transistor goes toward the inside of the board.
[_] 10) Add the bit of plastic 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. Use a heat gun or very small flame to shrink the tubing.
[_] 11) Install the ‘delay adj’ trim-pot, RV5.
[_] 12) All of the larger parts can go in now. Don’t forget to install C3, and the 2 fuses (lamps). Solder in the controls and the relays. Note that RV1 is a 1K pot. The others are 5K. Be sure that the pots are firmly seated against the board so that the front panel will align with the enclosure correctly. Some of the pots have a metal anti-rotation mounting tab that will interfere with mounting in the front panel. Cut or break that tab off of the 5K pots before soldering.
[_] 13) You can now install the front panel. Do a test fit then carefully bend the LED to line up the the hole. Attach the panel with the washers and nuts on the three controls, just finger tight for now. Make sure that the LED is firmly snapped into its bezel and solder it in place.
[_] 14) This is not critical but it is a good idea to electrically connect the ground plane of the main PCB to the back of the front panel. Just solder a bit of wire (a piece of resistor lead) from one to the other. Doing this will allow operation of the unit outside of the case for testing. (the only other ground for the front panel is through the case and the paint can insulate connection)
[_] 15) Cut one of the two pin cables (red/black wires) to about 2 inches and solder it to the power switch. Polarity doesn’t matter. Install the switch into the front panel and tighten the nut. Plug the cable into the PWR SW connector on the board.
REAR PANEL ASSEMBLY:
[_] 1) The rear panel is really a PCB. It will provide a location for the fuse and protection diodes for the noise input.
[_] 2) You will need to surface-solder a full wave bridge pack to the back of the rear panel. Note the orientation and match the + & -. This is as close as we get to doing surface mount.
[_] 3) You should install the remaining 4 connectors as indicated. Tighten well, and if you have a dab of Locktite TM ,glue, or nail polish, this would be the place to use it.
[_] 4) Solder a small lamp (fuse) from the center pin of the BNC connector to the L-shaped pad next to the four diodes.
[_] 5) A 5.6uH inductor is also soldered between the ‘L’ shaped pad and ground. It is easiest to cut one leg to about 3/8“ (8mm) and prep it with a small bend. Then you can hold the other long leg to solder it in place. After the short end is soldered cut the long end and bend it into place and solder. Depending on your noise source you may get better results without this inductor. For now, a good plan is to leave the ground end floating so you can easily try it later.
[_] 6) On the four pin connector with wires, cut the white and red wires (don’t cut the yellow and black) to about 3.5 inches long. Then wind 3 turns of both the yellow and black wires through the green ferrite ring. This choke helps to block RF from getting in or out through the power wire. It also a good idea to solder a 0.1uf cap across the power connector on the rear panel. The yellow and black wires can now be soldered to the power connector on the rear panel. The yellow wire is connected to the center conductor, positive terminal. The ground lead should also be jumpered to the pad on the rear panel.
[_] 7) Solder the white wire to the center pin of the RCA jack. Then, solder the red wire to the L-shaped pad. You can also solder a 0.1uf cap across from the center pin of the RCA jack to ground if you like. Although not necessary, it can keep some RF out of the power.
[_] 8) Strip and prep the thin coax cable with the gold SMA connector, and using the pad next to the BNC connector, carefully solder the shield to ground and use the connectors ground lug as a strain relief for the cable. The center conductor should be soldered to the L-shaped pad. Use minimal heat to avoid melting the center conductor.
[_] 9) Using three pieces of about 2.5 inches of 18-14 awg wire, connect the SO-259 connectors to the three pin Phoenix connector. Note, the center pin is ground (GND on the PCB silkscreen)
[_] 10) You can solder the remaining 2pin red and black wire connector to the LNA. Run the wires through one of the mounting holes as a strain relief and connect the red wire to + and black to -. Don’t install the LNA until you do some basic testing.
[_] 1) It’s not a bad idea to check to make sure that the board slides nicely into the case and that the front panel holes line up. You may have to loosen the controls or re-solder them to get a perfect fit, but don’t install the case just yet. Double check the rest of your work and verify that all of the transistors are in correctly and that all of the diodes are in the correct direction. The LNA can be left out for now. Steps 2 thru 4 can be done with the boards out of the case.
[_] 2) Before the 4 pin power cable is plugged into the board, plug in the power supply to the rear panel and verify that 12V is present on the yellow and black wires and that yellow is positive.
[_] 3) Now plug in the 4 pin cable and the green 3pin connector. When pressing the power switch, you should hear the relays click and the the LED should light in a yellowish color. If it is green, the LED is reversed. If nothing happens check for 12V power at the power switch, the orientation of Q4, 5V across D7, and the location and orientation of Q2. If C3 gets hot and explodes violently, it was in backwards.
[_] 4) If everything works so far, and with power on, try grounding the control input (the RCA jack). The relays should click and the LED should change to red. If this fails, check D7, and the other diodes and components around Q2. When you are satisfied that the power and relay control is working, then install Q1 and U2.
[_] 5) You can put everything in the case at this point but leave the top off. You can tighten the controls and install the knobs. (It’s good time to put the rubber feet on the bottom as well)
CAUTION: When 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.
[_] 6) Continue testing with the transceiver, the power supply, your main antenna, and a noise antenna, connected. PTT is optional since you will not be transmitting. Hook up a noise antenna to the BNC connector on the rear panel. Maybe a 2m antenna or just 5-10 feet of wire in the shack for now.
[_] 7) The LNA board can be installed now, it simply sits above the main board held in place by a 90 degree SMA coupler to the LNA’s output. Power is provided by one of the two, two-pin connectors. Use the 12V connector for testing. The signal input to the LNA comes from the rear panel cable (the one with the SMA male connector).
[_] 8) When everything is in the case and connected, turn the QRM-180 power on and off. Listen for the relays to click and observe the power LED. When the power is on the LED should be yellow-ish. Set the gain, and the rear attenuator to max.
[_] 9) Turn on the transceiver. With the QRM-180 off, the receiver should work normally.
[_] 10) When you turn on the QRM-180, there should be a lot of noise in the receiver. Play with the controls to get a feel for them and try it with and without the noise antenna connected.
[_] 11) At this point you should be able to adjust the two phase controls to get a sharp null point. If not, recheck your work and use an ohmmeter to verify that the rear panel cables are connected and not shorted. You can lift one end of L1 on the rear panel to get a check of the resistance of the SMA cable.
[_] 12) If everything works the unit is now complete!! Go to the section on operation and begin testing your options for a good noise antenna. If you still have issues, review the “list of common problems” and continue testing.
You can operate with or without the LNA as needed, depending on the noise level and size of noise antenna. If you remove it just plug the SMA cable from the rear panel directly into the main PCB. For less gain, you can also try plugging the LNA into the 9v power source. While normal is 12v, the LNA is a bit cleaner on 9V. Try both.
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 miss-read a component’s value. Start with getting the relays to click when the PTT input is grounded. When that works, you know that the power circuitry is right.
If you still have signal problems, try connecting to the receiver but without the antennas. Use a small probe or bit of wire, and following the schematic, 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.
Common Problems: Power issue or relays don’t click:
• 12V red/black wires switched on the rear power connector. Check the power at the board.
• The rear panel gets its ground through the green connector. Be sure that it is plugged in when testing the PTT function through the RCA jack.
• A 1N4148 diode switched for the Zener? There should be approx 5V across the Zener.
• Is the power tab transistor backwards? Tab toward C3.
• Check pads that have top traces, sometimes solder doesn’t flow to the top and the plated-thru hole can break leaving the top trace unconnected.
• A few pads are very close to the edge of the board and can short to the case if the leads are not trimmed flush on the back of the board.
• Check the resistance of the SMA coax cable to the rear panel, it is easy to overheat the shield when soldering and short it to the center conductor.
• Is the LNA in backwards? RF in goes to the rear panel, RF out goes to the board. Is the power correct to the LNA? Plus voltage to VCC on the LNA?
• Are the enameled wires of T1 sanded and soldered?
• Check all the fuses with an ohmmeter. It is difficult to tell when they are open. Spare fuses are included but if you need more, they can often be found in hobby shops or on eBay by looking for ‘model railroad lamps’. 6V 40-100ma lamps are best but small 12V lamps will work.
• Check the grounds between antennas and the radio. A loose connector will cause lots of grief.
All else fails, email me and I will try to help. firstname.lastname@example.org