FPM20 Rebirth of the hallicrafters FPM300
10/28/2016 ~ New Power Amp Stage
I have somewhat changed direction and added a 4 Watt Linear Amplifier Stage which uses a device I found in the junk box --a 2SC2075. Had a board layout in my computer so about 10 minutes worth of work on the CNC mill and I had a new board. This is shown below. With 4 watts I can drive thru an intermediate amplifier the SB200 to about 600 Watts out. This is a signal that can be heard on 40 Meters all the way to the right coast from the left coast.
|Schematic ~ the 2SC2075 is substituted for the 2SC2166 with no other circuit changes|
|The "As Built" amplifier ~ The metal case is the heatsink!|
Looks like crap works like Hell!
You too can build rigs like this!
10/24/2016 ~ More refinements -- improving the power output.
Initially I set the carrier oscillator frequencies in the Arduino sketch to the values indicated in the schematics. The USB frequency seemed way off. A quick and dirty test is to set the mode to USB and normally speak into the microphone. The output was much lower than LSB. A second part of the test is to whistle into the microphone (the rig was connected to a dummy load) and the output noted. On LSB the whistle test produced about 1/2 the output on LSB as compared to speaking into the microphone. On USB the whistle test produced about 1/10 the output as compared to the LSB with voice.
Using a separate external oscillator for the carrier input I adjusted the BFO frequencies until the whistle test on LSB and USB was at the same power level and these in turn matched the output using speech. These values were much different from the schematic values. But then on closer examination of the circuit schematic for the BFO both crystals had trimmer plus fixed caps connected across the crystals -- so the actual oscillating frequency was modified in production and different from the marked frequencies. In my rig the BFO is supplied by the Si5351 and the values are set in software. I suspect that I am really close but may be off by about 30 Hz on LSB, which I will further test to verify that hunch.
These changes have resulted in greater output! I switched the linear amp following the driver stage to the brick liberated from an Atlas 210X. Now I am easily seeing about 50 watts output and driving the SB200 produces about 450 watts on peaks. So we are cooking. This evening I had a QSO with a station in New York where I was running 50 watts and he had a KX3 cranked down to 1 watt. So with a modest power level you can have coast to coast contacts on 40M.
I am really excited about this rig! There are some plans in work to make this a two band rig covering 20 and 40 meters.
So far I have had about two dozen contacts with stations in California, Washington, Nevada, Utah, New Mexico, Arizona, Texas, Nebraska and New York.
|FPM20 now working at 50 watts with an external amplifier!|
10/23/2016 ~ The FPM20 is "Alive" and making QSO's
The rig went "live" on 10/22 and so far I have made about a dozen contacts. Some of the contacts were made using just the driver stage at 350 Milliwatts (this is the EMRFD variant with a 2N2222 and BD139). Several were made using the outboard SS amp running about 25 watts. One piece of DX was a QSO with a station in Nebraska. (KD7YUW) where I was running 25 watts.
This is how it looks but I desperately need to tidy things up.
|This is the rig "as is" as of 10/23|
|This is the 350 MW driver stage and low pass filter.|
Building a Junk Box Rig from a Commercial Transceiver Board.
In the photo below is a "breadboard" version of the FPM20. Essentially the heart of this rig is the main board from a hallicrafters FPM300 SSB/CW transceiver and the S Meter. I have added a 2N3904 Receiver RF amp stage, a band pass filter comprised of two 42IF123 10.7 MHz IF transformers padded to 7.0 MHz, a Si53551 providing the LO and BFO signals and a power supply board (the FPM used weird voltgaes0. Rounding this out is the SBL-1 that acts as a receive and transmit mixer stage. The audio output stage uses an LM-386-3.
In the video above the receiver was working but I got no output on transmit -- that is until I realized on the output chain (the final device on the board) consisted of a 40841 Dual Gate MOSFET. that has ALC applied to Gate 2. Upon close examination of another of the circuit diagrams I saw a note about ALC. On receive the voltage is "0" but on transmit with no signal applied the voltage was 6 volts supplied from the ALC circuit -- this was a negative ALC. As more signal (such as from over driving) is developed the ALC becomes less. I had applied no voltage to Pin 17 on the board so essentially the circuit was cut-off! I added a 5 volt regulator to Pin 17 on transmit and the circuit now works on transmit --and CW. The FPM 300 used a keyed tone for CW generation.
A new board will be built using my standard 2N3904 bi-directional circuit which acts as the RF amp on receive and the transmit pre-driver on transmit. There is sufficient output from the 2N3904 to fully drive the 20 Watt brick sold by CCI. This is why the rig is dubbed the FPM20. We are on our way.