10GHz Project

The finished 5760MHz conversion. Well hidden under the top box is the original fixed wireless broadband unit, consisting originally of a TX and RX board in milled aluminum case sandwiched together, and a long CPU/modem/Power PCB. For rover use, I wanted to repackage it for ruggedness, so I replaced the PCB with smaller DC-DC converters, and a PIC CPU on an inexpensive PIC proto board. Added in the Common IF relay, the 41MHz oscillator/PLL in it's own subsection, 3MHz OCXO, and used UT141 in most places for rugged handling and carriage in backs of bouncing vehicles on mountain roads (some do not classify as a road).

5.7GHz end of things. Filter and Isolator in the TX output, filter in the RX input, T/R relay, and flexible 141 coax bracketed to the case for antenna feed. I expect that when I add a LNA or TX amp, it might mount on the lid.

41MHz oscillator and simple PLL circuit. Home brew board layout for ExpressPCB. (Files at bottom)

SMA SPDT coaxial switch mounted internally to reduce outside clutter (failure points) acts as the common IF relay at 430MHz IF. Both are 28VDC relays, powered by two 12V to 5V DC-DC converters in series with the 12V supply voltage. for 20 to 23.8VDC range on a typical battery operation. The brown board is a single sided PCB that mounts the 12 to +/-15VDC and 12 to 5V DC-DC Converters, the 3MHz OCXO, and a IRF510 that switches the 24V for the pair of relays. There is also power supply filtering and 7805 5V regulator bolted to the case for heat sinking. The transverter and the oscillator/PLL both use the +5 and +/-15V.

Total current draw of the completed system come out to be 1.5A at 13.8V, with little change over 10 to 14V range. The CPU sequences the relays, TX_Inhibit, TX_Enable and handles the LEDs. It will lock out TX_enable and PTT LED if the PLL looses lock. I always operate the relays on PTT no matter what. Replacing the RX output MMC on the RX board takes about 1-2 hours due to the complex casing and number of screws.

The Common IF relay is supported by standoffs and a aluminum plate, though the UT-141 could do it by itself. A small pot on the CPU board controls 0-5V to the RX attenuator in the RX board removing the need for a coaxial attenuator. We removed the internal electronic TX attenuator, so I have a 3dB SMA coax attenuator in the TX line (430MHz) and I adjusted the FT-817 IF radio to -5dBm max output on UHF band. I had a different IF SMA relay fail to switch reliably and I blew the RX output MMC. Since that is no fun, I decided to use the FT-817 menu controlled settings to lower the output and also used the TX_Inhibit and the analog band decoder output as a very complete sequencing solution. With a CPU sitting there, why not? Finally found a reason to use the A/D converter in the 16F877 PIC CPU.

Top views of the control equipment casing. To reduce complexity, I found I could order 1/4" thick 5'x12" aluminum plate and any length of 1/4" x 2.5" flat bar. With this thickness I only needed to cut the flat bar to the proper lenght for side walls and drill and tap to bolt everything together. A little finish filing, and a sandpaper treatment to give it a smooth brushed aluminum appearance - no significant cutting or milling required, though I did break 4 taps in the process. Used 6-32UNC screws throughout.

The IF and control end. Here is used a thinner aluminum plate to accommodate the many connectors. A DB-25 handles power, TX_Enable, PLL programming signals and breaks out to the 2 2x10 headers on the transverter RX and TX boards. LEDs provided for PLL lock detect relayed via the CPU, and PTT also relayed by the CPU. The relays will always switch to protect the RX input, though the TX_Enable will only be activated if the IF radio is on the UHF band. When on the UHF band, TX_Inhibit is also applied. I release TX_Inhibit on the FT-817 to permit 2M liaison with the same radio while out on the tripod for convenience. There remains some risk I could setup the FT-817 RF ports wrong and blast the TX input with 2 watts at VHF, but the chances are small since I do not usually reconfigure the FT-817 much. I use a pair of power poles to extend the power supply cable to the FT-817 cleanly. Same arrangement on my 10GHz system. Since the FT-817 has an internal battery, I can disconnect it and plug in the weak signal source that uses a very stable 15.36MHz TCXO to verify RX operation and frequency on the dial. It operates at 5760.049MHz so is convenient as a calibration check. I know when the unit is warmed up, usually only a couple of minutes.

A 1.3GHz LMX2353 PLL inside the RX unit controls a 2665MHz VCO. The VCO output is halved for the PLL sampling, and the VCO output is doubled to 5330MHz for use with a 430MHz IF rig, in my case a FT-817. Using the configuration menu I lowered the power output to -5dBm. I use a 3dB attenuator in the TX input for the final -8dBm drive level.

The 41Mhz oscillator with a 3MHz Isotemp ovenized crystal oscillator module. Oscillator and PLL board custom designed. Board layout and component details available on request. Design adapted by Fred, WA7TZY from a November 1999 QEX article incorporated into the Experimental Methods in RF Design book published by the ARRL (2003), authored by Wes Hayward, W7ZOI, Rick Campbell, KK7B, and Bob Larkin, W7PUA.

A PIC16F877A controls several features. Source code available on request.

1. Program the LMX2353 PLL for 2665MHz
2. Detect when the FT-817 has UHF band (430MHz) selected using the analog band decoder output
3. Detect PLL lock and prevent TX_Enable or releasing TX_Inhibit of unlocked, operate T/R relays just in case though. Light the green PLL Lock LED
4. If the FT-817 is on the UHF band, apply TX_Inhibit to block RF output from the FT-817 (+12V).
4. Detect PTT
5. Operate the T/R relays
6. Delay for the relays to settle
7. Apply 5V to TX_Enable to the transverter
8. Release the TX_Inhibit
9. Turn On the red PTT LED

The source code and Excel program I created to calculate the best legal combo of reference frequency, IF frequency, N, and A/B values is here
The ExpressPCB and SCH files and parts list file are here