[MRCA] retransmit project phase 3

[W2HX]

Ok folks, I am sure you’ve all been on the edge of your seats waiting breathlessly for the next installment of this radio drama (oops, I thought this was the lone ranger show).  But seriously, folks.

Just to reiterate these are the phases of testing so far.
Phase 1 – get HF radio working on low power and sincgars VHF radio working on low power individually and use retransmission cable between them (completed successfully, or so I thought)
Phase 2 – get sincgars radio installed in vehicular mount with high power RF amp, test radio, mount, amp and AS-3900 antenna (completed successfully)
Phase 3 – (this phase) configure both radios for high power (not interconnected) and perform tests to observe interference and other possible nastiness. 
Phase 4 – (future phase) interconnect both high power radios using the retransmit cable and perform full system testing. This would be using a PRC-68A HT as the VHF “client” radio and a BCC39B manpack as the HF “client radio.” 
Phase 5 – (future phase) test gas generator and attempt to reduce ignition noise observed in the radios while operating 60 meters. Determine if gas generator is a viable power source. Also work to interconnect a 100AH 28V Li-Ion battery as a potential source of power for field operations.

The latest phase 3 testing, which I just completed, consisted of getting both radios running in high power to see what ill-effect might exist with interference (or worse, damage).  Here is a picture of the setup:
http://www.w2hx.com/x/RXMTProject/IMG_1470.JPG

However, to accomplish this I had to create a custom cable to interconnect my harris power supply with both the harris radio and the sincgars system.  This cable had to be customized because the pinouts for the harris amp are different than the pinouts for the sincgars mounting base, despite using the same MW series 4 pin “standard” military power connectors.  Here are some pix of the cable I made (thank you K4CHE!).

First, I had to wrestle it to the ground and get it in the vice.  The vice lost. 
http://www.w2hx.com/x/RXMTProject/Custom-PWRCable/IMG_1463.JPG
you will see I’ve started to solder the wires together.  Another angle
http://www.w2hx.com/x/RXMTProject/Custom-PWRCable/IMG_1464.JPG
Now we heat shrink
http://www.w2hx.com/x/RXMTProject/Custom-PWRCable/IMG_1466.JPG
Put back the original outer jacket
http://www.w2hx.com/x/RXMTProject/Custom-PWRCable/IMG_1467.JPG
and then put a really big heat shrink over the whole cable
http://www.w2hx.com/x/RXMTProject/Custom-PWRCable/IMG_1468.JPG
I really should have put some electrical tape on the outside of the cable before the big outside heat shrink to make the transition between cable halves smoother. Oh well, it works well enough.

With the cable made, I connected everything together and voila. Power.  With power to both systems now, I tested running both systems on high power (gradually increasing power from 1W to 5W to 20W to 125W/50W approximately. You get the idea). Good news is that neither radio seems to interfere with the other in any way that I could detect. The antennas were about 20 feet away from each other and I really could not detect any interaction whatsoever between them. This is great news and a testament to some really great radio engineering! This test completed very successfully.

Concerned about stressing the power supply with two radios connected, I went about doing some power consumption tests with both radios connected on high power. Below are three videos detailing the power tests. The result was, with both radios transmitting with full power (125W CW for HF, 50W FM for VHF) the entire system consumed 600W.  This is good news as the Harris power supply I have been using is rated to handle 30A which is about 800W.  And considering the two radios would never be transmitting at the same time, I think 600W is a decent worst-case-scenario.

http://www.w2hx.com/x/RXMTProject/MVI_1471.MOV
http://www.w2hx.com/x/RXMTProject/MVI_1472.MOV
http://www.w2hx.com/x/RXMTProject/MVI_1473.MOV

The long term plan is to have this all mounted in my 1967 land rover series 2A. As part of this, it is my intention to use this 28V 100AH battery (that I will obtain tomorrow if all goes well!) in the vehicular installation.  At 600W operating (both HF and VHF transmitting simultaneously) this battery should give somewhere in the neighborhood of 4 hours constant transmit time.  Of course, no one transmits 100% of the time and only one radio should be TX at any given time. The HF radio consumes the most power at about 400W during transmit (with sincgars in receive). This yields approximately 7 hours of constant transmit, again not likely. At a 4:1 (rx/tx) ratio (typically a 9:1 is used) I should get 25 hours of operating.  And this is assuming the vehicle is not running. While its running, the plan is to have its alternator charge the 100AH battery through a 30A DC-DC converter (12 to 24V). But that is a story for another time. For this phase of testing, we are happy to know about 400W is what will normally get consumed during HF transmit :)

More about Phase 4 tests in tomorrow's email ☺
 
73 Eugene W2HX