Upgrading the 6GHz FMTV system

Having got the 6GHz system going for the trip to Brown Clee, it soon became apparent that, although the system worked well on sunny days, it would be unuseable on rainy days. Time for a rebuild!

The system consisted of two boxes, one containing the FPV receive and transmit modules, the other containing the large Fujitsu power amplifier

Not very waterproof!

Looking in the junk box I rediscovered an  8W power amplifier module obtained from G3OHM. I also found the connection details and with the help of G4JNT constructed a power supply.  It worked fine and i discovered it worked with just +-10.5V on the opamp supply, good news when running off a car  battery. The only issue was that it was quite a chunky unit, hard to mount at masthead.  I found a suitable waterproof diecast box and worked out that by dismantling the amplifier modules and PSU board it would fit

I also discovered a smaller FPV transmit module with adjustable power output to avoid overdriving the amplifier. 20mW through a 10dB attenuator proved to be sufficient. The following is how it ended up

It is powered by a 6 pin Bulgin power connector (the same as used on my rotators) allowing the use of thicker/more cables to reduce the voltage drop on Transmit (it takes around 4A when it produces 7W of DATV) Video out of the receiver is via an N-type connector, video in to the transmit module is via a TNC connector (more waterproof than BNC) There is room for a receive preamp and filter if needed. Now to try it out

6m RBTV Outing to Titterstone Clee

Having failed to make a 2 way QSO with G8GTZ/P on 50 MHz RBTV from the Tump due to his PA issues we decided to try again over a longer path from Walbury IO91GI to Titterstone Clee, IO82QJ. It would also be an opportunity to try the 5665 MHz FMTV system. Path profiles looked good for 6m , but a bit iffy on 6cm

Approaching the site I was surprised to see snow on the ground! The 6m gear was assembled and Noel was a good signal on NBFM, although there was deep QSB. Transmitting 50 W of DVBS to Noel he could not quite get a picture decode. As I was using my Portsdown 2019 system, which is Limesdr mini based, I had the option of running DVBS-2 transmissions, which supposedly gives the system an extra 2 dB capability. Switching to that mode allowed Noel to get a decode.

Noel then transmitted around 10 W of DVBS-2 back to me. The minitune receiver could not quite get a picture , but I left it running while on a long meander around the site trying to find cellular coverage, and when I came back had captured his  test card. Two way QSO of 140 km completed for a new UK record.

I then assembled the 5665 MHz equipment, with its 2' dish and FPV modules with an 8W Fujitsu amp. The FPV Transmit module needed a 20 dB attenuator to avoid overdriving the Amplifier. Talkback was on 6m FM. Noel couldnt see my signal, and I couldnt see his 3 W, with the exception of a 15 second period, assumed to be aircraft scatter where his signal was identified. Partial success at least, perhaps confirming the predictions were correct.

G8GTZ/P

G4FRE/P