Monday, 10 June 2019

24GHz DATV World Record extended

As it was IARU contest weekend and G8GTZ was going to be portable at Dunkerry Beacon IO81FD it seemed an ideal opportunity to extend the 24GHz DATV record from Cleeve Common IO81XW81. It would also nice to try out the upgraded 6GHz FMTV system. so a trip to Cleeve common was setup for the Sunday morning

Friday night I checked out the 24Ghz system and was getting low transmit output on both DATV and SSB. Many hours were spent investigating with no success

Saturday morning I got out the spare 2W W2PED amplifier module. Over coffee I spotted that the replacement amp had 6 bias pots, the installed amp had 5 bias pots. Analysis showed that one of the Bias pots had come off the installed board. The multiturn pot is very small so I had to resort to raiding a 2Ghz amp board to harvest one. It was installed and the bias set to match the voltage on the replacement module. After many lost hours we were good to go

Sunday morning, Arriving on site at 1030 first the FMTV was setup

Noels picture was quickly seen:-

After the 2 way QSO the FMTV gear was then removed and the 24GHz equipment Installed.

 To align the antennas we had a 24GHz narrowband FM QSO, Noels signal pinning the s-meter on the FT817, looked promising. I then transmitted DATV and Noel instantly saw the picture:-

Noel then transmitted and I instantly saw TV data being received but no picture. After Noel trying lots of datarates and parameter permutations a picture was finally seen:- 

Wednesday, 5 June 2019

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