Activity weekend 17/18 April

[radiogareth]

OK, so it wasn't really the weekend but I spent some time on Friday going out portable/mobile doing DVB tests with Martin G4FKK providing the base station. Initially I drove to Botley Hill Farmhouse (now a pub, IO91XH) and using about 5 watts of DVBS2 on 437 accessed GB3HV with a triple colinear on a mag-mount....bit marginal and only successful once Martin swing the HV beam round for me. Onward back towards home took me to Sanderstead Church car park where I put up my full-wave 70cms dipole with its new dual mount (horizontal or vertical). Easy access and a good signal into HV. Switching to DVB-T I then drove across to Martins QTH, transmitting all the way (about 2 watts DVB-T). Once there a reboot produced a lock and we tested in the locality using 150,333, 500 SR on DVB-t, also using 7/8FEC. Still getting chopped up video though, even with the camera pointing at me in-car (so less picture content change). I did take a laptop and Pluto with me, but despite all good indications, I couldn't get any RF out from ExpressDVB TX. Maybe I pickedu p the wrong Pluto...
On Sunday (which is the weekend) we arranged to try cross-band duplex using 4 &2m. After various attempts using different combinations we eventually established reliable duplex with me running 1 watt DVB-T 150ks on 146.5 and Martin a few watts of 333ks on 4m. Other than the 2x4 seconds delay it eventually worked, with a little bit of help from 1.905MHz ssb talkback. I was unable to reliably receive MArtin on DVBS2 at much higher power, I suspect that the Knucker NIM has better ears than a MiniTiouner even with an Amsat SAW preamp (only 11dB gain). It would be interesting to know how much more gain I need to 'level the playing field' as despite having to run much less power for DVB-T it seems to make the trip easier with less. Not sure how to compare the raw signal levels and SR's etc.
I need to finalise my MRF300 amps for 6,4 & 2 and build a beam for 70cms use, possibly two, one for /P and a permanent one at home.
I had hoped to run my Nokia Dolphin amp (20W DVB-T or 50W DVBS-2), but the boost converter I was using to give 28V couldn't cope with the current demand. Another job....
Gareth G4XAT

[g8gtz]

Hi Martin,

Interesting experiments - my weekend was a dead loss with no real interest in 51 and 146 MHz during the Dutch contest - I should have taken 70cms!

. I was unable to reliably receive MArtin on DVBS2 at much higher power, I suspect that the Knucker NIM has better ears than a MiniTiouner even with an Amsat SAW preamp (only 11dB gain). It would be interesting to know how much more gain I need to 'level the playing field' as despite having to run much less power for DVB-T it seems to make the trip easier with less. Not sure how to compare the raw signal levels and SR's etc.

Don't forget a typical satellite LNB has ~55dB gain at 10GHz /L band IF so a low noise pre-amp at MH plus a 20 dB line amp seems to be about right to drive the 4344 NIM - a general guide is to get the MiniTuoine RF level meter to be around 60 - 70.

The Knucker 4762 NIM on the other hand is designed to connect directly to a terrestrial antenna so whilst it will benefit from a low noise pre-amp it gives reasonable results barefoot - it certainly does not work well when driven with the same level as the 4434 NIM.

Noel

[radiogareth]

Couple of pics for interest (?)...
Gareth

G4XAT-at_G4FKK.jpg (164.96 KiB) Viewed 1584 times

Martin_at G4XAT.jpg (139.55 KiB) Viewed 1584 times

[G8YTZ]

I maned to (just about) get into GB3EN on 23cm @ 1MS/s Changing the FEC down to 1/4 did not actually make much difference, but I got there. If I move the shack upstairs the much shorter feeder would probably make all the difference.