Activity weekend 17/18 April

Digital ATV - The latest generation, cutting edge ATV - Please discuss it all here.
Forum rules
This forum is run by the BATC (British Amateur Television Club), it is service made freely available to all interested parties, please do not abuse this privilege.

Thank you
Post Reply
radiogareth
Posts: 690
Joined: Wed Jan 06, 2016 9:46 am

Activity weekend 17/18 April

Post by radiogareth » Sun Apr 18, 2021 3:07 pm

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
Posts: 1448
Joined: Wed Apr 07, 2010 6:26 pm

Re: Activity weekend 17/18 April

Post by g8gtz » Sun Apr 18, 2021 3:58 pm

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
Posts: 690
Joined: Wed Jan 06, 2016 9:46 am

Re: Activity weekend 17/18 April

Post by radiogareth » Mon Apr 19, 2021 8:01 am

Couple of pics for interest (?)...
Gareth
G4XAT-at_G4FKK.jpg
G4XAT-at_G4FKK.jpg (164.96 KiB) Viewed 332 times
Martin_at G4XAT.jpg
Martin_at G4XAT.jpg (139.55 KiB) Viewed 332 times

G8YTZ
Posts: 34
Joined: Sun Feb 10, 2019 7:43 pm

Re: Activity weekend 17/18 April

Post by G8YTZ » Mon Apr 19, 2021 8:37 pm

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.

Image
Attachments
G8YTS 1MSs GB3EN 4x3.png
G8YTS 1MSs GB3EN 4x3.png (1.39 MiB) Viewed 254 times

Post Reply

Return to “DATV - Digital ATV”