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Re: ATV Network Day 22nd August 2010

Posted: Tue Aug 24, 2010 10:23 pm
by M0DTS
Hi All

Not a lot of Activity i my part of the world on Sunday...

Managed only 6 3cm ssb qso's due to playing with atv rx's...hi
Worked G7AVU on 23cm(p5) and 3cm(p0-p3 qsb) ATV over 108km path, best dx on 3cm from IO94LI so far!
One-way receive 70cm Analogue with G1JLB in Harrogate running 0.5W to a colinear!!

Hope it's better in September for ATV contest!



Re: ATV Network Day 22nd August 2010

Posted: Wed Aug 25, 2010 9:36 pm
by g8gtz

I had great fun on Sunday - the rebuilt shack and new mast worked well and the new 70cms DATV station was 100% reliable - details as follows:

19ele tonne at 30ft (with rebuilt G8ADM design driven element)
Mast head pre-amp (G0MRF ATF54143 design with 70cms bandpass filter on frontend) overall NF of MH box was 1.3dB.

Glenmore (ebay USA) 70cms to L-band rx converter
Alteia digital rxr

Ericsson 5710 encoder driving SD2020 modulator configured for 1/2 FEC and 2 Msymbols into a modified MM 148 to 436 transverter - 0dM out
Continental Microwaves driver and PA (courtesy G4CPE) producing in excess 100 watts (my bird 43 slug only goes up to 50 watts!) with -45dB shoulders.

I had 2 way 70cms DATV QSOs with G8ADM, G8ASI, G6MNJ and G6PYE/T at 139 Kms and a 1 way with G6LRQ. (I also managed to find time for 2 narrowband 10GHz QSOs)

I tried 70cms DATV with G3PYB and M0DTS and during setup was very surprised at the performance of 70cms FM on a decent system with both stations 100% readable and occasional fully quieting with aircraft flutter. However, we couldn't quite do DATV - this performance difference is borne by the numbers below which show we need a signal better than -106dB to get a lock where as a quieting FM signal can be acheived with -116dB, so a 10 dB difference...

The QSO with G6PYE/T was marginal, they recieved about 80% of my 1/2 FEC signal but I only recieved 20% of their 7/8 FEC transmission.

I have since done some "un scientific" tests at various FEC rates and produced the following results. The -dB levels are approximate but I think it is the relative not absolute which is important. These tests do seem to indicate that with the reciever I have there is a 3 - 4 dB difference between the FEC rates, equivalent to doubling the power at the Tx end - I for one will be sticking with 1/2 FEC!

FEC Drop out Recovery
1/2 -109dB -106dB
2/3 -107dB -105dB
3/4 -106.5dB -104.5dB
5/6 -106dB -104dB
7/8 -105dB -103dB

I tried to do the same tests with a consumer STB but couldn't get reliable lock levels - some form of AGC? - but when it did lock it seemed to be up to 8dB lower than the Altiea professional reciever, which is probably 10 years old, and is therefore approaching the narrow band FM signal levels! I think we need understand more about the amount of gain to put in front of these digital rxrs and also I need more reliable signal strength indicator in order to peak up the signal - I wonder if we can use Spectran or some similar program to look at the spectrum?

I'll continue to play to try and see what the optimised rx system could be...

Pity I'm not around for the September contest but IARU does insist on holding their annual TV contest on the same weekend as the largest European broadcast industry show in Amsterdam ;-(

Maybe we can organise another activity day before the winter weather really sets in...


Noel - G8GTZ (Basingstoke)

Re: ATV Network Day 22nd August 2010

Posted: Wed Aug 25, 2010 10:35 pm
by G8ADM
Due to the time it took to activate my new mast I got on quite late ~3pm BST
On 70cm DATV I worked, 2 way:
G8ASI, Mike near Hemel Hempstead.
G6MNJ, Paul near Hemel Hempstead
G8GTZ/P, Noel South of Basingstoke.

I had a reception report from:
G7LRQ, Anthony in Watford.

I heard G6PYE/T near Cambridge earlier but they had gone by the time I was operational.

My test with M0DTS, Rob, North Yorkshire Moors was not successful but we did just about work on 70cm narrow band voice FM which was surprising.

It was a very enjoyable day which I would like to see repeated some time. Well done Pete for organising it.

There were many other stations on that I did not hear including F6ANO.

The French stations tend to use 144.170 MHz SSB H for talkback.