47 and 76GHz tests

[g8gtz]

Last Friday I went out for a leisurely afternoon testing 47 and 76 GHz with G4FRE using the Langstone / Portsdown combo over a 66km path from IO91GI.

We had a narrow band QSO on both bands - my ODX on both bands plus I received Dave on TV on both bands which is probably a record on 76 GHz with almost 4 dB in hand - but he was running QRO at 300 milliwatts! He did not receive my 5 milliwatts!

The path was not really line of sight so room for improvement

Not sure why the P'down screen grab OSD is so fuzzy??

73 Noel - G8GTZ

BTW - added a few more points to the 6cms BATC ladder https://batc.org.uk/contests/6cm-ladder/

[G8GKQ]

Well done Noel and Dave!

The Portsdown screengrab is fuzzy because at 125 kS, FEC 1/2, the TS bitrate is only 123607 bits/sec which leaves only 80915 bits/sec for video after deducting overheads and the encoding saftey margin.

To get reasonable moving pictures at that bitrate using the RPi H264 encoder (this is FSTV, not SSTV, after all), the image size is reduced to 160x120 pixels.

On receive, VLC scales that up by 4 to 640x480 using a fuzzy algorithm.

Bet you wished you'd never asked!

Dave

[g8gtz]

No, obviously I understand about the transmitted video issues but wondered why the OSD, which is generated by Portsdown / LongMynd locally was particularly fuzzy?

I wondered if something had a momentary blip as it is also centred on screen - but I can't remember if that is normal...

The OSD on 333ks never seems degraded and I actually got a screengrab of Dave at 125 before the video decoded and that was sharp.

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Noel

[G8GKQ]

Once VLC starts, the OSD graphics are generated by VLC (based on text that is fed to it from Portsdown/LongMynd), at the same resolution as the incoming video. I had to adopt this solution as the Portsdown/LongMynd graphics are obscured by VLC as soon as it starts.

Dave

[g8gtz]

aah - makes sense....

Goes without saying, I never even took a PC with me on this trip (or the 2 day contest weekend) as Portsdown Tx and Rx are excellent when combined with Langstone for portable operation.

Thanks for the great product.

73
Noel - G8GTZ

[radiogareth]

Sounds like a great day out....I could have left my PC behind too if the Pluto firmware didn't overflow at 4.4GHz
Gareth

[G4FRE]

A relaxing afternoon out and it was nice to work Noel on 76GHz on NBFM / SSB

Changing from the W1GHZ horns I used on the contest, to the Pasolink dish on 47GHz really improved signals both ways, even though it added extra time to change between receive and transmit

BV_to_GI.JPG (1.27 MiB) Viewed 4079 times

I tried running computerless on the contest and paid the price when the Portsdown LCD failed, i now take the ryde and use the car's HDMI screen input as an emergency backup. On this outing with spare everything of course nothing failed!

Looking forward to trying some more paths

Dave
G4FRE