50 MHz DATV - plans and ideas...

The place to discuss reduced bandwidth fast scan amateur television on 70cms and below
G8PEF
Posts: 177
Joined: Mon Oct 30, 2017 6:42 pm

Re: 50 MHz DATV - plans and ideas...

Post by G8PEF » Tue Feb 13, 2018 7:34 am

Last night at a club meeting, I was asked if Portsdown could do RBTV on 50MHz …

I was sure I'd seen some discussion on the Portsdown thread(s), but I can't (despite a lot of s arching) find anything.

So, is anyone using Portsdown on 6m? Any particular frequency/SR? Any tips for setting up - filters, PAs etc?

73
John

g8gtz
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Joined: Wed Apr 07, 2010 6:26 pm

Re: 50 MHz DATV - plans and ideas...

Post by g8gtz » Tue Feb 13, 2018 8:49 am

Hi John,

The specs for Portsdown are here https://wiki.batc.org.uk/Portsdown_Output_Levels

As you can see it does not cover 50 MHz natively but an external; converter can be used - here's one Mike is proposing for 71MHz rxr and could be used on 50 MHz tx and Rx. viewtopic.php?f=76&t=4108

One or two people are "thinking" about 50 MHz so maybe it's time for some experimentation...

73's Noel - G8GTZ

g0mjw
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Joined: Sat Sep 20, 2014 9:15 am

Re: 50 MHz DATV - plans and ideas...

Post by g0mjw » Tue Feb 13, 2018 6:34 pm

Why can't the Portsdown be made to TX on 50 MHz? The LO goes down to 35MHz. Is it the modulator chip?

My receiver PCB (Noel has one now and is patiently waiting for me to send him the schematic) requires a 400MHz LO.
Converter prototype.jpg
Converter prototype.jpg (318.87 KiB) Viewed 3760 times
Plan is to use the spare output from the Portsdown in CW mode. It filters 50-70MHz, amplifies and converts it to 450 - 470MHz for input to the Minitiouner. There are many different ways you could use the board - no requirement to stick with it's intended use. For a TX converter for example. It can't make tea.

Mike

G8GKQ
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Re: 50 MHz DATV - plans and ideas...

Post by G8GKQ » Tue Feb 13, 2018 11:32 pm

Hi Mike

The problem with the Portsdown is that the QPSK modulator chip is only in-spec from 140 - 1000 MHz. It’s just about OK at 71 MHz, but gets worse quickly below that. The constellation becomes trapezoidal.

Dave

g0mjw
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Re: 50 MHz DATV - plans and ideas...

Post by g0mjw » Wed Feb 14, 2018 7:49 am

G8GKQ wrote:
Tue Feb 13, 2018 11:32 pm
Hi Mike

The problem with the Portsdown is that the QPSK modulator chip is only in-spec from 140 - 1000 MHz. It’s just about OK at 71 MHz, but gets worse quickly below that. The constellation becomes trapezoidal.

Dave
I see - so we either need a RX/TX frequency converter or another modulator. My current board will do that but only if the active device is bypassed to make it bi-directional. Then there would be a need for additional gain to overcome the ~10dB losses mostly important for the RX side. Maybe easier to use two boards one passive for TX, one active for RX. Or I could re-design I suppose but based on the level of interest so far I doubt there is any demand. The Pluto and Lime can do 50MHz and both are about to re breadily available again.

Mike

pe1itr
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Joined: Tue Jan 21, 2020 10:26 pm

Re: 50 MHz DATV - plans and ideas...

Post by pe1itr » Tue Jan 21, 2020 10:39 pm

Hi,

I am qrv on 6m datv. Setup: portsdown tx + minilimesdr + filter + pa output 30 watts into 5 element 1 wl yagi 6m agl. When condx are good I am happy to make a sked. I am experimenting now with some local stations.
I have peaked the yagi to the upper 6m band. Using mainly 51.750 MHz or 51.250 MHz. Attached a file with "the bandplan" we use.

73 Rob PE1ITR
JO21QK
Attachments
datv-6m.png
datv-6m.png (14.9 KiB) Viewed 2317 times

g6jyb
Posts: 26
Joined: Thu May 09, 2013 12:57 pm

Re: 50 MHz DATV - plans and ideas...

Post by g6jyb » Mon Jun 08, 2020 11:28 pm

As per the recent IARU R1 VHF newsletter, you are encouraged to report 50 MHz experimental progress and bandplan suggestions ASAP via your national society such as RSGB, Veron, DARC etc, in inputs to the Region 1 Conference.

We are expecting to hold a 50MHz working group discussion on this and other modern tech in the band to facilitate replanning and innovation/growth. Inputs need to be make by early July.

73

Murray G6JYB

radiogareth
Posts: 507
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Re: 50 MHz DATV - plans and ideas...

Post by radiogareth » Tue Jun 09, 2020 6:44 am

It would seem that TX is 'simple' by using a Lime Mini/LimeSDR.
Rx can be via DVBS2GUI using a RTL dongle, RSPxx or 'another lime' (Pluto does not 'properly' receive below 70MHz).
Just tried it across the shack, works fine. Just need an amp now....
At 125kS even a lowly Intel Atom tablet PC at 1.75GHz can cope at about 60% CPU.
Gareth G4XAT
***Edit*** Just fed it to my broadband HF/VHF amp and get +30dBm of nice clean signal. Now looking for the next PA with adequate linearity (MRF101 design looks promising....https://sites.google.com/site/rfpowerto ... xp-mrf-101 and I have a few spare PCBs for this design too.:-)
51.5MHz.PNG
51.5MHz.PNG (1.05 MiB) Viewed 563 times

G4HTZ
Posts: 180
Joined: Sat Aug 02, 2014 4:21 pm

Re: 50 MHz DATV - plans and ideas...

Post by G4HTZ » Wed Jun 10, 2020 8:55 am

radiogareth wrote:
Tue Jun 09, 2020 6:44 am
It would seem that TX is 'simple' by using a Lime Mini/LimeSDR.
Rx can be via DVBS2GUI using a RTL dongle, RSPxx or 'another lime' (Pluto does not 'properly' receive below 70MHz).
Just tried it across the shack, works fine. Just need an amp now....
At 125kS even a lowly Intel Atom tablet PC at 1.75GHz can cope at about 60% CPU.
Gareth G4XAT
***Edit*** Just fed it to my broadband HF/VHF amp and get +30dBm of nice clean signal. Now looking for the next PA with adequate linearity (MRF101 design looks promising....https://sites.google.com/site/rfpowerto ... xp-mrf-101 and I have a few spare PCBs for this design too.:-)
51.5MHz.PNG
Hi Gareth
I noticed you have 50mhz working ...think your in Kent somewhere ??
I potentially can get 50mhz working ..got the original portsdown ..got a 2m to 50mhz transverter somewhere ..also a ACOM 700w amp ...3 element LFA ...this line up may or not be suitable?.....no mast here currently so yagi would be fairly low ..

Also just took delivery of a Pluto for DATV ...but still trying to sus what’s required before I plug it in ...not very good with computer based equipment!!!

Anyway ...I’m located on east coast of Essex ..4miles east of Southend on sea ...best take off into Europe as overlooking North Sea ...but have worked several Kent stations on 437 DATV ....will let you know if I get anything lashed up .
Cheers
Steve G4HTZ
Steve G4HTZ
Great Wakering Essex JO01JN

radiogareth
Posts: 507
Joined: Wed Jan 06, 2016 9:46 am

Re: 50 MHz DATV - plans and ideas...

Post by radiogareth » Wed Jun 10, 2020 10:39 am

Hi Steve, Yes, I'm in Hayes, Bromley Kent when at home, not a great spot but I was able to work Easterly stations during a recent 6M phone contest. 4 Ele LFA in the garden which can be raised to about 4m and pointed in your direction so at some point that should be a possibility :-)
The best article seems to be here: https://wiki.batc.org.uk/Custom_DATV_Fi ... _the_Pluto it needs reading through a few times and doing some well-documented hacks. There is also the SATSAGEN software (http://www.albfer.com/en/2020/02/21/satsagen-2/) which I think does the main upgrades for you when first run, but its not difficult - I managed it!! Just found out that SDRAngel also decodes DVBS2 using a Pluto so all sorts of fun now becomes possible......'see' you some time :-)
73
Gareth

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