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Portsdown Tx

Posted: Wed Jan 09, 2019 5:04 am
by Russell
Hi I gather the portsdown Tx is DVB-S has anyone using DVB-T I'm in VK and as far as I can tell it is a legal format here is there a reason DVB-S is used in the UK forgive me for my ignorance of all this.

Re: Portsdown Tx

Posted: Wed Jan 09, 2019 10:28 am
by G8GKQ
Hi Russell

We do not have sufficient allocated spectrum (>6 MHz for broadcast standard DVB-T) in the UHF band in the UK to use DVB-T. Using lower bandwidth variants of DVB-S and DVB-S2 provides us with the flexibility to reduce spectrum usage and increase link budget margin.

DVB-T is too complex a waveform to be produced by the Raspberry Pi on its own; it could control an FPGA to generate the signal, but that is another level of complication and expense.

Dave, G8GKQ

Re: Portsdown Tx

Posted: Thu Jan 10, 2019 3:03 am
by Russell
Thanks Dave I asked because the club here has a person that wants to get a DVB-T repeater going and we are not sure in which direction to head.
My initial thoughts were that the public could tune a normal TV to watch but now I see domestic TV only go down to ch 27 which isn't low enough foe 70cm so there isn't any advantage in going DVB-T we might have a rethink about the project and go DVB-S
Thanks again.

Russ VK4DCM

Re: Portsdown Tx

Posted: Thu Jan 10, 2019 8:06 am
by g0mjw
The DATV Express can produce DVB-T, however those are no longer being made. If your club are absolutely fixated on DVB-T rather than DVB-S or DVB-S2 their options are very limited, but there are commercial offerings - e.g. the HIDES UT-100 USB DVB-T Modulator, which is not too expensive. It appears to do 2K which probably would fit in our 70cm band.

Mike

Re: Portsdown Tx

Posted: Thu Jan 10, 2019 9:37 am
by G4GUO
DATV-Express software can also do DVB-T with a Lime Mini but at low symbol rates it does not really have enough filtering.
Also the output is very very low (adequate for across the shack testing though).

You can also do it with GNURadio (even DVB-T2) but don't ask me how to do it with a live camera source :lol:

- Charles

Re: Portsdown Tx

Posted: Fri Jan 11, 2019 10:43 am
by G4GUO
Here is 8 MHz DVB-T using a LimeMini, the receive antenna was a hex spanner and the Lime is top right in a Hammond Enclosure.

- Charles
DSC_0236-min.JPG
DSC_0236-min.JPG (302.26 KiB) Viewed 519 times