Bent Pipe Repeater (Transponder)

Ideas, technical topics, help and discussion for ATV repeater builders
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Bent Pipe Repeater (Transponder)

Post by M0DTS » Mon Apr 11, 2022 9:49 pm

With the current SDR tech available this is now Very easy to do.
Easy to sharply filter the input passband etc...

For example a 1MHz section of 23cm band at 1249MHz as the 'input' and another 1MHz section at 1304MHz as the 'output'.
Users could use an sdr to monitor the output and tune to signals as they come in, or just use pre-defined channels withing the 1MHz section.
An on-site beacon could be transmitted at 333Ks just like QO-100 does.
A LOT less hardware involved!!

Licencing it would be a whole new thing as I've not even heard of anything like this mentioned before now...

Is this a possibility for the future?


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Re: Bent Pipe Repeater (Transponder)

Post by radiogareth » Tue Apr 12, 2022 7:24 am

Sounds feasible, especially as I have a nice diplexer for 3.4, just retuning it would be the main issue.
Or 70 CMS plenty of space and lots of diplexers sitting on people's shelves.

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Re: Bent Pipe Repeater (Transponder)

Post by g8gtz » Tue Apr 12, 2022 8:58 am

I like this idea.

I think we should work up a proposal and as BATC Spectrum forum rep and also ETCC TV manager, I'd be happy to take it through "the system" and see where we get to.

First thing to determine would be what band to operate on - I guess it could even be cross band - and suggest we would start with a small deployment from an average site before putting it at a real repeater site.

70cms is probably not the band of choice due to the primary user who may not want their signals repeated.

23cms is a possibility but I wouldn't want to encourage people to invest too much time and money in anything below 1300 MHz.

13cms and 3.4 could be possible...

I'm sure BATC would support any development as it is something that pushes the hobby forward.

Noel - G8GTZ

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Re: Bent Pipe Repeater (Transponder)

Post by g0mjw » Tue Apr 12, 2022 11:32 am

A transponder not on a satellite is not a new concept, it's how some TV relays work. Why not? All it would need would be a receiver and a transmitter and filter at IF. AGC as well probably. Instead of bent pipe we could have regenerative repeaters. That would be a lot better for SNR because the uplike errors are corrected before re-transmission. The RX locks on to the incoming signal and demodulates it to the TS which it then re-sends unchanged, or with some changes to the metadata but no need to encode/decode the data itself. That would need a specific symbol rate and FEC. Of course it could have multiple inputs, e.g. different input bands or antenna pointing with some priority (E.g. MER) determining on which one gets passed to the output. The output doesn't need to be the same rate or FEC as the input, it just needs to be at least the came capacity, so you could, theoretically, with extra processing, have a repeater outputting (2Ms on 23cm for the die hards) multiple input 333ks streams in the output multiplex.


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Re: Bent Pipe Repeater (Transponder)

Post by M0DTS » Tue Apr 12, 2022 6:07 pm

Yes AGC will be an essential part, avoiding the same issue as the satellite has with big signals!

Receiving and locking onto incoming signals is not an issue now with longmynd but re-muxing them is not going to be a straightforward task, although a totally viable option.
Having it purely a bent pipe was the main interest due to lowest cost and power consumption - A single raspberry pi and a pluto for example.
A bit of GNURadio trickery will get things going quickly.

I think later this year I'll have a go at building a system (probably try both bent pipe and re-muxing TS) and try some tests from my QTH and see how it goes, should be fun!


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