Front end protection for DATV

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radiogareth
Posts: 356
Joined: Wed Jan 06, 2016 9:46 am

Front end protection for DATV

Post by radiogareth » Thu Nov 28, 2019 12:20 pm

I'm wondering about front end protection for simplex DATV operation, especially for 2M use where the talkback is on the same band and may be at quite high power.
For HF I found this article: http://www.ad5x.com/images/Articles/FrontEndProt.pdf all of which makes good sense. But at rising frequencies won't the limiting diode junction capacitance to ground provide a significant path to ground, so reducing the hard earned received signal?
At the moment I'm planning on a horizontal beam for DATV and a similar one for talkback, but vertical. 'Theoretically' that should give 30dB of attenuation, possibly more depending on actual sidelobes and how they interact etc.
I picked up some DowKey coaxial relays at the recent CATS bazaar and their spec is -40dB isolation and have a good supply of the RS coaxial relays that they used to sell which probably have a similar spec.
How have people set up their receiver(s)(such as Minitiouner, RTL or Pluto) and the matching band linear amp / antenna?
Lots of quality RF relays and sequenced switching (Like Portsdown already does) or what?
Comments and guidance very welcome - I've not killed anything YET, mainly by swapping leads over. But not the ideal solution....

Gareth G4XAT

G4uvz
Posts: 168
Joined: Sat Dec 09, 2017 10:30 am

Re: Front end protection for DATV

Post by G4uvz » Sat Nov 30, 2019 12:01 pm

On 2M I use a mutiband vert for talkback ..which of course completely kills the incoming rx signal ..but 2M frontend is unprotected and remains intacct.

On 23cms I do not trust to a relay as I have had preamps fail using the usual SMA GHz relays ...doesn't take long to screw unscrew an N connector!

For 23cm repeater look through I have two yagis physically separated by < 1 M and an interdigital filter on rx leg..all works well.

radiogareth
Posts: 356
Joined: Wed Jan 06, 2016 9:46 am

Re: Front end protection for DATV

Post by radiogareth » Sat Nov 30, 2019 12:20 pm

Thanks for the 'it works for me' scenario. As I posted I haven't killed anything YET and I want to design in as much as is necessary. It it works then thats fine by me. Noted on 23. I think I'll aim for 6/4/2 next year, and some 3.6 GHz where I have a diplexer for the band.
Gareth

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