[amsat-bb] Protecting SDR

[Rolf Krogstad]

I use a diplexer, such as the MFJ-916B or equivalent, and it provides
enough isolation of the 2 meter signal to prevent problems.

Rolf    NR0T
EN34



On Fri, Jan 11, 2019, 11:14 AM Ryan Noguchi via AMSAT-BB <amsat-bb at amsat.org
wrote:

>  Is a transmit/receive switch necessary, or would a simple duplexer
> suffice? Something like the MFJ-916B offers 55dB or better isolation, and
> fairly low loss (0.2dB). It's a lot cheaper and more convenient to set up.
>
> My SDRPlay RSP1A arrived yesterday and I got it and my FT-857D working
> with CAT control using SatPC32 last night. I haven't worked a pass with it
> yet, though; maybe this weekend. The RSP1A is rated for 0dBm continuous,
> 10dBm momentary. The antenna is a dual-band Elk in the attic on a TV
> rotator, so there is no benefit of interantenna isolation. If I assume the
> duplexer's spec value of 55dB isolation, that would attenuate even 250W
> input down to less than 0dBm, correct? Patrick WD9EWK had commented on the
> subject of SDR protection in a QRZ.com posting, and has used a duplexer
> instead of a T/R switch with his SDRPlay SDR:
> https://forums.qrz.com/index.php?threads/kenwood-ts-2000-in-full-duplex-mode-on-single-coax-line.605225/#post-4613865
>
> Would love to know if my math is wrong, if the RSP1A's spec isn't
> trustworthy, and/or if there are any other considerations that make a
> transmit/receive switch better (or necessary) than just a duplexer, before
> I let the magic smoke escape.
>
> Thanks and 73, Ryan AI6DO
>
>     On Friday, January 11, 2019, 8:31:34 AM PST, saguaroastro <
> saguaroastro at cox.net> wrote:
>
>  Kevin,
> I've be looking at this. MFJ-1708. There are several versions. So look the
> up on Hro to compare
>
>
> 73Rick Tejera (K7TEJ)Saguaro Astronomy ClubWww.saguaroastro.orgThunderbird
> Astronomy ClubWww.w7tbc.org
>
> -------- Original message --------From: Kevin Zari <kk4yel at gmail.com>
> Date: 1/11/19  06:40  (GMT-07:00) To: amsat-bb at amsat.org Subject:
> [amsat-bb] Protecting SDR
> For those of you with an SDR dongle, for example the Funcube Pro +,  how
> do you protect it from not being damaged by TX energy? I’m thinking of
> hooking mine up to the 70cm antenna in my M2 LEO pack while I TX on the 2m
> antenna and was afraid I’d overload the SDR. I see folks using them for
> their RX on linear birds, so I’m just wondering how you have them hooked
> up.
> Thanks in advance for your advice.
>
> -Kevin (KK4YEL)
>
>
>
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