[amsat-bb] Protecting SDR

Sat Jan 12 15:32:14 UTC 2019

Use a 2/70cm duplexer and put a 50 ohm resistor on the 70cm port.  I use a
Comet and have used a diamond. In fact, I run my 70 cm uplink thru the
diplexer, and skip the Terminator.
73, N0AN

Hasan

On Fri, Jan 11, 2019, 3:55 PM Paul Stoetzer <n8hm at arrl.net wrote:

> Yes, I have. Though for Mode J, I would have a filter on TX or else the
> third harmonic certainly would overload it.
>
> I haven’t extensively done this, but I haven’t encountered any problems
> when doing it. I would recommend using a diplexer or filter on the input.
> Just be sure you use something that’s very low loss.
>
> 73,
>
> Paul, N8HM
>
> On Fri, Jan 11, 2019 at 16:50 Ryan Noguchi via AMSAT-BB <
> amsat-bb at amsat.org>
> wrote:
>
> >  When you say "without any protection on the input" do you mean you
> aren't
> > using any diplexer or filter (external to the SDR) on the input RF path
> to
> > the SDR, even for Mode J?
> >
> > 73, Ryan AI6DO
> >     On Friday, January 11, 2019, 10:03:30 AM PST, Paul Stoetzer <
> > n8hm at arrl.net> wrote:
> >
> >  I've used my AirSpy Mini and FCD+ without any protection on the input
> > without any damage, but your mileage may vary!
> >
> > 73,
> >
> > Paul, N8HM
> >
> > On Fri, Jan 11, 2019 at 12:55 PM Rolf Krogstad <rolf.krogstad at gmail.com>
> > wrote:
> > >
> > > 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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> _______________________________________________
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