[amsat-bb] FT-991A Transmit Interference

[Mike Sprenger]

Hi Alex,

Think of ways to identify the RF path from the Yaesu to the SDR thats
overloading and obfuscating what you want to see on the SDR receiver.   Is
it radiated or conducted in your cabling.

Have you isolated your power supplies between the SDR and the Yaesu ?

Perhaps RF is riding the DC cable.
(So run the SDR and the Yaesu on completely separate supplies, i.e. run the
Yaesu on a sufficient battery)


Also, if you transmit with the Yaesu into a dummy load directly attached,
is there RF overloading the SDR ?  (This may verify the effectiveness of
the shielding of the transmitter)
Do the same with the ID880 to know if your dummy load is radiating, which
is a good control test case.

Look at all of your cables and question "could that be the RF path to the
RX ?"   RF will ride a shield or a DC cable if permitted.

Interesting problem to solve.

73
Mike
W4UOO




On Thu, Aug 2, 2018 at 7:53 PM, Paul Stoetzer <n8hm at arrl.net> wrote:

> It sounds like the FT-991A’s harmonic suppression isn’t quite up to par.
>
> 73,
>
> Paul, N8HM
>
> On Thu, Aug 2, 2018 at 19:51 TERRY SURFACE <terrysurface1 at centurylink.net>
> wrote:
>
> > Hello. I have two 991A radios, and both do the same thing. I am unable to
> > use them for transmit on two meters without killing the 70 CM RX. I use a
> > Kenwood TS 2000 for transmit and 991A for receive. Not the way I want to
> do
> > it, but I am for now, this allows the spectrum and waterfall for checking
> > out the entire transponder.  Hope someone finds a solution.
> > 73,N4IQV, Terry
> >
> > ----- Original Message -----
> > From: "VA3ASE" <va3ase at gmail.com>
> > To: amsat-bb at amsat.org
> > Sent: Thursday, August 2, 2018 2:35:54 PM
> > Subject: [amsat-bb] FT-991A Transmit Interference
> >
> > Hi AMSAT friends,
> >
> > I'm having a technical problem and was wondering if anyone had any
> > suggestions. I've been experimenting with using an FT-991A transmitter
> and
> > SDR receiver to run full-duplex on the satellites. My problem is as soon
> as
> > I key the FT-991A transmitter, my SDR receiver waterfall goes completely
> > white and I don't hear anything but static. Classic overload symptoms.
> >
> > I've tried several things:
> > - Upgrading my receiver from an RTL-SDR to an SDRplay RSP1A: no
> > improvement.
> > - Adding a duplexer as a band pass filter: no improvement.
> > - Transmitting with a vertical antenna about 40' away from my yagis: YES
> it
> > did solve the problem but is not a suitable solution.
> >
> > I'm using the same yagi antenna setup that I've used successfully for
> years
> > with an FT-847, and have also had the same problem with a handheld Arrow.
> >
> > At last I tried transmitting with a different radio, and the problem
> > disappears. I figured the problem was in my FT-991A so I sent it for
> > warranty repair, but just got the call that they can't find anything
> wrong
> > with it. It has no measurable spurious or out of band emissions. I'm at a
> > loss here... I know people are using the same equipment (FT-991 +
> SDRplay)
> > successfully; Simon Brown comes to mind.
> >
> > Here is a video I created demonstrating the problem with the FT-991 and
> > showing that it doesn't appear with an Icom ID-880H.
> > https://youtu.be/gXOIK5gLjgs
> >
> > I still think the problem must be in the radio, but if they can't find
> > anything to fix then I'm out of luck. I'd love to hear any suggestions or
> > feedback.
> >
> > Thanks,
> > Alex VA3ASE
> > _______________________________________________
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> > to all interested persons worldwide without requiring membership.
> Opinions
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> >
> _______________________________________________
> Sent via AMSAT-BB at amsat.org. AMSAT-NA makes this open forum available
> to all interested persons worldwide without requiring membership. Opinions
> expressed
> are solely those of the author, and do not reflect the official views of
> AMSAT-NA.
> Not an AMSAT-NA member? Join now to support the amateur satellite program!
> Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
>



-- 
Thanks,
Mike Sprenger
(37.9167N  81.1244W is the Summit)