[amsat-bb] FT-991A Transmit Interference

Fri Aug 3 15:07:05 UTC 2018

Thank you to everyone who has replied, I appreciate it. I'll try to address
everything in one reply.

Paul, Alan and Trevor, I borrowed a duplexer rated for 40dB isolation. I
tried installing it on both the transmit side and on the receive side in
various configurations. I think that counts as a band pass filter. It made
no noticeable changes. I did read the QST report on the FT-991A mentioning
the output, but my impression was that it wasn't a huge deal. I would be
surprised if that was bad enough to cause this.

Zach my understanding is that the RSP1A is still shielded despite the
plastic box, but I actually have access to an RSP2pro in a metal case that
I can try out as well. I've never heard of a USB EMI filter before, I'll
look into that. I'm using a quality TrippLite USB cable with molded chokes
at each end.

Mike, I've tried both a linear power supply and a newer switching supply to
power the 991 with no change. In the video I was using the same supply on
both rigs. The SDR is powered through my laptop's USB port. I might have
already tried transmitting into a dummy load but I'll try it again. I do
know that switching the transmit antenna from my yagi to a rooftop vertical
eliminates the problem, which suggests to me that the interference is not
coming from inside the shack but from the transmit antenna's near field. I
made the switch at an outdoor patch panel, so nothing inside changed.

Terry, this is the first time I've heard of any other 991 owners with the
same problem. While it isn't what I want to hear, at least it might not
just be me.

My 991 is still in the shop (Radioworld) but I can try to pick it up this
weekend and keep experimenting. My original plan was to buy this FT-991A
and SDRplay to run a satellite base station, but I recently inherited an
FT-847 from a close friend, Brad VE3HII (SK). That opens a lot of  (probably
superior) options for my station but I'd still really like to see the
FT-991A working as originally planned, and as it should. My friend's
satellite antennas are still on his tower so I may also try to take my 991
there and repeat my tests.

73,
Alex VA3ASE

On Fri, Aug 3, 2018 at 9:19 AM, Mike Sprenger <mikesprenger at gmail.com>
wrote:

> 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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>> > _______________________________________________
>> > Sent via AMSAT-BB at amsat.org. AMSAT-NA makes this open forum available
>> > to all interested persons worldwide without requiring membership.
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>> > Not an AMSAT-NA member? Join now to support the amateur satellite
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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)
>