[amsat-bb] FT-991A Transmit Interference

[Alan Johnston]

> I'm using a quality TrippLite USB cable with molded chokes
at each end.

Hi Alex,

I've found that if I use any length of USB cable between my PC and SDR, I
get overloaded on transmit by my Kenwood TR-9500.  Only plugging my RTL-SDR
v3 directly into my PC avoids it.

Good luck with it!

73,
Alan
KU2Y

On Fri, Aug 3, 2018 at 9:35 PM, <amsat-bb-request at amsat.org> wrote:
>
> Date: Fri, 3 Aug 2018 11:07:05 -0400
> From: VA3ASE <va3ase at gmail.com>
> To: Mike Sprenger <mikesprenger at gmail.com>
> Cc: AMSAT-BB <amsat-bb at amsat.org>, Paul Stoetzer <n8hm at arrl.net>
> Subject: Re: [amsat-bb] FT-991A Transmit Interference
> Message-ID:
>         <CACgQwJ-w++Ww5eSyaToettQ2YO-VQT7We-dOJkkQNeMrRxu-XQ at mail.
> gmail.com>
> Content-Type: text/plain; charset="UTF-8"
>
> 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
>
>