Thanks to all who replied to the "Receiving Antenna + RF feedback" problem
Basically the hints below from KOK Chen, AA6TY are only good
if you (want to) use the main antenna input of the 990.
----
This is what you do when you -> "connect the RX Antenna Out of the FT-990
to the Antenna connector of the JPS, and connect the RX Antenna In of
the FT-990 to the Tranceiver connector of the JPS".
Then it works how KOK described it.
But I wanted to use the separate receiving antenna input of the 990
------------------
and the above suggestions don't solve the problem then.
With an oszilloscope I measured voltages peak to peak of up to 40 V
on the separate rx input during transmission. And this leads to drive
the 990 complete crazy (oszillating of power supply and/or tuner,
the supply voltage breaks down and S-meter lamp becomes dark and darker ...)
And it's right, if you look to the scematics of the circuits, you can see
that YAESU does not disconnect the aux. input during transmission as
they do for the main input. They included two voltage supressors but that's
all...
I sent an email (anyway) to them but there was no reply up to now (they say
in their web pages that they only reply to emails for their newer transceivers
- for older ones like the 990 you have to phone or write to them -
(the 1000mp has the same problem as we heard in the reflector ...))
So it seems, that the best way is using the home brew solution and ground
the input with a relay via transmission ...
Thanks again to anybody who replied !!!
Friedemann, DF2GX
In message "Receiving Antenna + RF feedback", gswanson@arrl.org writes:
>
>
> Greetings,
>
> Re: "having selected the separate receiving antenna, RF is fed back into the
> [radio]"
>
> If you notice RF feedback from an RX antenna as described (below, or with
> ANY radio/RX-antenna combo), I can suggest one possible fix that's easy to
> implement. This pertains to most ANY type of radio/receiving antenna, be it
> a Beverage, EWE or, something like K9AY's receiving loop system (QST Sept.
> 1997).
>
> (I think, but am not sure: The FT-100MP *might* have built-in protection
> form RF feedback via the RX antenna port, by perhaps the FT-990 *might*
> not??)
>
> While the suggestion below is good, you can get away by spending a LOT less
> money; just use a relay to send the RX antenna to ground during transmit...
> For more details on this, see the articles on my web page, where you'll find
> one titled "Beverage Notes," and, more to the point, my follow-up article,
> "More Beverage Notes," where this exact problem (RF feedback from an RX
> antenna) is discussed.
>
> The best way to get into the subject might be to read both article--in
> order--with "Beverage Notes" first, and then "More Beverage Notes." Again,
> the RF feedback issue could apply to most any RX antenna, so it's not
> Beverage antenna specific.
>
> You'll find other Beverage-antenna-related information on the "Beverage
> Info" page, too. Here's the URL's:
>
> My main page: http://www.geocities.com/CapeCanaveral/1138/index.html
> And the
> Beverage Info page:
> http://www.geocities.com/CapeCanaveral/1138/bev-page.html
>
> Hopefully, you'll find something of interest there...
>
> Enjoy!
>
> 73, Glenn Swanson, KB1GW
> Avon, Connecticut
> Home: kb1gw@snet.net
> Work: kb1gw@arrl.org
> ========================
>
> >>re:[Yaesu] FT990 Receiving Antenna
> >>
> >>Kok Chen (kchen@apple.com)
> >>Tue, 4 Nov 97 09:50:08 -0800
> >>
> >>During transmitting and having selected the separate receiving antenna,
> >>RF is fed back into the 990 which can lead so far, that the internal
> >>power-supply or the tuner oscillates and the supply voltage is breaking
> down,
> >>which can be seen because the S-meter lamp becomes dark and darker ...
> >
> >If you look at the diagram on page 27 of the manual (in the
> >side-bar titled "Receive-Only Antennas and Separate Receivers"),
> >it seems to bear your observation out. The TX/RX switch is not
> >where I would put it for connecting a receive antenna all the
> >time.
> >
> >However, there is a really nice use for the FT-990 "receive
> >antenna" connection if you are using a JPS noise canceller
> >(I think MFJ makes one too, and CQ Magazine published the
> >schematics for one recently -- I have no idea how that one
> >gets phase reversal, but the author swears it works).
> >
> >If you were to connect the RX Antenna Out of the FT-990 to the
> >Antenna connector of the JPS, and connect the RX Antenna In of
> >the FT-990 to the Tranceiver connector of the JPS, you get
> >three things:
> >
> >1) the TX/RX switch of the FT-990 is used instead of the TX/RX
> > relay in the JPS (much better switch over transients).
> >
> >2) RF power does not get into the JPS (I don't use a linear
> > amp, but this should do the trick too),
> >
> >3) you can enable and disable the noise processing by just
> > switching the RX ANT switch on and off, respectively.
> >
> >73
> >
> >Kok Chen, AA6TY
> >
>
>
>
> --
> FAQ on WWW: http://www.qsl.net/k7on/yaesu.html
> Submissions: yaesu@contesting.com
> Administrative requests: yaesu-REQUEST@contesting.com
> Problems: owner-yaesu@contesting.com
> Search: http://www.contesting.com/km9p/search.htm
>
--
FAQ on WWW: http://www.qsl.net/k7on/yaesu.html
Submissions: yaesu@contesting.com
Administrative requests: yaesu-REQUEST@contesting.com
Problems: owner-yaesu@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|