[Yaesu] FT990 Receiving Antenna

[Kok Chen]

>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