[Yaesu] Re: Pin Diodes FT-990

[John Bolduc]

Stuart
     I made a temporary fix to my 990. Heres what I did..... First of all
the hiss is from the 455 stage .. From the Murata 455 filter to the product
detector . The audio amps are very quiet , and are not the problem. Some rig
have noisy audio amp like the 1000MP,  it uses the old TDA2002 chip(very
common part) & the 990 uses the new TDA2003 much better!!

Ok back to it... I took out that crappy Murata filter & replaced it with a
Collins 2.8khz This is the same filter the 1000MP uses. And AES had them on
Closeout for $50.00 . But they're label for the FT-900 . Same filter mounted
on a different board, You don't need the board. Put it in the 990 with patch
cable's.

The big advantage of this filter other than it's superior to the Murata in
every way is ...... It has way less insertion loss so the input into the
first bipolar transistor is higher , So now you can go to the IF gain pot
located down stream in the circuit and turn it down. You still have the same
receiver sensitivity but the hiss is lower..... This is the same principle
that Inrad use's with the 1000MP mod they sell except the use an active amp
in the 70 meg IF .......And turn the IF gain down in the service menu .
This works well for a simple mod ... But the best way would be to use FET 's
in the 455 IF They have much less noise. My 940 Kenwood use's those and is
Way quieter than the 990.  But would be major surgery ..... I'm happy with
this simple update plus the IF shift work's better because of the Collins
great skirts & the audio is better too , because of less filter ripple &
overall receiver with is wider .........

73's john