[1000mp] FT1000MP post 455khz filter -FET amplifier noise

[Tom Rauch]

> Hi Tom,
> I remember that you tried on FT1000D or FT1000MP to change the noisy
> fet amplifier after 455khz filter. I think that you tried a gasfet
> amplifier. What has resulted?? Tks es 73 Ian IK4EWX

I replaced the FET following the last 455 filter with a low-noise 
GAsFET, and moved the tap to the top of the winding.

I'm not positive how much effect comes from moving the tap and how 
much from the better noise figure. Looking at the circuit virtually 
all of the the noise comes from that one single stage. I do not find 
that it degrades sensitivity. I find only that the noise annoys me 
when working CW with narrow filters selected.

The best manufacturing engineering fix would be either a narrow 4th 
IF filter switched in for CW or SSB, or more gain just in front of 
the narrow 455 filter and removing the post-filter 455kHz amplifier 
stage. That may not be practical.

Since the noise is totally removed with a good audio filter you might 
as well just use one with the receiver and save the trouble of 
working inside.

   73, Tom W8JI
W8JI@contesting.com