[Collins] Birdies on my 75S-3C

[Dr. Gerald N. Johnson]

On Thu, 2006-07-13 at 15:15 -0400, carl lowry wrote:
> Have both the 75S-3C & KWM-2A.
> The KWM-2A is a much -hotter- receiver.. better sensitivity .. better volume.
> The 75S-3C is down on both Volume & Sensitivity.
> What reads 5-9 plus on my KWM most of the time reads S-3-4 on the 75S-3C.
> I can tune across the 20Meter band & hear a lot of Birdies all across the band.
> No birdies on the KWM-2A.
> Even with the antenna switched over to the KWM & not connected to the 75S-3C i still can hear birdies.
> Birdies are same in Volume without the  antenna
> Suggestions please
> Thanks & 73s
> Carl, k4zrd
> ______________________________________________________________
Weak mixer or oscillator tubes. The inherent mixer noise hides many
birdies. Mixer gain can be low (and so the output noise can be low) when
the oscillator injection is low.

I changed my 75S-3B to a much lower noise second mixer and several
previously hidden birdies showed up.

There are many birdies inherent in a double conversion superhet. The
frequencies chosen keep them weak enough to not bother under the normal
mixer noise.

-- 
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer