SB-303 questions.

[Gerald C. Lemay]

I have to take issue with those who say the SB-104 noise blanker is
ineffective. Perhaps it's ineffective as installed in the SB-104. I've never
owned an SB-104. However, when the blanker is installed in the SB-303
exactly as described in the QST articles, it does work very well indeed. Of
course it doesn't work nearly as well as the one in my Drake R-4C but then
not many noise blankers do. I found the 104 blanker works best when the
attenuator control is reconfigured as a threshold level control for the
blanker. There is one major flaw in the design in that there is no
selectivity ahead of the blanker and it therefore "sees" the whole band at
once. If there's a strong signal somewhere in the band, the blanker starts
to clip signals and results in unpleasant-sounding audio not to mention the
overload responses it causes. The Drake blanker solved this by using a half
lattice, wide bandpass crystal filter ahead of the blanker. The SB-303 is
not my favorite Heathkit receiver. It's virtually useless on 40 meters in
the evening with a full size dipole at 50 feet. Works OK with short
antennas.


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