[Elecraft] K3 APF

[Bill W4ZV]

For my own curiosity I did some measurements of the latest APF. They agree
with
measurements of the first release with the exception that the filter peak is
now
zero beat instead of +10 Hz:

Zero beat = 7040.021
Flat passband = 021-020 (both 0.0 to -0.1 dB)
-1 dB passband = 026-018 (-1.2 dB and -0.8 dB)
-6 dB passband = 037-009 (-5.8 and -6.0 dB)

Flat = 2 Hz BW (at zero beat)
-1 dB = 8 Hz BW
-6 dB = 28 Hz BW

I didn't measure the -6 dB BW carefully on the first pass since I was more
interested in the -1 dB BW, but this looks similar and agrees with Lyle's 30
Hz
design goal. As mentioned previously, the -1 dB BW is important when trying
to
detect signals below the noise floor since the human ear can detect this
difference in marginal conditions.

I also checked the gain (APF vs not) which I didn't do before...+9.1 dB
which is
very close to Lyle's design goal of +9 dB.

Nice job Elecraft!

73, Bill


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