10. Use VFO B to go back to AFV for a few seconds to capture a new relative signal level. Then go back to
dBV, which should again show about 0.0 (bouncing a little).
11. Tune well off the carrier so you again hear only noise. Note the new (negative) dB reading.
Using this procedure in a quick test on 80m with a small antenna and with a persistent S-6 noise produced these
results:
Without APF: 1 dB S+N/N
With APF: 6 dB S+N/N
In fact, having turned APF on, quite a few little carriers may be discovered in the noise. The secret to discovery
is to tune slowly. Try hunting for DX with APF on at the low end of 40 or 80 m when the sun is just setting.
Additional notes from Bill, W4ZV:
1. I find an even wider WIDTH works better for me (400-450 Hz using a 500 Hz 8-pole). If I set WIDTH
too narrow (e.g. 50-100 Hz) I get too much ambient ringing.
2. Tuning is indeed very critical. This is why I only use APF for *extremely* weak signals buried in noise.
I never leave it on continuously and it would be unusable in a fast-paced activity like a contest.
3. Reduce AF Gain from its normal setting. APF compensates with Gain of ~9 dB at its exact center so the
signal will "pop up" when you get the critical tuning correct.
4. Indeed the effectiveness of APF seems to vary with the type of noise. I find it most useful in mild
atmospheric noise (lightning from a long distance) and less useful in white noise.
Elecraft • www.elecraft.com • 831-763-4211
To Previous Page
Loading...
