Topband: ANC-4 noise canceller

Michael Tope
Tue, 3 Dec 2002 22:42:32 -0800

> As for power handling, that shouldn't be an issue. The unit goes
> between the radio and the amplifier, and wouldn't see anything more
> than the exciter puts out whether you use an amp or not.  73, Tom
> W8JI

Just be sure you leave the unit off when you are adjusting your
antenna tuner. The RF sensing circuit didn't like the wide impedance
swings when I swept the capacitors on my Dentron T network
and ended up causing the the T/R relay to switch in and out
while I had RF applied. This fried the resistors that pad the signal
path from the external receive antenna. After that happened I added
an external keying input to the ANC-4 so that the exciter hard keys
the T/R relay in the ANC-4. I haven't had any problems since then.

BTW, I notice the same amplitude variation problem that Tom
mentioned with my ANC-4. This is really annoying. I measured
it once on a network analyzer about 5 years ago. I remember
that it was suprisingly bad, but I don't recall exactly what the
figure was (25 dB sticks in my mind). Despite the large amplitude
variation, the ANC-4 is still quite capable of producing very
deep nulls. Its just tricky to adjust because its easy to confuse
the amplitude dip (no SNR improvement) with a real null
(SNR improvement).

I used the MFJ unit one weekend at a friends house. We
burned out the small neon bulb that protects the receive path
from overload almost immediately (the TX antenna was too
close to our short beverage). After we replaced the bulb and put
a couple of back-to-back diodes across the receive antenna input,
the unit worked fine. The MFJ didn't have the large ampitude
swings that I see on the ANC-4 and it also produced excellent

Even though the ANC-4 unit is probably built better (the
workmanship is very good), I would go with the MFJ unit if
I had it to do over because of the better amplitude stability.

73 de Mike, W4EF................................................

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