Mike,
I agree that double-shielded coax might help (in fact, I should do that in
my shack!) I've found that stubs and filters don't always make a big
difference in the S-meter reading at the harmonic frequencies, but can
nevertheless be very effective. What I mean is, I don't think anything will
reduce a 2nd harmonic to the point where you can receive within 1-2 Khz of
it. However, effective stubs or filters can make it possible to receive
*more* than 1-2 KHz away.
The first thing I look for is interference away from the harmonic frequency,
up and down the band. For example, let's say you are transmitting on 7010
and listening on 14020. The signal strength might be S9+20 at the 2nd
harmonic, but when you tune more than 1-2 KHz away from it, the noise should
go away and there should be no S-meter reading. That's good. What's bad is
when you can hear that 2nd harmonic signal all over the 20m band! Depending
on the radios and strength of the signal, it can be modulated tones, clicks,
static, hash, rushing, etc. I believe phase noise plays a part in this
equation as well. Broadband interference makes it very hard to operate,
especially if it moves the S-meter. I've found that stubs and filters can be
quite effective at getting rid of that kind of interference. But even when
they do, you'll hear the 2nd harmonic loud and clear within 1-2 KHz.
I use a combination of stubs and filters. My stub box is setup pretty much
like the switched stub box described on K1TTT's site and comes after the
amps. I also use switchabale bandpass filters between the rigs and amps
(that's where I need to install double shielded coax.) I have the stubs and
filters configured so I can switch them off individually for testing (TX
stubs, RX stubs, TX filters, RX filter.) Sometimes the stubs work and
sometimes the filters work. Sometimes nothing works. I don't think I have a
case where both a stub and filter are required.
As it turns out, I have a nice pair of Dunestar 600 bandpass filters for
sale... :-)
73, Dick WC1M
> -----Original Message-----
> From: Mike Wetzel [mailto:mjwetzel@comcast.net]
> Sent: Friday, August 01, 2003 12:39 PM
> To: cq-contest@contesting.com
> Subject: [CQ-Contest] Testing Stubs
>
>
> I have just recently tried using the Top Ten stub box (double
> stub) and my own homebrew stubs (and stub switching box) on
> my main CQ radio and am puzzled by the ineffectiveness of
> both. I obviously must be doing something wrong but can't
> figure it out.
>
> The set up is radio-ICE 419-amplifier-LPF-wattermeter/sensor-stub
> box-wattmeter-WX0B 6 pack box-manual antenna switches
> -antennas. I also have a 419 in the receive loop on the second radio.
>
> The LPF and wattmeter/sensor are connected to amp using right
> angle connectors and the stub box using 10' of supplied RG-214.
>
> The test setup is transmitting on 3510, 7010 or 14010 and
> listening on the 2nd, 3rd, etc., harmonic on the second
> radio. 20 and main 40 meter antennas are on the same tower
> but all the other combinations are on different
> towers. What I am finding with this setup is no change in s
> meter reading
> on the second radio listening on the harmonics when I switch
> the stub box in/out.
>
> Thanks,
>
> Mike W9RE
>
>
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