There are several things you have to watch out for in testing stubs in
the real world...
1. leakage from before the stubs. Put a dummy load in place of the stub
box and measure how much harmonic you can hear that way. Fix cables,
grounds, and leaks in cases first.
2. harmonics generated after the stubs. Hard to track down, but if
something on the tower or near it is rectifying then no stub in the
world will help. Tx into a dummy load and use a short pickoff antenna
on a T on the dummy load to tx. (this makes #1 above even more important
to fix first)
3. harmonics generated in the receiver. Similar to above, if the rx you
are using is overloaded by the fundamental and makes its own harmonics
the stubs won't help there either... make sure you have a good bandpass
filter before the rx to reduce the wrong band fundamental on rx...
reverse the setup above and rx from a dummy load with a short pickoff
antenna T'ed to it, or use attenuator to limit input to rx.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> -----Original Message-----
> From: cq-contest-bounces@contesting.com [mailto:cq-contest-
> bounces@contesting.com] On Behalf Of Mike Wetzel
> Sent: Friday, August 01, 2003 17:39
> 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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