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[TowerTalk] RE: [CQ-Contest] Testing Stubs

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Subject: [TowerTalk] RE: [CQ-Contest] Testing Stubs
From: (Robert Shohet)
Date: Mon Aug 4 13:19:58 2003
Yeah, but what happens when the stubs get "testy"?    :-)

I made mine out of Fused Disc 75 ohm hardline cut for a compromise of SSB/CW
and I can tell you that even though I measured and cut them VERY carefully,
they do not work very well.  They do however raise the swr and reflected
power on a few bands and make their use on 40 meters (with a 40-2cd) out of
the question.

While it is possible that cutting them for a compromise freq. was not a good
idea, I just don't think that the stubs work very well at all.  I had
wondered if this had something to do with my using 50 ohm coax (RG213) with
stubs cut from 75 ohm Fused Disc hardline.  Although, when cut to the
appropriate electrical lengths, I don't think that this should not really

The manual Dunestar 500's work pretty well and help reduce the crud, but the
absolute BEST way to reduce interstation interference is to separate your
towers as much as humanly possible!

Bob KQ2M

> 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
> 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
> 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
> 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!
> on the radios and strength of the signal, it can be modulated tones,
> 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
> 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
> 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
> 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

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