Gee, I'm not alone in receiving less-than-stellar performance from stubs. I
have made several sets of stubs using various methods of tuning them and
they just don't work at my QTH. But I took one of my stubs to a friends QTH
and he was able to show me that my stub did indeed give 20 dB of suppression
on the second harmonic - just like it is supposed to. And he loaned me one
that he had made and used successfully at his location and it doesn't work
for me either. I run monobanders and 4 square phased arrays and he runs a
TH-11 and verticals. He does 16 ground rods arranged around his back yard
(in the city) whereas I only have 2 ground rods and I am in a rural area.
And we have used these same stubs on DXpeditions with good results.
It could be that there is such a thing as a 'hanging tree' for stubs.
de Paul, W8AEF
ZF2TA FO8DX FO0PLA 8Q7AA XZ0A
----- Original Message -----
From: "Dick Green" <firstname.lastname@example.org>
To: "Tower (Tower)" <email@example.com>
Sent: Monday, August 04, 2003 1:15 AM
Subject: [TowerTalk] RE: [CQ-Contest] Testing Stubs
> 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
> > -----Original Message-----
> > From: Mike Wetzel [mailto:firstname.lastname@example.org]
> > Sent: Friday, August 01, 2003 12:39 PM
> > To: email@example.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