[CQ-Contest] Coax Stubs for SO2R

Tue Sep 8 18:15:01 EDT 2015

>> (KR6X) I can confirm that quite often the source of trouble is not in the
front end nor finals of the rigs.  It can indeed be elsewhere.

I second Leigh's statement. Receiver overload and harmonics interference are
the easy ones to cure with bandpass filters and/or stubs.

In a typical Multi op environment you are flooding (W3LPL terminology) the
environment near your antennas with high level RF energy while trying to
copy signals at -130 dBm on other (or same) band, and anything that can
rectify YOUR OWN TX signal can raise the noise floor in almost the whole HF
spectrum, although it will normally be worse on your harmonics.

The interference sources can be VERY BIZARRE. In my case, a single tower
with antennas for the 6 HF bands -the very same tower being the 160m
radiator-, the worst interference source was not any "self-interference",
but that coming from rectification in my neighbour's phone-line/ADSL modem.
Nothing you do at your station (except reducing your TX power by a GREAT
margin) can cure this type of interference. The interference level and
spectrum signature was variable depending on whether the ADSL TX was on or
off depending on ADSL-PPoE protocol status. Easy to tell now, but it took me
literally years to find that out.

73
Juan EA5RS

-----Mensaje original-----
De: CQ-Contest [mailto:cq-contest-bounces at contesting.com] En nombre de Leigh
S. Jones, KR6X
Enviado el: martes, 08 de septiembre de 2015 19:46
CC: reflector cq-contest
Asunto: Re: [CQ-Contest] Coax Stubs for SO2R

Having extensive experience operating from multioperator stations on the
West Coast has given me some insight into interference issues.  I can
confirm that quite often the source of trouble is not in the front end nor
finals of the rigs.  It can indeed be elsewhere.  For instance, at W6HX we
had a big problem on 1810 kHz.  The pull-down cable hardware on a large
motorized crank-up tower mixed dissimilar metals.  In the wind it was
intermittent but it was in effect a 70 foot wire with a diode at the bottom
where it was grounded.  One AM broadcast station three miles distant at 1260
kHz was doubled and another at six miles distance on 710 kHz was subtracted,
resulting in a meter-pegging signal modulated by both.  If you have anything
in your yard that acts like a diode with wires connected there is a
potential for harmonics to be generated where filters cannot possibly be of
help.

Leigh S. Jones, KR6X

> On Sep 7, 2015, at 22:13, Dave Hachadorian <k6ll.dave at gmail.com> wrote:
> 
> Mike,
> 
> I guess the problem that you are seeing is that when radio A transmits on
40, you can hear interference on 20 and 15, around the harmonic frequencies?
> 
> I suspect that radio B is being overloaded by the 40 meter fundamental
energy, and is generating the harmonics and possibly wideband interference
internally, in the receiver.
> 
> In that case, you need stubs on the radio B antenna to pass 20 and reject
40, and to pass 15 and reject 40.  To test this hypothesis, take one of the
23' shorted stubs that you already made for 40,  convert it to a 23' open
stub, and connect it to radio B on 20 meters.  See if the 20 meter
interference is lessened when you transmit on 40.  A 23' open stub rejects
40 and 15 and passes 20 and 10.
> 
> Are you using bandpass filters?  A stub by itself may not provide
sufficient isolation, especially since both of your antennas cover all
bands.
> 
> Dave Hachadorian, K6LL
> Big Bear Lake, CA
> 
> 
> -----Original Message----- From: Mike Smith VE9AA
> Sent: Monday, September 7, 2015 6:07 PM
> To: cq-contest at contesting.com
> Subject: [CQ-Contest] Coax Stubs for SO2R
> 
> This is about coax stubs.
> 
> 
> 
> Sent this earlier to "Towertalk" then I thought perhaps it was better 
> suited to contesting.
> 
> 
> 
> Reposting, with some edits:
> 
> 
> 
> I've seen the K2TR stubs, K1TTT page and have recently bought the FB 
> book by W2VJN
> 
> Today, for a change, I had a little spare time so built 2 stubs, but 
> lets just concentrate on one.
> 
> It was supposed to be for the 40m transmitter (Radio A).
> 
> I will add  Radio A (transmitter) is using a multiband vertical.
> 
> Radio B (receiver) is attached to a multiband horizontal dipole 
> (ZS6BKW) in case it makes any difference in my question.
> 
> I see a signal of roughly S9 or S9+ 20/40 on the receiver (varies per 
> band &
> harmonic)
> 
> 
> 
> I roughed out the length, attached a T and a 2nd antenna switch (a la 
> VA2UP
> method) (which I'll only use for stubs), trimmed it with my AA-230pro
> 
> and when it's inline (parallel to my primary antenna switch) I see no 
> difference at all on 20m or 15m on my 2nd receiver when the stub is in 
> or out of line
> 
> NONE.  Like, not even a titch ESP hopeful. (hi)
> 
> 
> 
> I presume this is a type 1 stub (shorted 1/4WL type, x velocity 
> factor)
> 
> 
> 
> Thinking I had done something wonky, I made another stub from 
> different coax..same result.
> 
> Later I made one up for 20m - same result. No change whatsoever in the 
> received signal harmonic(s) on the receiver.
> 
> 
> 
> Anyone been down this road?
> 
> 
> 
> Too close to rig?
> 
> 
> 
> Interaction from my T and 2nd antenna switch?  Gremlins? Wrong method 
> using the AA-230 pro maybe?  I am close to that 23' mark on the 40m one.
> 
> 
> 
> de Mike (SO2R hopeful) VE9AA
> 
> 
> 
> 
> 
> Mike, Coreen & Corey
> 
> Keswick Ridge, NB
> 
> 
> 
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