[CQ-Contest] Coax Stubs for SO2R

Mon Sep 14 01:58:59 EDT 2015

Hi Mike,

I can think of a least one scenario, Mike, that meets all of the symptoms you've been describing...read below.

First of all, let me make an assumption that I glean from your first posting on this thread,
in  which you reposted your message from TowerTalk and you said:
" I see a signal of roughly S9 or S9+ 20/40 on the receiver (varies per band &
harmonic)"

My assumption, therefore is:  You are measuring your interstation interference by listening
to "the other radio's receiver" and watching that S-Meter.  (Not a problem, I just want to make sure you're not using any other meter in your analysis.)

Here's a scenario that meets all of the "symptoms" you have been seeing and posting to us, if my assumption is true.
Please read this carefully and read it in its entirety before drawing any conclusions.  Thanks:

SCENARIO PART 1
Radio A transmits a signal 1W -100W and you hear it in Radio B's receiver on RADIO A's 2nd harmonic.
That signal you are hearing in Radio B is mostly leakage from somewhere inside Radio A going into  Radio B's receiver without going to your transmit antenna.
Yes, Radio A transmits 1W to 100W (say 50W) out your antenna, but the 2nd harmonic is stronger coming directly from RADIO A to RADIO B, so
when you apply the stub, which you have told us you verified it is actually working (more on this below), the RADIO A 2nd harmonic that goes to the antenna is attenuated, but the direct "leakage" signal is still there,
 going directly from Radio A TX to Radio B's receive, so it sounds like the stub is not working. In fact, I'd say that the 2nd harmonic signal radiating from the antenna
is at a lower level in RADIO B than what RADIO B is hearing direct on the leakage path.  Since you said the stub did nothing, then the 2nd harmonic signal from the transmit antenna
must be lower level than the leakage 2nd harmonic signal.    Keep reading...

SCENARIO PART 2
When you run the Amp at 500W, none of that 500W signal "leaks" from the amp to Radio B's receiver.
However, there is still some leakage from the leakage noted in PART 1, above, BUT since you are
using your amp, RADIO A is no longer running 50W- 100W and is probably running more like 20 W, THEREFORE the leakage
from Radio A when you are using your amp is at a much lower level.
That's why you are now seeing the 2nd harmonic signal from your amp down 25 dB in Radio B's receiver from the action of the stub because any effect of the leakage signal
from RADIO A is now at a much lower level than the 2nd harmonic signal from the Amp, even with the stub.

ANALYSIS
The signal level heard in PART 1, causes RADIO B's RX to indicate S9 to S9+40dB, per your 1st posting.  -->  This is caused by local leakage of the RADIO A signal.
The signal level heard in PART 2, causes RADIO B's RX to indicate 20 to 25dB less than WHAT?  What was the fundamental signal level which dropped by  20 to 25dB in its 2nd harmonic?
I'll bet it, the fundamental when the amp was on, was a lot more than S9 + 40 dB and with the stub it was reduced by 25dB = S9 or less, right?
Again, the reason you didn't hear the same leakage in PART 2 as PART 1 -- you reduced the power output of RADIO A so you could drive the 500W amp properly.  You did not put 100W
into the amp. So, the local leakage was reduced dramatically and all you heard in RADIO B was the amp's output signal reduced on the 2nd harmonic by the stub attenuation.

THE WAY TO TEST THIS:
Transmit with RADIO A without the amp and without the stub and listen to RADIO A's 2nd harmonic on RADIO B.
Increase RADIO A's power out until RADIO B's receiver on the 2nd harmonic reads S9 + 20dB. (per your first posting)
Stop transmitting on RADIO A.
Insert the stub.
Transmit on RADIO A without changing any power setting.  Record what Radio B's S-meter reading is. (The first recorded S-meter reading) (You said this was not changed with the stub, fine, understood.)
Quit transmitting.
Remove the stub.
Again, listen to Radio A's 2nd harmonic on RADIO B.
Now, turn on your amp (driven by RADIO A).Transmit using your amp and increase the power out of the amp until 
RADIO B's S-meter reads S9 + 20dB (as in step 1 in this test).
Stop transmitting.
Insert the stub after the amp.
Without changing any settings, transmit with Radio A PLUS the amp and record the S-Meter reading on RADIO B. (the 2nd recorded S-Meter reading)
I'll bet, the 2nd recorded S-meter reading will be a whole lot less (maybe 20 -30 dB less) than the first recorded s-meter reading.
If  so, you've got significant leakage from RADIO A TX into RADIO B's RX that has nothing to do with your outdoor antenna system.

Bill N3RR

-----Original Message-----
From: CQ-Contest [mailto:cq-contest-bounces at contesting.com] On Behalf Of Mike Smith VE9AA
Sent: Sunday, September 13, 2015 8:51 AM
To: cq-contest at contesting.com
Subject: Re: [CQ-Contest] Coax Stubs for SO2R

You won�t believe this guys��but I turned on my amp yesterday (in between soldering up a really cool YCCC SO2R+ kit) just to blow some dust out as I haven�t used it in a long time and believe it or not�..running ~500w, the stub knocks down the 2nd harmonic 20-25dB or so, but when only running the exciter @ 1W to 100W, the harmonic does not get knocked down at all ! WTF ?! How can that even be? LOL

The harmonic also sounds slightly cleaner running the amp than NOT running the amp.

I hesitated to post this to CQ-CONTEST for fear you�ll all wonder just what the heck it is we�re drinking up here in NB�

I tend to joke around a lot, but I swear this is true.

Mike VE9AA

Mike, Coreen & Corey

Keswick Ridge, NB

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