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@contesting.com] On Behalf Of Mike
Smith VE9AA
Sent: Sunday, September 13, 2015 8:51 AM
To: cq-contest@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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