[CQ-Contest] SO2R technical questions

Jeff Blaine jeff at ac0c.com
Tue Jan 20 20:07:00 EST 2015


I want to caution you on one point.  From a receiver frying standpoint, the 
use of the amp is not at all the threat magnifier that you would think it 
is.  It's very easy to fry rigs with "only 100W."  100->1500 is around 13 
dB.  So 100W is around 50 dBm, and 1500W is around 63 dBm.  To put that in 
perspective, a good rule of thumb is that you don't want the 2nd rig to ever 
see anything over 0 dBm.  By point is not to diminish the 13 db, but rather 
to illustrate that even with 100W, getting to "safe" is not a trivial 

Get VJN's book and focus on the isolation.  The shack side gear for 
switching, etc, will be steered more by the mode you run and how much of an 
automatic life you want.  Those are all convenience things - isolation is 
about first keeping the 2nd rig from getting blasted away by the first, and 
secondly, about suppressing the harmonic and desense caused by one rig to 
the other - so that you can actually do some work on the 2nd rig when the 
first is transmitting.

Good luck!


-----Original Message----- 
From: Mike & Coreen Smith VE9AA
Sent: Tuesday, January 20, 2015 5:52 PM
To: cq-contest at contesting.com
Subject: Re: [CQ-Contest] SO2R technical questions

Just occurred to me that I had both preamps engaged in radio 2 which is an
IC746.  It's S-meter seems overly generous anyways.  Looks like 2nd and 3rd
harmonics are more like S9+10dB with no preamps on. (only time I would need
them would be maybe on a quiet 10m band to pull out super weak signals).the
initial "spike" is higher, which I think is a function of the Icom digital S
meters which I really don't like.

So, at constant S9+10dB readings (initial spike higher).solid dashes @ 30wpm
CW.am I safe?

Is there a better way to measure?  FM mode?  Readings with a scope of some
kind or ?


Mike VE9AA

Mike, Coreen & Corey

Keswick Ridge, NB

From: Mike & Coreen Smith VE9AA [mailto:ve9aa at nbnet.nb.ca]
Sent: January 20, 2015 5:40 PM
To: 'cq-contest at contesting.com'
Subject: SO2R technical questions

How can I tell if I have too much energy at the input of "radio 2" when
transmitting on "radio 1" ?

I've done a few DXpeditions  and field days (CY0AA, CY9AA etc.) and we had
some cheapie bandpass filters and some rapidly made crappy coax stubs
(without using any kind of device other than a calculator and a measuring
tape to verify the correct lengths).

At times we  operated w/o one or both (both LP and QRO) and sure, we had
interference, but nobody blew up a rig.

Now nearly 2 decades later I am just barely dipping my toe into the SO2R
waters so with N1MM+'s help, today hooked up my Winkey to 2 rigs (IC7410 &
746) and when transmitting on a wide variety of antennas on radio one
(HF9V, A3S, Inverted L's for 80/160), and limiting radio 2 to only a ZS6BKW
as an inverted Vee (G5RV like) antenna about 50-60' away from all the
various antennas, harmonics were fair to bad, but not what I would call
severe. (no stubs, no BPF's, nuttin' but air).

CW peaks looked like around *50-60/S9 and steady dits were *40/9 if those
cheezie Icom bar-graph S-meters are to be believed. *(if I was on the exact
2nd or 3rd harmonic frequency)

Is this too much signal?

I can build some coax stubs over time...and I am working on a YCCC SO2R box
as time permits but don't have a lot of spare dough for BPF's (2 of them
would run me $1200-$1400 CDN by the time I had them in the shack)

nor a SIX-PAK(another $1k_), thus I am wondering about cutting costs going
in.  Another local tried SO2R, didn't like it and had spent many thousands.
I don't have the spare dosh, nor will I, hence my question..

If I am willing to leave the amp turned off (sigh..), and antennas will all
be separated only 50', how do I know if I have too much signal at the input
of the 'other' radio?

Oh and feel free to school me on SO2R...I have nearly googled the internet
dry, so have done lots of reading, so if you have a web page up, I've likely
seen it ;-)  Just never tried it.

Technique is what I lack.

I figured it was time.  I find myself (especially in CW contests) calling CQ
and ALT-TABBING over to check my email, surf the net, watch the greyline
maps, stare out the window , talking to family etc. a LOT in contests.

Is SO2R the next step?

Mike VE9AA

p.s.- I will sorely miss using the amp, but if I try SO2R @ 100w and like
it, maybe I can stumble onto some cheap 419 BPF's and a 6-pack somewhere
later on.  I don't care a hoot about automation.  I like to flick the
switches manually.

Mike, Coreen & Corey

Keswick Ridge, NB

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