[TowerTalk] Front to Back Measurements

[Bill Hider (N3RR)]

Kim,

Your anecdotal report is something that all of us have experienced at one
time or another.

It's possible that it was a 50 dB F/B.

It's also possible that your S-Meter is not calibrated accurately.  I'm not
saying you can or should do something about it either.  S-Meters are very
interesting devices.  In the "old days" we used to call them Scotch
S-Meters.  Anybody remember that term from the 50s and 60s??  We had Bourbon
S-Meters, too.  Who wins the prize for being the first to tell me the
difference?  (I do know.)

Anyway, the way to tell whether you have a S-Meter issue/problem is to use a
calibrated signal source on the fundamental frequency, like a Motorola
network analyzer, and inject it into the RX at a known signal level
(including the attenuation of the cables between the source and the RX) and
measure the difference between S-9 and S-1 on your RX.

As you do this, create a chart of the dB difference between each S-Unit.
That way, in the future you'll know what each S-reading means.  Check the
calibration every 6 -12 months so you are reasonably sure it's stable.

Ok, who's the winner?

73,

Bill, N3RR

-----Original Message-----
From: owner-towertalk@contesting.com
[mailto:owner-towertalk@contesting.com]On Behalf Of Kim Bottles
Sent: Wednesday, December 12, 2001 6:05 PM
To: TowerTalk
Subject: [TowerTalk] Front to Back Measurements



Greetings Ladies & Gentlemen,

I claim to know very little about antenna theory. However I have noticed
something on a practical level with a new antenna and wonder if any of
you might be willing to comment on it and clarify for me what I have
observed.

I recently purchased a SteppIR variably tuned Yagi. (See page 129 of the
December QST or visit their website at www.steppir.com)

This is a three element yagi with the ability to tune each element
remotely from the shack. (Look at their website, they explain how it is
done better than I could here.)

I was listening to a fairly long winded SSB QSO last night on 20 meters
and had time to make several measurements of front to back on a loud
station. The SteppIR has a one button swapping of director and
reflector, so flipping the direction 180 degrees takes but a few
seconds.

The loud station was in North Carolina and I live on Bainbridge Island,
just west of Seattle, a distance of about 3000 miles. With the yagi
pointed at the Carolina station he was registering a solid 5 dB over S-9
with peaks to 10 dB over S-9. Flipping the director and reflector
dropped him down to barely peaking S-1. Is this really 50+ dB front to
back? The rig used was an Icom 756Pro. My yagi is at 60 feet in the
clear.

I have noticed the same kind of results on other stations, but this was
the first situation where I was able to switch back and forth numerous
times with the same results. (Thank goodness for long-winded SSB QSO's.)

I know this is not a valid scientific experiment, so please do not
attack me as if I was claiming it was. I am only reporting an antidotal
(as K7LXC would say) observation. (Is that how you spell "antidotal?)

Because this antenna is brand new to the market (and a heck of a lot of
fun to play with I might add), I thought some of you might find my
observations interesting and feel moved to comment.

Comments on this reflector always seem entertaining and sometimes
educational.

Best Wishes for a Happy Holiday Season,

Kim Bottles - K7IM



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List Sponsored by AN Wireless:  AN Wireless handles Rohn tower systems,
Trylon Titan towers, coax, hardline and more. Also check out our self
supporting towers up to 100 feet for under $1500!!  http://www.anwireless.com

-----
FAQ on WWW:               http://www.contesting.com/FAQ/towertalk
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com