Your rig's internal attenuator is generally quite accurate. Even using 5%
resistors, the maximum error is about a dB, and is typically much less.
This gives you accurate reference points with step size depending upon
the rig.
Another inexpensive technique is using an external step attenuator. I've
purchased a few HP step attenuators at the local flea markets for $10-$15
each that give me very accurate 10dB and 1dB reference points. Place them
in series with the antenna lead and dial up the attenuation so the STRONG
signal gives the same meter reading as the weak signal, and read the
F/rear from the attenuator setting. Maybe I got lucky; my step
attenuators actually work--no blown resistors, which I am told is a
common problem with flea market attenuators.
Now, all I need is the time (and inclination) to make such measurements.
Around here, the local terrain gives me a very strong pattern whether I
want it or not! (independent of antenna position).
73 de Bob, K6XX
On Wed, 12 Dec 2001 21:38:18 -0500 "Bill Hider (N3RR)" <n3rr@erols.com>
writes:
>
> 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
>
>
>
> List Sponsored by AN Wireless: AN Wireless handles Rohn tower
> systems,
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>
> -----
> FAQ on WWW: http://www.contesting.com/FAQ/towertalk
> Submissions: towertalk@contesting.com
> Administrative requests: towertalk-REQUEST@contesting.com
> Problems: owner-towertalk@contesting.com
>
>
>
> 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
>
73 de Bob, K6XX
k6xx@arrl.net
www.k6xx.com
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