[3830] ARRL 160 W1HIS Single Op HP

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                    ARRL 160-Meter Contest

Call: W1HIS
Operator(s): W1HIS
Station: W1HIS

Class: Single Op HP
QTH: Belmont, MA
Operating Time (hrs): 20

Summary:
Total:  QSOs = 606  Sections = 70  Countries = 26  Total Score = 128,160

Club: Yankee Clipper Contest Club

Comments:

One antenna, 20 ft (6m) high and 70 ft (20m) long.  Yes, one-eighth of a
wavelength long, and 0.03 wavelength high.  And ground-independent, i.e.,
having no radials or other counterpoise.  I wonder whether anyone else in this
contest used such a low and small antenna.

My antenna was a champ, but Murphy is clever.  A subtle failure, unique in my
53 years of hamming, knocked me off the air for three hours of prime time
(Saturday from 06 to 09h UTC, during which sunrise swept across Europe). 
First, my receiver began losing sensitivity.  Sometimes the sensitivity
recovered shortly after I switched from transmitting to receiving.

Suspecting a bad contact in a T/R relay in my power amp, I connected the coax
from my external antenna tuner directly to my transceiver, bypassing the amp. 
Now receiver sensitivity was normal, and stayed normal.  So I tore into my amp
and replaced the relay at its input. This was an easy plug-in replacement; and
I had a spare on hand because I'd had to replace this relay before.  It's a
cheap relay and its contacts aren't reliable for low-level signals.

But replacing this relay did not eliminate the problem.  I noticed that the SWR
indicated by the meter in the coax between the amp and the remote antenna tuner
had changed, and that this SWR was markedly different when I transmitted low
power as opposed to high power.

Now I suspected a bad contact in a relay or a variable inductor in my antenna
tuner.  So I fetched a ladder, got to the tuner (70 ft away, at the far end of
my house), and opened it up.  This time I was smart enough not to rush to
replace anything.  I checked the continuity of every relevant contact (in four
relays and two inductors) with a low-range ohmmeter.  Everything checked OK.

Finally I found the fault inside the directional-coupler "head" of the
aforementioned SWR meter.  Removing this coupler from the coaxial transmission
line eliminated all symptoms of trouble.

Without the SWR meter I needed another way to see whether/when my antenna
system was properly tuned.  I must retune when I QSY within the 160-m band,
because my antenna is so short.  The quick and dirty way that worked was to
look an RF field-strength meter in my shack -- which, for this band, is within
the near field of my antenna.  I thought it interesting to see that my 160-m
transmitted signal contributes less than half as much to the E-field strength
(and less than a quarter of the flux of power) in my shack as do AM broadcast
stations more than a mile away.  A remarkable demonstration of the
effectiveness of the common-mode chokes in my antenna feedline.


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