> How incorrect? My handy dandy hand held Wavetek LCR meter cant even read
> that low when I just tried to measure a few minutes ago. The insulator is
> a standard 502 with 1/4" guy grips. Should I drag the HP-4271B outside or
> is the actual C too low to be of any concern except to stimulate
> discussion on the reflector?
I'd toss that Wavetek over on the audio bench. Maybe that is the
same meter you used to determine the inductive metal film
resistors Mouser has are non-inductive?
The measured capacitance of a 502 insulator with the strand-loops
only (grip cut off at the point where it starts to lock) is 12 pF. That
amounts to 1.9 k ohms of Xc at 7 MHz, and 475 ohms Xc at 28
MHz.
That is a significant amount of capacitance!
Try this test.
Model a long length of guy strand on EZNEC, and insert loads
based on 12 pF every 38 feet (that is SUPPOSED to be a non-
resonant length). Excite a center section like a dipole, and
measure the source impedance and look at the currents.
Now change the loads to a few hundred k ohms and watch the
change in behavior!
I'm afraid it's a fact. Breaking your guylines up into non-resonant
lengths that are LONGER than 1/4 wl or so with high capacitance
insulators won't do what you think it will! Especially on higher
frequencies where Xc is under a few thousand ohms.
I use fiberglass links near 10 MHz and higher antennas, and break
the lines up every 3/8 wl maximum on ten meters near high
frequency antennas. Otherwise, the guylines might as well be
unbroken wires.
> I would also expect the loss of galvanized steel guy wire to have an
> increasing absorbtion effect as frequency increases. Has that been
> factored into the modeling programs?
Resistance wouldn't be a problem, as long as the line isn't
resonant or electrically long compared to the operating frequency.
Unfortunately, that isn't the case. Resistance might be a factor, de-
Q'ing the lines and making them broadband absorbers.
Why do you think AM BC stations break up lines every 50 feet or
so on the AM band? Because of insulator capacitance, something
totally overlooked in the "non-resonant length" tables we vainly
follow.
73, Tom W8JI
w8ji@contesting.com
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