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Of course, Silver! 'Can't think of why I wrote Gold!
'Guess I was thinking in terms of IR reflectivity! Our brass x-band
waveguide was coated with silver for conductivity, except for some that was made
from OFHC (oxygen-free, high-conductivity) copper.
Most talk of signal reception is of a subjective manner;
how strong, how far, how clear. The only really good means for determining the
merits of an antenna installation is to compare its performance to a standard
dipole, or to do a relative comparison of various installations on a
given airplane. To do this requires a receiver that has available an output
calibrated in terms of signal strength in dBm,
deci-Bels(relative to a)milliWatt. Often this is
derived from the AGC (automatic gain control) of the receiver. Radio people
often use signal strength in micro-Volts, but their systems are usually 75 ohms,
and so a conversion must be done to find the equivalence for our 50 ohm
systems. That's why dBm, power, is a much better scale; it's independent of
system impedance. Why subjective measurements are useless is that unless you
know the front-end noise figure of the receiver, or the transmitted power it's
receiving, there can be lots of error! Does the reciver use a low-noise, 1.5dB
NF pre-amp, or a 6dB NF crystal mixer front end. That 4.5 dB better
preamp is worth 68% more range for the same S/N than the mixer front-end.
Was the transmitter 4W or 8W; that's another 41%, for a total of 137% more
range! How about the coax loss which adds to the front end noise? Was it high
loss RG 58, medium loss RG 400, or low loss FSJ1-50.
Here's something an enterprising individual might
consider: replace the LE of the Hstab with fiberglass and insert a VOR or GS
dipole in it, or do the same with the Vstab LE and put your Comm dipole there.
Dipoles are much, much better in radiation toward the horizon than are
monopoles with their miniscule "ground-planes", miniscule, that is, relative to
several wavelengths.
Attached is a drawing of the antennas I just incorporated
in two wingtips I designed. One is for glide-slope, the other is for VOR and
localizer.
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