John,
Wagon wheel antennas were the first practical mobile antennas on the
railroad, so they came into use when the railroads started using radio
communication. I don't know the dates, but some of the old heads can provide
them. As for the rhyme and reason, wagon wheel antennas were a compromise
design to keep antenna height short in a mobile application. Antenna size
and configuration is determined by the resonant frequency desired for radio
communication. High frequency antennas are smaller than lower frequency
antennas so when railroads switched from HF to VHF and UHF, antennas became
smaller, e.g. firecracker antennas instead of wagon wheels. The wagon wheel
is a short center loaded vertical antenna, which means that it radiates a
horizontal doughnut shaped pattern, i.e. it radiates outward in a 360 degree
pattern around the antenna. The wheel and spokes provide capacitive loading
for the short vertical portion of the antenna so it could be turned to the
desired resonant frequency. Wheel diameter was determined by height of the
vertical portion of the antenna and the radio frequency used by the
railroad, hence the amount of center loading required to tune the antenna.
In radio terms, the wheel functions as a 'capacitance hat'. Vertical
antennas have little gain, but that's not a problem since railroad radio
communication as short range in the early years. The photo in RPC Volume 8
of CB&Q 9358 shows a clear view of a wagon wheel antenna, and the radio box
mounted in just in front of the cab. The coaxial cable connecting the
antenna to the box is visible on both ends. The photo shows other details
you may find interesting and applicable to 9355.
Nelson Moyer, KU0A
-----Original Message-----
From: CBQ@yahoogroups.com [mailto:CBQ@yahoogroups.com] On Behalf Of jonnyo55
Sent: Sunday, December 02, 2012 8:53 AM
To: CBQ@yahoogroups.com
Subject: [CBQ] VO-1000 questions, cont'd
Okay, here's phase II of my relentless search for VO-1000 detail
information. What was the rhyme and/or reason behind the "wagon wheel"
antennae, i.e when and where were they installed, and on what units?
Specifically, I'm looking at #9355, but general info is desired...
John O'Connell
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