On 02/07/2018 04:49 AM, Gareth's Downstairs Computer wrote:
A question for those who work HF mobile; do you feel that
having a loading coil and a short whip materially affects
your QSO capability, as the text books suggest, for if
not it would seem to suggest that we could all manage
with such antennae as our main base air transducers?

Hello, and that's difficult to answer as you would have to do a
side-by-side comparison of two or more antennas and it gets more
complicated if ionospheric propagation is involved with constantly
varying receive signal levels. Most mobile HF antennas are electrically
short monopoles and as a result look like a capacitor in series with a
small "radiation" resistance (the conductive material of the antenna and
the vehicle body ground plane also provides some ohmic contribution).
The problem is matching the transmitter's RF output impedance (nominally
50 ohms) to the antenna feedpoint. For a longer antenna having a larger
radiation resistance we need a lot less inductance in the loading coil
and less turns means less RF power dissipation in the coil or any other
components comprising the matching network. I'm unsure what you mean by
"base air transducer" but keep in mind this discussion is essentially
about omni-directional antennas. So a mobile/fixed comparison could be
between a vehicular-mounted monopole and, say, a shunt-fed tower or an
RF-fed vertical wire supported between two structures (a common antenna
used in the U.S. for MW (AM) broadcast stations in the early 20th c.
(also aboard ocean liners like Titanic but having rotary spark-gap
transmitters). Sincerely, and 73s from N4GGO,

--
J. B. Wood e-mail: