I remember (some years ago) when I was a kid travelling a lot overseas
with my parents, embassy rooftops and ships seemed to sprout HF
Biconical antennas.

This was when satellites were not as widespread as they are now, and I
guess most diplomatic (ciphered I guess) and maritime traffic passed
over HF.

Why would this type of antenna have been preferred? Why don't
amateurs use this type of antenna more? How do HF Biconnicals stack
up against other HF antennas? Can they be trapped for mulitband use
and/or loaded to reduce size?

I'd kind of like to home-brew a 20m one. Any ideas? Designs?
Modelling software for them?


Tommie

wrote in message
...
I remember (some years ago) when I was a kid travelling a lot overseas
with my parents, embassy rooftops and ships seemed to sprout HF
Biconical antennas.

This was when satellites were not as widespread as they are now, and I
guess most diplomatic (ciphered I guess) and maritime traffic passed
over HF.

Why would this type of antenna have been preferred? Why don't
amateurs use this type of antenna more? How do HF Biconnicals stack
up against other HF antennas? Can they be trapped for mulitband use
and/or loaded to reduce size?

I'd kind of like to home-brew a 20m one. Any ideas? Designs?
Modelling software for them?


Tommie

Tommie,

Embassies needed to have reliable communication links. Most foreign
embassies were equipped with transmitters capable of generating kilowatts of
power if needed across the whole HF band. Efficiency wasn't a high priority,
being able to send and receive messages reliably was all that mattered. Most
of the routine daily traffic would have been encrypted teleprinter stuff
sent via permanent scheduled radio links. In times of diplomatic tension,
the regular frequencies might be jammed and hence the necessity to have
equipment that was frequency agile and of sufficiently high power output to
punch through deliberate interference.

Biconical antennas can be tuned across a wide range of frequencies and
require less real estate than many other arrangements. Height is always good
with antennas and the costs of providing lofty rooftop support structures
and high powered transmitters with non interruptable power supplies are not
really an issue for any diplomatic service.

Most of the old cargo ships used wire antennas running from the masts at
either end of the ship. These were quite efficient and cheap. The
disadvantage was that the rope halyards needed maintenance together with the
hoisting blocks and wire antennas themselves. Funnel fumes wreak havok on
phosphor bronze wires and insulators in a marine salt environment. Then the
antennas needed to be lowered and stowed every time cargo was loaded or
discharged so that the cranes could work. The phosphor bronze wires would
become work hardened through stretching and eventually break unexpectedly. I
always had a complete new set of antennas with insulators and couplings made
up in the radio room ready to replace any failures.

Oil tankers switched to whips fairly early on as the prospect of insulator
arcing near to vapour venting from a fuel tank presented real hazards for
the crews. Container ships also tend to rely on whip antennas because their
stay in port is usually measured in the number of hours between successive
high tides. There isn't time to keep raising and lowering antennas running
the length of the ship.

The inefficiency of the whips is compensated for by increasing transmitter
power. Not the most cost effective or ideal way for an amateur station to
run.

As you can see, the requirements of commercial radio traffic are very
different from those of amateur stations, although amateur stations may well
use and adapt commercial techniques when necessary due to site restrictions
or to provide reliable emergency communications for disaster relief, etc.

There is plenty of antenna modelling software that will allow you to explore
their performance on the web, try EZNEC for a start.

Hope this helps.

Mike G0ULI