To obtain obtain some idea of the numerical values involved with
mobile, short, antennas on 160 meter and other low frequency bands,
download programs -

HELICAL3
VERTLOAD
LOADCOIL

from website below. Takes only a few seconds to download. Not zipped
up. Run immediately.

With a very short antenna, to obtain a useful efficiency, a physically
large loading coil is essential. The only space available is up the
antenna. So the best thing to do is extend the coil up the antenna
from near the base, in the form of a long slender helical winding on a
pvc plastic pipe.

The whole thing behaves as a short 1/4-wave resonant vertical. There
is a short rod at the top which is pruned to resonate the antenna in
the required band. It is inevitably a single frequency job. The
bandwidth on 160m is only a few kHz.

With a 100 watt transmitter, when both vehicles are in the low-noise
countryside, it is possible to work 100 miles or more, on groundwave,
in daylight. Much further via skywave in darkness. G3YXM has worked
transatlantic from a car in Scotland to a base station in Canada on
occasions.

Maximum overall antenna heights are about 9 feet above roof of car
with the coil about 2" in diameter, the coil extending to a height of
6 or 7 feet.

The most tedious procedure is pruning all antenas in a group of
mobiles to the same frequency on the 160 meter band. But it has been
done. Mobile to a base station is easy. For many years the standard
UK frequency for mobiles was 1930 kHz.

Matching from antenna base to a 50-ohm transmiier can be accomplished
by a single or bank of mica capacitors of several hundred pF.

For quite a number of years, mobile working on 160m was quite popular
in the UK using helically-wound antennas.
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

Gary:

First, you are off by a decade, the Texas DPS moved from 1658 kcps. to 42.9 Mc. in 1949. Prior to the move, they used
(very successfully, I might add) a earlier version of Reg's antenna, which was a 10 foot bamboo pole helically wound
with waxed cotton insulated bell wire. IIRC, the winding was spaced about 1 to 1½ wire diameters apart . The
transmitter was directly connected to the base of the antenna with a short piece of 8 gauge wire, so there was no SWR to
worry about, and final tuning of the antenna was done in the transmitter output pi-network. Black '41 and '48 Fords
with 10 foot cane poles on the rear bumper brackets, brings back memories.

--
Crazy George
The attglobal.net address is a SPAM trap. Please change that part to: attdotbiz properly formatted.
wrote in message ups.com...

snippety

I read somewhere that in the 50's, law
enforcement 2-way radios operated close to our 160m ham band. Wonder
what kind of antennas they used on the police cars. Of course the
distances they were interested in are different from hams.
Gary N4AST

Crazy George wrote:
Gary:

First, you are off by a decade, the Texas DPS moved from 1658 kcps.
to 42.9 Mc. in 1949. Prior to the move, they used
(very successfully, I might add) a earlier version of Reg's antenna,
which was a 10 foot bamboo pole helically wound
with waxed cotton insulated bell wire. IIRC, the winding was spaced
about 1 to 1=BD wire diameters apart . The
transmitter was directly connected to the base of the antenna with a
short piece of 8 gauge wire, so there was no SWR to
worry about, and final tuning of the antenna was done in the
transmitter output pi-network. Black '41 and '48 Fords
with 10 foot cane poles on the rear bumper brackets, brings back
memories.

--
Crazy George
The attglobal.net address is a SPAM trap. Please change that part
to: attdotbiz properly formatted.
wrote in message
ups.com...

snippety

I read somewhere that in the 50's, law
enforcement 2-way radios operated close to our 160m ham band.
Wonder
what kind of antennas they used on the police cars. Of course the
distances they were interested in are different from hams.
Gary N4AST


Hi C. George, Thanks for the interesting info. I certainly did not
know the 160m radios dated to the 40's. My memories of 1950's law
enforcement are "Highway Patrol" starring Broderick Crawford on the BW
TV. I remember watching him standing outside his police car and saying
"10-4" into the mike. Then, he would sometimes put the mike to his
ear, as if it were a speaker.
At the time I didn't wonder about the antenna on his car. I would
expect from your post it would be 43mhz. I don't remember if that show
was any good or not?
Gary N4AST

My dad was a policeman in the 40s, right after the war, his operated 40
something mHz. About 8 yrs old and an interest in radio helped me to
remember radio things, many other things didn't have sticking power,
like english and such )

KF5DE

wrote:
Crazy George wrote:

Gary:

First, you are off by a decade, the Texas DPS moved from 1658 kcps.

to 42.9 Mc. in 1949. Prior to the move, they used

(very successfully, I might add) a earlier version of Reg's antenna,

which was a 10 foot bamboo pole helically wound

with waxed cotton insulated bell wire. IIRC, the winding was spaced

about 1 to 1½ wire diameters apart . The

transmitter was directly connected to the base of the antenna with a

short piece of 8 gauge wire, so there was no SWR to

worry about, and final tuning of the antenna was done in the

transmitter output pi-network. Black '41 and '48 Fords

with 10 foot cane poles on the rear bumper brackets, brings back

memories.

--
Crazy George
The attglobal.net address is a SPAM trap. Please change that part

to: attdotbiz properly formatted.

wrote in message

ups.com...

snippety

I read somewhere that in the 50's, law
enforcement 2-way radios operated close to our 160m ham band.

Wonder

what kind of antennas they used on the police cars. Of course the
distances they were interested in are different from hams.
Gary N4AST



Hi C. George, Thanks for the interesting info. I certainly did not
know the 160m radios dated to the 40's. My memories of 1950's law
enforcement are "Highway Patrol" starring Broderick Crawford on the BW
TV. I remember watching him standing outside his police car and saying
"10-4" into the mike. Then, he would sometimes put the mike to his
ear, as if it were a speaker.
At the time I didn't wonder about the antenna on his car. I would
expect from your post it would be 43mhz. I don't remember if that show
was any good or not?
Gary N4AST

Chicago once dispatched their cars on a frequency of about 1700 kHz. Used
to listen with a Wilcox-Gay receiver (made in Charlotte, Michigan) that had
a knob used to switch from broadcast band to the MF police band. Long time
ago!
I was of the opinion that the Chicago system was one way. Does anyone
remember?
Some of the police HF frequencies were used on CW into at least the
mid-60s. They were not allowed to use RTTY as it was thought to compete too
much with The telephone company. I visited the main HF site for Ohio in the
early 60s - the site was controlled from Columbus with a microwave link.
The engineer liked to call it the longest IF in the world.

73, Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
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