Hello All,

I have just found my old Hi-Gain mobile-mount whip antenna, circa
1980's, I'm guessing.

I have just looked at the antenna and it is made in 4 parts; the whip,
the chrome spring that the whip gets screwed into, a metal tube [with a
plastic sleeve covering it. could this be the loading coil?] and lastly,
the mag base. A small quantity of RG 58 is soldered to the underside of
the "loading coil", making a very compact antenna.

If I loosen the set screw in the base and pull out the whip, it is 28"
long; I'd like to cut it so that it will receive/resonate center of the
151-174 MHz band. where I do most of my summer monitoring, using my old
[but still working] BC 210.

How long should I cut the whip to accomplish this? Or is the whip too
short already!?

I wouldn't bother the group with such an easy question, but I don't know
where to look for the formula!

Many thanks for taking the time to respond!

Alain

"A. Pismo Clam" wrote in message
...
Hello All,

I have just found my old Hi-Gain mobile-mount whip antenna, circa
1980's, I'm guessing.

I have just looked at the antenna and it is made in 4 parts; the whip,
the chrome spring that the whip gets screwed into, a metal tube [with a
plastic sleeve covering it. could this be the loading coil?] and lastly,
the mag base. A small quantity of RG 58 is soldered to the underside of
the "loading coil", making a very compact antenna.

If I loosen the set screw in the base and pull out the whip, it is 28"
long; I'd like to cut it so that it will receive/resonate center of the
151-174 MHz band. where I do most of my summer monitoring, using my old
[but still working] BC 210.

How long should I cut the whip to accomplish this? Or is the whip too
short already!?

I wouldn't bother the group with such an easy question, but I don't know
where to look for the formula!

Many thanks for taking the time to respond!

Alain

Beg, borrow a swr meter! Extend/lower radiator between tests to find lowest
swr...

JS

How long should I cut the whip to accomplish this? Or is the whip too
short already!?



Considering that there is an unknown coil in the base, I guess a normal
formula for figuring the length of the antenna won't apply... I would
suggest you take an inch, or maybe inch and a half off the length of the
whip and just go with that.... of course remember, it will never be usable
on 2M again.

Ed

"John Smith" wrote in
:

"A. Pismo Clam" wrote in
message ...
Hello All,

I have just found my old Hi-Gain mobile-mount whip antenna, circa
1980's, I'm guessing.

I have just looked at the antenna and it is made in 4 parts; the
whip, the chrome spring that the whip gets screwed into, a metal tube
[with a plastic sleeve covering it. could this be the loading coil?]
and lastly, the mag base. A small quantity of RG 58 is soldered to
the underside of the "loading coil", making a very compact antenna.

If I loosen the set screw in the base and pull out the whip, it is
28" long; I'd like to cut it so that it will receive/resonate center
of the 151-174 MHz band. where I do most of my summer monitoring,
using my old [but still working] BC 210.

How long should I cut the whip to accomplish this? Or is the whip too
short already!?

I wouldn't bother the group with such an easy question, but I don't
know where to look for the formula!

Many thanks for taking the time to respond!

Alain

Beg, borrow a swr meter! Extend/lower radiator between tests to find
lowest swr...

JS



That would work, assuming he has a transmitter in the 150-170 VHF
range he could use as an RF source.


Ed

Find a ham in your area who has an antenna analyzer.

Use the ham/analyzer to find the resonance of your antenna. Once it is known,
then adjustments can easily be 'gesstimated intelligently'.

I'm in New Hampshire. If close I'll do the measurement for you.

Where do you live? Nearest large city and state will do for info.

/s/ DD

A. Pismo Clam wrote:
Hello All,

I have just found my old Hi-Gain mobile-mount whip antenna, circa
1980's, I'm guessing.

I have just looked at the antenna and it is made in 4 parts; the whip,
the chrome spring that the whip gets screwed into, a metal tube [with a
plastic sleeve covering it. could this be the loading coil?] and lastly,
the mag base. A small quantity of RG 58 is soldered to the underside of
the "loading coil", making a very compact antenna.

If I loosen the set screw in the base and pull out the whip, it is 28"
long; I'd like to cut it so that it will receive/resonate center of the
151-174 MHz band. where I do most of my summer monitoring, using my old
[but still working] BC 210.

How long should I cut the whip to accomplish this? Or is the whip too
short already!?

I wouldn't bother the group with such an easy question, but I don't know
where to look for the formula!

Many thanks for taking the time to respond!

Alain

I have just found my old Hi-Gain mobile-mount whip antenna, circa
1980's, I'm guessing.

I have just looked at the antenna and it is made in 4 parts; the whip,
the chrome spring that the whip gets screwed into, a metal tube [with a
plastic sleeve covering it. could this be the loading coil?] and lastly,
the mag base. A small quantity of RG 58 is soldered to the underside of
the "loading coil", making a very compact antenna.

If I loosen the set screw in the base and pull out the whip, it is 28"
long; I'd like to cut it so that it will receive/resonate center of the
151-174 MHz band. where I do most of my summer monitoring, using my old
[but still working] BC 210.

If it's an old 2-meter antenna, then I'd guess from the whip length
that it's probably a 5/8-wave, with some form of inductive loading to
make it resonant.

If that's the case, it'll probably receive reasonably well for
monitoring purposes in the 151-174 range without any modification.

Or, you could shorten it by an inch or two, gradually trimming the
whip until the received signal strength around 160 MHz is at a peak.

Another option would be to bypass the loading coil (or whatever it is)
with a wire jumper, and shorten the whip to around 16.5". This will
convert the antenna into a quarter-wave vertical, resonant at around
160 MHz.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

If you're just going to use it for receiving, you can use it as is. It
should work quite well. If, however, you have it set in your mind you
need perfection and the value of the loading coil is unknown, you can
scale the antenna whip. It probably still won't be perfect, but since
it is pretty hard to change the coil's physical properties, this might
be the best you can do. Take the center of the band the antenna was
built for (I assume 2M band, which is 146 MHz) and divide it by the
center frequency of the range you want to convert to (162.5 MHz in this
case) and multiply that number by the length of the whip as it exists
now (28"), which gives a new whip length of about 25 and 1/8". Give it
a try...

Scott
N0EDV

A. Pismo Clam wrote:
Hello All,

I have just found my old Hi-Gain mobile-mount whip antenna, circa
1980's, I'm guessing.

I have just looked at the antenna and it is made in 4 parts; the whip,
the chrome spring that the whip gets screwed into, a metal tube [with a
plastic sleeve covering it. could this be the loading coil?] and lastly,
the mag base. A small quantity of RG 58 is soldered to the underside of
the "loading coil", making a very compact antenna.

If I loosen the set screw in the base and pull out the whip, it is 28"
long; I'd like to cut it so that it will receive/resonate center of the
151-174 MHz band. where I do most of my summer monitoring, using my old
[but still working] BC 210.

How long should I cut the whip to accomplish this? Or is the whip too
short already!?

I wouldn't bother the group with such an easy question, but I don't know
where to look for the formula!

Many thanks for taking the time to respond!

Alain

I have just looked at the antenna and it is made in 4 parts; the whip,
the chrome spring that the whip gets screwed into, a metal tube [with a
plastic sleeve covering it. could this be the loading coil?] and lastly,
the mag base. A small quantity of RG 58 is soldered to the underside of
the "loading coil", making a very compact antenna.

If I loosen the set screw in the base and pull out the whip, it is 28"
long; I'd like to cut it so that it will receive/resonate center of the
151-174 MHz band. where I do most of my summer monitoring, using my old
[but still working] BC 210.

How long should I cut the whip to accomplish this? Or is the whip too
short already!?

Short out the coil and use length(cm)=7300 / MHz as the total length,
including the bridge over the coil.

You could alternatively use the coil to correct the excessive high.angle
radiation of a 5/8-wave antenna. Use total length(cm)=1860 / MHz including
the length of the turns of the coil. If in practice you find you have less
gain than a simple 1/4-wave then go back to plan #1 above.

Note that these lengths are correct, but reality has a habit of varying, so
cut too long and clip the length for best VSWR.

On Tue, 07 Nov 2006 08:41:03 -0800, "A. Pismo Clam"
wrote:

If I loosen the set screw in the base and pull out the whip, it is 28"
long; I'd like to cut it so that it will receive/resonate center of the
151-174 MHz band. where I do most of my summer monitoring, using my old
[but still working] BC 210.

If all you are doing is receiving then I suspect that the length
really doesn't matter a great deal. Clearly an antenna half as long
wouldn't hear distance signals as well but that would be about it.

Tony