Hi

I was given a Omni antenna from a ham who claims the best thing since sliced
cheese. I want to use it for receive at first and when licenses come in for
transmit. I would like to transmit on as many frequencies as practical and
possible as I have a good tuner.
This is an omni, aluminum, telescopic and it 19 feet long. It has 4 ground
planes about 8 feet long.
As I was cleaning it up, I noticed a coil at the base of the antenna
connecting ground to center. Right at the female connector within the base
of the antenna. There is a coil that has approx 20 windings and connects to
ground. The center also feeds to the piping that stretches the full 19 feet.
The coil is pretty rough shape.
My question is in regards to this coil. Is it necessary? What function will
it serve? I can rebuild it if need be but is that necessary? And is 19 feet
a good length for utilizing as many useable frequencies as possible?
Any advice?
Thanks
Bob

First you need to find out what model it is.
http://www.antennaproducts.com/omnilpaindex.htm
might help.
or http://www.drbott.com/prod/db.lasso?code=9141-QUSO
http://www.wavehunter.com/hfant1.htm

if i gather correctly what you are saying those are loading coils for the
bands it's good for. YES you need them. If none of these websites help
just do a google search for an hf omni antenna
Robert
VE3 something or other

"Bob" wrote in message
...
Hi

I was given a Omni antenna from a ham who claims the best thing since
sliced
cheese. I want to use it for receive at first and when licenses come in
for
transmit. I would like to transmit on as many frequencies as practical and
possible as I have a good tuner.
This is an omni, aluminum, telescopic and it 19 feet long. It has 4 ground
planes about 8 feet long.
As I was cleaning it up, I noticed a coil at the base of the antenna
connecting ground to center. Right at the female connector within the base
of the antenna. There is a coil that has approx 20 windings and connects
to
ground. The center also feeds to the piping that stretches the full 19
feet.
The coil is pretty rough shape.
My question is in regards to this coil. Is it necessary? What function
will
it serve? I can rebuild it if need be but is that necessary? And is 19
feet
a good length for utilizing as many useable frequencies as possible?
Any advice?
Thanks
Bob

Hi,

The purpose of the coil is the following:

1) to shunt electrostatic buildup to ground, thus protecting your
receiver.
2) to provide an impedance match from 50 ohms to the very high impedance
of an electrically short whip.
3) to make the whip appear to be electrically longer than it really is.

The coil you have is pretty robust, and looks pretty good to me. I
would clean out the cobwebs, and try it out.

Oh, receivers don't much care what you use for an antenna. A long wire
strung through the air works just fine. Directivity is useful in
extreme conditions.

-Chuck Harris

Bob wrote:
Hi,
Thanks for helping,

The coil I am concerned about is the coil that is in the attached photo. It
is the coil that is at the very bottom of the 19ft aluminum whip antenna. It
is a coil that shorts out the center to the ground right at the female
coaxial connection. (sorry, forget the part number of that). Please see
attached photo of the inner workings of the base of this antenna. My
question is do I need to rebuild this coil and what does the coil do and is
it necessary. I want to use the antenna for an all band use and get up as
high as possible as I have a good tuner.

Thank you Chuck for your comments.

I will do exactly as you suggested and clean up the existing coil and re-use
it. I suspect that coil is there from the original engineering of the omni
that included those three traps.

What would you do about those three traps? I suspect should I put them in
the air, a good wind storm would blow them down as they are very heavy. The
previous owner had replaced those three traps with a straight whip and
suggested good results. I plan to use the same whip (no traps) and tune it.
Any pros or cons in this strategy? Is this the best I can do with what I
have? Preferably I would prefer to do this as I know it is windy where I am
and do not want to keep climbing but would also like to maximize my
transmission performance and receive performance.
Thanks again for any thoughts...








"Chuck Harris" wrote in message
...
Hi,

The purpose of the coil is the following:

1) to shunt electrostatic buildup to ground, thus protecting your
receiver.
2) to provide an impedance match from 50 ohms to the very high impedance
of an electrically short whip.
3) to make the whip appear to be electrically longer than it really is.

The coil you have is pretty robust, and looks pretty good to me. I
would clean out the cobwebs, and try it out.

Oh, receivers don't much care what you use for an antenna. A long wire
strung through the air works just fine. Directivity is useful in
extreme conditions.

-Chuck Harris

Bob wrote:
Hi,
Thanks for helping,

The coil I am concerned about is the coil that is in the attached photo.
It
is the coil that is at the very bottom of the 19ft aluminum whip
antenna. It
is a coil that shorts out the center to the ground right at the female
coaxial connection. (sorry, forget the part number of that). Please see
attached photo of the inner workings of the base of this antenna. My
question is do I need to rebuild this coil and what does the coil do and
is
it necessary. I want to use the antenna for an all band use and get up
as
high as possible as I have a good tuner.

"Bob" wrote in message
...
Hi again,
Please help on another question.
This antenna came with a lot of pieces. What many of you think is that the
coils I was talking about are those traps that are along the length of the
antenna like in this attached photo. These three traps allow the use of
other frequencies BUT I am not sure if they are working and I do not think
when I put this up on my tower, that the wind will not blow them down the
next day. I would prefer to simply use the straight telescoping aluminum
piping that is now together. Yes it would be a 5/8 wave, 10meter ground
plane antenna. But is this useable for most bands as an omni? With the
tuner? Seems it is about the longest, highest I can get it and then tune
it
for useable frequencies.
Please give me some pros or cons as to how I can utilize this for maximum
usage. As I said, I would prefer to simply use the light weight tubing,
keep
the antenna looking exactly like a 10m, 19foot, ground plane antenna and
tune it for best results. What are your comments? Pros? Cons? Thanks for
any
or all advice....

P.S. Please remember, the photo attached shows the band traps that I have,
I
DO NOT want to use them if I do not have to. They are heavy and the wind
will bring them down quickly.

Thanks
[snipped rest]

Bob,

Any multiband antenna is a compromise between radiation efficiency, cost,
wind loading, and weight. In other words, the designer of your vertical will
have already accounted for the wind loading that the traps represent, and
unless you're in an extremely heavy wind area, or are prone to frequent ice
storms followed by high winds, the traps shouldn't be a problem.

If you remove them, then the antenna will be capacitive at all frequencies
below resonance. That means you'll need to add inductance to get it to
resonate: you may have a good tuner, but unless it's located at the antenna,
you'll suffer a lot of RF loss in the feedline (I assume you're using coax)
and might even "punch through" the insulation if you're running high power.

I recommend you keep the antenna as-is, and mount it with the traps intact:
they're designed to offer a good compromise impedance on the ham bands, and
you probably won't need the tuner with them in the line. That means much
faster band shifting if you're a contester, and less worry about your finals
in any case. If it can't take the wind load, it shouldn't be up there, and
you'll have an answer to that question fairly quickly.

If the effort or cost of putting it up is on the wrong end of your
risk/reward curve, then I suggest you use the tower to support a random-wire
or tuned-feeder dipole, and put your tuner to use.

FWIW. YMMV.

Bill

(Filter noise from my address for direct replies)

Hi Bob,

You really need to put the antenna back the way it was originally.

If you remove the traps, you will have a very short vertical whip
antenna, and your tuner will have to do alot to match it. Your tuner's
only job is to make an ugly load look nice to your transmitter. It
does nothing to improve the way the antenna looks to the transmission
line. The traps and tuning coil, on the otherhand, fix the ugly load
problem right at the antenna. They give your tuner and coax a break.

Coax, and connectors get really unhappy when you run high VSWR loads
at any kind of power. At the voltage peaks, the voltage can reach
thousands of volts in a bad mismatch condition.... BUZZZAP!...

Get yourself a copy of ARRL's Antenna book. It will better explain
what is going on with your vertical. Once you understand how the
antenna is supposed to work you can start to think about modifications.

-Chuck Harris

Bob wrote:
Thank you Chuck for your comments.

I will do exactly as you suggested and clean up the existing coil and re-use
it. I suspect that coil is there from the original engineering of the omni
that included those three traps.

What would you do about those three traps? I suspect should I put them in
the air, a good wind storm would blow them down as they are very heavy. The
previous owner had replaced those three traps with a straight whip and
suggested good results. I plan to use the same whip (no traps) and tune it.
Any pros or cons in this strategy? Is this the best I can do with what I
have? Preferably I would prefer to do this as I know it is windy where I am
and do not want to keep climbing but would also like to maximize my
transmission performance and receive performance.
Thanks again for any thoughts...








"Chuck Harris" wrote in message
...

Hi,

The purpose of the coil is the following:

1) to shunt electrostatic buildup to ground, thus protecting your
receiver.
2) to provide an impedance match from 50 ohms to the very high impedance
of an electrically short whip.
3) to make the whip appear to be electrically longer than it really is.

The coil you have is pretty robust, and looks pretty good to me. I
would clean out the cobwebs, and try it out.

Oh, receivers don't much care what you use for an antenna. A long wire
strung through the air works just fine. Directivity is useful in
extreme conditions.

-Chuck Harris

Bob wrote:

Hi,
Thanks for helping,

The coil I am concerned about is the coil that is in the attached photo.

It

is the coil that is at the very bottom of the 19ft aluminum whip

antenna. It

is a coil that shorts out the center to the ground right at the female
coaxial connection. (sorry, forget the part number of that). Please see
attached photo of the inner workings of the base of this antenna. My
question is do I need to rebuild this coil and what does the coil do and

is

it necessary. I want to use the antenna for an all band use and get up

as

high as possible as I have a good tuner.