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Kevin Debbie

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Since: Sep 04, 2003
Posts: 45



(Msg. 1) Posted: Mon Sep 13, 2004 10:22 pm
Post subject: VHF antenna wiring question
Archived from groups: can>rec>boating (more info?)
Hi Group
Simple question. I replaced my VHF antenna and I would like to know if I should cut the lead in cable shorter prior to
soldering the connector on or should I leave it the factory supplied length as that is included in the tuning of the
antenna.
TIA.
Kevin

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Greg Moore3

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Since: May 21, 2004
Posts: 22



(Msg. 2) Posted: Tue Sep 14, 2004 8:22 am
Post subject: Re: VHF antenna wiring question [Login to view extended thread Info.]
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In almost any RF, antenna tuning is done in the radiating portion, coax is
made to not radiate, therefore you can shorten it. Depending on how much
you take off, you may even gain a 1/2 or 1 db of output to boot!

Do make certain you do a perfect job of the new connector though, even a
slightly sloppy job there can cause the loss of a few db of gain. We just
completed a large cellular project and while it operates at 1.9 gig, you
would be amazed at what little it takes to cause a measurable loss in tx or
rx values. It is critical since every gain of 3db is equal to doubling the
effective wattage, of course ever loss of 3db is equal to halving the
wattage too..


Greg


"Kevin & Debbie" <kevdeb.DeleteThis@golden.net> wrote in message
news:41464884.6050602@golden.net...
 > Hi Group
 > Simple question. I replaced my VHF antenna and I would like to know if I
should cut the lead in cable shorter prior to
 > soldering the connector on or should I leave it the factory supplied
length as that is included in the tuning of the
 > antenna.
 > TIA.
 > Kevin
 ><!-- ~MESSAGE_AFTER~ -->

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Tim Mackinlay

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Since: Aug 24, 2004
Posts: 2



(Msg. 3) Posted: Tue Sep 14, 2004 9:21 am
Post subject: Re: VHF antenna wiring question [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
On Mon, 13 Sep 2004 21:25:24 -0400, Kevin & Debbie <kevdeb.DeleteThis@golden.net>
wrote:

 >Hi Group
 >Simple question. I replaced my VHF antenna and I would like to know if I should cut the lead in cable shorter prior to
 >soldering the connector on or should I leave it the factory supplied length as that is included in the tuning of the
 >antenna.
 >TIA.
 >Kevin
 >


You can trim the coax cable to the length you need. Actually, by using
the shorter run of cable, there will be less transmit/recieve losses.
(a small amount) I assume this is one antenna and not some fancy
phased array or something like that!!

Tim<!-- ~MESSAGE_AFTER~ -->
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Terry Spragg4

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Since: Mar 05, 2004
Posts: 157



(Msg. 4) Posted: Tue Sep 14, 2004 4:22 pm
Post subject: Re: VHF antenna wiring question [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
Kevin & Debbie wrote:
 > Hi Group
 > Simple question. I replaced my VHF antenna and I would like to know if I
 > should cut the lead in cable shorter prior to soldering the connector on
 > or should I leave it the factory supplied length as that is included in
 > the tuning of the antenna.
 > TIA.
 > Kevin
 >

As others have said, you might gain a db or 2 by shortening it as
much as 10 feet or more, not much to worry about, really.

Leave a little extra at the ends for replacement connectors, etc.
Leave a good rain loop at the top, and a foot extra or two for
future repairs or a move, below. If you don't get it right the
first time, you won't want to run a new cable to avoid a splice.

An error techs hate is to require a head behind the dashboard to
pull the chassis. Leave enough extra power, AE leads, etc. for an
on the bench internal fuse / voltage check without disconnecting
everything and making up test jumpers.

Terry K<!-- ~MESSAGE_AFTER~ -->
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Kevin Debbie

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Since: Sep 04, 2003
Posts: 45



(Msg. 5) Posted: Tue Sep 14, 2004 6:22 pm
Post subject: Re: VHF antenna wiring question [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
Thanks to all for the responses. The base of the antenna is about 1 foot away from the radio and it came with about 15
feet of cable. I'll shorten it down to about 5 and this will allow me to set the radio on the dash while it is still
connected to power and the antenna.
Thanks again
Kevin

Kevin & Debbie wrote:
 > Hi Group
 > Simple question. I replaced my VHF antenna and I would like to know if I
 > should cut the lead in cable shorter prior to soldering the connector on
 > or should I leave it the factory supplied length as that is included in
 > the tuning of the antenna.
 > TIA.
 > Kevin
 ><!-- ~MESSAGE_AFTER~ -->
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guser

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Since: Jan 29, 2005
Posts: 67



(Msg. 6) Posted: Wed Sep 15, 2004 1:37 am
Post subject: Re: VHF antenna wiring question [Login to view extended thread Info.]
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Michael Wright

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Since: Nov 03, 2003
Posts: 10



(Msg. 7) Posted: Wed Sep 15, 2004 11:10 am
Post subject: Re: VHF antenna wiring question [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
I just recommend using a solder on jack rather that the crimp or solderless
ones. And of course making sure you get a good connection. Cheers Micheal
"Karl Pollak" <guser RemoveThis @nospam.org> wrote in message
news:4147821f.7667043@news.pacificcoast.net...
> x-no-archive: yes
> Kevin & Debbie <kevdeb RemoveThis @golden.net> wrote:
>
>>Hi Group
>>Simple question. I replaced my VHF antenna and I would like to know if I
>>should cut the lead in cable shorter prior to
>>soldering the connector on or should I leave it the factory supplied
>>length as that is included in the tuning of the
>>antenna.
>
> The antenna lead is shielded specifically not to be part of the antenna.
> However, once you have installed the radio the way you want it, you should
> have somebody with a SWR meter come and tune up your antenna to make sure
> you are getting your signal out as much as you are supposed to.
>
> One day, your life could depend on it.
>
> --
> Greetings from Lotusland
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Kevin Debbie

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Since: Sep 04, 2003
Posts: 45



(Msg. 8) Posted: Wed Sep 15, 2004 4:49 pm
Post subject: Re: VHF antenna wiring question [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
Hi Karl,
How do you tune a fibreglass whip?

Karl Pollak wrote:
> x-no-archive: yes
> Kevin & Debbie <kevdeb DeleteThis @golden.net> wrote:
>
>
>>Hi Group
>>Simple question. I replaced my VHF antenna and I would like to know if I should cut the lead in cable shorter prior to
>>soldering the connector on or should I leave it the factory supplied length as that is included in the tuning of the
>>antenna.
>
>
> The antenna lead is shielded specifically not to be part of the antenna.
> However, once you have installed the radio the way you want it, you should
> have somebody with a SWR meter come and tune up your antenna to make sure
> you are getting your signal out as much as you are supposed to.
>
> One day, your life could depend on it.
>
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guser

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Since: Jan 29, 2005
Posts: 67



(Msg. 9) Posted: Thu Sep 16, 2004 6:02 am
Post subject: Re: VHF antenna wiring question [Login to view extended thread Info.]
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Greg Moore3

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Since: May 21, 2004
Posts: 22



(Msg. 10) Posted: Thu Sep 16, 2004 7:23 pm
Post subject: Re: VHF antenna wiring question [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
If it is an 8' whip it probably has its base load built internally in the
mast unlike smaller stainless style whips (it more likely has no load and is
spiral wound). It is probably tuned at the factory as close as it gets, the
higher frequency and use of FM over AM like a CB allows that. The frequency
spread used in a VHF radio is very tight compared to old AM CB radio's..
The tuning was also more critical as the length of the antenna was less then
a full wave as apposed to more then. In CB's, the wave length is 10 meters,
unless the antenna element was 10 meters long, it was a fractional antenna
(ie 1/4 wave etc). The VHF band used for marine is a much much shorter wave
length and the 8' whip allows for gain. As in the wattage, the antenna gain
is in direct proportion to its length vs the wave length. If the antenna is
listed as a 6db gain then it is 4 times the wave length in physical length.
Also, if 6db gain, then at 25 watts output, it will effectively radiate 100
watts of transmitter power.. Go to a 9db 16' whip and you get an effective
200 watts output power, and so on.. Of course at about 50 watts, gain
becomes useless since VHF is line of site and 50 watts is more then enough
to go as far as the curvature of the earth permits assuming a base within
4-5ft of water.. Put her up on a 50' sail boat mast with a 9db ant, ship to
shore (assuming 150' tower at shore), huge distances!

(I know, rambling Smile

Greg


"Karl Pollak" <guser.DeleteThis@nospam.org> wrote in message
news:41491d91.49422096@news.pacificcoast.net...
> x-no-archive: yes
> Kevin & Debbie <kevdeb.DeleteThis@golden.net> wrote:
>
> >Hi Karl,
> >How do you tune a fibreglass whip?
>
> You don't tune the fiberglass, obviously.
> It should have a coil in the base, no?
>
>
> --
> Greetings from Lotusland
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guser

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Since: Jan 29, 2005
Posts: 67



(Msg. 11) Posted: Fri Sep 17, 2004 11:48 pm
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