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#4585487 - 11/26/17 11:51 AM CB Antenna Cable Question
IndyFan Offline


Registered: 06/16/05
Posts: 542
Loc: Danville, Indiana
Is there any advantage to a shorter or longer antenna cable, or is it a wash, given a correct tune for each?

I'm deciding which side of my Jeep to run the antenna cable to my new hood antenna mount. I'd like to go 9' and run it through the driver side firewall, but I've already got cables crammed in there from auxillary lights and I'm not sure I can squeeze even the low profile connector through it. The passenger side would require an 18' cable, but that firewall opening has space, so I know I could easily run it through there.

I want to know if there is an advantage to either before I make the final decision as to which to order.

Thanks!
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#4585511 - 11/26/17 12:07 PM Re: CB Antenna Cable Question [Re: IndyFan]
beanoil Online   content


Registered: 10/17/04
Posts: 2951
Loc: Midwest, Illinois
18' is OK. You'll see no performance difference between 9 and 18 feet in your case.
Over 25', I would go to an RG-8. Same if you are using a linear, although I know everyone here is a law abidin' citizen, and such things are only talked about, never implemented.
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#4585527 - 11/26/17 12:12 PM Re: CB Antenna Cable Question [Re: IndyFan]
Linctex Offline


Registered: 12/31/16
Posts: 6148
Loc: Waco, TX
My 2 meter antenna is up a 50' tower with about 60-70 feet of coax cable. I never once thought about it as long as the SWR is good.
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#4585560 - 11/26/17 12:41 PM Re: CB Antenna Cable Question [Re: IndyFan]
IndyFan Offline


Registered: 06/16/05
Posts: 542
Loc: Danville, Indiana
Thanks! It will be much easier to run it through the firewall on the passenger side, for sure. Appreciate the help!
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#4585568 - 11/26/17 12:46 PM Re: CB Antenna Cable Question [Re: IndyFan]
Papa Bear Offline


Registered: 08/11/05
Posts: 7046
Loc: Leamington, ON, Canada ..... r...
Coax has an inherent loss the longer the run and the loss is frequency dependant.
http://www.timesmicrowave.com/calculator/
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#4585628 - 11/26/17 01:40 PM Re: CB Antenna Cable Question [Re: IndyFan]
JHZR2 Offline



Registered: 12/14/02
Posts: 41767
Loc: New Jersey
Isn't the key to match swr for the combo of antenna and cable?

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#4585638 - 11/26/17 01:50 PM Re: CB Antenna Cable Question [Re: IndyFan]
RF Overlord Offline


Registered: 11/08/03
Posts: 3755
Loc: Cape Cod, MA
what they all said^^^

As long as the transmitter output, the cable, and the antenna are all impedance-matched, you should have an acceptably low SWR and maximum power transfer. The actual length of the cable is not relevant except for calculating power loss.
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#4585652 - 11/26/17 02:01 PM Re: CB Antenna Cable Question [Re: IndyFan]
i_hate_autofraud Offline


Registered: 05/19/16
Posts: 705
Loc: Canada


To get most transmit power out, long or short coax will require an antenna matcher box
at the CB coax output (a PL259 connector) AND an SWR meter. I don't rely on the radio's SWR meter.

The idea is to tune all the coax with the antenna.

For example we tuned an antenna and coax to channel 20, when you go up or down 2
channels SWR starts to climb a lot!

Car /truck mount antennas are 1/8 wave antennas and are very peaky and don't
resonate equally across the band, so you need an external SWR and antenna tuner.
That means you'll need 2 18" lengths of coax with connectors then the long coax.
Some SWR meter can have a tuner built in, then you only need 1 short coax.

The loss factor of 20' of coax is nothing compared to hi SWR due to a bad tune!

The benefit is you'll have nearly twice the range, since untuned antenna and coax
can go to 3:1 SWR in the blind of an eye!

The CB band only is only 190 Khz wide! From CH 1 at 27.215 MHz to CH 40 at 27.405 MHz

If the CB antenna was a full-wave 11M antenna, it would be 34 feet long! but will be less sensitive
then a car mounted 1/8 wave antenna!

I tacked mine together with vintage Radio shack SWR and separate tuner second hand! For fun
a few years back range tested it to see the difference with hi and lo SWR!

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#4585859 - 11/26/17 04:42 PM Re: CB Antenna Cable Question [Re: IndyFan]
i_hate_autofraud Offline


Registered: 05/19/16
Posts: 705
Loc: Canada

TYPO: missed text:

If the CB antenna was a full-wave 11M antenna, it would be 34 feet long! and will be less sensitive to tuning
on any specific CB channel
then a car mounted 1/8 wave antenna!

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#4586495 - 11/27/17 11:18 AM Re: CB Antenna Cable Question [Re: IndyFan]
supton Online   content


Registered: 11/09/08
Posts: 11923
Loc: NH
Once matched, the coax length isn't that important--at 27MHz any decent coax won't be that lossy. Most likely the antenna mounting method will cause more loss than the coax.

A quarterwave antenna is what, 9' long? bit too much for most people. Many of those shortened whips use mumbo-jumbo to make them sound better--if it's less than 8' long, it's not going to be as good, but it can be good enough, down to 3 or 4 feet or so. Don't pay extra because it says it has "5/8's wave performance" yet is only 3' long. That's bunk.
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