9' of coax in mobile install to lower SWR?

[CB590]

So I bought a used Ford Escape as my old truck is deemed caput.

Going to mount my Uniden 78 in center console as it's very deep.

Antenna is a 5' FS 2. Worked well on prior pickup but had 18' of coax that came with it as a kit.

Only need about 7' run to get to console. Anyone see any issues as to running just say 9' of coax?? I don't want to run 18' in a coil. Lol.

Also keep in mind the radio has RFX95 so I'm trying to keep SWR low and was thinking that whole increment of 9' thing with coax.

I may swap in a 102" whip for less wind resistance than the FS 5'.

 

[2NC995]

The 9' increment makes little sense, if you think about it. Every coax would have to have the same velocity factor to equal the same proportions of a wavelength....and they don't.

You can run shorter coax. You can run 7' if that's what you want.

The only time length comes into play is hiding another problem, IMO.

EDIT: and with phasing arrangements.

 

[secret squirrel]

Like 2NC995 said the amount you need for the run from antenna feed point to radio is all you need. It is easier for shops to sell 1/4 wave increments. The 1/4 wave increments may assist common install issues as an ideal ground plane in a vehicle is not an everyday finding. That all being said try the 18 foot piece you have already see if you are happy with results. Spool the extra up like an extension cord and place under a rear floor mat or under passenger seat Try out how you like you new install. I have a similar install on my Nissan Rouge but the antenna is on drivers side and the radio is up front at the console I ended up with extra from the 18 foot piece. The coax runs under the back deck the under the door jam trim. Then across under the dash to the radio.

 

[TheRealPorkchop]

Get a 500ft spool. Drag it out to the Ford. Start running the coax like you need it, through all the little nooks and crannies. When you make the run, chop it off and install your connectors, I suggest crimps, if my opinion counts.

That’s it! If it’s 4ft 4in or 9ft 2in, that’s all you need. So many of these “myths” that I too wish we could eliminate from this hobby. But sadly the koolaid brigade has spread this misinformation and false propaganda over the years.

 

[midnight special]

my ranger uses 9 feet of rg213 from the antenna to the amp and 6 feet of rg8x from amp to radio,,,, i didnt do no formalas or figureing,, just what i needed from point a to b,,,,i have a good match and it gets out very good,,

 

[Captain Kilowatt]

....... I'm trying to keep SWR low and was thinking that whole increment of 9' thing with coax.

Tell me......what is it with the 9 foot increments that you are trying to stick with? It means NOTHING. It is NOT a quarter wavelength since velocity factor has to be taken into account. Throw out the idea that length matters. If changing length changes SWR you have other issues at play that need to be corrected. How do ham operators run multiband antennas mobile without having "special" lengths of coax for each band? Also NOTHING wrong with rolling up a few feet of cable and tucking it under the seat or wherever. The cable is shielded and will NOT form an inductor like a regular coil of wire will.

 

[2NC995]

Throw out the idea that length matters.

hang on now.....

 

[Slowmover]

(Yawn). So with the pencils.
Shorter club. Rules.


The idea about bulk coax is VERY good. These discussions focus on theoretical (proven) which is only right.

Mobile means noise.

If, as me, you wish to treat for such at both ends . . . don’t cut until ferrite toroids are wound-in-place.

Your choice may be different (something else or nothing), but . . .

. . a seven-foot run may need another thirteen-feet of windings for two FT-240-31 toroids (one each end) thus totaling a little over twenty-feet of coax to match that initial seven.

The total amount of coax needed isn’t obvious until the physical layout is done.

You might also want other devices in line. If not today then where would you mount them?

As length doesn’t matter, (just girth; for, as some may be RG59, others are 1-5/8” Heliax), tickling her signals comes down to enough.

For some reason I was looking at the WILSON 18’ Mini-8 Coax here at the North Forty truck stop three hours ago. Guess I was receiving the signal. Has an FME-end for easier threading INTO vehicle from outside. Performance is good enough that I can say it’s an easy, expensive ($32) AVAILABLE choice nationwide.

I’ve been thinking about a BALUN DESIGN 1:1 cube at the feedpoint. (Already have a bandpass from ARRAY DESIGN. Battle of the MetroPlex Baluns & Bandpass from a few miles apart). Beat me to it, wilya? Ha!

.

 

[CB590]

Thank you for the responses.

After considering the options for radio placement. I will once I get the radio in and route wire around abit. Probably end up at like 12' or so.


Thank you.

 

[ForestRunner98]

I thought the same. Adding coax length would lower SWR or raise wattage. I was wrong. I added 6’ then another 6’ from amp to LP filter for a total of 12’. So that’s 30’ of coax. WRONG... removed the 12’ and added the 3’ jumper and it was the same.

Isn’t mobile radio fun?? LOL

 

[Highway Man]

I'd use the same 18' Firestik coax. It makes the swr meter happy
http://www.firestik.com/Tech_Docs/63Things.htm

 

[Shadetree Mechanic]

I know people who tune their coax with the MFJ antennalyzer. Does this really do anything? I gather not, judging by the previous responses.

 

[Highway Man]

It hides the coax as in no reactance.
I believe this is in the MFJ 259 book

 

[Highway Man]

If you tune at feed point then it doesn't matter about length however if you tune from radio or a SWR meter with jumper and with amplifiers the meter looks at everything as a whole.

 

[TheRealPorkchop]