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Coax type for mobile use


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#1 Fuggawi

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Posted 08 February 2020 - 01:59 PM

Looking for advise (and I may be over thinking it).

Searched here and online and couldn't really find info on a mobile application.

So here goes.

 

I will be installing 3 radios in utv's and basically wondering what would be a decent coax to go with.

Not sure if the 'bigger the better' theory is in play here or not.

Was thinking anywhere from RG-58/LMR-195, RG-8x/LMR-240, and RG8/LMR-400.

 

Specs we are using are: Radios are all Kenwood TK-880H (40w).

2 NMO antennas that are 1/2 wave NGP hooked on a roll bar. 1 NMO antenna 1/4 wave going in center of his roof.

Will be about a 15ft (+/-) run?

Pretty much using on simplex mode for the most part.

 

Thanks.

 

 



#2 WRAK968

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Posted 08 February 2020 - 02:20 PM

Your best bet is to use the coax that comes preinstalled on the NMO mount. This cuts out SWR issues caused by poor solder jobs and takes less time at that point. With such a short run you shouldn't have much loss. I can tell ya upfront installing anything the size of LMR400 in a vehicle, then attempting to attach it to an NMO connection and your just asking for a troublesome install. (LMR400 doesn't flex easily and is quite thick, about 1/2 inch.)


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#3 Gary - WRAF233

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Posted 08 February 2020 - 04:23 PM

Just finished installing TK-880 (25w) in my '19 Wolverine X4.  As WRAK968 said, I just used the cable that came with the NMO from the Antenna Farm.

 

Why 3 antennas?


Gary

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#4 Jones

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Posted 08 February 2020 - 05:24 PM

At less than 15 feet, the standard RG-58 type coax that comes on the NMO mount will be fine, unless you are getting those NMO mounts that have an N connector on the bottom, in which case go with LMR-240.  If you are using those NMO mounts with the SO-239 connector on the bottom, send them back and start over.

 

Why 3 antennas?

I read that as if he is installing 1 each on 3 different vehicles.



#5 Gary - WRAF233

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Posted 08 February 2020 - 11:53 PM

ah.. d'oh..  thanks


Gary

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#6 marcspaz

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Posted 09 February 2020 - 01:27 AM

... If you are using those NMO mounts with the SO-239 connector on the bottom, send them back and start over.  ...

 

I laughed so loud I woke my wife up.

 

A friend of mine was going to put one on his Range Rover.  I told him to just give me the $10 and sell his radio, because the end result would be the same, only I will at least be able to get a cheeseburger and a coke.  LOL


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#7 kb2ztx

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Posted 09 February 2020 - 07:25 AM

As others have said, just buy 3 NMO mounts with pre-attached cables. I like the larsen as it is crimped on vs soldered and a bit better for places that are out in the elements.



#8 Fuggawi

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Posted 09 February 2020 - 12:31 PM

Thanks all for the advise.

Sorry to have such a newb question but I guess I have to start somewhere.

Just wasn't sure if using smaller diameter cable would have an effect on the radio performance per some of the discussion I read about.

Yes there are three vehicles I will be installing on.

Thank you everyone for helping me out.

Now to read up on attaching the SL-259 connectors...



#9 Jones

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Posted 09 February 2020 - 12:53 PM

"...Just wasn't sure if using smaller diameter cable would have an effect on the radio performance per some of the discussion I read about."

 

The small cable to stay away from is RG-174u and its equivalents.  That is the small stuff you find as the stock cable on the Midland Micro-Mobile antennas.

Most NMO mounts come with preinstalled RG-58u, which is slightly smaller in diameter than a #2 pencil.  RG-174u is about the diameter of the ink tube inside of a Bic pen.


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#10 berkinet

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Posted 09 February 2020 - 01:05 PM

...Just wasn't sure if using smaller diameter cable would have an effect on the radio performance per some of the discussion I read about.

...

Now to read up on attaching the SL-259 connectors...

 

Cable thickness is not the issue as much as cable quality. In particular, the way the shield is constructed.  For example, at UHF frequencies, RG-174u has around 17dB loss per 100ft, while RG58u has around 11dB loss.  Take a look at this page and this page for more information.

 

Also, you mention an SL-259 connector. Did you mean PL-259, commonly called a UHF-Connector?


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#11 Fuggawi

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Posted 09 February 2020 - 01:24 PM

Thanks berkinet.

Yes I did mean PL-259 connector. Sorry, typing to fast for my brain.

So, looking at your table, at 15 ft of RG-58 my loss should be 1.68 db. Which sounds very acceptable.

I guess the key for this application is, keep line as short as possible and minimize/eliminate connectors.

Thanks again.


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#12 WRAK968

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Posted 09 February 2020 - 08:51 PM

Thanks berkinet.

Yes I did mean PL-259 connector. Sorry, typing to fast for my brain.

So, looking at your table, at 15 ft of RG-58 my loss should be 1.68 db. Which sounds very acceptable.

I guess the key for this application is, keep line as short as possible and minimize/eliminate connectors.

Thanks again.

 

Most common NMO mounts come with about 15 feet of coax. I've run mounts from the back of a ford explorer, down the rear piller, across the bottom of the SUV, up through the dashboard and to the back of the radio without needing any extensions, it was just long enough. With my new truck I didn't need as much cable, but rather than cutting the cable, I coiled it up under the dash. Again, 15' isnt going to affect much and as you said Application is key. For the antenna on the roof of my house, I used 40' of LMR400 which gave me much better signal quality over RG8x and even the meter showed this. I believe the meter showed 40W at the back of the radio, maybe 25W at the antenna for the 8x and about 36W with the 400. I also believe there may have been issues with the 8x but from what everyone has told me, 8x is meant more for VHF/Low band use.



#13 marcspaz

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Posted 09 February 2020 - 10:00 PM

Most coax doesn't have a minimum or minimum frequency cutoff.  Almost all commercially available cable is usable from 0.3MHz to 3GHz.  Some higher.  Coax cable attenuation ratings are tested at 750MHz, for instance.  The big things to be aware of is the conductor thickness for the power levels (not too thin), the impedance (which is not frequency specific), and the length of the cable.

 

Most people have no idea how much matching the coax length to the wavelength (or half-wave length) impacts performance.  However, most of the stuff we do in VHF and UHF, unless you are doing really high power (1,000-1,500 watts), the performance gain is negligible.  It's most noticeable at the bottom end of VHF and lower.

 

With GMRS, as long as the impedance is correct and you don't have some crazy types or numbers of adapters, you should be okay.



#14 quarterwave

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Posted 10 February 2020 - 12:28 PM

Motorola shops still carry what I called a bare mount. It's RG58 and an NMO, with the ring, seal and either a PL259 or Mini UHF you can install after mounted. We used the same one for 30-470Mhz. They did at one time have a low loss mount which was a white coax with teflon in it's jacket, made it a little more stiff to install, but more resistant to cuts. I think it was primarily for 800Mhz but I used them at 450 before. 



#15 Gary - WRAF233

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Posted 12 February 2020 - 03:07 PM

Installing 880 or 880H in my '18 F350.  Had thought I'd run the antenna cable through the rear of the cab (antenna on the headache rack) using a 3/16 x 5/16" rubber grommet to avoid additional connections, but, in case the cab ever has to be removed this might be a better option: 

 

UHF Connector Female Nut Bulkhead Panel Mount to SO239 Jack - RF Coaxial Coax Cable Adapter Plug FOR PL-259. 

No big deal regarding loss, correct?  Other thoughts?

 

I guess if the cab has to come off I'll have bigger issues than re-routing a cable.


Gary

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#16 Jones

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Posted 13 February 2020 - 10:20 AM

Installing 880 or 880H in my '18 F350.  Had thought I'd run the antenna cable through the rear of the cab (antenna on the headache rack) using a 3/16 x 5/16" rubber grommet to avoid additional connections, but, in case the cab ever has to be removed this might be a better option: 

 

UHF Connector Female Nut Bulkhead Panel Mount to SO239 Jack - RF Coaxial Coax Cable Adapter Plug FOR PL-259. 

No big deal regarding loss, correct?  Other thoughts?

 

I guess if the cab has to come off I'll have bigger issues than re-routing a cable.

Forget all of that bulkhead connector stuff.  That is a problem waiting to happen.  If the cab ever has to come off, just replace the whole mount if needed. That would be cheaper than all of the added connectors for that bulkhead setup, and those connectors ARE lossy.

 

Here's another better idea... just drill a hole in the top center of the cab roof, and mount the antenna there.  If the cab ever needs to come off, the antenna comes with it.  You will also get better results with the antenna on the roof than you would with it on the rack due to a more evenly distributed ground plane around the base of the antenna.


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#17 Gary - WRAF233

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Posted 13 February 2020 - 10:37 AM

Forget all of that bulkhead connector stuff.  That is a problem waiting to happen.  If the cab ever has to come off, just replace the whole mount if needed. That would be cheaper than all of the added connectors for that bulkhead setup, and those connectors ARE lossy.

 

Here's another better idea... just drill a hole in the top center of the cab roof, and mount the antenna there.  If the cab ever needs to come off, the antenna comes with it.  You will also get better results with the antenna on the roof than you would with it on the rack due to a more evenly distributed ground plane around the base of the antenna.

 

Except when hauling the kayak on the rack it would cover the antenna.  Those travels are probably when I would most use the radio.  

When not carrying the kayak I can easily set it up to slide the mount on the rack (8 x 8 x 1/4" aluminum) to the center,extended over the back portion of the CC roof, but doubt the roof would contribute much at 3 - 4 inches below the antenna. 

I will be grounding the headache rack to the truck frame/body. 


Gary

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#18 berkinet

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Posted 13 February 2020 - 11:17 AM

Except when hauling the kayak on the rack it would cover the antenna. ...

 

What material is the kayak made out of, fiberglass or plastic? If so, think of it as a radome and don't worry.  In any case, you can always run a test by supporting the kayak on two sawhorses, have someone get under it with an HT and see how far away you can work them. Then, have them try the same test standing outside the kayak (with the HT at the same height).


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#19 Gary - WRAF233

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Posted 13 February 2020 - 11:40 AM

What material is the kayak made out of, fiberglass or plastic? If so, think of it as a radome and don't worry.  In any case, you can always run a test by supporting the kayak on two sawhorses, have someone get under it with an HT and see how far away you can work them. Then, have them try the same test standing outside the kayak (with the HT at the same height).

 

Hmm... I was going to ask about that but thought it would be a silly question.  It's plastic.  I will definitely give it a try.  I have no real issue drilling into the roof (it's my truck, right -  and probably my last).  Maybe move the 8 x 8 plate over to the UTV rack/antenna.

 

As always, thanks!


Gary

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#20 Fuggawi

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Posted 13 February 2020 - 04:38 PM

I want to thank all you guys with great information and patience for us new guys.

I wouldn't have thought twice about using some of these adapters and connectors.

I'm all about the gidgits/gadgets, erector set type of building stuff.

One wouldn't think that they have that much loss by looking at them.

It makes me feel a lot better that this project will have a better chance of working.

Thanks again.


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