Mobile installation question: SO-239, N, TNC - what should I use?

[smokeyjones666]

I'm planning on installing two NMO mounts in the trunk lid of my '96 Accord. One is for a scanner antenna, and one will be for a possible future 2m/70cm transceiver (providing I can't talk myself out of it.)

So while my kid was napping today, I pulled out the back seat and ran two lengths of RG-8U from the trunk, under the carpet and up under the driver's seat. (Perhaps a little premature, considering I don't even have the NMO mounts or antennas, but with a feisty 18-month old you have to take your opportunities when you can. )

To the point, I'm struggling with a final decision on what connectors to solder on to the cables where they come up under the driver's seat. SO-239? All of the mobile transceivers seem to have it, but every article I read says the performance above 30MHz makes this a bad choice. N? Seems like a solid choice, RF-wise, but I'll certainly need adapters to get to BNC for my scanner and SO-239 for the mobile transceiver I don't own. TNC? I don't even know why I suggested this.

Anyway, I'm just trying to make a solid choice so if I change my mind in the future and try something weird I won't be limited by my choice of connector. N sounds good, but I don't know where to find one locally. SO-239 can be had at (almost) any local RS, where I only have to stiff-arm the sharks trying to sign me up for a family plan while I fight my way to the parts drawers in the back. (Free phone! Free phone!)

Am I thinking too much about this? Is the SO-239 fine, since I've already limited myself by using my (free) RG-8U? Is the N a good choice, since adapters can be readily had and my scanner goes up to 1.3GHz? What are your thoughts, people?

 

[fineshot1]

I think you wasted that time. NMO mounts come with a cable attached(machine soldered) already and they are usually an RG-58 type of cable that is approx 15 or 17 feet in length.
There may be a connector on them already(i prefer to crimp on my own) or depending on how you buy them there may not. Usually connectors are of the crimp type these days but that is not to say you can not solder if you prefer to. If I were you I would use a BNC male connector due to most scanners having a BNC female connector built into them. That way there are no adapters in the mix.

EDIT: Forgot to mention that if the second one was for ham(thats what it seems to be) then you will probably need a PL259 connector due to most dual band mobiles having an SO239 connector.

 

[smokeyjones666]

I think I needed to add a little bit more detail. My plan is to terminate the RG-8U underneath the seat, and then run a foot or two of RG-58 with a BNC adapter to the scanner since the RG-8 is quite thick and unforgiving. Now that I think about it, any future mobile tranceiver installation would probably have a detachable front panel and go under the driver's seat, so I think I may have answered my own question! I'll probably just solder on a couple of PL-259s, and get an adapter to BNC for the scanner cable.

 

[af5rn]

RG-8U? That's going to be a challenge to attach to most NMO mounts. RG-8X would have been a lot easier.

It is a common mistake to get too carried away with coax concerns on mobile installations. You simply aren't going to make one bit of difference in a fifteen foot run. In fact, by trying to use the bigger, better coax, you are raising your risk of getting a faulty centre conductor as you manipulate the stiff coax. I agree with fineshot1 that you're probably wasted your time, except for the "dry run" value of it all.

Just get a pre-cabled NMO with whatever coax is on it, and run it all anew. Just like the coax, the connectors don't make any noticeable difference in a mobile installation. The best connector you can get is which ever connector matches your radio, period. Your ham radio is going to need a PL-259. You don't tell us what kind of scanner you are using, but again, choose which ever connector that will fit it directly. If you use some other connector in an attempt to lessen loss, then have to use an adaptor to plug it into your radio, you have done worse than to defeat your purpose.

 

[smokeyjones666]

You know, as I was working the cable through the nooks and crannies in my automobile, I was thinking to myself "How interesting is this going to get when I have to solder these puppies on." I guess the whole reason for the RG-8U was that it was free, I just happened to have a roll of it in my basement. The 'dry run' statement most certainly applies, if I decide to run a different cable I can probably do it in 1/5th the time now.

I suppose the most important thing is the solid mount to the trunk lid, drilling a hole for an NMO mount has so far been the only consistent thing in my plan.

Oh yeah, and the scanner is a PSR-500.

 

[af5rn]

I suppose the most important thing is the solid mount to the trunk lid, drilling a hole for an NMO mount has so far been the only consistent thing in my plan.

Hey, that's a better start than most people! Most people come here wanting to know what the best antenna they can get is, but only if it doesn't require a hole, glue, tape, a mag mount, more than twenty dollars, and isn't longer than 6 inches. :lol:

If you're drilling a roof or deck hole and actually giving serious thought to lessening your loss, you're headed for greatness. Have you got antennae picked out yet?

 

[smokeyjones666]

For the scanner, I was planning on a Larsen NMO150/450/800. I understand the performance on 2m leaves something to be desired, but I'm mostly listening to ARMER and I want at least a little reception on other bands. I haven't decided on anything regarding a transceiver yet, since I just got my license and have only recently started to listening to traffic on the local repeaters. (Gotta figure out the radio etiquette before I start spewing RF everywhere, right?)

Now that I think about it, my plan is to place the NMO mounts on opposite sides of the trunk lid, about 4-6 inches from the edge, a couple of feet apart perhaps. If I place my antennas too close together, am I going to burn out the receiver in my scanner when I key the mic on a 50w tranceiver?

You know, when I was dreaming this whole thing up, I was envisioning a metal box with two RF jacks of some sort bolted to the floor under the seat. God that seems so silly to me now.