GMRS antenna recomendations

[Hillbilly Heaven]

Bill excellent antenna. Can take some serious tree limb banging Having no open coil in the whip, no worries about catching a limb and pulling the whip out or worse do body damage.

Excellent point about the RG8X. Never tried to solder 8X to an NM0 mount, but I guess it just takes patience. If you are going to go to the trouble of making your own cable I would suggest LMR240UF. It is the same diameter as 8X, just as flexible with stranded center conductor, and has 3db less loss. Davis RF or RF Parts both carry it.

 

[DaveInDenver]

Here is a good 5/8 wave antenna, 5.15 dbi gain. Pulse-Larson makes some really good quality stuff.
https://www.hamradio.com/detail.cfm?pid=H0-009385
Spec Sheet: https://pulselarsenantennas.com/product/nmo4503cs-2/

Compare like to like. A 5/8λ gives 3 dB of real gain. Larsen in this case is specifying against dBi but a 1/4λ gives you a gain of 2.15 dBi so that's the baseline. It's really 3 dBd of gain you're getting.

They make magnetic mounts out there with NMO connectors, but most of them have RG-58 cable. I highly recommend a traditional "through the roof" NMO with RG-8X cable or at least try to find a mag mount with RG-8X cable. GMRS is UHF and it will lose a lot more signal with RG-58 than with RG-8X. It is almost criminal that they include RG-174 with that 1/4 wave antenna with the kit. If you calculate the loss from the cable and the gain from the antenna, the 15 watts end up with 9.9 watts of Effective Radiated Power (ERP).

You make a good point, but bear in mind we're talking short runs. At 400 MHz RG-174 attenuates at 0.173 dB/foot, RG-58 at 0.112 dB/ft and RG-8X at 0.079 dB/ft. So if you have a typical run of 10 feet the difference is about 1 dB between the worst and best. Your example 15 watts is 11.76 dBw, so a 1.73 dB loss with RG-174 leaves an ERP delivered to the antenna of your ~10 watts but even RG-8X at 0.79 dB is going to be effectively 12.5 watts. And remember RF range follows the inverse square law. Going from 12.5 down to 10 watts is only an 11% change in expected signal strength. But for this you may gain much easier routing, so it may be a worthwhile trade-off.

FWIW, though, I run RG-8X whenever I can. But my point is in a vehicle it's not quite the impact as you'd have running a feed line on a 100 foot tower. Also, don't neglect that SO-239/PL-259 is terrible at UHF, so you're really losing more with the discontinuity of those connectors than the coax you select. SMA and N-type are much better choices but for some reason (ease of construction I assume) ham radios stick with the UHF (poorly named) connectors. In a real situation I'd bet RG-174 with an SMA is going to perform better than a SO-239 with RG-8X, anyway.

 

[Billoftt]

Why don't modern radios, cables and antennas just come with N connectors? Seriously? Less loss, waterproof connection. Construction can't be that bad.

 

[DaveInDenver]

The radio I'm using in the truck right now has an N, a Connect Systems CS800D. Making up an N isn't difficult, although you really kind of need to invest in a stripper and crimper to make them up cleanly. I dunno why we/they hang onto the UHF connectors. From what I gather it's really only U.S. hams that do.

 

[Hillbilly Heaven]

We are on the bottom of the food chain when it comes to cable connectors. Commercial users gave up on UHF and N connectors years ago and have since then have gone away from even 7/16 DIN connectors. While N connectors are more waterproof than UHF most of them suffer from a problem of center pin migration in long cable runs in extreme temperature swings. As the center conductor heats and cools the length changes, with a non captured center pin this can cause connection issues. Sorry for drifting off topic just wanted to add the point that while N connectors are good they are no great if used wrong.

 

[Billoftt]

Also, don't neglect that SO-239/PL-259 is terrible at UHF, so you're really losing more with the discontinuity of those connectors than the coax you select. SMA and N-type are much better choices but for some reason (ease of construction I assume) ham radios stick with the UHF (poorly named) connectors. In a real situation I'd bet RG-174 with an SMA is going to perform better than a SO-239 with RG-8X, anyway.

Agreed. I found a very thorough and interesting analysis of this very subject.
https://www.hamradio.me/connectors/uhf-connector-test-results.html

Now all we need to do is have that guy perform the same test, only with RG-174, RG-58 and RG-8X.

This kinda makes me want to replace the SO-239 on my Kenwood with an SMA connector.

 

[DaveInDenver]

Indeed @Billoftt, this chart tells even the casual ham what he needs to understand. Using PL259 for UHF (real UHF, not the pre-WWII definition of >30MHz) isn't doing you any favors. That antenna you linked earlier, almost all of it's gain is consumed by the connectors.

And you know what I think is really overlooked is there are a lot of antennas that use a SO239 base. Compared to a person using an NMO and N you're giving up several dB between attenuation and reflection on 70 cm by using an antenna with a SO239 base and a UHF connector.

 

[Hillbilly Heaven]

That Larsen antenna has NMO mount not an SO239.

 

[DaveInDenver]

That Larsen antenna has NMO mount not an SO239.

That was just a general statement since Comet and Diamond antennas often do and they were mentioned earlier in the thread. Larsen doesn't make anything with SO239 as far as I'm aware, but this is consistent with their intended market of commercial and public service land mobile. And to their credit I think the Midland accessories are also NMO bases.

 

[Billoftt]

I have literally been thinking about this all last night. I even found a very thorough video on YouTube of the Midland MXT275 and at 6:27 it actually shows the RG-174 terminated with a PL-259. This is actually bothering me now, probably more so than what any normal sane person should. What purpose does that even serve? Ditch the PL-259/SO-239 setup, use an SMA on the unit and you will have better performance AND a much smaller connector to deal with when routing the cable around in your vehicle.

 

[DaveInDenver]

I don't know if an SMA is the answer. Of course the performance is superior however mechanically they aren't well suited. Perhaps a BNC if the size an N doesn't work. That's kind of the problem, the UHF connector for it's electrical faults is robust mechanically. I wonder if anyone's tested the mini-UHF that Motorola uses. Or even the TNC like on routers would be excellent on 70cm.