Looking for potential gotchas using a mobile antenna with a HT

[WRTQ298]

Hey folks, this is my first post in this wonderful community! 

I want to be able to use my HT (a Radioddity GM-30) from my vehicle. I know, I know, the car acts as a faraday cage or whatever. Duh, it's made of metal!

I'm not quite at the point where I'm ready to invest in a mobile radio (okay, okay, my wife isn't ready to invest in a mobile radio), but I do still want to be able to check in with home while in the car.

For the curious, the main use case I have right now is to communicate with home (to another GM-30) from around our little town. The range we're talking about here is literally less than four miles in most cases. The furthest I'll actually need to be able to reach is only 6 miles, and even then I have more or less perfect line of site to home. We tested! But, unsurprisingly, I get zero signal from inside my vehicle when more than about a mile away from the house.

To resolve this problem, I plan on grabbing a mobile GMRS antenna, plopping it on the trunk, and running coax up to my console, where I'll be able to screw it directly to my HT and talk! Right? I don't actually know!

On to the actual question:

Are there any gotchas I should be aware of when plugging a mobile antenna into my HT radio?

I know it won't transmit as far, given it only has 5 watts, I know it's not the ideal setup for an HT, but I'm also reasonably sure it should work for my use-case. Are there any problems that I may need to solve, or that make this solution completely untenable?

 

Thanks in advance!

[KAF6045]

Most mobile antennas have a PL259 plug. That's a bit of a mass to connect to an SMA connector. If the radio and the coax are snugly held it may not be a problem, but you don't want to have motion of one of the set -- that could add a lot of torque to the SMA. Also, be advised that the specifications for SMA are just 500 connect/disconnect cycles.

Many of the smaller (10-20W) GMRS mobiles (Midland MXT115, though that is NFM-only and has no ability to add customized "channels" for repeaters; Radioddity DB20G, though mine is showing lower power on repeater channels than the lower-power MXT115) are equipped with a cigarette light plug for power. With a large enough "phone/tablet" clamping holder in a cup-hole and a mag-mount antenna would allow mobile use without making a permanent mount. Or something like

https://midlandusa.com/products/micromobile®-mxtarm1-tough-wedge-radio-mount-for-mxt115-and-mxt275 or https://midlandusa.com/products/micromobile®-mxtarm3-tough-claw-radio-mount-for-mxt115-and-mxt275 NOTE: I don't know if the mounting plate is compatible with slots in other radio brackets, could maybe track down the actual maker (RAM https://rammount.com/ ) though strangely their site doesn't show any radio mount models.

ADDENDUM: If you can get them to stick, 3M Command Strip Picture Hanger (the strips that have paired velcro for removal/adjustment of the bottom of the picture frame) might be an option (my rust bucket has an oily plastic and nothing sticks except dirt -- even after cleaning with alcohol swabs, Clorox wipes, Kleenex glass cleaner). You'd have to put the strips on the top of the mobile as most have bottom-firing speakers -- possible mount locations: driver side of central console, knee well of lower dash.

Edited September 16, 2022 by KAF6045
Added addendum

[Borage257]

For a magnetic mount antenna, you'll need an adapter cable/fitting if the antenna doesn't match the radio. You don't necessarily need a mag mount to transmit from a car or truck. You get calls and texts while driving right? While some signal may be blocked and reception may be reduced a tiny bit, a car has enough glass for you to talk on your radio. I transmit regularly to a repeater about 12 miles away from inside a metal building. Its not perfect, but I am perfectly readable.

You losing signal with your wife is likely not a function of being in the car. I cant talk to my wife when she is on her HT and I'm on mine 1.5 -2 miles apart. Terrain and location (rural, urban, suburban) have a lot to do with range too. 

Bottom line: Height is king, get that antenna up higher if you want "more Fars" (put the antenna on the roof of the car) and check for local repeaters.

Btech sells the Nagoya UT-72G for about $35, it comes with the adapter for the radio too. I've had good luck with mine so far.

[WRTQ298]

@KAF6045, Thanks for the reply!

Quote

If the radio and the coax are snugly held it may not be a problem, but you don't want to have motion of one of the set -- that could add a lot of torque to the SMA. Also, be advised that the specifications for SMA are just 500 connect/disconnect cycles.

I was actually planning on terminating the coax from the antenna in my dash and slapping an adapter on it (I have, er, a few, because I've been listening to ham with an SDR for a few years now), then using a shorter SMA cable from the adapter to the HT.

That said, if it really is only rated for so few cycles, that might be the best argument against this whole effort. I had no idea there were 12v plug mobile radios (really showing my lack of research there!), so that would make both my wife and me happy about not having to potentially tear apart the car to get power to it! That was my biggest concern, actually, that getting power to it would cost me as much or more than the radio.

 

@Borage257, thank you as well. I suspected that the reason I couldn't get a good signal from the car was because I was sitting and kind of below some of the rather tall burms we have beside our roads here. Makes sense that getting up out of my car would let me clear them and be heard further away. I guess I would be solving my problem with a mobile antenna anyway, eh?

[Borage257]

Yes, a mobile with antenna AND a mobile as base station at home with an antenna 30' above ground level would solve some ore most of that problem.  

Getting clear of the berms would help.

[WRTQ298]

You don't work for Radioddity, do you? You're gonna get me in trouble with the wife, my Amazon cart is getting really heavy.

[MichaelLAX]

27 minutes ago, WRTQ298 said:

I had no idea there were 12v plug mobile radios (really showing my lack of research there!), so that would make both my wife and me happy about not having to potentially tear apart the car to get power to it! That was my biggest concern, actually, that getting power to it would cost me as much or more than the radio.

I have never owned or used a Midland, but I have read comment after comment on this Forum about their shortcomings and limitations and the only primary advantage of them seems to be: easy to use out of the box (then why so many problems requiring posts here and elsewhere?).

For years, I have declined using an HT inside my car for all of the obvious reasons.

When I purchased my first Anytone AT-779UV a/k/a Radioddity DB-20G with a $29 mag mount antenna my whole attitude towards mobile communications changed 180 degrees!

With the addition of a cup-mount holder from Amazon, it is easily installed/uninstalled from my vehicle and 18/20 watts pushes my signal well past the limited distances that HTs would provide.

Unfortunately @KAF6045has measured the output of two separate units and has published his results here that his units are woefully underpowered.

With all due respect to him, others have reported power output as claimed by the manufactures, and I cannot recall any other similar report of low power output.

$99 - $109; plug in cigarette lighter, mini-sized, easy to use on GMRS out of the box, 18 watts GMRS and an inexpensive mag-mount and you will be able to hit your wife's GM-30 for greater distances that you could with another GM-30 and mag-mount.

I will be buying another one soon, as unfortunately someone broke into my garage and stole my bike and my 2nd mobile AT-779UV while it was out of my car.

Any questions? 

[WRTQ298]

@MichaelLAX Thanks for the input!

I've been really pleased with every bit of Radioddity equipment I've interacted with (and now owned!) and they generally sit in a nice price-to-review area, as far as I can tell. It'll definitely be on the short list when I look at buying.

Sorry to hear about your bike! 

[MichaelLAX]

4 minutes ago, WRTQ298 said:

@MichaelLAX

Sorry to hear about your bike! 

And not sorry to hear about my stolen AT-779UV... because you are looking at the "used market"?!? 

PS: I have the GM-30 clone, the Pofung 15UV and was very happy with it and gave it to my grandson to use!

[BoxCar]

1 hour ago, WRTQ298 said:

Hey folks, this is my first post in this wonderful community! 

I want to be able to use my HT (a Radioddity GM-30) from my vehicle. I know, I know, the car acts as a faraday cage or whatever. Duh, it's made of metal!

I'm not quite at the point where I'm ready to invest in a mobile radio (okay, okay, my wife isn't ready to invest in a mobile radio), but I do still want to be able to check in with home while in the car.

For the curious, the main use case I have right now is to communicate with home (to another GM-30) from around our little town. The range we're talking about here is literally less than four miles in most cases. The furthest I'll actually need to be able to reach is only 6 miles, and even then I have more or less perfect line of site to home. We tested! But, unsurprisingly, I get zero signal from inside my vehicle when more than about a mile away from the house.

To resolve this problem, I plan on grabbing a mobile GMRS antenna, plopping it on the trunk, and running coax up to my console, where I'll be able to screw it directly to my HT and talk! Right? I don't actually know!

On to the actual question:

Are there any gotchas I should be aware of when plugging a mobile antenna into my HT radio?

I know it won't transmit as far, given it only has 5 watts, I know it's not the ideal setup for an HT, but I'm also reasonably sure it should work for my use-case. Are there any problems that I may need to solve, or that make this solution completely untenable?

 

Thanks in advance!

About 1/3 the  way down the page are adapters for SMA to PL/SO-259 connectors.

Tower Electronics Online Wholesale Catalog - Page One (pl-259.com)

[Borage257]

6 hours ago, WRTQ298 said:

You don't work for Radioddity, do you? You're gonna get me in trouble with the wife, my Amazon cart is getting really heavy.

No, I don’t. Buy a little here and there. 

[KAF6045]

19 hours ago, WRTQ298 said:

That said, if it really is only rated for so few cycles, that might be the best argument against this whole effort. I had no idea there were 12v plug mobile radios (really showing my lack of research there!), so that would make both my wife and me happy about not having to potentially tear apart the car to get power to it! That was my biggest concern, actually, that getting power to it would cost me as much or more than the radio.

Units in the 10-20W range tend to be supported by "lighter outlets" (and if the unit has bare lead ends, one could probably fit a lighter plug to it -- just pick a suitable fuse for the plug itself). Most such are rated for 10A (my deceased* Cherokee had a 10A lighter and 20A power outlet), and a 20W radio should only draw 40-60W (it is common that the output transistors may lose half the power drawn). That comes to 60W / 13.8V => 4.35A (I wouldn't want to run 10A through a lighter socket for long periods -- that's 138W)

40-50W needs much higher power capability and are best wired directly to the battery (using 150W draw 150W / 13.8v => 10.87A). I went 20 years with a (near) no-hole installation of a 100W Yaesu FT-100 (HF-6m/2m/70cm). Clamp-on screwdriver antenna (ATAS-100) on edge of tailgate, double-face carpet tape holding main unit and diplexer (to combine the 2m/70cm output with the HF-6m for feeding a single antenna) under passenger seat, all wiring tucked under the plastic trim and door sills (except for the wires crossing from left to right under the flip-up rear seat). Control head mounted (more carpet tape) essentially under parking brake lever, but just off to the side enough to reach controls. Power lead went along door sill and up kick panel, then around door frame (over gasket) and snaked inside the fender, coming out at the battery.

Current rust bucket I found a rubber plug covering a 2-3" diameter hole high up the firewall. Popped it out, cut an X-slit in the middle, and ran the power leads through the plug (obviously putting the plug back in place -- the hole itself would have had sharp edges that could fray the power leads) to the battery.

 

 

 

 

* roll-over, a year ago. 22 years old and only 75K miles, AND a factory order TWO-DOOR.

 

[Over2U]

This may have been covered already (I am ‘late to the party’) but, if the signal from your HT cannot reach your home when you are standing outside your car, then a car mounted antenna may or may not make the distance you require.

[MichaelLAX]

3 hours ago, Over2U said:

This may have been covered already (I am ‘late to the party’) but, if the signal from your HT cannot reach your home when you are standing outside your car, then a car mounted antenna may or may not make the distance you require.

I went back and reread the OP, and I don't see anything about his inability to reach his home with his HT while standing outside his car; Maybe I missed it in a later post?

In any event he is looking for solutions to communicating to his home while driving around his town which is about 4 miles from his home.

[Over2U]

 From MichaelLAX: “went back and reread the OP, and I don't see anything about his inability to reach his home with his HT while standing outside his car; Maybe I missed it in a later post?”

I only meant to suggest that as test of the HT’s ability to cover the four miles over the actual terrain before investing in a car mounted antenna.

Bill

Edited September 22, 2022 by Over2U
Clarify author of quoted text.

[MichaelLAX]

Sure: good idea.

If you actually hit the "Quote" button under my post, it not only quotes me in your post, it alerts me that someone has quoted me.

I did not see your new post until just now otherwise.

[Over2U]

I wasn’t sure how to use the “quote” button (confused me since I do not see the quoted material). Thanks for the info!

[WRTQ298]

On 9/22/2022 at 1:47 AM, Over2U said:

 From MichaelLAX: “went back and reread the OP, and I don't see anything about his inability to reach his home with his HT while standing outside his car; Maybe I missed it in a later post?”

I only meant to suggest that as test of the HT’s ability to cover the four miles over the actual terrain before investing in a car mounted antenna.

Bill

Hey there Bill, thanks for the reply! 

I am able to hit home while standing outside of my vehicle. It came up in one of the posts, but we have rather large burms next to most of our roads. When I get the HT antenna up over the burms, I hit home just fine, even in the next town over, about 7 miles from home! It helps, too, that this town is a little bit higher than home is. It's only a couple dozen feet of elevation, but that makes a lot of difference! 

Since I'm generally not higher than the burms when I'm driving, that's probably a bigger contributor to my signal woes than my car!

[Over2U]

Yes indeed, antenna height is critical for ‘line-of-sight’ GMRS communications. Even a temporary installation of a ‘borrowed’ magnetic-mount antenna (placed on the highest surface of your vehicle) should help you evaluate the viability of this proposed H/T use.