20w mobile with 5w handhelds

[RogerSpendlove]

I'm still fairly new to radios and GMRS and trying to get my mind wrapped around the technical concepts. My intended use is for communications between multiple drivers transporting a group of young men to camping outings (we're a Trail Life USA troop). I'm contemplating getting a 20w mobile to install into my car (because, or course, I'm attracted to the possibility of farther range ). But most of the other dads would likely be using 5w handhelds in their vehicles. My question is:  I, with my 20w would be able to transmit farther (in most conditions) than the 5w handhelds -- so does that mean that if we got separated a number of miles on the highway, they would be able to hear me from farther away, but that I would probably NOT be able to hear them calling back, due to their lower power?

For transportation communications like this, would it be better for all of us to have the same power handhelds?

Thanks for any help and insight you'all could give me.

[WRTC928]

Probably, but not for the reason you think. The biggest factor is that the antenna of a mobile radio is outside the vehicle while the HT antennas are inside the vehicle -- essentially a Faraday cage. Transmission and reception will both be adversely impacted by being inside the vehicle. Second, a mobile radio antenna is usually a better antenna in general, because it doesn't have to be short enough to be easily carried. Third, a VHF or UHF radio signal is significantly impacted by obstacles -- mostly hills and buildings in the case you're describing. 

The rule of thumb is that in order to double the distance of the signal, you have to quadruple the power of the radio. All other things being equal, your radio should yield about twice the effective distance of the HTs, but all other things are not even close to equal in your case. 

Short answer -- yes, I would expect them to hear you further than you can hear them, but it has less to do with power than with other factors. You could learn a lot by simply doing the experiment. Try communication between your mobile and an HT under different conditions and see what you get.

[WRTC928]

14 minutes ago, RogerSpendlove said:

For transportation communications like this, would it be better for all of us to have the same power handhelds?

I don't think so. The probability of getting separated is about the same no matter what radios you have, but with the mobile, you at least have a chance of getting a message to them even if they can't effectively respond. One-way is better than no-way, IMO.

[nokones]

You might get a couple extra yards of farz out of the extra power, but I wouldn't bet on it.

[AdmiralCochrane]

If nothing else the 20w radio will sound louder. You will have the clear commanding voice.

[WRUE951]

i can give you my experience while RV' ing with RV friends.  Most of the time we travel  in groups of 3 to 4 other RV's on the road. We all have GMRS radios and we all started out using HT's.  After the first time together using HT's we discovered communicating with HT's pretty much sucked.  We were lucky to reach each other when we got separated by as little as a mile.  The low profile HT antenna and fact we all were pulling huge signal blocking clumps of fiberglass and steel was the problem.  Once we all got mobile radios this problem pretty much went away.   With the mobiles we can stay in touch easily as far as 20-25 miles apart and sometimes further, especially when we are hitting repeaters.  Traveling through canyons is a bit of a problem even with a mobile but dependable within 2 miles.    I will say one of they guys in our group 'was' using a Midland Ghost antenna, which worked pretty good for the most part but he was the first guy we lost in the canyons..... Early on i did adapt my HT to a Mobile antenna, which helped a little but no comparison even close to using a good 50W Mobile..  In my case i use a Hytera HM782 

[amaff]

1 hour ago, RogerSpendlove said:

My question is:  I, with my 20w would be able to transmit farther (in most conditions) than the 5w handhelds -- so does that mean that if we got separated a number of miles on the highway, they would be able to hear me from farther away, but that I would probably NOT be able to hear them calling back, due to their lower power?

For transportation communications like this, would it be better for all of us to have the same power handhelds?

As has been said, you may get SOME additional punch through trees and what not at 20W over 5W, but the biggest thing is putting the antenna outside of the big metal box.

The nice thing about it though is that with the antenna on the outside, not only does it improve your transmit range, but you'll be able to hear them from further away than you otherwise would as well, with a handheld inside the car without an external antenna.

All that said, if staying in touch is super important to the group....if a large separation happens, have a plan for correcting that / regrouping.

[WRYZ926]

Many of us have used hand held radios with an external antenna with good results. As others have said, getting the antenna outside of the vehicle is the biggest improvement you can make. Adaptor cables that go from SO239 to SMA are cheap and make connecting an external antenna to most hand held radios easy to do.

[LeoG]

Using an external antenna gets the antenna up higher and out of the metal box of the vehicle.  I set up my wife with the Nagoya UT72 and a handheld microphone with an H3 radio.  Makes using it much easier and gives much better range than the short antenna on the HT.

[GreggInFL]

On 7/26/2025 at 12:35 PM, LeoG said:

Using an external antenna gets the antenna up higher and out of the metal box of the vehicle.  I set up my wife with the Nagoya UT72 and a handheld microphone with an H3 radio.  Makes using it much easier and gives much better range than the short antenna on the HT.

That's what I did, with the same antenna. A good first-step improvement. I still use it occasionally with a DB25-G.

[Bogieboy01]

On 7/26/2025 at 12:35 PM, LeoG said:

Using an external antenna gets the antenna up higher and out of the metal box of the vehicle.  I set up my wife with the Nagoya UT72 and a handheld microphone with an H3 radio.  Makes using it much easier and gives much better range than the short antenna on the HT.

Second this, i have 2 vehicles, and have only had time to install a mobile in one of them, when i want to drive the other AND talk to anonymous men on the radio in the other vehicle, i have a mag mount antenna that i hook to a Boofwang ar5rm with a hand mic, crazy part is the range is not all that different with an 8w handheld than it is with my 25w mobile rig... granted both of them are operating on stubby ghost antennas....

[WRTC928]

13 hours ago, Bogieboy01 said:

Second this, i have 2 vehicles, and have only had time to install a mobile in one of them, when i want to drive the other AND talk to anonymous men on the radio in the other vehicle, i have a mag mount antenna that i hook to a Boofwang ar5rm with a hand mic, crazy part is the range is not all that different with an 8w handheld than it is with my 25w mobile rig... granted both of them are operating on stubby ghost antennas....

I have BNC connectors on the radios I use a lot. It makes connecting to a mag mount antenna much easier and doesn't stress the SMA connector nearly as much.

[WRYZ926]

BNC connectors is the way to go if you plan on connecting and disconnecting the external antenna often. Breaking the SMA connector is always possible when using a SMA to SO-239 adaptor cable.

[RogerSpendlove]

Thanks, everyone for the excellent advice! Much appreciated!

I decided to purchase a mag-mount antenna for myself. It will give me the additional flexibility of being able to put it on another vehicle, in case I'm driving the church van with a bunch of boys and dads, instead of my personal vehicle. Plus, it was a lot less expensive than the mobile unit! Maybe I'll eventually be able to convince the other dads to invest in one as well (first have to convince them to get their own handhelds and license!) Thanks again!

[LeoG]

And if you bought a mobile unit you would have to purchase some sort of antenna anyway.  This is a good way to prep yourself for the upcoming upgrade to a mobile unit in the future.

[Bogieboy01]

23 hours ago, WRTC928 said:

I have BNC connectors on the radios I use a lot. It makes connecting to a mag mount antenna much easier and doesn't stress the SMA connector nearly as much.

The radio i use in the secondary vehicle has a BNC installed on it, the rest of my radios all basically have a single use in mind, so the antenna stays put most of the time...

[Lscott]

23 hours ago, WRYZ926 said:

BNC connectors is the way to go if you plan on connecting and disconnecting the external antenna often. Breaking the SMA connector is always possible when using a SMA to SO-239 adaptor cable.

I've standardized on BNC wherever possible.  You can usually find and adapter for some weird RF port to a BNC. For example I have a few Icom HT's that use a rather strange port. I had to special order adapters so I could use an external antenna with them.

https://forums.mygmrs.com/gallery/image/500-ic-f3162dt-front-and-back-sidepng/?context=new

BNC jumper cables are easy to find. As long as they are kept short the usual RG-58 coax doesn't cause much of a loss.

[WRYZ926]

I always used either 6" or 12" numbers when using a hand held in vehicles. I use to run a hand held CB radio with an external antenna for a while back in the early to mid 90's.

Adding another 6-12 inches of RG58 to the antenna coax won't hurt. Most mag mounts use between 13 and 15 feet of RG58 on average.

I have SMA to BNC adaptors for when I want to use my hand held with my portable yagi or faraday cloth j pole antennas. Having a box full of adaptors comes in handy.

[WSHH887]

Here's a question for the RV set. Does anyone mount an antenna on your trailer and have it connected to your tow vehicle while traveling?

[GreggInFL]

13 minutes ago, WSHH887 said:

Here's a question for the RV set. Does anyone mount an antenna on your trailer and have it connected to your tow vehicle while traveling?

No, but I like the idea. I'll report back later.

[WRTC928]

46 minutes ago, WSHH887 said:

Here's a question for the RV set. Does anyone mount an antenna on your trailer and have it connected to your tow vehicle while traveling?

Assuming you have enough slack in the coax to allow turning, I can't think of any reason it wouldn't work.