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24V mobile install questions


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Hi team,

I'm new to mobile radio but would like to use it for convoy management in remote areas; just spent a month chasing remote beaches in Baja with two other vehicles and it seems to be so helpful for navigating through the poorly mapped backroads. From my understanding, GMRS seems ideal for this without the testing/licensing 'hassle' of ham (so far), especially with mixed vehicles in the convoy who may not be as motivated to study for a ham license. We had some FRS handhelds on this trip, but the range was insufficient for much independent exploration without totally losing each other.

With that use case overview out of the way, complicating matters I have a 24V diesel Land Cruiser that I'd like to install the mobile system in. Most mobile radios still seem to have 13.8V nominal power input, presumably to simplify the design of the analog amplifier sections. Please correct me if I'm wrong on the reasoning here, but I guess it likely doesn't matter. Will I run into trouble if I use a DC/DC switching converter to step down from 24V to 12V? I don't know how noise-free these DC/DC converters are at the frequencies these radios are operating at internally. Do most radios have enough filtering on the inputs to clean this stuff up, or will I have to figure out some sort of external filter?

I have been looking at used Kenwood TK-8180H and Vertex VX-5500 for remote faceplate capability in 40-50W range and I understand Part 95A compliance. Are there any other devices I should be considering? I think I'm comfortable enough with the wiring and programming hassle to prefer a used commercial radio over a Low Part Count SDR, but am open to contrary reasoning. I'd also probably like to get a ~5W handheld to send with a family member into vehicles that have temporarily joined the convoy to enable them to communicate as well. Suggestions for a handheld for this use case are appreciated.

Also I have long since ditched the stock 'radio' in the vehicle, so I have the mounting hole for the stock antenna available on the front right quarter panel. From looking at some of the other posts it sounds like a 1/2 wave antenna is recommended - is this a good enough location or should I be aiming for something somewhere else?

Thanks for humoring my journey out of noobness!

overrulecaratmutt

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Samlex makes some decent 24 to 12 volt step down converters for around $100.  No matter what, pay attention to the Amp rating, the cheaper ones are often limited to just 10 or 15 amps advertised, which might be under what your 50 watt radio will pull under transmit. (Note that the actual ratings are often less for continuous draw - as compared to the "advertised" max instantaneous rating.)   I wouldn't get too worried about DC noise getting into your radio from the converter. More noise comes from bad grounding and alternator whine.

If you're planning to use a 1/2 wave antenna, then no ground plane should be necessary. Fender mounts are not ideal, but they work.  Fender mounts will far exceed the range of any portable you're talking simplex with.

You're asking good questions - but don't let perfection become the enemy of good. Your setup will be good enough.

 

 

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Hi team,
I'm new to mobile radio but would like to use it for convoy management in remote areas; just spent a month chasing remote beaches in Baja with two other vehicles and it seems to be so helpful for navigating through the poorly mapped backroads. From my understanding, GMRS seems ideal for this without the testing/licensing 'hassle' of ham (so far), especially with mixed vehicles in the convoy who may not be as motivated to study for a ham license. We had some FRS handhelds on this trip, but the range was insufficient for much independent exploration without totally losing each other.
With that use case overview out of the way, complicating matters I have a 24V diesel Land Cruiser that I'd like to install the mobile system in. Most mobile radios still seem to have 13.8V nominal power input, presumably to simplify the design of the analog amplifier sections. Please correct me if I'm wrong on the reasoning here, but I guess it likely doesn't matter. Will I run into trouble if I use a DC/DC switching converter to step down from 24V to 12V? I don't know how noise-free these DC/DC converters are at the frequencies these radios are operating at internally. Do most radios have enough filtering on the inputs to clean this stuff up, or will I have to figure out some sort of external filter?
I have been looking at used Kenwood TK-8180H and Vertex VX-5500 for remote faceplate capability in 40-50W range and I understand Part 95A compliance. Are there any other devices I should be considering? I think I'm comfortable enough with the wiring and programming hassle to prefer a used commercial radio over a Low Part Count SDR, but am open to contrary reasoning. I'd also probably like to get a ~5W handheld to send with a family member into vehicles that have temporarily joined the convoy to enable them to communicate as well. Suggestions for a handheld for this use case are appreciated.
Also I have long since ditched the stock 'radio' in the vehicle, so I have the mounting hole for the stock antenna available on the front right quarter panel. From looking at some of the other posts it sounds like a 1/2 wave antenna is recommended - is this a good enough location or should I be aiming for something somewhere else?
Thanks for humoring my journey out of noobness!
overrulecaratmutt



I have not had any first hand experience with any of the DC-DC switch-mode power supplies, but that is where I would go if I were in your shoes. Here is a link to one that I would consider under your conditions.
https://www.amazon.com/Samlex-America-SDC-23-Amp-Converter/dp/B0002D6KO0

I do use a high-power AC-DC switching power supply from Alinco for the 12v radio equipment I operate in my home. I do not experience any discernable noise from it on UHF so I would anticipate similar acceptable results from a high-quality DC-DC version in a mobile situation. You could easily purchase a unit, test it, and you if you have negative results, return it for refund.

If you do use the inverter, make sure it does not present any parasitic load to your vehicle battery when vehicle is not running otherwise you will experience dead-battery syndrome.

I would choose a unit that is rated with 50% or more than I need. Gives headroom additional loads in future and often times products perform their best at less than maximum capacity.


Michael
WRHS965
KE8PLM
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Thanks for the clarification @Radioguy7268and @mbrun!

I do use some other 24/12V DC/DC converters for other stuff (mostly cigarette lighter powered things which have power supplies that only accept 12V) and have had luck with smaller 1-2A converters, this'll likely be the biggest draw item on 12V so will have to do some rewiring there and see if I can put everything on one 15A-ish converter. Will put an ignition relay upstream to cut the supply to prevent parasitic drain when not in use.

Regarding programming - I assume most of the software is about the same between Kenwood/Vertex/... for older commercial radios. Is it worth sorting out the software myself, or given that there are relatively few GMRS frequencies should I just try to get the ones I'm interested in pre-programmed by whoever I get the radio from? Once the frequencies are programmed, is it straightforward to adjust PL tones (should I need them) from the front panel, or is that typically a config software activity on this type of radio?

Looking forward to getting this thing up and running, and yes definitely aware of the perfection being the enemy of the good problem 😜

 

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Thanks for the clarification [mention=1480]Radioguy7268[/mention]and [mention=3409]mbrun[/mention]!
I do use some other 24/12V DC/DC converters for other stuff (mostly cigarette lighter powered things which have power supplies that only accept 12V) and have had luck with smaller 1-2A converters, this'll likely be the biggest draw item on 12V so will have to do some rewiring there and see if I can put everything on one 15A-ish converter. Will put an ignition relay upstream to cut the supply to prevent parasitic drain when not in use.
Regarding programming - I assume most of the software is about the same between Kenwood/Vertex/... for older commercial radios. Is it worth sorting out the software myself, or given that there are relatively few GMRS frequencies should I just try to get the ones I'm interested in pre-programmed by whoever I get the radio from? Once the frequencies are programmed, is it straightforward to adjust PL tones (should I need them) from the front panel, or is that typically a config software activity on this type of radio?
Looking forward to getting this thing up and running, and yes definitely aware of the perfection being the enemy of the good problem
 

I will leave the Kenwood/Vertex programming questions for RadioGuy as he is the expert on that. Me personally, I want the capability to change the programming of my radios myself, even though the learning curve may be more than I wish.


Michael
WRHS965
KE8PLM
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I'm hardly an expert. I've learned by doing, and I've just been doing for a long time. I still get twisted up sometimes. I once spent nearly an hour trying to figure out why I wasn't seeing an option that I knew should be there on a Vertex repeater, before I realized I hadn't set my new software to 'expert' mode. Rookie mistake, 20 years in.

If you never programmed radios before, Kenwood and Vertex are probably 2 of the easier commercial software programs to learn on. Kenwood keeps a very common software platform among most of their programs, so once you learn their software, you're pretty familiar with where to look for most any settings you might need to adjust.

For a first timer, I'd say that getting a basic codeplug set up for you from the start is a good jumping off point, and at least you have a working codeplug to refer to if you want to start modifying stuff on your own. Rule #1 if you start programming - SAVE YOUR ORIGINAL CODEPLUG before you do any modifications. Keep that original archive untouched, and you'll always have something to go back to.

 

 

 

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Great advice @mbrun and @Radioguy7268, thanks much. I would like to be able to change the programming as well, just don't really have a good understanding of how much that is ahead of time.

I pulled the trigger on an eBay VX5500U radio chassis and (separate listing) head unit, and will have to see if I have the right crimpers in storage to make up the cable between the two - we certainly would have had at work before that place imploded.

Just need to confirm what sort of clearance I've got through the grommets on the back of the vehicle and should be able to get an antenna and cable/mount ordered this weekend, along with the programming cable and software.

Once I've dug my bench supply up to get everything up and running on my desk I'm sure the questions will recommence :)

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There are switching converters in just about everything electronic - especially anything with batteries.  So you are already operating your radios in the presence of switching converters.  Your vehicle probably has several switching converters in it already.    I would be more worried about radiated interference than conducted interference.  If you have issues consider locating the converter in an area that is shielded from the antenna.

Switching converters can be very clean but higher power converters will make more noise.  I would by a quality brand.  Cheaper brands are more likely to cheat.

Chances are you will be fine with it but there is some luck involved.  Most switching converter noise (especially broad band noise) tends to be well below 400Mhz.  So I would be optimistic.  It'll probably be just fine.

Vince

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