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Mobile Radio Antenna Mount Install Advice

WBA

Member
Joined
Apr 3, 2024
Messages
22
So, I have been reading many different thoughts on what is needed/not needed between the antenna and the radio.

First issue: Based on this connector, is it just as simple as running the pre-installed coax to the radio in the most direct route possible with as little bending/crimping of the coax as possible? Also, does it make more sense to just get a pre-installed pl-259 connector on the end of the wire, and coil up the excess, or is it worth cutting out the excess cable for the Db loss? I'm guessing the quality of the crimp makes a difference too.

Second issue: If my concern is trying to reach a distant repeater (UHF GMRS Freqs,) how important are the following considerations and what rough rank-order improvement does each bring?

-Increase TX watts
-Increase antenna Db gain rating
-Increase (insert specific quality here) rating of antenna
-Increase Antenna Height
-Reduce coax run length
-Upgrade to lower loss cable
-Anything else?

I get the basics of better line-of sight, but given the same obstructions, conditions, etc.... any thoughts? Anyone worked out a rule of thumb or simulator?
 

mmckenna

I ♥ Ø
Joined
Jul 27, 2005
Messages
24,052
Location
I am a lineman for the county.
So, I have been reading many different thoughts on what is needed/not needed between the antenna and the radio.

First issue: Based on this connector, is it just as simple as running the pre-installed coax to the radio in the most direct route possible with as little bending/crimping of the coax as possible?

That's a way to look at it.
Yeah, you drill the hole and route the cable. Not necessarily shortest/most direct. You need to pay attention to the routing. You need to avoid airbags. You ideally want to avoid existing vehicle wiring if you can. You want to avoid sharp edges.
The bend radius of RG-58 is really small, so running through a vehicle where the cable makes some sharp turns is not an issue.
You also want the cable hidden and protected. Removing trim and running the cable under that keeps it from getting damaged and it looks much better. Do not run under carpet where people put their feet.

Also, does it make more sense to just get a pre-installed pl-259 connector on the end of the wire, and coil up the excess, or is it worth cutting out the excess cable for the Db loss? I'm guessing the quality of the crimp makes a difference too.

It's MUCH easier to route the cable with the connector removed. Routing the cable with a PL-259 installed is going to be more difficult.

Ideal option:
Run the cable without a connector installed. Cut cable to length. Install connector.
if you can't do that,
Get an NMO mount with the FME connector on the cable. This is a small diameter connector that is easier to route. When you get it installed, you thread on a PL-259 adapter.

A few extra feet of good quality RG-58 isn't going to kill anything. It's just easier to get rid of the unnecessary cable if you don't need it. If it's just a few feet and you don't have the tools/skills to install connectors, then just carefully fake it out rather than coil it up. The radio is still going to work.

Second issue: If my concern is trying to reach a distant repeater (UHF GMRS Freqs,) how important are the following considerations and what rough rank-order improvement does each bring?

-Increase TX watts

Not as important as noobs think. Usually the issue is line of sight. If the antenna can see the repeater, it's probably going to work, even with just a few watts. Going from 10 watts to 20 watts does NOT double the range. In a perfect location, it would take 4 times the power to double the range, but like I suggested, line of sight tends to be the bigger issue.

With GMRS, you can only run 50 watts out of the radio. A lot of commercial LMR radios run only 35-45 watts on UHF, and they work just fine. For our PD, we actually turned the transmitter power output down to reduce stress on the radios.

-Increase antenna Db gain rating

That is a trade off.
Higher gain sends more power at the horizon. Great if the repeater is on the horizon, not so great if it is on a tall mountain directly above you.
Nice thing is that the NMO mounts make it easy to swap antennas. What works best for one person will not necessarily be the perfect solution for someone else. Experiment.
I found a simple 1/4 wave antenna works best for me.

-Increase (insert specific quality here) rating of antenna

Not sure what you mean.
Antenna radiation pattern has to do with gain, so like I said, a trade off.

-Increase Antenna Height

Line of sight. This makes a big difference. But for mobile use, it's hard to change this enough to make a difference. Putting the antenna on the top of the car roof is the way to go. Putting it down low on the trunk or fender bracket is a drawback.

-Reduce coax run length

In a mobile install, there's usually not enough coax to make a difference. A few extra feet isn't going to kill things. But, less is better and a lot of incremental improvements can add up.

-Upgrade to lower loss cable

Again, not really. I use RG-58 on all my stuff at work. It does fine. The fraction of a dB (at best) you'd gain would not make much of a difference. Lower loss cable is often larger/stiffer, and harder to run.

-Anything else?

Remember to have fun and not get hung up on numbers.

Don't buy Cheap Chinese Stuff.

I get the basics of better line-of sight, but given the same obstructions, conditions, etc.... any thoughts? Anyone worked out a rule of thumb or simulator?

Obstructions are going to be a challenge, and nothing you can do about them in a mobile install, other than move the car. But RF will pass through some things well enough and things will work. Remember, your local PD/Fire/EMS agency is communicating just fine.
 

slowmover

Active Member
Joined
Aug 4, 2020
Messages
1,998
Location
Fort Worth
Putting the antenna on the top of the car roof is the way to go. Putting it down low on the trunk or fender bracket is a drawback.

OP, men get fearful about how things should look when they should care about performance.

What I feel others will feel about it
VS
What I know to be true & beautful.

.
 

K6GBW

Member
Joined
May 29, 2016
Messages
468
Location
Montebello, CA
mckenna's advise is all solid. I would also add, have reasonable expectations! So many buy a radio and envision these really long distance ranges that are just not possible. VHF and UHF are line of sight radios. There is no magic that will make a VHF radio talk over a bunch of hills or through a bunch of buildings. The US Army uses 25 watt radios in their tanks, Jeeps and other vehicles and out in the open they are good for 7-10 miles. Cranking them up to 100 watts wouldn't change that range, but driving to a high ridge or hill top would. I find many radio users starting to go down a rabbit hole of 'improvements' looking for that magic antenna combo only to get very frustrated. Just do the best you can and then enjoy it!
 

JustinWHT

Member
Joined
Apr 16, 2022
Messages
44
"Alex...I'll take 'Communications' - Engineering Practices. 'What is a rule of thumb?"

For every 6 dB of gain or loss, you double or half your range. The inverse square law.

-Increase TX watts - going from 12 watts to 50 watts doubles range.
-Increase antenna Db gain rating - every 6 dB of antenna gain doubles your range.
-Increase (insert specific quality here) rating of antenna - a typical UHF antenna may have 6 dBd of gain (over a unity gain dipole), but advertised as 8.15 dBi (over a theoretic isotopic antenna). A $50 3 dBd can be replaced with $1,200 9 dBd antenna to double your range.
-Increase Antenna Height - going from say 50' in the air to 100' will get you from 15 miles to 18 miles
-Reduce coax run length - negligible most cases
-Upgrade to lower loss cable - every 6 dB less coax loss will double your range.

Once you go NMO, you never go back. Or something like that
 
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