Advise on Mounting three antennas on a Dodge Charger Trunk

Cowley639

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Mar 22, 2016
Messages
89
Hey everyone,

I have a 2016 Dodge Charger, and I am looking for advise on mounting three antennas on the vehicle. I will start off by saying I WILL NOT be drilling any holes in the vehicle. I am looking for the optimum location to mount all three antennas. I would like to keep the antennas in the trunk area because two of the three radios will be mounted in the trunk (both are remote mount). I do have three trunk-lip mount NMO antenna mounts to use.

Here's what I have;
Kenwood NX-5800 UHF - (used for my duties as a first responder in my county)
- Laird TRAB4503 antenna

Motorola XTL2500 UHF - (used for my day job in P25 conventional)
- Laird TRAB4503 antenna

Uniden BCD996P2 - (used to monitor 800 mhz. state radio system)
- PCTEL BMAX8155S antenna

Both the NX-5800, and the XTL2500 were issued to me by the county and my job respectively. I use the XTL2500 everyday, however the NX-5800 only gets used for first response activities, which are few and far between. NOTE: The XTL and NX are never transmitted on at the same time (and are rarely even turned on at the same time).

So I guess I am trying to figure out the best location on my trunk to orient the antennas to get the best performance. I would assume I would need to keep both UHF antennas spaced as far apart as I can? Possibly on the driver and passenger sides of the trunk, then the middle (closest to the rear window) for the 800mhz antenna?
 

mmckenna

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I will start off by saying I WILL NOT be drilling any holes in the vehicle. I am looking for the optimum location to mount all three antennas.
Well, optimum probably isn't the right word. Optimum would be a permanent mount on the roof. You will take a performance hit by not having them on the roof, and having trunk lip mounts. Using the low profile UHF antennas is going to impact performance even more. But as long as you understand that, you have some things to consider.

Is this a persona vehicle, or a work provided vehicle?

Trunk lip mounts are not damage free mounts. They will damage the underside, as you need to crank the set screws down pretty hard to get them to bite through the paint into the metal trunk lid (that vehicle does have a metal trunk lid right, not composite?)

Sticking them out at the edge of the trunk compromises the ground plane. So they are going to be slightly directional. The back window, if it has metal film tinting or defroster wires, is going to create issues, too. It can work if the system you are connecting to is designed well, but you've got a number of things working against you if you want this to work optimally.

Since the XTL sounds like it gets the most use, you'll probably want to give that one the prime location. Problem is, trunk lip mount low profile antennas are not going to be good performers. Usually going center of the trunk lid is best. Even if you mount it on the front edge of the trunk, you'll be up against the rear glass and expose rear seat passengers to high RF levels. Less than ideal. I'd probably take the directionality issue over that, and mount the XTL on the left or right side of the trunk, and try to center it front/rear, but make sure you have it at least 6 inches forward of the rear edge to get the most ground plane you can.

I'd probably mount the NX-5800 on the opposite side, again, giving it better performance and keeping RF as far away from rear seat passengers as you can.

I'd put the scanner antenna in the center. Problem might be that it'll hit the rear window when you open the trunk. That might get to be annoying really quick. You could probably mount it on one of the trunk sides, but you'll want as much separation as you can from the transmitting antennas.
High RF levels from a transmitting antenna coupling with the scanner antenna can cause damage. Doesn't matter if the scanner is turned off or not, the power switch does not disconnect the antenna from the receiver circuitry.

You might want to consider mounting the scanner antenna up front with a trunk lip mount bracket. At least that'll get it away from the transmitting antennas.
 

Cowley639

Member
Joined
Mar 22, 2016
Messages
89
This is a personal vehicle, (although I do use it for work) yes I do understand the issues with trunk lip mounts (and yes it is metal)

The phantom antennas were both issued to me, so I really had no say in that.

I rarely have any rear seat passengers (and if I do, I wouldn't be at work, or responding to anything) thus the High RF problem wouldn't be an issue. If anything, I might have the scanner on, but that would be it.

I have tested the scanner antenna in the middle, and it actually still does have a little bit of clearance to the back window when the trunk is up, so we are good to go there.

Ill try the two UHF antennas on either side of the trunk, and the scanner in the middle and see what I get...
 

Reconrider

Trx-1 or Sds100
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Sep 26, 2017
Messages
782
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Well, optimum probably isn't the right word. Optimum would be a permanent mount on the roof. You will take a performance hit by not having them on the roof, and having trunk lip mounts. Using the low profile UHF antennas is going to impact performance even more. But as long as you understand that, you have some things to consider.

Is this a persona vehicle, or a work provided vehicle?

Trunk lip mounts are not damage free mounts. They will damage the underside, as you need to crank the set screws down pretty hard to get them to bite through the paint into the metal trunk lid (that vehicle does have a metal trunk lid right, not composite?)

Sticking them out at the edge of the trunk compromises the ground plane. So they are going to be slightly directional. The back window, if it has metal film tinting or defroster wires, is going to create issues, too. It can work if the system you are connecting to is designed well, but you've got a number of things working against you if you want this to work optimally.

Since the XTL sounds like it gets the most use, you'll probably want to give that one the prime location. Problem is, trunk lip mount low profile antennas are not going to be good performers. Usually going center of the trunk lid is best. Even if you mount it on the front edge of the trunk, you'll be up against the rear glass and expose rear seat passengers to high RF levels. Less than ideal. I'd probably take the directionality issue over that, and mount the XTL on the left or right side of the trunk, and try to center it front/rear, but make sure you have it at least 6 inches forward of the rear edge to get the most ground plane you can.

I'd probably mount the NX-5800 on the opposite side, again, giving it better performance and keeping RF as far away from rear seat passengers as you can.

I'd put the scanner antenna in the center. Problem might be that it'll hit the rear window when you open the trunk. That might get to be annoying really quick. You could probably mount it on one of the trunk sides, but you'll want as much separation as you can from the transmitting antennas.
High RF levels from a transmitting antenna coupling with the scanner antenna can cause damage. Doesn't matter if the scanner is turned off or not, the power switch does not disconnect the antenna from the receiver circuitry.

You might want to consider mounting the scanner antenna up front with a trunk lip mount bracket. At least that'll get it away from the transmitting antennas.
I just want to say that when I see you name in a reply, I know I’m going to read a long post that’s nothing but knowledgeable and help a new guy like me. I plan on putting a cb antenna on my roof(sedan), how far apart should I keep it away from my scanner antenna(tri band Larson antenna nmo)?
 

mmckenna

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I have tested the scanner antenna in the middle, and it actually still does have a little bit of clearance to the back window when the trunk is up, so we are good to go there.

Ill try the two UHF antennas on either side of the trunk, and the scanner in the middle and see what I get...
Sounds like you are good to go then.
 

mmckenna

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I just want to say that when I see you name in a reply, I know I’m going to read a long post that’s nothing but knowledgeable and help a new guy like me. I plan on putting a cb antenna on my roof(sedan), how far apart should I keep it away from my scanner antenna(tri band Larson antenna nmo)?
Coupling between the antennas is the issue. A legal CB should be putting out 4 watts maximum, probably will find it's a bit less. Keeping that RF from getting into the scanner is the idea.
When looking at the RF levels involved, you'd need to consider feed line losses (both the CB and the Scanner), how close the antennas are spaced, and how much the scanner will tolerate.
The part that's hard to determine is what the scanner will tolerate. Too much RF getting into them and the soft expensive bits on the inside go "poof". Even if it's not enough to do that, the scanner might stop receiving when you transmit on the CB due to receiver desense. The receiver desense is what happens when a strong out of band signal is present (CB) in close proximity to the scanner. Basically it'll temporarily deafen the scanner. Not really a big deal, but something to be aware of.

But that doesn't really answer your question.
Answer is to experiment. I'd start at something like 2 feet or so and try it out. Ideally having the scanner antenna on the trunk and the CB antenna on the roof would be ideal.
 

doctorbubba010

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Mar 15, 2017
Messages
37
Location
NC/SC
I just want to say that when I see you name in a reply, I know I’m going to read a long post that’s nothing but knowledgeable and help a new guy like me. I plan on putting a cb antenna on my roof(sedan), how far apart should I keep it away from my scanner antenna(tri band Larson antenna nmo)?
Same brother.
 

doctorbubba010

Learner
Joined
Mar 15, 2017
Messages
37
Location
NC/SC
Coupling between the antennas is the issue. A legal CB should be putting out 4 watts maximum, probably will find it's a bit less. Keeping that RF from getting into the scanner is the idea.
When looking at the RF levels involved, you'd need to consider feed line losses (both the CB and the Scanner), how close the antennas are spaced, and how much the scanner will tolerate.
The part that's hard to determine is what the scanner will tolerate. Too much RF getting into them and the soft expensive bits on the inside go "poof". Even if it's not enough to do that, the scanner might stop receiving when you transmit on the CB due to receiver desense. The receiver desense is what happens when a strong out of band signal is present (CB) in close proximity to the scanner. Basically it'll temporarily deafen the scanner. Not really a big deal, but something to be aware of.

But that doesn't really answer your question.
Answer is to experiment. I'd start at something like 2 feet or so and try it out. Ideally having the scanner antenna on the trunk and the CB antenna on the roof would be ideal.
So your suggesting that although the scanner may stop receiving during transmission it should be mostly safe besides the annoyance. Could be good for me. Quiets other Audio while I transmit on the >4 watt Cobra 75
 
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