Vehicle Antenna Placement Question

[Net-5]

Howdy:

I'm going to be installing 3 antennas on a vehicle: a VHF radio antenna, a CB radio antenna and a scanner antenna (primarily for VHF).

Just wondered if anybody out there knows how far apart these attennas should be spaced from each other, or if it matters all that much?

Thanks a bunch!

 

[INDY72]

Usually you want to space them as far from each other as you can... Example-
Trunk/rear deck mounting-
Far right- Scanner
Far left- VHF Hi
Center- CB

Also will you be doing NMO hole mounts, lip mounts, or magnet mounting??? What kind of vehicle? And a good idea is to ask in the installation forum.

 

[tekshogun]

As made clear by milf, placement can and will depend on several factors.

So some things to bring to the table:
vehicle details (trunk, hatch, etc)
types of antennas: so, I am guessing VHF high band (something like 136-174 or 144-148 for ham or a dual band), an all band antenna for the scanner, and a 11-meter antenna for the CB.

What sizes are we talking about? Quarter-wave, 5/8 wave, etc.

Is one of the antennas going to be really long (such as 38" or higher), if so, do you want to do a trunk/hatch mount set low in the back, the other antennas may be short enough to be roof mounted or another could go on the other side of the trunk/hatch. Remember, quarter waves work best when roof mounted but can be made to work just fine on a trunk/hatch mount granted proper grounding is done.

Since the CB should only be 4-watts, you shouldn't have to worry about burning anything out with that radio. Your VHF transceiver may overload your scanner being used for VHF so those will need to be furthest away to prevent desensing and even overloading your scanner.

 

[Net-5]

As made clear by milf, placement can and will depend on several factors.

So some things to bring to the table:
vehicle details (trunk, hatch, etc)
types of antennas: so, I am guessing VHF high band (something like 136-174 or 144-148 for ham or a dual band), an all band antenna for the scanner, and a 11-meter antenna for the CB.

What sizes are we talking about? Quarter-wave, 5/8 wave, etc.

Is one of the antennas going to be really long (such as 38" or higher), if so, do you want to do a trunk/hatch mount set low in the back, the other antennas may be short enough to be roof mounted or another could go on the other side of the trunk/hatch. Remember, quarter waves work best when roof mounted but can be made to work just fine on a trunk/hatch mount granted proper grounding is done.

Since the CB should only be 4-watts, you shouldn't have to worry about burning anything out with that radio. Your VHF transceiver may overload your scanner being used for VHF so those will need to be furthest away to prevent desensing and even overloading your scanner.

Thanks for the responses, milf and tekshogun. The vehicle is a full-size van. Antennas are 1/4 wave VHF high for a Motorola Spectra 50w, an all band antenna for the scanner, and the CB is an 11-meter antenna @ 4w.

There is a roof rack and some equipment on the van that puts some limitations on where the antennas go (unless I remove those, something I'd like to avoid). Gutter mounts won't work all that well with this. The VHF antenna will be mounted with a hole being drilled for it (don't recall the tech name for that type of mount), the other two are magnetic with the wires trailing off to the sides, intended to be run through a door or a window. I'm going to see about modifying the mounts though, as I'd like to run cable through the roof and seal it up.

Sorry if I posted this in the wrong place, I didn't realize that there was an installation section here.

I've driven lots of vehicles with all the radios installed but never did it myself. The radios are no problem, I just don't want to blow something by an overload of energy too close to one of the antennas up top. I'll space them as far apart as I can, down the center of the roof is what I'm thinking.

If I had both a roof and a trunk lid to work with it would be easy, but no such luck here.

Any other tips would be appreciated. Thanks!

 

[mrweather]

The drilled mount is mostly like an NMO. Pretty standard in the radio install business.

Because the CB antenna will (should?) be the longest, you may want to consider an L-bracket mount off one of the front fenders. Ideally it should go in the middle of the roof because CB needs lots of sheetmetal for a proper counterpoise but that doesn't sound doable.

Try to separate the scanner and Spectra antennas as much as possible. 50 watts of RF could do nasty things to your scanner's front end.

Since the Spectra antenna will be drilled you might as well drill for the scanner antenna as well.

My $ 0.02.

 

[INDY72]

Full size van... OK this actually makes this easier..... front hood lip mounted NMO near the driver's or passenger door area would be the best bet actually for your VHF, but if you must roof mount it, then do an longer cable run and NMO mount it iether center front, or center towards the rear. The magmount CB and scanner ants can be done in a row behind this as long as you leave a couple of feet between them all.. You can drill and add a ring to run the cables from the mag mounts in the roof, but youd be better off doing all around NMO... The best set up I have seen on a work van was middle center roof CB, right rear VHF, left rear scanner, and hood lip mounted 800/900 MHz. Magnet mounted CB and scanner ants do give the flexibility to place anywhere pretty much, and move around for best performance... Seriously look into NMO hood lip mounting that VHF. It helps eliminate too much clutter rooftop. On average your antennas will add around 30-40 inches of hieght overhead. Average VHF is as follows- iether 3 inch coil base, and 32 inch whip, or an non coiled 12 inch whip. CB mag mount is usually 2 to 4 inch coil base depending on if its a high gain supertuned, or standard, and about 40 inch whip. Scanner mag mounts vary depending on type.. but the Hustler MRM, and RS models if not modded, have an 3ish inch base assembly with total whip of 32 inches. The RS can be modded to an single coiled 16/17 incher.

 

[N1BHH]

I would never mount an antenna near the engine compartment. On a van, get them all on the roof, mine are on the roof and work superior to anything else.

 

[tekshogun]

There are many types of mounts for roof racks as well, so if you don't care to drill anything, well there is something for everyone.

 

[Net-5]

Thanks to all of you, and sorry I didn't respond earlier. Great advice and it really helped.

Thank you!!

 

[jim202]

It is interesting to look at all the comments that the different people have posted here. My
comments to many of them would have to be with held due to the flack that they would
come back with. Based on working in the radio field for well over 45 years now and doing installs
in vehicles for most of that time, I tend to just let them vent.

I do have a few pointers that you might want to consider. If you are going to use a mag mount for
more than a few days, expect the paint where it is mounted to become damaged. Long time
use of a mag mount will have rain water migrate into it and damage the coax connection.
Been there and done that. Found out the hard way, mag mounts are for very short duration use.

If you mount a VHF antenna down on the front fender area, expect to pick up engine noise and
have it be directionally limited due to the shielding of the rest of the van.

Consider mounting the CB antenna on the rear of the van. That way you can reach it to remove
it when you go into low overhead areas like parking garages and hotel areas. Take the small
loss on omni coverage with not having a total suround metal coverage. You won't be able to
see much difference. been running low band antennas on pickup roof for well over the 45 years
now and had no ill effects. The rear dome light allows you to be able to fish the coax cable
much easier in the pickups when you remove it during the install.

Before you go drilling any holes, check to make sure you can get the coax cable fished from
your planned hole area to one of the side posts in the van. It might be a pain in the rear to
remove the trim, but you will be glad you did to see what issues you might run into.

Running the heavy power cable for the Spectra radio should not be much of a problem. I have
always found the rubber boot on the drivers side firewall around the shift cable, linkage and or the
emergency brake cable as a good place to punch through.

They make fuses today that have wire coming off of them from one side. These are great for
obtaining the switched ignition source. Make sure you place the fuse back into the socket
so that the wire is coming from the hot side. this way your not placing any additional load
on the original fuse value. Then add a fuse of the correct value to the loose wire from your
new fuse to feed the new installed radio.

The choice of type of mounts are up to you. The more common style that is used with the
drilled hole as you put it are the NMO style. These normally use a 3/4 inch hole. Most radio
installers have a special bit to make these holes. they have a ring around the outside of the
hole saw to prevent the saw from going too deep into the vehicle and tearing up a head liner.
The actual mount has a brass threaded ring on the outside that is used to tighten down on the
roof. It is about a 1/4 inch high when your done. I always put some silicon grease on the
threads and the O ring gasket to make install easier. It helps a little to seal better. Don't over
tighten the out ring when you sock it down.

Have fun with the radio installs.

Jim

 

[Net-5]

It is interesting to look at all the comments that the different people have posted here. --/snip/--

Hi Jim,

Thanks for the info! It would be cheaper if I just stick with mag mounts but I've decided to go with NMO for all of them, in addition to the NMO I've already installed for the Spectra.

I drilled the VHF NMO with a hole saw. I managed not to tear-up the headliner, but just barely. I didn't know there was a special saw for antenna installs. Think I'll be getting one. I fished the coax just by luck. When I do the other two antennas, I'll take your advice. And using the rear dome light to help fish is a great idea!

Can I ask one more question? I have a spare VHF antenna, 1/4 wave, that was cut for 155.xxx (don't recall the exact freq anymore but it was 155.something). I attached the antenna to a weather radio and it is not picking up too well. The weather freq is 165.xxx, I think. The weather freqs are factory programmed and the radio worked fairly well with the small antenna that came with it. Was hoping to improve reception with the spare (longer) VHF antenna though.

Would I need an antenna cut to 165.xxx, or something closer than 155.xxx to have it work? I'm curious about that.

Thanks again, Jim. And thanks to everybody else. RR is a great place to learn things, because of experienced people like you.

 

[INDY72]

If you can get an VHF ant tuned to the 160-174 band it would do great on the WX chans as they are 162 MHz.... Though one that is set to run on 15x-16x may work, but not as good. (Know anyone that used to work for the federal government,.. great source for the 160-174 MHz area...) I have always wondered about CB's that do WX.... I ponder how good the WX band is coming in on a antenna designed speciffically for the 20 MHz band.... If you decide to get rid of the VHF Hi whip I would love to add it to the available whips... I do a lot of experimenting, and my faves are the VHF Hi, UHF, and 700.800/900 whips...

 

[Net-5]

If you can get an VHF ant tuned to the 160-174 band it would do great on the WX chans as they are 162 MHz.... Though one that is set to run on 15x-16x may work, but not as good. (Know anyone that used to work for the federal government,.. great source for the 160-174 MHz area...) I have always wondered about CB's that do WX.... I ponder how good the WX band is coming in on a antenna designed speciffically for the 20 MHz band.... If you decide to get rid of the VHF Hi whip I would love to add it to the available whips... I do a lot of experimenting, and my faves are the VHF Hi, UHF, and 700.800/900 whips...

Thanks for the response, milf. And if I ever decide to part with some antennas or other gear, I'll send you a PM.

 

[Gunmetal]

Roof mount them, or on the side of the van slightly below the roof.