Scanner/VHF/CB Antenna Solutions

Joined
May 10, 2015
Messages
442
Location
San Angelo, TX
#1
Hello Everyone,
I am currently waiting on my 2007 Ford Crown Victoria P71 to be shipped to me. I just purchased a console for it and will get started on the installation once it arrives. I plan to install a BCD536HP, Harris/MACOM M7100 VHF (100watt) radio and a Uniden PRO520XL 4watt CB. I am having trouble thinking of antenna solutions.
I'm wanting to install the NMO CB antenna in the center of the trunk, the NMO 1/4 VHF antenna centered on the roof and a window mount antenna at the very top centered back window. The problem with the window mount is that the window is tinted and well, glass mount antenna's are garbage. I wouldn't be against taking the vehicle to the my local window tinting shop and having them cut a square out of the tint to mount the antenna if that's possible. I was also thinking of doing a trunk lip mount for the scanner, but am unsure about the antenna spacing between the scanner antenna and the CB antenna.
As far as the scanner goes, I am wanting to scan VHF/UHF (Aviation & Public Safety) as well as 800Mhz. Does anyone have any advise or solutions?
 
Joined
Apr 1, 2004
Messages
521
Location
NM
#3
Use the duplexer on the NMO CB antenna, and feed the scanner with it, and put a NMO on the roof, center mounted for the VHF if you plan on transmitting with it.

You're not going to be scanning anything under 30 mhz, a long whip makes an excellent all band scanner antenna, and 4 watts from a CB isnt going to cause any issues into a commercial radio like the harris.

I would be slightly concerned with 100 watts of RF coming off the VHF into the scanner. The duplexer will help cut it down a bit, but its still possible to overload the scanner.
 
Joined
Jul 18, 2014
Messages
8,884
Location
PA
#4
a long whip makes an excellent all band scanner antenna
Not once it gets longer than 3/4-wave; the gain pattern goes vertical rather than horizontal. It will work OK for 6-meter and maybe FM broadcast, but not anything above that, especially UHF/800.

I would be slightly concerned with 100 watts of RF coming off the VHF into the scanner. The duplexer will help cut it down a bit, but its still possible to overload the scanner.
No "slightly" about it; you run a major risk of frying the scanner. The duplexer won't offer any protection, given that VHF is in its passband. I have 500mW feeding into my scanner coax when I key up a 25-watt radio, and a 100W radio could feed 2W or more into your scanner's front end. That is an excellent way to fry it.

Before cennecting your scanner, hook up a decent watt meter to the scanner coax, and key up the 100W radio at full power to see how much power feeds into the scanner coax. You'll probably be surprised.
 
Joined
May 10, 2015
Messages
442
Location
San Angelo, TX
#5
No "slightly" about it; you run a major risk of frying the scanner. The duplexer won't offer any protection, given that VHF is in its passband. I have 500mW feeding into my scanner coax when I key up a 25-watt radio, and a 100W radio could feed 2W or more into your scanner's front end. That is an excellent way to fry it.
So the distance between the trunk (VHF Antenna) and the roof (Scanner Antenna) is not enough distance? If that is the case would buying an antenna switch solve the problem? Could I connect the scanner to a watt meter, then from there to an antenna switch that would switch between the scanner antenna on the roof and a dummy load? That way then I need to transmit on the VHF radio I could switch the scanner to a dummy load.
 
Joined
Aug 26, 2006
Messages
366
Location
Vancouver BC
#6
For Scanner this is my go to preference in a mobile environment, every vehicle from service to personal I have put one of these on and for me it works like a hot damm.I have used it exclusively for close call and picked up from AM all the way to 800 mhz, I have driven thru my Province and and across the Country with it. Its low profile , you could mount wherever there is space.
https://www.wearecb.com/bmaxscan1000-scanner-antenna.html
 
Joined
Nov 1, 2005
Messages
316
Location
JoCo, KS (SoDak native)
#7
scanner/cb

a couple of comments

the duplexer is a possible solution, but.... If the MNO CB antenna has a grounded coil (most do), it will be very deaf above 27 mhz.... on the other hand, if it is a whip with elevated coil, then you may be OK.....

I would just use a trunk lip mount for the scanner. I have done that on several vehicles, the CB doesn't put out enough RF to damage the scanner input.

Just a note, the P71's had non metal trunk lids for several years.....

$.02
 
Joined
May 10, 2015
Messages
442
Location
San Angelo, TX
#8
a couple of comments

the duplexer is a possible solution, but.... If the MNO CB antenna has a grounded coil (most do), it will be very deaf above 27 mhz.... on the other hand, if it is a whip with elevated coil, then you may be OK.....

I would just use a trunk lip mount for the scanner. I have done that on several vehicles, the CB doesn't put out enough RF to damage the scanner input.

Just a note, the P71's had non metal trunk lids for several years.....

$.02
Thank you for the reply,

This is the antenna I plan on using (https://www.theantennafarm.com/catalog/laird-technologies-c27-690) from what I can see it does not have a grounded coil.

My concern is not the CB putting out to much RF, its the 100watt radio putting out to much RF that I am worried about.
 
Joined
Nov 1, 2005
Messages
316
Location
JoCo, KS (SoDak native)
#9
cb/scanner

the antenna you referenced is a DC grounded antennas. it is in the description......

you will not see much isolation on a vehicle if the only separation is horizontal. Putting the scanner antenna on the trunk gives "some" isolation, but at 100watts VHF you will at minimum see desense on the scanner. Whether it does damage is to be determined.....

Do you really need 100watts?

$.02
 
Joined
Sep 30, 2006
Messages
155
Location
Southern California
#10
... and well, glass mount antenna's are garbage....
Not necessarily. I had an Antenna Specialists 2 meter glass mount antenna and it worked just fine. It lasted about 10 years until the dual sided tape and silicone chaulking started to go bad. I simply cleaned the surfaces with denatured alcohol and reattached it with 3M external grade, dual sided "tape". Lasted many more years.
 
Joined
May 10, 2015
Messages
442
Location
San Angelo, TX
#11
the antenna you referenced is a DC grounded antennas. it is in the description......

you will not see much isolation on a vehicle if the only separation is horizontal. Putting the scanner antenna on the trunk gives "some" isolation, but at 100watts VHF you will at minimum see desense on the scanner. Whether it does damage is to be determined.....

Do you really need 100watts?

$.02
Wow... First thing in the description box. Totally looked right over that. As far as needing 100watts, I wont need it most of the time, I could get away with 50. One of the counties I work in is 3000 sq mi, so there will be times where 100watts will be required.

How far apart would the scanner antenna need to be from the radio antenna?
 
Joined
Jun 16, 2013
Messages
3,201
Location
Texas
#13
a couple of comments

the duplexer is a possible solution, but.... If the MNO CB antenna has a grounded coil (most do), it will be very deaf above 27 mhz.... on the other hand, if it is a whip with elevated coil, then you may be OK.....

I would just use a trunk lip mount for the scanner. I have done that on several vehicles, the CB doesn't put out enough RF to damage the scanner input.

Just a note, the P71's had non metal trunk lids for several years.....

$.02
Non-metal? State your source please. It's a well known fact that P71's had aluminum trunk lids for select model years but this is the first I've heard of fiberglass trunk lids.

Sent from my SM-T713 using Tapatalk
 
Joined
Nov 1, 2005
Messages
316
Location
JoCo, KS (SoDak native)
#15
scanner antenna

Since on a car, horizontal separation differences of 3-6 feet are practically the same, it really doesn't make much difference. if you have a short scanner antenna, the roof of car will provide "some" shielding for tthe 100w tx, just don't expect miracles....

$.02
 

FFPM571

Member
Premium Subscriber
Joined
Mar 11, 2003
Messages
1,049
Location
Chicago area
#16
a couple of comments

the duplexer is a possible solution, but.... If the MNO CB antenna has a grounded coil (most do), it will be very deaf above 27 mhz.... on the other hand, if it is a whip with elevated coil, then you may be OK.....

I would just use a trunk lip mount for the scanner. I have done that on several vehicles, the CB doesn't put out enough RF to damage the scanner input.

Just a note, the P71's had non metal trunk lids for several years.....

$.02
Ford PI has not had a aluminum trunk lid since 1997
 

SCPD

Member
Joined
Feb 24, 2001
Messages
65,128
Location
Virginia
#17
Not necessarily. I had an Antenna Specialists 2 meter glass mount antenna and it worked just fine. It lasted about 10 years until the dual sided tape and silicone chaulking started to go bad. I simply cleaned the surfaces with denatured alcohol and reattached it with 3M external grade, dual sided "tape". Lasted many more years.
I had an antenna specialists cellular band antenna years ago... I had to replace it every few months it just kept falling off.
 
Joined
May 10, 2015
Messages
442
Location
San Angelo, TX
#18
I have decided not to put a CB in my vehicle. The console I have does not have room for it. Plus, with putting a scanner in, I will still be able to at least monitor the CB Band. I decided to go with the Larson NMO150/450/800 antenna (https://www.theantennafarm.com/catalog/larsen-nmo150-450-800-1050) for the scanner that will go on the roof of my crown vic. I also decided to go with the Laird QWB144 (https://www.theantennafarm.com/catalog/laird-technologies-qwb144-719) that will be mounted in the center of the trunk for my VHF P25 radio. 95% of the time I will be only monitoring 144-160mhz. When I do transmit, I will mostly transmit in the 2M amateur band at 50watts, but will occasionally need the 100 watts and will occasionally also be transmitting in the 155-158mhz area also at 50 watts , 100watts depending on how far out I am.

I went to go order the ICE RF Protector (model 199) but found that they no longer make it. I have found several different makes and models from protection from 0.5mhz-150mhz, but that is not high enough for the RF Protection I need to the scanner. Can someone point me in the right direction as to where I can find something to protection my scanners front end for RF overload from my VHF radio when I transmit. Everything will be in a console so I wont be able to just disconnect the scanners antenna when I transmit.
 
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