Ham damage to CB antenna

Status
Not open for further replies.

KK4JUG

Member
Premium Subscriber
Joined
Dec 13, 2014
Messages
3,282
Location
GA
I decided this forum (rather than CB) because, overall, I'll probably get a more informed answer.

I spend quite a bit of time on the highway and I'm considering the Midland all-in-the-mic CB radio. Overall, I'm not that crazy about CB but, on the highway, it's usually a better source of information than ham radio.

I don't want to permanently install a CB antenna on the vehicle because I won't be using it in town, only on the open road. I know many are anti-magnetic antenna people out there but that's probably what I use.

Anyway, what's it gonna take to blow out the CB radio if I transmit on the Yaesu FT-8900R? I usually keep it on 50 watts on the road. I don't have privileges and won't be using the 10 meter band of the radio. It'll be mostly 2 and .70 meters.
 

Kb2Jpd

Member
Joined
May 6, 2016
Messages
207
Location
New York City, NY
I decided this forum (rather than CB) because, overall, I'll probably get a more informed answer.



I spend quite a bit of time on the highway and I'm considering the Midland all-in-the-mic CB radio. Overall, I'm not that crazy about CB but, on the highway, it's usually a better source of information than ham radio.



I don't want to permanently install a CB antenna on the vehicle because I won't be using it in town, only on the open road. I know many are anti-magnetic antenna people out there but that's probably what I use.



Anyway, what's it gonna take to blow out the CB radio if I transmit on the Yaesu FT-8900R? I usually keep it on 50 watts on the road. I don't have privileges and won't be using the 10 meter band of the radio. It'll be mostly 2 and .70 meters.

A well designed CB radio will not be affected by a vhf/UHF radio. If you are using a modern CB radio, the front end is protected with protection diodes that conduct whenever the RF voltage exceeds a safe level. The other thing is the frequency. 144 and 440 Mhz is much higher than 27 MHZ. Your antenna for the CB will attenuate the vhf uhf signal then the diodes will protect the front end.

Adam Kb2Jpd


Sent from my iPhone using Tapatalk
 

kb5udf

Member
Premium Subscriber
Joined
Apr 7, 2004
Messages
578
Location
Louisiana
Should be fine

Keep the antennas 2 feet apart or so and you should be fine. Many of us have done it for years
and your CB and 2m/70cm should happily co-exist.
 

KK4JUG

Member
Premium Subscriber
Joined
Dec 13, 2014
Messages
3,282
Location
GA
.......and that's why I posted it here. I got the information I wanted. Thanks, guys.
 

W8RMH

Feed Provider Since 2012
Joined
Jan 4, 2009
Messages
8,112
Location
Grove City, OH (A Bearcat not a Buckeye)
When I was a LEO back in the 70s we had CBs at 27 MHz. along with the 39 MHz. and 154 MHz. mobile police radios and later UHF body packs and never had any issues. The CB antenna was a lip mount on the trunk lid and the 39/154 was in the middle of the roof or trunk lid or a whip ball mount on the left rear fender.
 

Seven-Delta-FortyOne

Member
Premium Subscriber
Joined
Apr 24, 2014
Messages
229
Location
The Emerald Triangle
I know you already got the answer, but I have a FireStik CB and a 1/4 wave VHF/UHF on the head-ache rack on my flatbed.

When I key up on the VHF, the signal meter on the CB shows an S-9 signal, but there is no audio whatsoever. There has also been no problem with the CB.

On my last truck, I had a 5/8 wave VHF, a 5/8 wave UHF, and the Fire-Stik, and the VHF did the same thing. Again, never a problem with he CB.

With all the radios I have in the truck, I have no idea how to completely eliminate desence. But the little bit that is there, doesn't seem to be a problem.

As an aside, in some of the larger cities that I visit, I see police and even fire/rescue rigs, with so many antennas that the roof looks like a porcupine. I mean, like between 10 and 20. Makes my 5 or 6 look like nothing. I've always wondered what they do about desence.



Delta
 

KK4JUG

Member
Premium Subscriber
Joined
Dec 13, 2014
Messages
3,282
Location
GA
I know you already got the answer, but I have a FireStik CB and a 1/4 wave VHF/UHF on the head-ache rack on my flatbed.

When I key up on the VHF, the signal meter on the CB shows an S-9 signal, but there is no audio whatsoever. There has also been no problem with the CB.

On my last truck, I had a 5/8 wave VHF, a 5/8 wave UHF, and the Fire-Stik, and the VHF did the same thing. Again, never a problem with he CB.

With all the radios I have in the truck, I have no idea how to completely eliminate desence. But the little bit that is there, doesn't seem to be a problem.

As an aside, in some of the larger cities that I visit, I see police and even fire/rescue rigs, with so many antennas that the roof looks like a porcupine. I mean, like between 10 and 20. Makes my 5 or 6 look like nothing. I've always wondered what they do about desence.

Delta
You bring up a good point. This never occurred to me but I help operate a mobile command post that has so many antennae that it attracts porcupines. It's a 40' bus with a flock of radios. There are five 800 mHz trunked radios, three 144/430 mHz ham radios, 1 HF radio, 1 aircraft band radio, one low-band FM radio, one marine band radio plus programmable UHF & VHF radios that we use strictly for public safety frequencies. (In addition, there's 5' satellite dish for 8 satellite phone lines and high-speed Internet with wifi and a DISH satellite receiver.) Each radio has it's own antenna that stays in the ready position (except for the HF). I don't know that we've ever transmitted on all of them at the same time but I know that several have operated simultaneously and I don't recall ever having a problem.
 

mmckenna

I ♥ Ø
Joined
Jul 27, 2005
Messages
13,829
Location
SNCZCA01DS0
A regular/legal CB radio is going to put out 4 watts at best. Most I've tested were actually putting out around 2 or 2.5. Add in coaxial cable losses, and you're going to get something less at the antenna.

Coupling signals between antennas is going to vary depending on the antenna sizes. A 1/4 wave 800MHz antenna isn't going to have much coupling to a CB whip, same for UHF, VHF, etc.

Add in feed line losses on the other radio, and you really are looking at a small amount of power actually making it into the other radio.
Good radios have good filtering. Crappy radios have crappy filtering. That all plays in.

Can you damage a radio by having antennas too close? Sure, but there are a lot of variables. Saying "it's never happened to me, so it's not real" isn't the same as it not being a real issue. Just means that you had good filters protecting you, different amounts of coupling between antennas, different power levels, etc.

I've seen an Icom UHF radio damaged by a dual band amateur radio with an antenna too close. Protection diodes blew out. Easy to fix, but when it's preventable, it's just annoying.

How to big city police cars do it?
Good radios with good filtering. Not amateur/consumer gear.
Proper separation between antennas.
Well planned out placement of antennas, it's not just a random placement, thought often goes into which band antennas go where.
 

SpugEddy

Member
Premium Subscriber
Joined
Oct 4, 2015
Messages
419
Location
Camden County South Jersey
I'm considering the Midland all-in-the-mic CB radio.

Kb2Jpd said:
A well designed CB radio will not be affected by a vhf/UHF radio. If you are using a modern CB radio, the front end is protected with protection diodes that conduct whenever the RF voltage exceeds a safe level.
I have a sneaky suspicion that this Midland all-in-the-mic radio is NOT going to have any
type of front end protection. Probably a CB in it's rawest form. Just my opinion.

Other than that, I have been running a dual radio setup in my Hyundai Veracruz.
GMRS radio and a CB. The antennas are about 2' apart. The GMRS 1/4 wave is
overhead just behind the driver's seat and the CB antenna is closer to the rear
of the vehicle. No problems.
I just switched to an Wouxun KG-UV950P quad-band radio. Used for GMRS and CB
The antennas are in the same place.
 

KK4JUG

Member
Premium Subscriber
Joined
Dec 13, 2014
Messages
3,282
Location
GA
Good, bad or indifferent, I'm sticking with the all-in-one Cobra. Actually, the model number is 75WXST. Suitable radio space is at a premium in my vehicle. It's a '16 Sorento. The radio will only be used during extended highway trips. It will not usually be in the car except at those times.

The antenna for the Yaesu is semi-permanently installed on a luggage rack cross member almost in the middle of the roof, front-to-back and side-to-side.. There is about 2.5' between that antenna and the back of the roof. I'll be using a center-loaded magnetic CB antenna very near the back of the vehicle, probably on one side or the other of the "shark fin."

Although the CB can be useful on the road, I'm not going to bend over backwards to install and maintain it in the car. If it works, it works. If it doesn't, well, I gave it a shot.
 

SpugEddy

Member
Premium Subscriber
Joined
Oct 4, 2015
Messages
419
Location
Camden County South Jersey
I understand completely. My SUV is the same. Very limited space
and having the 2 radios was not very nice. That's why I decided to
go with the Wouxun quad band as it will do 11 meter AM and it also
transmits on those channels.
The CB is used only on road trips. Some really good company can
be found on CB on those late night trips.
Good luck
 

Token

Member
Premium Subscriber
Joined
Jun 18, 2010
Messages
2,151
Location
Mojave Desert, California, USA
Anyway, what's it gonna take to blow out the CB radio if I transmit on the Yaesu FT-8900R? I usually keep it on 50 watts on the road. I don't have privileges and won't be using the 10 meter band of the radio. It'll be mostly 2 and .70 meters.
Really the CB is not in danger in the scenario you have set up. However the 8900R might be. I have known of several 8900Rs that have suffered damage to the 10 meter section from close CB (even at legal powers) or ham 10 meter transmitters.

T!
 

KK4JUG

Member
Premium Subscriber
Joined
Dec 13, 2014
Messages
3,282
Location
GA
I thought about that but since no one else brought it up, I wasn't gonna worry about it. The radio will see almost no use in the next few months on 10m. In reality, use of the band is limited, especially in mobile units. Even so, I would hate to hate to mess up the radio.
 
Status
Not open for further replies.
Top