Adventure IQ
Explorer
I am mounting both a cb and ham (kc5yjq) in my wrangler this weekend. Wondering on where to mount the antaneas so they dont interfere with each other....any ideas?
Positioning antaneas
- Thread starter Adventure IQ
- Start date
1911
Expedition Leader
The cb won't interfere with the ham; cb's are weak and ham equipment is much better made and shielded. Ham radios on higher power settings will bleed through on the cb no matter where (how far apart) you put your antennas, because ham radios have so much power and also because cb radios are cheap and most are not shielded well at all. You can help the cb interference a lot by putting some ferrite chokes on the cb antenna coax.
gary in ohio
Explorer
It has nothing to do with weak or high powered signals. It has to do with receiver selectivity. From the original commenters note, I assume he is talking VHF/UHF radio and not HF. While you dont want the antennas touching, a foot or two is all you need. The freq for CB and VHF/UHF freq are apart from each other.
DaveInDenver
Middle Income Semi-Redneck
There is a limit to what Lee is saying. You never, ever, want to let conductive (metal) whips touch if one of them is transmitting regardless if they are completely different types of radios. It's also generally bad if the antennas are very close, for example a few inches.
For a CB transmitting, I wouldn't worry as long as there's a couple of feet between it and a VHF/UHF ham radio. A ham VHF radio front end is only wide enough to hear CB harmonics. For example the NOAA WX stations sit right at the 6th harmonic of 27MHz, so any radio capable of hearing these will have filters that don't provide much blocking against this harmonic. But there's not going to be much energy in the 6th harmonic from a 5W EIRP radio, so as long as the CB antenna does not actually touch the ham antenna your radio shouldn't be hurt by it. It could theoretically be desensitized to a very weak 2m station, though the reality is this would be in the noise compared to your ignition and stuff.
Going the other way, even a 50W VHF radio shouldn't produce enough spurious harmonic interference to upset a CB. My CB doesn't seem to care much about my dual band radio with a hood's width of separation. So my guess is this is a secondary effect, maybe RF getting into the power or something. CB uses AM, which is inherently less noise immune. I bet if you listened to VHF aviation traffic while transmitting with your CB, your ham radio would get some of the same interference, which leads me to suggest that you might need to filter your power or check that you don't have long parallel length of feedline coax.
Like Gary mentions, in the case of an HF rig, all bets are off. CB sits right in the middle of 10m and 12m ham bands, which means there is essentially no isolation. Throwing the CB in a ditch is the preferred solution. In reality putting the antennas on different ends of the truck is about all you can do, but a 100W 10m TX is going to make the CB unhappy.
For a CB transmitting, I wouldn't worry as long as there's a couple of feet between it and a VHF/UHF ham radio. A ham VHF radio front end is only wide enough to hear CB harmonics. For example the NOAA WX stations sit right at the 6th harmonic of 27MHz, so any radio capable of hearing these will have filters that don't provide much blocking against this harmonic. But there's not going to be much energy in the 6th harmonic from a 5W EIRP radio, so as long as the CB antenna does not actually touch the ham antenna your radio shouldn't be hurt by it. It could theoretically be desensitized to a very weak 2m station, though the reality is this would be in the noise compared to your ignition and stuff.
Going the other way, even a 50W VHF radio shouldn't produce enough spurious harmonic interference to upset a CB. My CB doesn't seem to care much about my dual band radio with a hood's width of separation. So my guess is this is a secondary effect, maybe RF getting into the power or something. CB uses AM, which is inherently less noise immune. I bet if you listened to VHF aviation traffic while transmitting with your CB, your ham radio would get some of the same interference, which leads me to suggest that you might need to filter your power or check that you don't have long parallel length of feedline coax.
Like Gary mentions, in the case of an HF rig, all bets are off. CB sits right in the middle of 10m and 12m ham bands, which means there is essentially no isolation. Throwing the CB in a ditch is the preferred solution. In reality putting the antennas on different ends of the truck is about all you can do, but a 100W 10m TX is going to make the CB unhappy.
I'd recommend the mounts that bolt in between the tail light and the tub. I used those on my previous wrangler and they worked awesome. Ham on 1 side and CB on the other. Unfortunately i can't use them on my current wrangler since i have a roof rack whose mounting gets in the way.
1911
Expedition Leader
You may be right about RF getting into the power Dave, all I know is that transmitting 2M on my Yaesu 2800 will break any squelch on the Cobra cb in my 2007 FJC, and the feed lines and power for both radios are completely separate and not parallel. The antennas are several feet apart too (one on the roof, one on the front bumper). The FJC has a pretty well-shielded and grounded electrical system as far as I can tell, i.e. no alternator whine or ignition noise in either radio.
On the other hand, I also have 2M/70cm and cb radios in my 40, which generates a ton of RF interference from the alternator and ignition. The Uniden cb isn't bothered at all by 2M transmissions. My (possibly incorrect) conclusion was that the Uniden cb is much better shielded than the Cobra in the other truck.
I've asked this same question here and never got a definite answer. My roof space is limited so I have 2 NMO mounts (2M and CB) about 8 inches from each other. Both work fine and I've had zero problems. Sure the 2m breaks the squelch of the cb but it's no big deal.
If I run my Larsen 150, 2m antenna I pill my cb antenna because the 150 is a big whip and can be flexed to touch the cb antenna. If I need to run both I run my 1/4 wave 2m antenna and my standard cb antenna which is about the same length but much stiffer than the 1/4 wave.
If I run my Larsen 150, 2m antenna I pill my cb antenna because the 150 is a big whip and can be flexed to touch the cb antenna. If I need to run both I run my 1/4 wave 2m antenna and my standard cb antenna which is about the same length but much stiffer than the 1/4 wave.