Another Newbie Antenna Question

[NonHyphenated American]

If I am running a GMRS radio, mostly likely going to be a Midland MXT275 15w, with a CB; can both be on and not interfere with the other if the antennas are on opposite sides of the vehicle? Also, does having a CB antenna close to the AM/FM antenna get any interference if the radio is not on AM or FM? I mostly listen to satellite anyway. I plan on running my cables through the firewall. Will both antenna cables cause any interference running next together?

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[Radio Guy]

If I am running a GMRS radio, mostly likely going to be a Midland MXT275 15w, with a CB; can both be on and not interfere with the other if the antennas are on opposite sides of the vehicle? Also, does having a CB antenna close to the AM/FM antenna get any interference if the radio is not on AM or FM? I mostly listen to satellite anyway. I plan on running my cables through the firewall. Will both antenna cables cause any interference running next together?

The GMRS and CB radios will not know each other exists when transmitting, even if their antennas were just a few inches apart. I have not seen a CB or GMRS radio interfere with an AM/FM radio from transmitting but any time you get antennas close to each other it changes their radiation pattern, so a CB antenna on the same side and close to the stock AM/FM antenna could change their directional characteristics some. In this case it might be better to put the small GMRS antenna near the AM/FM antenna and the CB on the drivers side.

 

[kg4wsv]

If the coax isn't garbage, the signals will be shielded while on the coax.

The fundamental distance to think about with antennas is an integer multiple of 1/4 the wavelength - e.g. 1/4, 1/2, 3/4 wavelengths. The wavelength of GMRS is about 7", so if your GMRS antenna is 7" from the CB antenna or FM antenna, the oher antenna will affect the radiation pattern of the GMRS antenna. It's best if you can keep them at least a couple wavelengths apart. But vehicle antenna mounting is a whole set of compromises anyway, so do what you can and see how it works.

 

[Radio Guy]

If the coax isn't garbage, the signals will be shielded while on the coax.

The fundamental distance to think about with antennas is an integer multiple of 1/4 the wavelength - e.g. 1/4, 1/2, 3/4 wavelengths. The wavelength of GMRS is about 7", so if your GMRS antenna is 7" from the CB antenna or FM antenna, the oher antenna will affect the radiation pattern of the GMRS antenna. It's best if you can keep them at least a couple wavelengths apart. But vehicle antenna mounting is a whole set of compromises anyway, so do what you can and see how it works.

A wavelength at GMRS is closer to 2ft and a 1/4 wavelength is about 6". If you stick a GMRS whip about 6" from a vertical mass of metal like another antenna it can make a 2 element beam with most of the signal going away from the metal mass. Even at 1 wavelength or 2ft away you will get some noticeable pattern changes.

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