Placement of more than 1 Mag Mount antenna on car roof.

[JoshuaHufford]

Getting ready to do a railfan (train watching) trip this weekend, and I will probably have up to 3 antennas on the roof, all mag mount, 1 for voice (160Mhz) hooked to a scanner, and 2 for ATCS (896-952Mhz).

I've always read that mag mount antennas work best when in the center of the vehicle, but what about when you have more than 1? Should I put them as close together as possible in the center? Space them out? What is best?

Thanks!

 

[ladn]

I'd try for some spacing between the antennas to mitigate interference.

The center of the roof is technically the best location, especially for transmit antennas, but I doubt you will notice any received signal degradation with the antennas spaced a bit apart. Put the 160 MHz antenna closest to the center (since it requires the largest ground plane area) and the ATCS antennas on either side.

 

[w1av]

I have an old Larsen dual band ham antenna (vhf/uhf) that is in center of roof of my SUV. I actually get BETTER reception mobile on some frequencies than I get from my base station. Roof center is the best. The antenna is very old....bought it back in the 90's. Was originally a trunk lip mount. I used to have a Chevy Caravan with 3 antennae on roof.... I just separated them all equally and never had problem.

 

[KB4MSZ]

I drive a V6 powered porcupine. Believe me, it works ok.

 

[mmckenna]

Without going into too much detail, placing antennas too close together can make them directional. An antenna of similar or taller size can act like a reflector and impact performance. Unlikely you'd really notice with a scanner, but it's something to consider. Sometimes you can use it to your advantage if you are attempting to make a radiation pattern slightly directional.

Getting a 1/4 wave length of ground plane under the antennas is all you need. At 160MHz, you'll want about 18 inches in radius around the base of the VHF antenna.
For the 800/900MHz stuff, you only need 3 inches.

Shouldn't be hard to get that on any hard top vehicle.

 

[JoshuaHufford]

Thanks!

 

[WRCM]

I drive a V6 powered porcupine. Believe me, it works ok.

I used to drive a V6 powered porcupine: a 1970 Jeepster Commando with the Dauntless V6 and radios covering 160 Meters to 70cm.