Minimum distance between scanner antenna and V/U ham ant on truck roof?

[K2GMZ]

What would be a safe minimum distance between a scanner antenna and V/U ham antenna on a truck roof? Don't feel like blowing the front end of my scanners. My thought is like a 2-3ft minimum?

My plan is install 3 NMO mounts, use a Larsen Tri-Band for scanning and Larsen 2/70 for ham. The 3rd NMO will be in case I want throw in a CB, Moto, or whatever.

My though is mount the NMO for the 2/70 as close to the roof dead center as I can but going slightly more toward the front of the roof, mount the other 2 in the rear corners so everything is at least 3ft from each other. Any advise on this would be appreciated.

Thanks!

 

[jparks29]

power output plays a big role...


At the MINIMUM you want to have EACH antenna placed 1/4 wavelength away from each other...

Example... You have one VHF antenna and one UHF antenna, 1/4 wave on VHF would be about 19", UHF would be about 6", so you want about 25" spacing (ideally) between those two antennas..

For scanners, it's a bit different, but try to isolate them, mounting a rx only antenna isn't as critical as a transmitting antenna.. I would probably use a hood mount or something similar if running high power...

 

[Hooligan]

Cool -- your nickname thing reads K2AUX, but your icon thing indicates K2AXU...


The best answer is to separate them all as far apart as possible, not only to try to minimize front-end overload on any receiver(s) but also so that when you're transmitting, other antennas don't end up being passive re-radiators.

Whichever is more important to you -- ham transceiving or scanner monitoring, should normally get the optimum antenna location (center roof of pickup truck).

While scanner-geekery is more important to me than "Fine business, QSL, hi hi" ham radio is, the main VHF/UHF ham transceiver antenna is located atop the roof because of the ground-plane effect, but also because that VHF/UHF ham transceiver has broad-band receive capability too. The scanner is tapped into the 31" AM/FM whip (& it works better than most people expect, including on 800/900MHz). That gives good physical separation, plus the top of the 31" AM/FM whip is lower than the bottom of the VHF/UHF transceive antenna. I mentioned that 'scanner' stuff is more important to me than the ham stuff -- the benefit of this setup is that I can & will often park the dual-band VHF/UHF ham transceiver on two public safety frequencies (such as PD & FD for the community I'm in) or use that setup to receive VHF/UHF signals that are weak on the scanner setup, while the scanner continues to scan/search.

For your third antenna, if you end up with some sort of HF radio like a CB, I'd just go with a bumper-mount or ball-mount in the rear of the vehicle.

If you're concerned about proper spacing for antennas, another issue you might as well look into is EMI/EMC concerns with your car & where you mount the radios, antennas, and coax routing. This can especially be an issue with HF.

And just for the record, I think the Diamond/Comet/Maldol etc. series antennas generally have better performance than Larsens.

 

[K2GMZ]

power output plays a big role...


At the MINIMUM you want to have EACH antenna placed 1/4 wavelength away from each other...

Example... You have one VHF antenna and one UHF antenna, 1/4 wave on VHF would be about 19", UHF would be about 6", so you want about 25" spacing (ideally) between those two antennas..

For scanners, it's a bit different, but try to isolate them, mounting a rx only antenna isn't as critical as a transmitting antenna.. I would probably use a hood mount or something similar if running high power...

Thanks, I thought about a hood mount for the scanner antenna even though I didn't think I would be running a lot of power, just to keep them apart. Or a lip mount on the rear door is an option too...

 

[w8jjr]

This question has been addressed like at least 5 times in the last few weeks.
3 feet min further the better.

Thanks, I thought about a hood mount for the scanner antenna even though I didn't think I would be running a lot of power

Only takes a a couple 100 mw or less to blow the front end

 

[K2GMZ]

Cool -- your nickname thing reads K2AUX, but your icon thing indicates K2AXU...


The best answer is to separate them all as far apart as possible, not only to try to minimize front-end overload on any receiver(s) but also so that when you're transmitting, other antennas don't end up being passive re-radiators.

Whichever is more important to you -- ham transceiving or scanner monitoring, should normally get the optimum antenna location (center roof of pickup truck).

While scanner-geekery is more important to me than "Fine business, QSL, hi hi" ham radio is, the main VHF/UHF ham transceiver antenna is located atop the roof because of the ground-plane effect, but also because that VHF/UHF ham transceiver has broad-band receive capability too. The scanner is tapped into the 31" AM/FM whip (& it works better than most people expect, including on 800/900MHz). That gives good physical separation, plus the top of the 31" AM/FM whip is lower than the bottom of the VHF/UHF transceive antenna. I mentioned that 'scanner' stuff is more important to me than the ham stuff -- the benefit of this setup is that I can & will often park the dual-band VHF/UHF ham transceiver on two public safety frequencies (such as PD & FD for the community I'm in) or use that setup to receive VHF/UHF signals that are weak on the scanner setup, while the scanner continues to scan/search.

For your third antenna, if you end up with some sort of HF radio like a CB, I'd just go with a bumper-mount or ball-mount in the rear of the vehicle.

If you're concerned about proper spacing for antennas, another issue you might as well look into is EMI/EMC concerns with your car & where you mount the radios, antennas, and coax routing. This can especially be an issue with HF.

And just for the record, I think the Diamond/Comet/Maldol etc. series antennas generally have better performance than Larsens.

Yeah, I know on the icon thingy... just been too lazy/busy to fix it

The ground plane effect is exactly the reason for center mounting the V/U ham antenna, its everything else in relation to that, and not tanking a $500 scanner. Don't think I'll ever do HF from the truck, the closest I'll get to that is throwing a CB in for long trips.

 

[K2GMZ]

This question has been addressed like at least 5 times in the last few weeks.
3 feet min further the better.

Only takes a a couple 100 mw or less to blow the front end

Thanks, I'll search for the threads.

 

[K2GMZ]

That brings up another item on my home setup, and might sound like dumb questions, so excuse them.

In my attic I have a Diamond X-50 for V/U op's and a RS Discone for scanning, antennas are about 8 ft apart, both with 9914 Bury Flex Coax, discone goes to an152mhz notch filter then Electroline 8-way splitter. I'm assuming that anything inline will NOT help as a buffer to anything that could harm receivers/scanners? My ham ops will reflect that running no more that 10w. Not an issue in the Phoenix area as most repeaters are easy to ding with low power.

Also does it make a difference from an RF standpoint if the scanners/receiver are off when operating V/U ham gear? I think not