Antenna Spacing

[Tom Stefanac]

I know I know.. the more antenna's the better, it is best to have a good 75 watt 2m radio strictly for simplex with a nice 5/8 whip and a dual-bander so you can listen to skywarn and be ready to report without interrupting your simplex stuff. You probably should also have something else dedicated to APRS and a nice big Wilson 1000 or 5000 for the CB. You might even have a few scanners, one for emergency services and another for EMWIN decoding and wx band scanning. Then of course it is nice to have a good Wilson cellular antenna to pull signal like mad (with a 3 watt amp under the seat). Optionally a satellite dish can be useful to collect rain and on occasion provide entertainment and if you are really into it, why not just throw on two good HF antennas, maybe one for 20 meters and the other for a band of your choice.

Oh I almost forgot, you still need room for that 2.4 gig Wi-Fi antenna and probably should use something external for that FRS/GMRS radio. Oh and can’t forget the weather station transmitters either!

Do you guys see where I am going with this?

Has anyone ever had an issue where they have killed the RX on any of their equipment? I don't mean de-sensitized it, I mean burnt out a diode or connector pin from pure RF feeding in.

Last year I killed the RX on a 250D scanner by keying up 50 watts UHF. The antennas were UHF 1/4 wave apart, in fact they were 1/2 a wave VHF apart (~1m). Yet I still cooked the poor thing and reception on all the bands is pretty poor with 700 meg - 1.3 gig suffering the most.

With roof space on most chase vehicles at a premium it is easy to see why cooking stuff becomes a concern, in particular amateur gear and scanners. I personally have not been able to cook the CB, cellular or wi-fi stuff yet but there is always a first I am sure!

So, does anyone have bad experiences or similar concerns? I see some guys with antennas like 2 inches apart LOL but it is not RF, what if they touch when one is keyed up? LOLOLOL

 

[Andrew Herron]

I'm going to forward this post to my father. He's got 5 antennas on his truck without issue. I'll get back to you by Monday with his setup and recommendations.

 

[Tim Stoecklein]

I'd say you have too many antennas, but that's just me Really though, I've not even noticed an issue with the distance between antennas being more than a couple of feet. I have experienced some desens on my 2m a couple of times, but that was running HF at 100watts on 20m. I rarely even hear a click on my scanner (if it's in there) when I key up my dual-bander at 50watts.

I'd say it depends more on the sensitivity of your equipments' receivers than it does with antenna proximity. Good luck with the porcupine farm!

 

[Mike McDonald]

I used to drive a Suburban that had 8 antennas on the roof. Now I have a quad cab pickup with 5. Occasional intermod is a problem, but that's the only problem I've had. I know a couple of people that had direction finding antennas which use a diodes in the switching circuitry, and the diodes were blown. In those cases, though, I think they had the DF antennas too close to the transmitting antennas.

The antennas will influence the radiation pattern of each other. But trying to optimize placement to least affect radiation patterns is pretty futile. Keeping them as far apart as possible, but still providing some ground plane around them is the best one can do.

Mike/K0LPM

 

[Tom Stefanac]

Thanks guys!

No I don't have an antenna farm on the vehicle, I only have the Wilson 1000 CB whip, 5/8 2m whip and dual band whip. The scanner antenna is a Hustler BNC whip, other than that I only have a small 301 Wilson Cellular Antenna (no amp).

Would be nice to have all the other stuff but how much of it would I really use? Probably not much! The laptop, GPS and cell phone provide most of the info your eyes cannot.

But getting back to burning up stuff, I guess the scanner taught me a lesson about spacing and input. The HAM radio gear does not react on TX but the scanners will click on anything above 50 MHz as long as I am TXing above 50 MHz.

If I key up anywhere on the 2m band it will kill the cell phone data connection. The dual band antenna has its 1/4 wave 2m section between the base and capacitor/coil, the UHF 5/8 section is above that. The Wilson 301 is only about 12 inches tall and sits 1 inch away from the 2m section of the antenna. It will kill the data stream if I use more than 15 watts, but even the full 55 watts will not kill a voice conversation on the phone.

 

[John Diel]

I have 4 antenna on a 2000 Explorer. They are about 12 inches apart. Dual band 5/8, VHF 5/8 and 2 cell. No issues on any of them.

 

[Tim Stoecklein]

I'm not sure if you spaced them closely for the photograph or not, but if that's your usual position I'd definitely space them further apart than shown.

I'd really be interested to hear why the data connection is interrupted if you have the antennas spread further apart than that.

 

[David Drummond]

Be sure to post pictures of the big dents in your car or broken side glass when the first semi you pass going the other way at high speed blows them off

Seriously though. Stick your ham antenna dead center. Put your CB antenna back on the truck and stick the cell antenna center about halfway between the ham and the windshield.

 

[Brad Berry]

When I worked for a Motorola dealer doing installs, Mother M recommended 18" on center for minimum spacing. I do mine this way, and have had no problem.

 

[Andrew Herron]

Be sure to post pictures of the big dents in your car or broken side glass when the first semi you pass going the other way at high speed blows them off

No joke, happened to my dad when he was vacationing in the family car. The semi ripped the mag mount off the top and left a huge scratch.

 

[mrobinett]

Yup, me too, last March near Bartlesville, OK. It was a Wilson Trucker Cell antenna on two 5 inch mag mounts, dump truck passed with about a 25mph cross wind, blew it off, it reached the end of its "tether" and slammed into the left rear quarter panel above the tire, nice dent!

 

[Bart_Comstock]

I also had the same thing happen to me. To solve the problem I took some zip ties and used them to secure the antennas to my luggage rack on the roof so that they don't move at all. Also my jeep is dedicated solely to chasing so I tend to just not ever remove the antennas and thus it isn't a hassle for me to constantly re-secure them. Of course this isn't an option on all vehicles, but if you use mag mounts and have a vehicle with a rack on the roof might as well save the pain of a nasty dent or scratch or busted window and give the zip ties a try. As far as their spacing on my roof. I have them at opposite corners so they are about 3-4ft apart. I have 3 in total.

Man, just look at that great paint and shiny clear coat!

 

[david diehl]

WE were just talking on this in a General Class that I am taking.
You will have a problem with that much Equiptment on a VEhicle.
You need a switch that will shut off all receivers when you transmit a radio that is pushing that kind of wattage.
but I will say. That is way too much Radios in a vehicle.
I only use a Dual band IC-2720, and a Radio shack CB for WEather band, Laptop uses a Cingular wireless air card.
No Scanner That way I don't hear of all the sherriff-nadoes when I am chasing

 

[Shawn Scovel]

hmm, this is kinda weird for me.. I seem to have problems getting a lip mount to stay on at 70 mph vs the magnet. Actually happened to me the other day when i was on the interstate, i herd a mighty THUD, pulled off and found out my magnet antenna stayed and the 4 allen screws backed off on the lip mount, causing it to fall.

-Shawn

 

[David Drummond]

Good ol' Motorola NMO mounts.....best of the best!