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Author Topic: mounting mulitple antennas on roof of truck  (Read 3578 times)
KB8WPD
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« on: January 17, 2012, 12:50:32 PM »

Hey all, I am just getting back into HAM radio after a long break. Grin I am really excited about setting up a cool mobile rig in my F-250 crew cab.  It has a large roof and I am not worried about drilling holes.  My question is, how far apart do antennas need to be from each other?  I plan to istall CB (I still use CB and can be helpful on road trips) and a 2m/440 rig.  So that is 2 antennas.  I am also considering a 6m or 220 rig as well.  This would be added later so I am not planning a tri-band radio.  Is there enough room for 3 antennas on the roof or the truck or will they interfere with each other?  I could put the 220 or the 2m/440 on a front fender?  The bed and stake pockets are not available as I haul things with this truck and sometimes have a topper on the truck.  Please tell me how you would mount multiple antennas.  Thanks!

Kevin
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G8YMW
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« Reply #1 on: January 17, 2012, 01:59:06 PM »

My own thoughts are put 2/70 antenna on the roof. VHF (and even more so 70 cms) need to be as high as you can get and will not be too long (1 metre for a 1/2 wave on 2 and 2*5/8 on 70). I think I'd put the CB on the passenger side front wing. I dont know which CB whip you will be using but if its a full length 1/4 wave or 7ft Firestick then you will have to consider what you're going to hit
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73 de Tony
Sent by WW2 Royal Navy signal lamp
KB8WPD
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« Reply #2 on: January 17, 2012, 02:32:43 PM »

I have a 4' K40 fiberglass whip that I plan to use for the CB, but I could use something else if someone has any strong recommendations.  I thought the CB would need the largest ground plane so it would need to be on the roof.  Is there a problem with putting both 2m and CB on the roof?
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G8YMW
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« Reply #3 on: January 17, 2012, 04:11:02 PM »

No probs at all, Kevin. I have a DX27 and a 6/2/70 whip on my car's roof  and have not noticed any problems with radiation pattern. Your CB whip is only 9" longer than the dual band aerial  thats neither here nor there.
As for alternative CB aerials I suggest borrowing various whips and "suck it and see". The DX27, or Sirio Hi power 4000 are as good as it gets for mobile, the full length 1/4 wave and big Firestick are probably a bit OTT for on the move (OK for static mobile)

Cheers Tony
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73 de Tony
Sent by WW2 Royal Navy signal lamp
KB8WPD
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« Reply #4 on: January 17, 2012, 06:27:33 PM »

Thanks Tony.  I'll probably mount both on the roof then.  I'm not up to speed on the lingo yet though so can you tell me what a DX27 is?  Also, what is OTT?  Thanks.
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G8YMW
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« Reply #5 on: January 18, 2012, 02:51:41 AM »

OTT = Over the top
The DX27 is a helical 5/8 fibreglass whip about 5 1/2 ft long for CB which in my case has the 3/8 UNF screw thread mount (Pretty well standard for HF)
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73 de Tony
Sent by WW2 Royal Navy signal lamp
KB8WPD
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« Reply #6 on: January 18, 2012, 05:25:29 AM »

Thanks Tony.  Are DX27s being made anymore?  I did a quick search and one website I found said those antennas were made in the 80s.  Where would I find one, ebay?  Also does anyone sell the Sirio here in the US or do you have to import one from the UK?  The only ones I found were all UK websites.  Thanks!
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K5LXP
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« Reply #7 on: January 18, 2012, 06:24:55 AM »

Quote from:  link=topic=80363.msg569002#msg569002 date=1326833432
I am not worried about drilling holes.

You don't hear that too often.


Quote
Is there enough room for 3 antennas on the roof or the truck or will they interfere with each other?

I have twice that many on the roof of an S-10.  There is some interaction and the more distance between them the better, but you'll have plenty of room for what you want do do.  Maybe put a couple extra mounts up there for "future expansion" while you're at it.


> Please tell me how you would mount multiple antennas. 

Pick a spot, being mindful of any support ribs underneath, and drill the hole.  Repeat as necessary.  Depending on which pillar you want to bring the coax down you probably won't need to mess with the headliner.  I use a 10' piece of electrician's fish tape through the hole to pull the coax through.


Mark K5LXP
Albuquerque, NM
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KB8WPD
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« Reply #8 on: January 18, 2012, 06:57:21 AM »

Nope, drilling holes is no big deal.  I have 217,000 miles on this truck.  I plan to drive it another 300,000.  I never plan to sell it.  What are a few holes??? Grin  I want the best signal I can get!
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K3GM
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« Reply #9 on: January 18, 2012, 09:11:19 AM »

Hey Kevin.  I have two NMO mounts in the roof of my Tahoe.  In my case they are inline to the direction of travel as opposed to side by side.  I have the mounts located about 2.5' apart.  I mount an assortment of antenna on them, but typically there's a 70cm/2m/6m whip up front, and a 10m Larsen whip in the rear.  Note the term "whip".  These are not spiral wound loaded hamsticks, but light stainless whips which yield to overhead branches.  Use of anything sout or stiff risks sheet metal damage.  Mine have been on for years, and have been fine aside from an occasionalbent whip.  You can see pictures of my installation on K0BG's gallery site.
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KE7VUX
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« Reply #10 on: January 18, 2012, 09:17:37 AM »

http://www.tmcom.com/~tsm1/gallery2/main.php?g2_itemId=90787
http://www.tmcom.com/~tsm1/gallery2/main.php?g2_itemId=90792

I mounted the CB antenna in the center, just behind the windshield.  On my 100" WB, that puts the 11m antenna about even front to back, with the hood and the roof, and as much side to side groundplane as I can manage.

I mounted the hamstick on the LF corner of the roof - I wanted it high, but also needed to be able to lay it down.  This location lets me lay the antenna down alongside the spare tire, and it's also handy for me to reach out the window and fold it over.

On the opposite (passenger) side, I put a 2m antenna, arranged so it has a full 19" of metal all around it.

Works well.

Later, I put a second VHF antenna on the driver's rear of the roof, again, 19" from the edges, but also as far from the first as I could manage.

I used the second (rear) antenna for a 25w APRS station, while the front antenna is for the 65w VHF voice station.

I found that I had to bump the squelch up on the CB just a bit above "normal" - if I adjusted it just to where the background noise goes away, when I would key the VHF radio I would get some noise out of the CB.  Another smidge of squelch cured it.

Operating 100w HF, however, did some unpleasant things to the CB. Cheesy
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