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Author Topic: Two antennas on the roof  (Read 2506 times)
KF6DBZ
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« on: July 16, 2011, 01:26:40 PM »

Hello,
I use a 2 meter mag mount and a wilson (both wilson) CB mag mount on the roof of the car. I usually put one up and take one down as i change bands. I am using a Icom 706 MIIG radio. The question is can i leave both antennas on the roof of the car about 1 foot apart and leave them both connected straight to the radio? or do i need to add a duplexer?
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K0BG
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« Reply #1 on: July 16, 2011, 03:16:39 PM »

You'll have desense for sure, but little damage should be expected. However, you should mount them as far away from one another as you can.

by the way, mag mounts add all sort of common mode, which may be more bothersome than the closeness of the antennas.
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K5LXP
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« Reply #2 on: July 17, 2011, 07:10:14 AM »

You didn't specify what two bands are being operated.  One is 2M, the other Wilson CB mount is for what, 11M or something else?  Hooked up to a 706 it could be any band.

As Alan points out, desense may be an issue if they're both being operated on the same band.  But if they're not, say 2M and an HF band, you should be fine. 

If the scenario you have is the 2M antenna is hooked up to the V/U port on the 706 and the CB mag mount (band X) antenna is hooked up to the HF port, you can leave both on the roof at the same time.  The 706 isn't a duplex radio, so any potential desense wouldn't be an issue.

One foot separation is kind of close, if for no other reason than if the whips should inadvertently touch each other while you're transmitting, you could do some damage to the radio. 


Mark K5LXP
Albuquerque, NM
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KI4SDY
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« Reply #3 on: July 17, 2011, 08:48:19 AM »

Why not try placing the smaller 2 meter antenna on the trunk or a front or rear fender? That will solve the proximity problem and will have little effect on communications reliability with local repeaters.  Wink

If your in a situation where your trying to make contact on a distant repeater, changing the direction of the vehicle or placing the 2 meter antenna on the roof temporarily will usually take care of it. That is the beauty of magnetic antennas. They can be relocated or removed as needed!  Grin
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KF6DBZ
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« Reply #4 on: July 17, 2011, 03:53:17 PM »

Sorry about that. I use 2 meters and 10 meters. I drive a honda Fit so both antenna will fit on the roof. I just get tired of changing the antennas on the car when i cahnge bands. On a different subject i drove to the top of
Palos verdes today (as i do every weekend) and 10 mjeters was dead. On 2 meters there was very little activity even on sideband. I drove up to point Mugu seding out CQ's all the time on 10 meters and 2 meters sideband and 146.520 and there was only on guy i heard on 2 meters sideband and that was for a contest. I just thought there would be more people on.
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AI4NS
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« Reply #5 on: July 17, 2011, 05:41:26 PM »

Most SSB work on VHF uses a beam, not a vertical. Build a small beam and try that on SSB, and you will be surprised at how much better it works.
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G8YMW
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« Reply #6 on: July 18, 2011, 03:35:44 PM »

For SSB on 2 you need a horizontal aerial and if you are mobile, mobile as opposed to stationary mobile then you need a horizontal omni as in "halo" or if you can manage it, a "Cloverleaf " aka " Big Wheel"
See what this lad did in Oz

http://www.qsl.net/vk3bjm/
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73 de Tony
Windows 10:  Making me profane since March 2017
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