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Author Topic: MFJ telescoping antennas - Make good mobile whips?  (Read 4283 times)
WN2C
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Posts: 440




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« on: September 09, 2012, 11:53:55 AM »

I was thinking of puting a ball mount on my truck and using the SGC 237 coupler instead of going with a screwdriver (the 237 I have) but I have been told that using a 108" whip I may not get to 40 meters.  Then I started looking at other options and found the MFJ 1977 and 1979 - a 12 ft and 17 ft telescoping whip.  Has any one used these? Will they stand up to being on a vehicle driven at 75 mph?  I know that I can't use the 17 footer on the highway fully extended but the 12 footer I might.

on a side note,
Allan, k0bg what are you using that is 14 feet?

Rick wn2c
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K0JEG
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« Reply #1 on: September 09, 2012, 12:15:23 PM »

Absolutely not! They will not even tolerate being held horizontally for any length of time. I'm sure they will rust easily too.

They are very good for portable use though.
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K0BG
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« Reply #2 on: September 09, 2012, 02:13:42 PM »

It was only 13.5 feet! I used a GLA mast, but even though Main is now selling GLA products, they're hard to come by. Not to worry, however.

Wilson makes 3/8x24 threaded masts, and they also sell a 3/8x24 coupling which you almost can't find elsewhere. They're 6 inches to 4 feet depending on the model. Along with a heavy-duty spring, the overall length, mount and all, is about 13.5 feet. Remembering that radiation resistance is a square function of the length, the difference between an 8 foot CB whip, and a 13.5 foot one is about 3 to 5 dB on 20 meters, depending on how well, and where you mount it.

The question remains, can you use the height? If you can't, the use a shorter mast, and a cap hat.

By the way, I echo the comment about the MFJ mast. The longer one will indeed fail if held horizontal for too long of a time. Good for testing, but that's about all!
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W5DXP
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« Reply #3 on: September 10, 2012, 06:29:14 AM »

Will they stand up to being on a vehicle driven at 75 mph?

A better solution would be a CB whip with a Hustler 4 foot bottom section under it. I once ran a 12 foot mobile whip like that driven by an SG-230. It worked well for 20m-10m and I did make a few 40m contacts with it. I estimated that it was one S-unit down from my screwdriver on 40m.
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
WN2C
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Posts: 440




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« Reply #4 on: September 10, 2012, 10:57:55 AM »

Thanks for the replies.  I should have put in my original post that the vehicle is a 2006 Chevy Sierra w/ a cap or camper shell. I hadn't thought about the Hustler mast.  I have one of those too along with some of the resonators. I guess I'll have to get a spring so it will lay back some as I am driving.  I'll probably have to guy it so it don't go back to far.  How good is the Hustler ball mount?  Should I be looking for something better?  My main thing is to be able to get down to 40 meters.  I am not worrying about 75 or even 160.  
Like Don Johnson said, "ground, ground and ground some more" and "hf mobile is not easy, it takes a lot of work (to get it to work properly) and a lot more work to keep it working."  I had one of his screw driver antennas, worked great for me.  I am planning on taking a road trip this November back east and was hoping to have hf as there are no contacts on 2/440.  Did that last year and had 2 short QSOs for the entire trip!
Again thanks for the help!!

de Rick wn2c
« Last Edit: September 10, 2012, 11:08:52 AM by WN2C » Logged
KE5PPH
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Posts: 73




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« Reply #5 on: September 10, 2012, 07:26:25 PM »

On the ball mount, I guess it depends on how old it is. they just don't make'em like they used to.  Check Breedlove or geotool.
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M6GOM
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« Reply #6 on: September 12, 2012, 05:20:19 PM »

I was thinking of puting a ball mount on my truck and using the SGC 237 coupler instead of going with a screwdriver (the 237 I have) but I have been told that using a 108" whip I may not get to 40 meters. 

I'd hope you would. 108" is 30" longer than the whip on my Little Tarheel and that'll do 80m.
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W5DXP
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« Reply #7 on: September 12, 2012, 06:26:06 PM »

108" is 30" longer than the whip on my Little Tarheel and that'll do 80m.

But his 108" whip doesn't have a loading coil - just an autotuner at the base.
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
KA4NMA
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Posts: 327




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« Reply #8 on: September 22, 2012, 08:11:28 PM »

Check out some of the mast at dx enginering
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