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   Home   Help Search  
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Author Topic: 6 meter FM whip  (Read 1752 times)
KG4WOA
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Posts: 18




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« on: December 04, 2004, 05:03:19 PM »

I am looking to build a 6 meter whip for FM mobile use. Sitting in the corner is an unused CB stainless whip, off a K40 antenna. I also have a mount from an Opek VU-1501 2/70 antenna (PL-259 mount). I'm not sure if the mount has a coil, it probably does.
The whip is more than enough for a 6m quarter wave antenna. I am not sure about the mounting. It will go on the side of my farm pickup,or on the bed rail or toolbox. Any thoughts about mounting?
Also, with the antenna cut for 6m FM, I assume it would resonate on 2 and 440 FM, since there is enough length for both.
I do not have an antenna analyzer, only a SWR meter for checking.
Alan KG4WOA
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AA4PB
Member

Posts: 14360




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« Reply #1 on: December 04, 2004, 06:36:26 PM »

If you remove the coil from the base and cut the whip to 1/4 wavelength on 6M it should work fine. It won't work on 2M and 440 however (unless of course you mean cutting it to be 1/4 wavelength on those frequencies). The whip must be an odd multiple of 1/4 wavelength (i.e. 1/4, 3/4, etc) for any band you want it to work on. For example, a whip cut for 1/4 wavelength on 53 Mhz would also work on 159 Mhz and 477 Mhz.

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Bob  AA4PB
Garrisonville, VA
WA4MJF
Member

Posts: 1003




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« Reply #2 on: December 05, 2004, 11:11:52 AM »

As short as it is, here are some
suggestions that NCDOT Div of Highways
use for their 1/4 whips on 47 MHz.

The center of the roof.

On the side of cab, above where the
door closes.

On the side of the bed.

On the top of tool box.

All of these are on the driver's
side as their is usually more clearance,
except of course the one in the center of
the roof cab.

Use a good quality mount and Spring.

Happy Holidaze!

73 de Ronnie

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KE4SKY
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Posts: 1045


WWW

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« Reply #3 on: December 06, 2004, 11:30:48 AM »

In my experience most 2 meter 5/8 wave whips work fine as 1/4 waves on 6m FM if you have a good shield to ground connection on the vehicle mount (not a mag mount) and the antenna is either centered on the vehicle roof or is high on the vehicle.   Before I upgraded and became interested in HF mobile, I used a Larsen 5/8 wave 2 meter whip with a Comet CF-706 duplexer on both 2 meters and 6m because this gave better isolation than trying to use separate 2m and 6m whips on the same vehicle.  
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WA6BFH
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Posts: 646


WWW

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« Reply #4 on: December 08, 2004, 05:10:29 PM »

Take a look at the below article to see things taht you might do!

www.geocities.com/SiliconValley/2775/6mjant01.html
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KG4WOA
Member

Posts: 18




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« Reply #5 on: December 09, 2004, 03:02:35 PM »

Thanks for all the replies. I checked out the internet site, and found the information very useful. It may be more pratical to use a Larson or Hustler 5/8 wave 2 meter antenna, with a duplexer or since this is on a work truck, individually.

KE4SKY wrote "In my experience most 2 meter 5/8 wave whips work fine as 1/4 waves on 6m FM if you have a good shield to ground connection on the vehicle mount (not a mag mount) and the antenna is either centered on the vehicle roof or is high on the vehicle."

So I have another question. On the coax attached to the mount, I would peel away about one inch of black sheathing, and use some braid for grounding?

Alan  KG4WOA
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KG4WOA
Member

Posts: 18




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« Reply #6 on: December 09, 2004, 03:09:12 PM »

I had another thought. I have a 102" whip sitting and gathering dust. This could be cut for a quarter wave 6 meter FM antenna and mounted on a spring.
I assume I would have to factor in the spring length but am not sure if I would not need a tuner or matching network. Any thoughts? Thanks again.   Alan  KG4WOA
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KE4SKY
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Posts: 1045


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« Reply #7 on: December 13, 2004, 10:58:23 AM »

Install an NMO "hole" mount through the vehicle roof, about the dome light panel in the head liner, so that you can remove the dome light to access the mount location so that you don't have to pull the headliner.
After you locate and drill the hole with a hole saw, deburr the edges, then sand away the paint for about 1/2" around the hole with coarse sandpaper.  Clean and degrease the exposed sheet metal with a rag and mineral spirits, then coat the bare steel with copper bonding paste or Penetrox before you install the mount.  That will ensure a good ground to the vehicle body metal.
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W0FM
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Posts: 2080




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« Reply #8 on: December 16, 2004, 10:23:39 AM »

A helpful tip.  I have cut a lot of CB and commercial stainless steel whips.  That stuff is hard!  I use a bench mounted grinding wheel to do the cutting and fine tuning.  Much easier that a hack saw or bolt cutters and you de-bur the end at the same time.

73,

Terry, WØFM
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KG4WOA
Member

Posts: 18




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« Reply #9 on: December 18, 2004, 10:43:49 AM »

Thanks for all the replies, good too know there is a helpful group of operators out there ready to lend a hand without fussing.
I have cut to whip to proper length, have it mounted on the spring and mirror mount. Today, I am making a stainless steel bracket for mounting on the toolbox, away from the side. This should help avoid any reflection, and the toolbox should provide a good ground.
Alan  KG4WOA
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