I plan to install a 2 meter radio in my 1980 CJ5 Jeep (softtop). My plan
is to construct a mount that will attach to my rear tire mount. Because
this will be a custom mount, I can have the base of the antenna even with
the top of the spare tire, or I can elevate it some for greater height. I
use this Jeep only in mountain areas. Here are some of my questions:

1. What is the "best" 2 meter antenna type for me (I don't need a dual
bander. I will only use 2 meters). I know that a 5/8 whip will have
the best gain, but I have seen some comments that a 1/4 wave may work better
in the mountains, because of the angles involved. Yet, I know that a 1/4
wave needs a good ground plane, which a softop probably will not do very
well. It would seem that with a 1/4 wave, I would want the base of the
antenna at or near the top of the Jeep. I am also aware of a colinear
antenna, but that would be quite tall for me !!

2. Is it best to have the antenna element fully above the top of the top of
the Jeep ?

3. If I use a spring to offer some protection for the whip, doesn't the
spring add to the length of the antenna, and I would have to tune the whip
for resonance ?

4. What is the best (maybe strongest?) mount type ? I am accustomed to
the 3/8" - 24 type stud mount. It seems strong to me. What are the
advantages of the NMO and other mount types for my purpose ?

5. After choosing the antenna type ( 1/4 wave, 5/8 wave / etc) what is
the best antenna ? Larsen, Diamond. Other ?

---------------------------------

Thanks for any comments and advice, based on actual experience.

73 de Jim K4PYT

 

On Fri, 4 Jan 2008 17:08:10 -0500, "James" <jnipperxxx@nospamfdn.com>
wrote:

>1. What is the "best" 2 meter antenna type for me (I don't need a dual
>bander. I will only use 2 meters).

Hi Jim,

If that is asking for a manufacturer recommendation, I will leave that
to others.

>I know that a 5/8 whip will have
>the best gain, but I have seen some comments that a 1/4 wave may work better
>in the mountains, because of the angles involved.

Either works fine. Mountains are immaterial unless you are trying to
work off the pointy end of the vertical (even then, there is no
difference they both provide nulls). There is certainly a lower
directivity with higher angles, but higher angles also suggest closer
proximity. Any proximity that allows you to "see" the source would
also allow you to talk to the source. You don't need any
extraordinary amount of gain/power to accomplish that when a handheld
can talk to the space shuttle.

>Yet, I know that a 1/4
>wave needs a good ground plane, which a softop probably will not do very
>well.

So would a 5/8ths. You may be tempted with halfwaves (no ground plane
required). Take care, they can be wildly mistuned by nearby metal
and/or coax length, or any number of other considerations. This
follows the rule: no such thing as a free lunch.

> It would seem that with a 1/4 wave, I would want the base of the
>antenna at or near the top of the Jeep. I am also aware of a colinear
>antenna, but that would be quite tall for me !!

So stick with a single element. Gain is not all that it is cracked up
to be. Your intended mounting position will work just fine.

>2. Is it best to have the antenna element fully above the top of the top of
>the Jeep ?

If it were a hard top, then mounted dead center would be best. You
aren't likely to notice any difference anyway (and you don't have a
hard top).

>3. If I use a spring to offer some protection for the whip, doesn't the
>spring add to the length of the antenna, and I would have to tune the whip
>for resonance ?

Ya sure, you betcha. Buy a whip that is springy in its own right
(maybe using piano wire - this suggestion will probably attract flack,
just make it thicker wire).

>4. What is the best (maybe strongest?) mount type ? I am accustomed to
>the 3/8" - 24 type stud mount. It seems strong to me. What are the
>advantages of the NMO and other mount types for my purpose ?

All very fine. You can get by with less, but what is important is a
tight weather seal.

>5. After choosing the antenna type ( 1/4 wave, 5/8 wave / etc) what is
>the best antenna ? Larsen, Diamond. Other ?

All of the above.

73's
Richard Clark, KB7QHC

 

James wrote:

> ...
> Thanks for any comments and advice, based on actual experience.
>
> 73 de Jim K4PYT

Having been the owner of a CJ5 back in the 70's, I'd leave the soft-top
alone, leaks bother me. Darn cover leaked air so bad it challenged the
heater and won in cold/snow country--easily! Actually, wasn't that
great even for California winters!

A pipe/tubing mounted to the bumper (are the bumpers still metal?) and
one of the commercial 1/2 or 5/8 sounds good.

One of the helical wound fiberglass will get you going, remember, it
won't be the last antenna you buy in life. Better yet, construct it
yourself off some freely shared plans on the internet ...

Others recommendations may differ ... your choice. I'd just leave the
soft-top alone ...

Regards,
JS

 

John, thanks for the input. But, since I have had the softop since 1980 and
love it, I think I will keep it. That is 28 years of being satisfied.
Why mess up a good thing ?

73 de JIm K4PYT

 

James wrote:
> John, thanks for the input. But, since I have had the softop since 1980 and
> love it, I think I will keep it. That is 28 years of being satisfied.
> Why mess up a good thing ?
>
> 73 de JIm K4PYT

James:

ABSOLUTELY MAN!

Have always kept a 4WD myself, jeeps, IH scouts, ford broncos, chevy 4WD
pickup, now a ford explorer--just NO MORE SOFT-TOPS. <LOL>

You could go mirror mount(s) also ...

Regards,
JS

 

James wrote:

> I plan to install a 2 meter radio in my 1980 CJ5 Jeep (softtop). My
> plan
> is to construct a mount that will attach to my rear tire mount. Because
> this will be a custom mount, I can have the base of the antenna even with
> the top of the spare tire, or I can elevate it some for greater height. I
> use this Jeep only in mountain areas. Here are some of my questions:
>
> 1. What is the "best" 2 meter antenna type for me (I don't need a dual
> bander. I will only use 2 meters). I know that a 5/8 whip will
> have the best gain, but I have seen some comments that a 1/4 wave may work
> better
> in the mountains, because of the angles involved. Yet, I know that a
> 1/4 wave needs a good ground plane, which a softop probably will not do
> very
> well. It would seem that with a 1/4 wave, I would want the base of the
> antenna at or near the top of the Jeep. I am also aware of a colinear
> antenna, but that would be quite tall for me !!

Based on mounting a lot of two-way radios in logging trucks in my younger
years, I suggest mechanical strength is a prime consideration, and that if
you are driving on unpaved roads the radiation pattern will vary anyway
from bouncing around on the roads.

I suggest a Larsen 5/8 wave antenna in either NMO or 3/8 in hole mounts.
Personally I prefer the NMO, but you need a 3/4 in hole saw unless you use
one of the available "L" brackets. (Which come in both variants). I suggest
the Larsen because it's tough. I know at least one logger who was still
able to call for help from his overturned pickup with a Larsen on the roof.

As for ground plane, you can probably mount it to the spare wheel bracket or
someplace similar. And while theory says you need to put it in the centre
of a metal roof, you'll be able to communicate very effectively with all
sorts of non-optimum placements. Make it mechanically secure, and out of
the way of opening doors, hatches, windshields or hoods. Keep in mind the
higher up you put it the more trouble you have with the whip hitting things
overhead, like garage lightbulbs.

The other good thing is that the Larsens are easy to unscrew for going
through the car wash after a muddy expedition! And the metal in the antenna
whip is flexible enough you don't need an antenna spring that can come
loose on rough roads.

>
> 2. Is it best to have the antenna element fully above the top of the top
> of the Jeep ?
>
> 3. If I use a spring to offer some protection for the whip, doesn't the
> spring add to the length of the antenna, and I would have to tune the whip
> for resonance ?
>
> 4. What is the best (maybe strongest?) mount type ? I am accustomed
> to
> the 3/8" - 24 type stud mount. It seems strong to me. What are the
> advantages of the NMO and other mount types for my purpose ?

There's no need to go to the weight and heft of a 3/8 24 mount - it's really
designed for heavy (and huge) HF antennas. Either the 3/8 snap in or NMO
mounts work fine for the smaller, lighter VHF antennas. The NMOs also are
very low profile when the antenna itself is unscrewed, and both 1/4 wave
and 5/8 wave antennas can be interchanged with the same style mount.

I have no connection with Larsen other than using them for the past twenty
years and more, including all my vehicles.

Bob, VE7HS

 

"James" <jnipperxxx@nospamfdn.com> schrieb im Newsbeitrag
news:OemdnY9Xh4nUM-PanZ2dnUVZ_v2pnZ2d@comcast.com...
>I plan to install a 2 meter radio in my 1980 CJ5 Jeep (softtop). My
>plan
> is to construct a mount that will attach to my rear tire mount. Because
> this will be a custom mount, I can have the base of the antenna even with
> the top of the spare tire, or I can elevate it some for greater height. I
> use this Jeep only in mountain areas. Here are some of my questions:

That's the best place to install it on this vehicle.

> 2. Is it best to have the antenna element fully above the top of the top
> of
> the Jeep ?

It would be but difficult to realize with a lot of constraints.

> 3. If I use a spring to offer some protection for the whip, doesn't the
> spring add to the length of the antenna, and I would have to tune the whip
> for resonance ?

Yes, you have to add every thing behind the feed point.
Keep in mind that a spring is an extra instability of this antenna, and with
this length isn't necessary

> 4. What is the best (maybe strongest?) mount type ? I am accustomed
> to
> the 3/8" - 24 type stud mount. It seems strong to me. What are the
> advantages of the NMO and other mount types for my purpose ?

In this case I would you recommend to use a 5/8 because the length would be
maybe reach near the top of an installed hardtop then a 1/4.

73 Ralf, DL2MRB

 

Thanks for all the great replies here guys !! Very good points made by all
!!


73 de Jim K4PYT

 

If you haven't committed to one design yet, you might look around for
or fabricate a tail light mount. Basically, the ones I;ve seen unbolt
the tail light, and are a stainless steel plate that has the same hole
patern as the bolts that secure the light. on top is a flap that is
bent forward drilled for the antenna mount. Advantages are, you don't
have to mess with it to change tires, it doesn't move to open the
tailgate (no extra coax to be stuffed somewhere), and if you put it on
the driver's side, it is very unlikely to be in you field of view on a
regular basis. As for sepcific antennas, I'd go for an inexpensive one
as long as reasonable.
Scott
N2WMD

On Fri, 4 Jan 2008 17:08:10 -0500, "James" <jnipperxxx@nospamfdn.com>
wrote:

>I plan to install a 2 meter radio in my 1980 CJ5 Jeep (softtop). My plan
>is to construct a mount that will attach to my rear tire mount. Because
>this will be a custom mount, I can have the base of the antenna even with
>the top of the spare tire, or I can elevate it some for greater height. I
>use this Jeep only in mountain areas. Here are some of my questions:
>
>1. What is the "best" 2 meter antenna type for me (I don't need a dual
>bander. I will only use 2 meters). I know that a 5/8 whip will have
>the best gain, but I have seen some comments that a 1/4 wave may work better
>in the mountains, because of the angles involved. Yet, I know that a 1/4
>wave needs a good ground plane, which a softop probably will not do very
>well. It would seem that with a 1/4 wave, I would want the base of the
>antenna at or near the top of the Jeep. I am also aware of a colinear
>antenna, but that would be quite tall for me !!
>
>2. Is it best to have the antenna element fully above the top of the top of
>the Jeep ?
>
>3. If I use a spring to offer some protection for the whip, doesn't the
>spring add to the length of the antenna, and I would have to tune the whip
>for resonance ?
>
>4. What is the best (maybe strongest?) mount type ? I am accustomed to
>the 3/8" - 24 type stud mount. It seems strong to me. What are the
>advantages of the NMO and other mount types for my purpose ?
>
>5. After choosing the antenna type ( 1/4 wave, 5/8 wave / etc) what is
>the best antenna ? Larsen, Diamond. Other ?
>
>---------------------------------
>
>Thanks for any comments and advice, based on actual experience.
>
>73 de Jim K4PYT
>
>
>
>

 

On Fri, 4 Jan 2008 17:08:10 -0500, "James" <jnipperxxx@nospamfdn.com>
wrote:

>I plan to install a 2 meter radio in my 1980 CJ5 Jeep (softtop). My plan
>is to construct a mount that will attach to my rear tire mount. Because
>this will be a custom mount, I can have the base of the antenna even with
>the top of the spare tire, or I can elevate it some for greater height. I
>use this Jeep only in mountain areas. Here are some of my questions:
>
>1. What is the "best" 2 meter antenna type for me (I don't need a dual
>bander. I will only use 2 meters).

Whatever one you want...

>I know that a 5/8 whip will have
>the best gain, but I have seen some comments that a 1/4 wave may work better
>in the mountains, because of the angles involved. Yet, I know that a 1/4
>wave needs a good ground plane, which a softop probably will not do very
>well. It would seem that with a 1/4 wave, I would want the base of the
>antenna at or near the top of the Jeep. I am also aware of a colinear
>antenna, but that would be quite tall for me !!
>
>2. Is it best to have the antenna element fully above the top of the top of
>the Jeep ?

For a softtop, no. For a (metal) hardtop yes. For a glass hardtop no.

>
>3. If I use a spring to offer some protection for the whip, doesn't the
>spring add to the length of the antenna, and I would have to tune the whip
>for resonance ?

If the spring is part of the antenna, yes. But only use a spring
designed for that particular antenna. Otherwise just make a spring
assembly for the entire mount instead.

>
>4. What is the best (maybe strongest?) mount type ? I am accustomed to
>the 3/8" - 24 type stud mount. It seems strong to me. What are the
>advantages of the NMO and other mount types for my purpose ?

Whatever matches your antenna?

>
>5. After choosing the antenna type ( 1/4 wave, 5/8 wave / etc) what is
>the best antenna ? Larsen, Diamond. Other ?

Didn't you ask that in question 1?

You are a Ham, you should know all about antennas. <g>

>
>---------------------------------
>
>Thanks for any comments and advice, based on actual experience.
>
>73 de Jim K4PYT
>
>
>
>