Have been looking around for plans for a 1/2 or 5/8 2 meter mobile
antenna to play with. I have several Iron Horse whips I no longer use
and thought id use them as a starting point for a 5/8 2 meter mobile
whip I could use on my CB mount for most of the time. (I use the CB only
when our RV club travels as a group).


I did a ton of google/bing searches but have come up fairly empty. I
know I could buy one cheap but thats not what ham radio is about .

On Monday, January 27, 2014 2:06:56 PM UTC-6, R. Scott wrote:
Have been looking around for plans for a 1/2 or 5/8 2 meter mobile

antenna to play with. I have several Iron Horse whips I no longer use

and thought id use them as a starting point for a 5/8 2 meter mobile

whip I could use on my CB mount for most of the time. (I use the CB only

when our RV club travels as a group).





I did a ton of google/bing searches but have come up fairly empty. I

know I could buy one cheap but thats not what ham radio is about .

The tricky part is rigging up the matching/loading coil.
About the easiest way to rig up a 5/8 2m whip is to take one
of those old CB antennas with the base loading coil which has
a plastic sleeve over the coil. Very common back in the day..
Pull the sleeve up and redo the coil to act as a loading coil
for 2m. Usually will end up maybe 4-5 turns or so, but will
have to be tweaked. That's about all I can think of offhand
that is easy to make, and still looks OK after it's finished..
Naturally you'll need to trim the whip, or get one the right
length. I have no idea what an "iron horse" whip is, so couldn't
say much about those.

In article ,
"R. Scott" wrote:

Have been looking around for plans for a 1/2 or 5/8 2 meter mobile
antenna to play with. I have several Iron Horse whips I no longer use
and thought id use them as a starting point for a 5/8 2 meter mobile
whip I could use on my CB mount for most of the time. (I use the CB only
when our RV club travels as a group).


I did a ton of google/bing searches but have come up fairly empty. I
know I could buy one cheap but thats not what ham radio is about .

It has been many years, but I recall some CB antennas that were
outwardly similar to a 5/8 wave Two Meter antenna. They consisted of a
base loading coil connected to the vertical whip. The Two Meter antenna
had a grounded coil with whip at the top, with a connection from the
connector's center conductor to a tap on the coil.

The CB whip may have been a little shorter than 5/8 wave on Two Meters,
but it might still be possible to rework the CB coil to match it.

Fred
K4DII

Have been looking around for plans for a 1/2 or 5/8 2 meter mobile
antenna to play with.

The tricky part is rigging up the matching/loading coil.

Also, you might want to read up on actual (as opposed to simple-model)
results with a 5/8-wave mobile antenna, on a typical mount.

I've read a couple of reports which state that the theoretical gain
advantage of a 5/8-wave antenna, over a quarter-wave monopole, depend
a great deal on the 5/8-wave being mounted over a large ground plane
(several wavelengths at least). Without a large ground plane, the
5/8-wave tends to "squint upwards" - its primary gain lobe takes off
at an angle significantly above the horizon, rather than directly out
forwards and backwards from the vehicle. This can result in poorer
signal "towards the horizon" than a quarter-wave would give you - not
good if you're trying to do simplex communication between vehicles,
and maybe-not-good if you're using repeaters (depending how high above
horizontal the direct line to the repeater antenna lies).

5/8-wave antennas are also more prone to "lean back" away from the
vertical when you're driving at highway speeds as a result of air
pressure, and this also can cause the pattern to squint upwards more
than is true for a quarter-wave. The thin "spaghetti noodle" 5/8-wave
antennas such as Radio Shack used to sell (and perhaps still does)
would really have a problem with this, I think.

Anyhow, here's one set of plans:

http://www.vk4adc.com/web/index.php/...58th-wave-whip

The article has some comments attached which make reference to plans
in the ARRL Handbook (doesn't say which edition) which use a tapped
loading coil for impedance matching. Most of the 5/8-wave antenna
designs I've seen use this approach... it has the advantage that the
whole antenna is DC-grounded through the tapped coil, and thus static
buildup on the whip isn't an issue.

I believe I've seen other 5/8-wave mobile plans in various of the ARRL
Antenna Compendium collections.

http://www.arrl.org/files/file/Techn...df/8009022.pdf has
some other interesting approaches.

"David Platt" wrote in message
news
Also, you might want to read up on actual (as opposed to simple-model)
results with a 5/8-wave mobile antenna, on a typical mount.

I've read a couple of reports which state that the theoretical gain
advantage of a 5/8-wave antenna, over a quarter-wave monopole, depend
a great deal on the 5/8-wave being mounted over a large ground plane
(several wavelengths at least). Without a large ground plane, the
5/8-wave tends to "squint upwards" - its primary gain lobe takes off
at an angle significantly above the horizon, rather than directly out
forwards and backwards from the vehicle. This can result in poorer
signal "towards the horizon" than a quarter-wave would give you - not
good if you're trying to do simplex communication between vehicles,
and maybe-not-good if you're using repeaters (depending how high above
horizontal the direct line to the repeater antenna lies).

5/8-wave antennas are also more prone to "lean back" away from the
vertical when you're driving at highway speeds as a result of air
pressure, and this also can cause the pattern to squint upwards more
than is true for a quarter-wave. The thin "spaghetti noodle" 5/8-wave
antennas such as Radio Shack used to sell (and perhaps still does)
would really have a problem with this, I think.


From years of using several kinds of 2 meter antennas I have found there is
not one that will work best in every case. Several times another ham and I
would swap antennas in the same mount and look at differant repeaters. One
type of antenna would work good in one direction and another in a differant
direction or repeater that is up higher or lower.
Even a 40 meter loaded whip that had a low swr on 2 meters worked beter in
some directions than the other 1/4 to 5/8 wave length antennas.

The thin whip that lays back is not too good. Another one is the ones that
are about 5 or 6 feet long that tend to whip around and give lots of
flutter at highway speeds.

While the antenna programs will show you alot about the patern of the
antenna, it is difficult for them to take into account everything around
them and repeaters mounted at differant heigths. The best is the roof of a
car or van. For the most part if you are in the low rolling hills like
around here , just put a 1/4 or 5/8 on and forget about it.

If you are in an area that is very flat your results may be differant. Where
I am the land is from about 600 to 1000 feet above sea level for the most
part. The repeaters may be from 300 to 1000 feet above that with a few up
to 4000 feet or more above that.

Now that I have been using the dual band antennas there is not really a
choice of what kind to use. Just try to get it stiff enough it does not lay
back or whip around.

All that is based on my and a couple of local hams expierance over the last
40 years.




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Dave Platt already beat me to the answer.

The bottom line is that it would be a waste of a perfectly good 10 / 11 meter antenna to modify one to work on two meters just because you already had the mount on the vehicle - even though the mount was in the wrong place.

On Monday, January 27, 2014 6:03:19 PM UTC-6, Ralph Mowery wrote:

If you are in an area that is very flat your results may be differant.

The area around here is real flat. The 5/8 was always the best
when we compared them. They were the best at low angles at long
distances, and gave less picket fencing when driving around town
for some reason.
Back then I was using a Larson, and it was on the center of the roof.
But these days I have simple 1/4 wave whips on the trucks.
I'm not as picky these days about 2m, and they hit less stuff overhead,
being they are also mounted on the roof of the cabs, which sits fairly
high.

When comparing all the various vertical types on 10m at the house,
the 5/8 ground plane always beat the 1/4 wave, and 1/2 waves I tried.
And the half wave was decoupled, and did work very well.
But.. The 5/8 beat it quite noticeably on distant local paths where
the angles used are very low.

Now, when I tried 5/8 ground planes on 2m, they were horrible if
you used 1/4 wave radials. So in that case, the problems did show up.
But if I used 5/8 lower elements and rigged it as a collinear, it
did fine.

Anyway, in the cases I tried with the whips on the vehicle roofs,
the 5/8 seemed to work pretty well. But a vehicle is larger than
the 1/4 wave radials which did not work well.
I've always felt a 5/8 element should really be paired with another
5/8 element as a collinear. That is a very good antenna if decoupled
from the feedline.

So you never really know for sure about the 5/8's until you try them
in each case.
I've heard many prefer the shorter 1/4 wave whips if in a valley
with the repeaters up on nearby mountains and such.
But Houston is not really like that and the 5/8's usually won
if mounted on decent metal.

On Monday, January 27, 2014 6:41:34 PM UTC-6, Channel Jumper wrote:
Dave Platt already beat me to the answer.



The bottom line is that it would be a waste of a perfectly good 10 / 11

meter antenna to modify one to work on two meters just because you

already had the mount on the vehicle - even though the mount was in the

wrong place.

If he's got several, why would it be a waste if it's adding another
band? He can only use one CB antenna at a time.. :/

And he hasn't mentioned where the mount is. If it's on the roof or
a decent trunk, it will work OK. But mirror mounts and such, a 5/8
will usually not work too well at all. But mirror mounts are about
the worst place you can mount a whip, no matter what type.

But one problem about converting a base load CB antenna I forgot about..
It's not a 3/8x24 thread.. They use a different type of wider screw
on mount, and would need to be modified, or use a base load mount.

With a 3/8x24 thread mount, I would just use a 1/4 wave.. So much
easier and better looking. Most loading/matching coil schemes are going
to look fairly ugly in a case like that as you usually can't enclose
them in anything.

On Monday, January 27, 2014 8:01:29 PM UTC-6, wrote:

With a 3/8x24 thread mount, I would just use a 1/4 wave.. So much

easier and better looking. Most loading/matching coil schemes are going

to look fairly ugly in a case like that as you usually can't enclose

them in anything.

Pondering.. About the only other easy way to make a 5/8 whip
that would screw into that mount would be to take a glass whip
and then rebuild it into a 5/8 for 2m. You would need to strip
the original wire, or at least partly, then wind a loading coil
at the base, and then pretty much straight up to make the
5/8 element.
That would work.. The reason I call the coil for the 5/8 a
loading coil, rather than matching coil, is the coil is
tuning the 5/8 whip to be a 3/4 wave electrically, which is
resonant. Some ground the coil, and tap at the best match.
But I prefer an ungrounded coil. Why? If it's ungrounded, it
can also be used on other bands. IE: a 1/4 wave whip on a lower
freq.. I used to use my 10m 5/8 ground planes on 30m as 1/4 waves.
But you can't do that with a grounded coil. Works fine ungrounded.

wrote in message
...
But I prefer an ungrounded coil. Why? If it's ungrounded, it
can also be used on other bands. IE: a 1/4 wave whip on a lower
freq.. I used to use my 10m 5/8 ground planes on 30m as 1/4 waves.
But you can't do that with a grounded coil. Works fine ungrounded.

I have not tried it, but have seen where an ungrounded coil on the 5/8 2
meter antenna is good for a loaded whip on 6 meters. Suspose to match with
a low swr.



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