"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 6:41:34 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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On 1/28/2014 1:25 AM, wrote:
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.






I will give that a try. Thanks for the discussion gents, let me clear
some things up that I should have posted from the start.

The Iron Horse Whips are loaded HF Whips, I have them for all the bands,
but I dont have a 706 anymore as I changed to a 746pro and that doesnt
do Mobile well. Plus I have several CB antenna whips as people give
them to me thinking I could use them HI. So I could easily go buy a
3/8x24 2 meter antenna I would rather experiment with the whips on a 5/8
loaded base.

Im in the Seattle area so most of the 2 meter repeaters are high up ...
not an issue with hitting them. I have not used my FT-1500 in a while
and thought I would see if anyone is on any more.

The vehicle is a 2011 F-350 and I have the Fender Mount CB. Like I said
I use it only for the RV runs. Thus I would like to experiment with one
of the whips to run a 2 meter. I could have easily did a 1/4 wave
vertical but thought that 5/8 would be better experiment.

the loaded 5/8 ungrounded as NM5K posted just might be what I need. I
was looking for how many turns of wire might do the trick. Problem is I
dont have a GDO to get the right turns so thats why I was hoping to
find someone whom ad done it before .

Anyway ... Ill start with 3/4 wave of wire and wrap the 1/2 wave section
in a coil and have the last 1/4 go vertical up the fiberglass ...

Ill let you know how it comes out.


Scotty W7PSK.

"R. Scott" wrote in message
...
On 1/28/2014 1:25 AM, wrote:

The vehicle is a 2011 F-350 and I have the Fender Mount CB. Like I said I
use it only for the RV runs. Thus I would like to experiment with one of
the whips to run a 2 meter. I could have easily did a 1/4 wave vertical
but thought that 5/8 would be better experiment.

the loaded 5/8 ungrounded as NM5K posted just might be what I need. I was
looking for how many turns of wire might do the trick. Problem is I dont
have a GDO to get the right turns so thats why I was hoping to find
someone whom ad done it before .


I saw an antenna similar to what you are wanting to do. I think it was 47
inches long. The coil will only be a few turns. I don't recall the number
of turns on the form for that antenna, but it was only about 2 or 3 turns.
I would start with 3 turns and check the swr and trim the turns for a low
swr.



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In message , Ralph
Mowery writes

"R. Scott" wrote in message
...
On 1/28/2014 1:25 AM, wrote:

The vehicle is a 2011 F-350 and I have the Fender Mount CB. Like I said I
use it only for the RV runs. Thus I would like to experiment with one of
the whips to run a 2 meter. I could have easily did a 1/4 wave vertical
but thought that 5/8 would be better experiment.

the loaded 5/8 ungrounded as NM5K posted just might be what I need. I was
looking for how many turns of wire might do the trick. Problem is I dont
have a GDO to get the right turns so thats why I was hoping to find
someone whom ad done it before .


I saw an antenna similar to what you are wanting to do. I think it was 47
inches long. The coil will only be a few turns. I don't recall the number
of turns on the form for that antenna, but it was only about 2 or 3 turns.
I would start with 3 turns and check the swr and trim the turns for a low
swr.

Most 5/8ths on 2m are more-or-less electrically 6/8th (=3/4) waves, but
with the first 1/8th being the coil. With mine, the whip is 50" long,
and the coil is 3.5 turns, 1" dia, appx 10 gauge well spread steel
spring, 1.75" long. The feed impedance over a flat groundplane (7"
magmount in the centre of the car roof) should be around 50 ohms,
whereas a 1/4 is more like 37 ohms. In most situations, I've not found
it remarkably better the a 1/4 wave (maybe a couple of dB on a good
day).
--
Ian

On 1/29/2014 9:25 AM, Ralph Mowery wrote:

"R. Scott" wrote in message
...
On 1/28/2014 1:25 AM, wrote:

The vehicle is a 2011 F-350 and I have the Fender Mount CB. Like I said I
use it only for the RV runs. Thus I would like to experiment with one of
the whips to run a 2 meter. I could have easily did a 1/4 wave vertical
but thought that 5/8 would be better experiment.

the loaded 5/8 ungrounded as NM5K posted just might be what I need. I was
looking for how many turns of wire might do the trick. Problem is I dont
have a GDO to get the right turns so thats why I was hoping to find
someone whom ad done it before .


I saw an antenna similar to what you are wanting to do. I think it was 47
inches long. The coil will only be a few turns. I don't recall the number
of turns on the form for that antenna, but it was only about 2 or 3 turns.
I would start with 3 turns and check the swr and trim the turns for a low
swr.

Thanks, My figuring was all wrong . Just so everyone knows, its a
standard Firestik wound loaded about 4ft long. So its not base loaded,
they distributed the coil from top to bottom (tighter winding at the top).

Ill experiment when I have time.

W7PSK

Ive experimented with many wire antennas over the years, but never
loading types. Thats why I came to the experts .

On Wednesday, January 29, 2014 11:15:17 AM UTC-6, R. Scott wrote:


Anyway ... Ill start with 3/4 wave of wire and wrap the 1/2 wave section

in a coil and have the last 1/4 go vertical up the fiberglass ...

That will be way too much coil, and not enough vertical.
I think a 5/8 for 2m is around 48-50 inches or so, depending on
freq. The coil will only be a few turns. If the converted base
loaded CB version is 5 turns, with the thinner glass whip form,
it would take just a few more turns. Like maybe 8 or so using a
thin glass whip form. You could hang a 5/8 length of wire from
something, and then wind a coil on a pencil or something about
the same dia as the whip to get an idea on the number of turns.
The vertical section up the glass must be the correct length.
IE: 48-50 inches. Otherwise it will not be a 5/8 whip.
With a 1/4 wave going up the whip, it's a 1/4 wave with a loading
coil at the base detuning it.