Thanks John but that's not what I meant. For the record,
I'm trying to understand some manufacturer's claims that
the antenna they sell, while smaller than a 1/4 wave whip
on 10m, puts out a better signal.

================================

There ARE such things as Human Rights.
Antenna salesmen have to make a living.
They have wives, children and mortgages just like anybody else.

"Ken Bessler" wrote
For the record, I'm trying to understand some manufacturer's
claims that the antenna they sell, while smaller than a
1/4 wave whip on 10m, puts out a better signal.
Here are the rules:
1) The antenna is at least 25% shorter than a 1/4 w whip
2) The antenna is made with ordinary materials - no friggin gold.
3) The antenna is omni-directional & vertically polarised
4) The feedline is Flexi 4XL, aka CQ-102
5) The antenna is mounted dead center on the roof of a van.
6) The antenna's mount is non magnetic - I.E. There is a good
DC/RF ground at both the base of the antenna & the radio.
__________

A perfectly "omni" azimuth pattern is unlikely from a v-pol whip of any
length when mounted on the roof of a van, however ~ 2.15dBi lobes could
exist in some directions. The electrical environment around the van will
shape the pattern further.

This could be modeled in NEC to give some insight into the situation.

RF

Ken, KG0WX wrote:
'Is it possible to make a mobile 10m antenna that is physically shorter
than a 1/4 wave whip yet will perform better than a 1/4 wave whip?"

In general, the full-sized 1/4-wave whip is a very good compromise
mobile antenna because it can be self-resonant, and it is almost
omnidirectional in azimuth. Physically, slightly shorter than a CB
antenna, it is readily available by trimming a CB antenna to resonance,
literally, or by using a low-loss variable capacitor in series.

It is possible to use an antenna less than 1/4wavelengrh against ground
as an efficient radiator but it requires care to minimize loss.
Shortening the radiator reduces its vertical directivity. If gain is the
performance measure, vertical directivity lost by shortening must be
replaced, perhaps by horizontal directivity. Gain from horizontal
directivity needs to cover not only lost vertical directivity, but
losses caused by loading too-short elements in the array. These
elements may produce horizontal directivity where none exists with a
sole avertical element.

In the September 1973 "QST" is "A Bite Size Beam". This article refers
the reader to an earlier March 1973 QST article by Sevick, "The W2FMI
Ground-Mounted Short Vertical".

Summary: Can you do it? Yes. Is it practical? Maybe.

Best regards, Richard Harrison, KB5WZI

On Wed, 13 Apr 2005 12:49:29 -0500, Cecil Moore
wrote:


I just ginned up a 5 foot tall antenna with 3.8 dBi gain. That's
half the height and considerably more gain than a 1/4WL whip.
With more time, I could do better.

What is the dBi gain of a 1/4 ground plane?


--
73 for now
Buck
N4PGW

The way I see it is there is no way to make an antenna that
meets all those rules and STILL has more than 2.14dbi gain
due to resistave losses.

Am I right?

I was a friend of Jim Taylor and Jim Taylor Jr. of Taylor Radio back
in the good-ole CB days. Sitting at lunch one day we were discussing
the old Big-Stick and Grand Slammer antennas (I think those are the
names of the 5/8 wave base verticals most popular in that day). They
told me that the market ting departments of the two companies made
more antenna gain progress than their engineering departments did.

I was slow to understand the statement at that time, so they explained
that every time one came out with an ad, the competitor had to match
or beat it. While the comparisons started with a 1/4 wave vertical,
Jim said that if it continued, antenna manufacturers would have to
start comparing gain to their antennas against loaded coat-hangers.

In the truck stops, there are several antennas that are shortened 5/8
antennas. I think that is the case with Fire-stick. I can't tell you
if it has a gain or loss over a 1/4 wave whip.

Just a side-note tho... I have a 706 MKII in the car. I had a 6
meter whip on a mag-mount connected to the HF side where I was
listening to a local beacon. I removed the 6 meter whip and replaced
it with a White GMS/Volvo CB whip about an inch shorter (the cb
antenna is just under 4 feet long.) The signal of the 6 meter beacon
came up from 1/2 to full scale. I swapped back and forth and tested
the SWR to make sure. The CB antenna was maximum SWR but sounded
considerably better. I have several of these antennas so I am
planning to try to trim one for 6 meters and use it instead of the
whip I am using now. I don't have enough data to determine what
causes the improvement, but I believe I have ruled out propagation.

Buck
N4PGW

--
73 for now
Buck
N4PGW

Just a side-note tho... I have a 706 MKII in the car. I had a 6
meter whip on a mag-mount connected to the HF side where I was
listening to a local beacon. I removed the 6 meter whip and replaced
it with a White GMS/Volvo CB whip about an inch shorter (the cb
antenna is just under 4 feet long.) The signal of the 6 meter beacon
came up from 1/2 to full scale. I swapped back and forth and tested
the SWR to make sure. The CB antenna was maximum SWR but sounded
considerably better. I have several of these antennas so I am
planning to try to trim one for 6 meters and use it instead of the
whip I am using now. I don't have enough data to determine what
causes the improvement, but I believe I have ruled out propagation.


You should have checked several becons in diffearant directions. A few
years back a friend and I had several 2 meter antennas that would fit the
same mount. While checking out several repeaters in differant directions we
found one antenna would be beter in one direction and another in a differant
direction . It may have been due to the differance in the lobes of the
antennas and the height of the repeaters.

Buck wrote:
What is the dBi gain of a 1/4 ground plane?

Rule of thumb: zero dBi
--
73, Cecil, W5DXP

----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

On Mon, 18 Apr 2005 10:49:31 -0400, Buck wrote:
What is the dBi gain of a 1/4 ground plane?

Hi Buck,

-0.22dBi to +2.2 dBi depending on the proximity of ground and the
level of screening with radials.

73's
Richard Clark, KB7QHC

On Mon, 18 Apr 2005 11:20:01 -0700, Richard Clark
wrote:


-0.22dBi to +2.2 dBi depending on the proximity of ground and the
level of screening with radials.

I take it that +2.2 is with radials on an elevated ground plane?

--
73 for now
Buck
N4PGW

On Mon, 18 Apr 2005 15:33:06 GMT, "Ralph Mowery"
wrote:

Just a side-note tho... I have a 706 MKII in the car. I had a 6
meter whip on a mag-mount connected to the HF side where I was
listening to a local beacon. I removed the 6 meter whip and replaced
it with a White GMS/Volvo CB whip about an inch shorter (the cb
antenna is just under 4 feet long.) The signal of the 6 meter beacon
came up from 1/2 to full scale. I swapped back and forth and tested
the SWR to make sure. The CB antenna was maximum SWR but sounded
considerably better. I have several of these antennas so I am
planning to try to trim one for 6 meters and use it instead of the
whip I am using now. I don't have enough data to determine what
causes the improvement, but I believe I have ruled out propagation.


You should have checked several becons in diffearant directions. A few
years back a friend and I had several 2 meter antennas that would fit the
same mount. While checking out several repeaters in differant directions we
found one antenna would be beter in one direction and another in a differant
direction . It may have been due to the differance in the lobes of the
antennas and the height of the repeaters.


Thanks,

That was the only 6 meter beacon I could hear. I knew/know that the
one beacon wouldn't be a good sample but I was/am still surprised that
the difference was 1/2 scale on the radio. It went from scratchy to
full quieting and full scale. I didn't spend much time on it as my
objective was to trim the antenna for ten meters.

It is interesting though.

Buck

--
73 for now
Buck
N4PGW