On Mon, 28 Mar 2005 18:21:52 -0800, "John Smith"
wrote:

Interesting... so electrical length is affecting gain and EZNEC supports
it--that will probably silence those who claim the physical length is all
important... ya suppose?

Hi "Fred,"

It will take more than supposition and superstition.

So back to rote:
The physical size in relation to wavelength dominates launch
characteristics, NOT electrical length.

73's
Richard Clark, KB7QHC

John Smith wrote:
Interesting... so electrical length is affecting gain and EZNEC supports
it--that will probably silence those who claim the physical length is all
important... ya suppose?

The important point is that the web page claim of bettering
three end-to-end 1/2WL dipoles misses by about 3 dB and a few
degrees on TOA.
--
73, Cecil http://www.qsl.net/w5dxp


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On Mon, 28 Mar 2005 18:21:52 -0800, "John Smith"
wrote:

Interesting... so electrical length is affecting gain and EZNEC supports
it--that will probably silence those who claim the physical length is all
important... ya suppose?

Regards

..07 DB might be gain, but I somehow get the feeling that I would never
notice it on my HF rig. What would that gain represent on a 1000
watts? I don't know the formula, just the generalization that 3 db =
double power.


--
73 for now
Buck
N4PGW

The SlimJim resembles the J-Pole. The 1/4 wave section is a matching
network and it is probably not critical that it be vertical so the
height may be reduced by about 1/3. I am not sure what the folded
section does for it. but without the 1/2 wave section coming back
down from the top, the antenna is just a J-Pole.

Yea, I finally realized that, after Cecils reply.
I would still prefer a gamma loop feed I think...MK

In some situations it is better to have a 'shortened' antenna than the
absolute last tiniest fraction of a db. I realize a cap hat can
reduce the size of a vertical with reasonably low loss, I am wondering
if it would do as well with the J-Pole?

For example, a quarter wave matching network for the J-Pole would be
whatever works best, be it original design or some form of balun, but
the 1/2 wave vertical might be reduced in size by forming a capacity
hat above it.

How well would that work for shortening a J-Pole? would it be better
to use a shortened 1/2 wave dipole or would the J-Pole design be
better?

Buck

--
73 for now
Buck
N4PGW

Becareful Buck!!! It is catching, you are starting to think like me!

Regards

--
Hay, if'n ya'll cun't konstructivly partecipete in this har disscusion, haw
aboot speel-checkin it fer me?


"Buck" wrote in message
...
In some situations it is better to have a 'shortened' antenna than the
absolute last tiniest fraction of a db. I realize a cap hat can
reduce the size of a vertical with reasonably low loss, I am wondering
if it would do as well with the J-Pole?

For example, a quarter wave matching network for the J-Pole would be
whatever works best, be it original design or some form of balun, but
the 1/2 wave vertical might be reduced in size by forming a capacity
hat above it.

How well would that work for shortening a J-Pole? would it be better
to use a shortened 1/2 wave dipole or would the J-Pole design be
better?

Buck

--
73 for now
Buck
N4PGW

On Tue, 29 Mar 2005 13:41:50 -0800, "John Smith"
wrote:

Becareful Buck!!! It is catching, you are starting to think like me!

Regards


hmmm, maybe I should killfile you for being contagious?

(sorry, couldn't resist.)

As for the topic, I am interested to know. I am eznic challenged.


--
73 for now
Buck
N4PGW

I am a software engineer but, I am glad you commented on eznec--I am finding
it a bit of challenge to utilize it meaningfully--it has brought me to my
knees and humbled me.
You know the old saying, "Garbage in, Garbage out", eznec just won't arrange
my garbage in a meaninful way.

Warmest regards

--
Hay, if'n ya'll cun't konstructivly partecipete in this har disscusion, haw
aboot speel-checkin it fer me?


"Buck" wrote in message
...
On Tue, 29 Mar 2005 13:41:50 -0800, "John Smith"
wrote:

Becareful Buck!!! It is catching, you are starting to think like me!

Regards


hmmm, maybe I should killfile you for being contagious?

(sorry, couldn't resist.)

As for the topic, I am interested to know. I am eznic challenged.


--
73 for now
Buck
N4PGW

On Tue, 29 Mar 2005 15:09:25 -0500, Buck wrote:

How well would that work for shortening a J-Pole? would it be better
to use a shortened 1/2 wave dipole or would the J-Pole design be
better?

Hi Buck,

You may have noticed the vacuum of response - most have already seen
this movie and skipped out. However, for your benefit:

Like any small antenna, narrow bandwidth. Like any Hi-Z antenna, very
skitterish. Like any small antenna, lower gain.

For a helix standing roughly 4M tall for 40M band (which isn't
particularly short) under an 8 spoke top hat 6M wide, this exhibits a
drive point Z of 40000 Ohms. Put 100W into it and you will see 2KV at
the connector. That should take care of grass growing nearby.

EZNEC boldly announces there is loss, and the best gain is -2.6dBi.

The bandwidth spanned from 7.18MHz to 7.25MHz.

From there it is only a matter of adding the critical matching
section.

OR

Throw away the helix and use a straight support, shorten the 8 spoke
top hat to 4M wide and the drive point is an easier match at 13 Ohms.
No lethal voltages at the drive point, lower loss, more gain (albeit
of 0.65dBi), more bandwidth 7.14MHz to 7.4MHz.

Still reduces to it's hardly worth the effort to change from one to
the other, but all the signs point to a better implementation without
the air cooled wire wound resistor. If you want to keep a coil in the
picture, you can put it in the conventional place, shorten the top hat
spokes yet some more, and find no more gain, and less bandwidth.

OR

Buy an SGC which proudly proclaims it will match a wet string.

OR

Throw away all this folderol, and build a full size antenna (roughly
twice as tall as these gomers). No matching issue, bandwidth up the
kazoo (7-7.5 MHz), no appreciable change in gain though (in other
words, that imperceptible 1dB delta).

All modeling performed using "Real/MiniNEC Ground" (not usually my
choice, but then no one else has stepped up to the bar).

OR

Go watch a movie you haven't seen before, it may have a surprise in
it.

73's
Richard Clark, KB7QHC

My gawd! Is this the same Richard Clark which I just reported to mental
health for a three day observation???
Quick, where is a phone--I will and cancel that! grin

Regards

--
Hay, if'n ya'll cun't konstructivly partecipete in this har disscusion, haw
aboot speel-checkin it fer me?


"Richard Clark" wrote in message
...
On Tue, 29 Mar 2005 15:09:25 -0500, Buck wrote:

How well would that work for shortening a J-Pole? would it be better
to use a shortened 1/2 wave dipole or would the J-Pole design be
better?

Hi Buck,

You may have noticed the vacuum of response - most have already seen
this movie and skipped out. However, for your benefit:

Like any small antenna, narrow bandwidth. Like any Hi-Z antenna, very
skitterish. Like any small antenna, lower gain.

For a helix standing roughly 4M tall for 40M band (which isn't
particularly short) under an 8 spoke top hat 6M wide, this exhibits a
drive point Z of 40000 Ohms. Put 100W into it and you will see 2KV at
the connector. That should take care of grass growing nearby.

EZNEC boldly announces there is loss, and the best gain is -2.6dBi.

The bandwidth spanned from 7.18MHz to 7.25MHz.

From there it is only a matter of adding the critical matching
section.

OR

Throw away the helix and use a straight support, shorten the 8 spoke
top hat to 4M wide and the drive point is an easier match at 13 Ohms.
No lethal voltages at the drive point, lower loss, more gain (albeit
of 0.65dBi), more bandwidth 7.14MHz to 7.4MHz.

Still reduces to it's hardly worth the effort to change from one to
the other, but all the signs point to a better implementation without
the air cooled wire wound resistor. If you want to keep a coil in the
picture, you can put it in the conventional place, shorten the top hat
spokes yet some more, and find no more gain, and less bandwidth.

OR

Buy an SGC which proudly proclaims it will match a wet string.

OR

Throw away all this folderol, and build a full size antenna (roughly
twice as tall as these gomers). No matching issue, bandwidth up the
kazoo (7-7.5 MHz), no appreciable change in gain though (in other
words, that imperceptible 1dB delta).

All modeling performed using "Real/MiniNEC Ground" (not usually my
choice, but then no one else has stepped up to the bar).

OR

Go watch a movie you haven't seen before, it may have a surprise in
it.

73's
Richard Clark, KB7QHC