Helical-wound Monopoles
 

On Sat, 02 Apr 2011 18:51:06 -0500, John - KD5YI
wrote:

Your posts are occasionally informative, but usually not, as
demonstrated here. You have not offered anything of technical substance
in so many of your posts. It is obvious that you are knowledgeable in
the subject, but you seem to have a problem communicating that
knowledge. We could all benefit from your knowledge, but please do so
with direct technical information rather than the example above.

Hi John,

Technical chaff is rarely useful information. I am pretty sure that
was the point (but it is a rather Baroque discussion) Richard was
trying to illustrate.

Simple observation will reveal how this thread has become about trying
to get the camel through the eye of the needle: Richard's link points
to data that reveals differences displayable (and arguably
measureable) only out to 10% - that is pretty meager steam for heated
rhetoric in this engine of discussion (it has been far more about
purple prose than substance before I dipped my oar here).

73's
Richard Clark, KB7QHC

Helical-wound Monopoles
 

On Apr 2, 7:33*pm, Wimpie wrote:
I would like to see what happens when you
extend the helix until it gets its second (half wave) high impedance
resonance (current maximum in the middle).

Also at its third (3/4WL) low impedance resonance where there are two
current maximum points on the helix.
--
73, Cecil, w5dxp.com

Helical-wound Monopoles
 

"Wimpie" wrote
If it is not time consuming, I would like to see what happens when you
extend the helix until it gets its second (half wave) high impedance
resonance (current maximum in the middle). I expect some gain increase
due to small change in antenna pattern and reduced ground loss.

The NEC software that I used for the results shown earlier doesn't allow
enough segments to double the length of that helix. So I reconstructed the
model in one that does -- link to screen clip from it below:

http://i62.photobucket.com/albums/h8...onopole_6m.gif

Helical-wound Monopoles
 

On 3 abr, 21:11, "Richard Fry" wrote:
"Wimpie" wrote

If it is not time consuming, I would like to see what happens when you
extend the helix until it gets its second (half wave) high impedance
resonance (current maximum in the middle). I expect some gain increase
due to small change in antenna pattern and reduced ground loss.

The NEC software that I used for the results shown earlier doesn't allow
enough segments to double the length of that helix. *So I reconstructed the
model in one that does -- link to screen clip from it below:

http://i62.photobucket.com/albums/h8...onopole_6m.gif

Hello Richard Fry,

Thanks for taking the time to do the simulation.

It seems from your graph that the electrically half wave (180 degr)
helical has slightly more gain than the physically and electrically
quarter wave (90 degr) radiator (5.61 dBi for the helical versus 5.14
dBi for the quarter wave whip).

Given the about 4 kOhms for 1/(Re(Y)), the loss in the 10 Ohms ground
resistance is negligible (so at can be significantly higher before
presenting significant loss). 900Vp at the feed point (100W input)
will not give problems with matching.

With kind regards,


Wim
PA3DJS
www.tetech.nl
without abc, PM will reach me very likely

Helical-wound Monopoles
 

On 4/2/2011 6:51 PM, John - KD5YI wrote:

Your posts are occasionally informative, but usually not, as
demonstrated here. You have not offered anything of technical substance
in so many of your posts. It is obvious that you are knowledgeable in
the subject, but you seem to have a problem communicating that
knowledge. We could all benefit from your knowledge, but please do so
with direct technical information rather than the example above.

What fun would that be? We should cast away our aspergian proclivities
and embrace the occasional foray into acerbic wit.

Which is to say that Yes Richard knows something, and sometimes he'll
make an amusing comparison. If you ask, I'm certain he'll explain a
subject he's commented on if you ask.

And there is something in the donuts versus apples comparison.

The only one we're not allowed to use is apples and oranges.

- 73 de Mike N3LI -

Helical-wound Monopoles
 

On Apr 3, 3:42*pm, Wimpie wrote:
It seems from your graph that the electrically half wave (180 degr)
helical has slightly more gain than the physically and electrically
quarter wave (90 degr) radiator (5.61 dBi for the helical versus 5.14
dBi for the quarter wave whip).

A full-length half-wave monopole has gain over a full-length 1/4WL
monopole because the current maximum point on the half-wave is
elevated by 1/4WL. The same concept has to be a technical fact for the
helical even though muted by the smaller physical distance between the
current maximum points.
--
73, Cecil, w5dxp.com

Helical-wound Monopoles
 

Richard Fry wrote:
Followup -- the link below compares the relative current distribution,
directivity and radiation efficiency of a helical and a linear radiator
system when the helical radiator described in my earlier post is
operating at the frequency of its first self-resonance, and the linear
monopole height is set for its first self-resonance at that same frequency.

It is interesting to note that linear form has better performance than
the helical form.

http://i62.photobucket.com/albums/h8..._Resonance.gif


One antenna is physically larger, though, right: 5.535m vs 3m?

How is radiation efficiency calculated here? Integral over hemisphere of
radiated power vs applied power Seems like that would be
12.17/(10+12.17) vs 36/(10+36), so you're really just seeing a
manifestation of the different feedpoint impedance vs ground losses
(which you've assumed fixed..)

I'm not sure the assumption of fixed ground losses is reasonable here.
(Actually, now that I think about it, it might actually be worse for the
shorter element, in real life)


The other thing is that the shorter radiator is going to have a "lower
directivity" pattern vs the longer. That is, a shorter one will tend
towards the "Hertzian infinitestimal dipole" with 1.6dBi while the
longer will be closer to the 2.15dBi.