Just found this; looks interesting; no connection with the author;
all in the spirit of free dissemination of knowledge to fellow
radio amateurs ...

http://www.cvarc.org/tech/antenna_my...enna_myths.pdf

On Friday, February 14, 2014 1:59:15 PM UTC-6, gareth wrote:
Just found this; looks interesting; no connection with the author;

all in the spirit of free dissemination of knowledge to fellow

radio amateurs ...



http://www.cvarc.org/tech/antenna_my...enna_myths.pdf

Several parts of it are pure unadulterated horse doo-doo..
I find it to be in very poor taste to post a page claiming to
expose and list myths and mysteries, only to replace them with
other myths and mysteries. :+
That is akin to chasing one's tail while barking at the moon.

wrote:
On Friday, February 14, 2014 1:59:15 PM UTC-6, gareth wrote:
Just found this; looks interesting; no connection with the author;

all in the spirit of free dissemination of knowledge to fellow

radio amateurs ...



http://www.cvarc.org/tech/antenna_my...enna_myths.pdf

Several parts of it are pure unadulterated horse doo-doo..
I find it to be in very poor taste to post a page claiming to
expose and list myths and mysteries, only to replace them with
other myths and mysteries. :+
That is akin to chasing one's tail while barking at the moon.

I confess to only have 'scan read' the reference and I thought it was still
pretty good.

What in particular do you have an issue with, please?

--
73
Brian
G8OSN/W8OSN

On Friday, February 14, 2014 11:21:01 PM UTC-6, Brian Reay wrote:
wrote:

On Friday, February 14, 2014 1:59:15 PM UTC-6, gareth wrote:

Just found this; looks interesting; no connection with the author;



all in the spirit of free dissemination of knowledge to fellow



radio amateurs ...







http://www.cvarc.org/tech/antenna_my...enna_myths.pdf



Several parts of it are pure unadulterated horse doo-doo..

I find it to be in very poor taste to post a page claiming to

expose and list myths and mysteries, only to replace them with

other myths and mysteries. :+

That is akin to chasing one's tail while barking at the moon.



I confess to only have 'scan read' the reference and I thought it was still

pretty good.



What in particular do you have an issue with, please?



--

73

Brian

G8OSN/W8OSN

Well, I suppose most is OK, but there are a few problems.

Take this one..

More recent HF tests by Al Christman - KB8I; "Eleva
ted Vertical Antenna Systems,"
QST, August 1988, p 35; have shown that
fewer "elevated" radials will perform
about as well as 120 ground mounted ones.
A base mounting height above ground
of about 1/10 to 1/16 of a wavelength seems optimu
m for 4 radials.........but will vary
with soil conductivity.

I don't know how he ran his tests, but this is not right.
1/10 WL is way too low for four elevated radials to equal
120 on the ground. I was harping about this "myth" in
another post not long ago..

There is no free lunch. :|

For four radials to equal 120 on the ground, they will
need to be nearly 1/2 wave up. Four radials at 1/4 wave
up are equal to about 50-60 on the ground.

Seems optimum? If the radial system were optimum, it really
wouldn't matter what the conductivity of the ground was.

This is actually proving my point that four radials at 1/16
to 1/10 WL are not nearly enough to actually equal 120 on the
ground. If they were equal, you wouldn't have to raise the
antenna and radials.

That's the whole point of using so many radials on the ground.
So the quality of the ground, good or bad, really doesn't matter.
Efficiency will be high either way.

Some of his 1/2 vertical design statements could be argued
with, but I'll be here all night if I start into that.. :/

Then you have this..

Myth:
A 5/8 wave antenna has 3dB
more gain than a ground plane.
False

This can be true in many cases.
But it can also be false in many cases.


*
The losses in the required matching coil at the base
of the 5/8 wave antenna reduce the gain difference
to a max of about 2dB (with a perfect ground plane)
to zero difference in some installations. **
--------------------------------------------------

This is fairly absurd.. The loss of the loading coil
is quite negligible. I bet not even enough for most
people to accurately measure.

The coil has nothing to do with why some types of
5/8 verticals show little or no gain vs a 1/4 GP,
or isotropic.

Those are a couple of my issues anyway..
The "Free Lunch" elevated radial system being one of my
pet peeve myths.. :|

On Sat, 15 Feb 2014 01:44:31 -0800 (PST), wrote:

Myth:
A 5/8 wave antenna has 3dB
more gain than a ground plane.
False

This can be true in many cases.
But it can also be false in many cases.


*
The losses in the required matching coil at the base
of the 5/8 wave antenna reduce the gain difference
to a max of about 2dB (with a perfect ground plane)
to zero difference in some installations. **
--------------------------------------------------

This is fairly absurd.. The loss of the loading coil
is quite negligible. I bet not even enough for most
people to accurately measure.

The coil has nothing to do with why some types of
5/8 verticals show little or no gain vs a 1/4 GP,
or isotropic.

Just a minor note on this issue. If the coil actually did contribute
a 1dB power loss, the lost power would need to be either reflected or
dissipated by the coil if it's not being radiated as RF. I haven't
seen any high VSWR 5/8 wave antennas, so it's not VSWR. I haven't
seen the matching coil on my Larsen 5/8 wave antenna, with a 45 watt
VHF mobile, become warm. If it was dissipating 4.5 watts, I should be
able to see it get quite warm[1]. I pointed an IR thermometer at the
coil and transmitted for about 5 minutes. No change. However, I did
see a very slight temperature rise from a mercury thermometer taped to
the stainless steel antenna rod (which could be attributable to my
sloppiness). The test is easily reproduced. Have fun.

However, he is right about the minimum VSWR point shifting, but
neglects to quantify the effect. A typical 5/8 wave antenna is fairly
narrow band and will not cover the entire 2m band. If you miss the
minimum VSWR point, there may be additional losses.
http://vk2zoi.com/articles/single-five-eighth-flower-pot/
His graph shows 1.5:1 at the band edges which is a mismatch loss of
0.18dB. Not even close to the claimed 1dB loss.

I consider the article quite good in that it's a survey of things to
consider when building or using antennas. It covers quite a range of
topics and is therefore understandably lacking in detail.


[1] For entertainment value, take a 33 ohm resistor and put it across
a 12v battery. Find something that has approximately the same mass as
the Larson loading coil. Give it a few minutes to get warm. Feel the
heat? That's what a 1dB (10%) power loss with a 45 watt transmitter
should feel like.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

"Jeff Liebermann" wrote in message
...
The coil has nothing to do with why some types of
5/8 verticals show little or no gain vs a 1/4 GP,
or isotropic.

Just a minor note on this issue. If the coil actually did contribute
a 1dB power loss, the lost power would need to be either reflected or
dissipated by the coil if it's not being radiated as RF. I haven't
seen any high VSWR 5/8 wave antennas, so it's not VSWR. I haven't
seen the matching coil on my Larsen 5/8 wave antenna, with a 45 watt
VHF mobile, become warm. If it was dissipating 4.5 watts, I should be
able to see it get quite warm[1]. I pointed an IR thermometer at the
coil and transmitted for about 5 minutes. No change. However, I did
see a very slight temperature rise from a mercury thermometer taped to
the stainless steel antenna rod (which could be attributable to my
sloppiness). The test is easily reproduced. Have fun.


Just the same type of easy test that can be done with the old saying of 1 db
loss per connector. Connectors have a very small loss in them. If they
did have the 1 db or even 1/2 of a db loss and you put 100 to 1000 watts
through them you could really feel the heat after a short transmission.



---
This email is free from viruses and malware because avast! Antivirus protection is active.
http://www.avast.com

On Saturday, February 15, 2014 11:39:51 AM UTC-6, Jeff Liebermann wrote:
I haven't
seen any high VSWR 5/8 wave antennas, so it's not VSWR.

Actually, a 5/8WL antenna is a standing wave antenna. Therefore, there is a standing wave *on the antenna element* no matter what the feedpoint impedance. The SWR on the loading coil will be higher than the SWR on the antenna element. All that a resistive feedpoint on a standing wave antenna means is that the forward wave *on the antenna element* is in phase with the reflected wave *on the antenna element* at the antenna feedpoint.
--
73, Cecil, w5dxp.com

wrote in message
...
On Friday, February 14, 2014 11:21:01 PM UTC-6, Brian Reay wrote:

BIG SNIP



What in particular do you have an issue with, please?

little snip

Brian

G8OSN/W8OSN

Well, I suppose most is OK, but there are a few problems.

BIG SNIP

I had a question about his j-pole analysis. He says "A J-pole, like ANY end
fed antenna, needs radials, a counterpoise or ground plane to work
properly."

I've never seen this anywhere else, even as a suggestion or hint. I can
envision places to fit one but what would it do? As built, both the pattern
and the impedance already seem to be what I want.

Thoughts?

"Sal"

On Saturday, February 15, 2014 3:27:15 PM UTC-6, Sal wrote:
As built, both the pattern
and the impedance already seem to be what I want.

And it already has a counterpoise. The counterpoise is where the current flowing on the inside of the coax shield goes when it leaves the coax. The J-pole has a radiation pattern of a 1/2WL vertical, i.e. the lower 1/4WL doesn't radiate (much) and is part of the matching section and counterpoise. Quite often, the outside of the coax braid is also part of the counterpoise.
--
73, Cecil, w5dxp.com

On Sat, 15 Feb 2014 13:27:15 -0800, "Sal" salmonella@food
poisoning.org wrote:

I had a question about his j-pole analysis. He says "A J-pole, like ANY end
fed antenna, needs radials, a counterpoise or ground plane to work
properly."

I've never seen this anywhere else, even as a suggestion or hint. I can
envision places to fit one but what would it do? As built, both the pattern
and the impedance already seem to be what I want.

Thoughts?

I agree with the author (Terry Graves K7FE).

The rule-of-thumb is that an end fed antenna requires a shield ground
to act as a counterpoise and to keep the coax from radiating. The
J-pole (and Zepp) antennas are not exactly end fed, but are close
enough. A possible exception to the rule is a 1/2 wave end fed
antenna, which allegedly does not require a ground plane. I'm
undecided on that point.

However, a J-pole (or Zepp) is not a 1/2 wave antenna. The driven
element is a 1/4 wavelength long, and therefore DOES require a ground
plane. This article covers the point (and more):
http://www.w8ji.com/end-fed_vertical_j-pole_and_horizontal_zepp.htm
Quoting:
Summary End-feds Without Grounds
ANY END-FED ANTENNA REQUIRES A LARGE GROUNDPLANE OR OTHER
EXTRAORDINARY ISOLATION METHOD OR METHODS TO PREVENT FEEDLINE
OR MAST COMMON MODE CURRENTS!
This is true for 5/8th waves, Zepp antennas, R7's, R5's, or
even common J-poles. End-feeding antennas is bad news unless
you have a large well-established ground at the feedpoint.
Even 1/4wl groundplanes have common mode problems. When I
designed a commercial 1/4 wave groundplane with four 1/4 wave
long radials, I had to insulate the radials from the mast and
isolate the coax shield from the mast and radials with a 1/4
wave stub that formed a choke balun. Without the decoupling,
I could change SWR simply by changing mast or feedline grounding.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558