Re: Topband: 1/2 wave inv L

[Rob Atkinson]

A 180 or 190 degree vertical radiator presents a few different
problems compared to one 90 degrees long, due to the high voltage at
the feedpoint.   You can have ground loss there, but since it is more
of a coupling problem than a return current problem, the earth shield
is usually a copper mesh that extends out around the pier about 20
feet.  Think in terms of the loss at the ends of an inverted V when
the ends are anchored near the ground.

Since the feedpoint is high voltage, the way in which the base of the
radiator is insulated becomes more important, and the ball gap must be
adjusted accordingly, and access to the area kept more secure to
prevent casual contact with the excited base of the radiator.  If a
concrete pier is used to hold a ceramic base insulator, the pier must
be bypassed with copper ground strap so it is not part of the voltage
gradient between the mesh and the radiator, as concrete is conductive.

For ham (in my opinion) none of this is worth the trouble, and I'd go
with a quarter wave antenna.

73

Rob
K5UJ
_
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Re: Topband: 1/2 wave inv L

[Charles Moizeau]

That is probably true but ONLY for an antenna that is 0.25 wavelength high 
where the current maximum is at the base feedpoint, right where those radials, 
also the same 0.25 wavelength in their length, connect.


Once the vertical antenna is made longer than 0.25 wavelength, e.g., 0.5 
wavelength, its current maximum will no longer be at ground level.  Rather, it 
will be, and always be, at 0.25 wavelength back from the/an open end.


With the maximum radiation occurring at a higher point, it strikes the ground 
further away; hence the need for longer radials to gather it in and return it 
to the feedpoint.


Charles, W2SH




From: Mark K3MSB <mark.k3...@gmail.com>
Sent: Sunday, February 18, 2018 7:40 PM
To: Charles Moizeau
Cc: Mike Waters; Roger Kennedy; topband@contesting.com
Subject: Re: Topband: 1/2 wave inv L

I've read that the minimum lengths for ground radials is no shorter than the 
height of the antenna and that 50% of ground losses occur in the first 
one-quarter wavelength distance from the antenna.

This tells me that "too long" radials have diminishing returns.

I've played the radials on ground game for years;  I think this year I want to 
try a pair of elevated radials as Mike W0BTU suggests.

73 Mark K3MSB


On Sun, Feb 18, 2018 at 6:56 PM, Charles Moizeau 
<w...@msn.com<mailto:w...@msn.com>> wrote:
Well it is understandable.  The current maximum in the half-wave antenna is 
lifted well above ground level.  Had there been a radial system it would have 
had to employ very long radials, for most of the vertical's radiation would 
have been hitting the ground at points far away from the base of the vertical.  
It is only at those distant points that very long radial wires would be able to 
gather the radiation from the ground's surface and feed it back to the 
feedpoint.


Charles, W2SH



From: Topband 
<topband-boun...@contesting.com<mailto:topband-boun...@contesting.com>> on 
behalf of Mike Waters <mikew...@gmail.com<mailto:mikew...@gmail.com>>
Sent: Sunday, February 18, 2018 6:31 PM
To: Roger Kennedy
Cc: topband@contesting.com<mailto:topband@contesting.com>
Subject: Re: Topband: 1/2 wave inv L

Yup! The lack of a radial system explains why the 1/2w vertical worked
better. :-)

73, Mike
https://nam03.safelinks.protection.outlook.com/?url=www.w0btu.com=02%7C01%7C%7C45041a0e70384ee2478008d57727b9e9%7C84df9e7fe9f640afb435%7C1%7C0%7C636545934864203108=Pk6iMJXzsyQupFqxoKoeDy7Qn7WTNUF%2BOgHr40Q5n6E%3D=0

On Feb 18, 2018 4:55 PM, "Roger Kennedy" 
<ro...@wessexproductions.co.uk<mailto:ro...@wessexproductions.co.uk>>
wrote:


Many years ago, a friend of mine used to operate on 160m with vertical
antennas suspended on a big Weather Balloon filled with hydrogen . . .

After using Quarter-wave verticals for a few months, he changed over to
Half-wave verticals . . . he found they worked much better !

He didn't have much of a radial system (due to lack of space), mainly just
earth rods at the base . . . so I suspect that's one of the reasons why.

Roger G3YRO
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Re: Topband: 1/2 wave inv L

[Mark K3MSB]

I've read that the minimum lengths for ground radials is no shorter than
the height of the antenna and that 50% of ground losses occur in the first
one-quarter wavelength distance from the antenna.

This tells me that "too long" radials have diminishing returns.

I've played the radials on ground game for years;  I think this year I want
to try a pair of elevated radials as Mike W0BTU suggests.

73 Mark K3MSB


On Sun, Feb 18, 2018 at 6:56 PM, Charles Moizeau <w...@msn.com> wrote:

> Well it is understandable.  The current maximum in the half-wave antenna
> is lifted well above ground level.  Had there been a radial system it would
> have had to employ very long radials, for most of the vertical's radiation
> would have been hitting the ground at points far away from the base of the
> vertical.  It is only at those distant points that very long radial wires
> would be able to gather the radiation from the ground's surface and feed it
> back to the feedpoint.
>
>
> Charles, W2SH
>
>
> 
> From: Topband <topband-boun...@contesting.com> on behalf of Mike Waters <
> mikew...@gmail.com>
> Sent: Sunday, February 18, 2018 6:31 PM
> To: Roger Kennedy
> Cc: topband@contesting.com
> Subject: Re: Topband: 1/2 wave inv L
>
> Yup! The lack of a radial system explains why the 1/2w vertical worked
> better. :-)
>
> 73, Mike
> https://nam03.safelinks.protection.outlook.com/?url=
> www.w0btu.com=02%7C01%7C%7C45041a0e70384ee2478008d57727b9e9%
> 7C84df9e7fe9f640afb435%7C1%7C0%7C636545934864203108=
> Pk6iMJXzsyQupFqxoKoeDy7Qn7WTNUF%2BOgHr40Q5n6E%3D=0
>
> On Feb 18, 2018 4:55 PM, "Roger Kennedy" <ro...@wessexproductions.co.uk>
> wrote:
>
>
> Many years ago, a friend of mine used to operate on 160m with vertical
> antennas suspended on a big Weather Balloon filled with hydrogen . . .
>
> After using Quarter-wave verticals for a few months, he changed over to
> Half-wave verticals . . . he found they worked much better !
>
> He didn't have much of a radial system (due to lack of space), mainly just
> earth rods at the base . . . so I suspect that's one of the reasons why.
>
> Roger G3YRO
> _
> Topband Reflector Archives - https://nam03.safelinks.
> protection.outlook.com/?url=http%3A%2F%2Fwww.contesting.
> com%2F_topband=02%7C01%7C%7C45041a0e70384ee2478008d57727b9e9%
> 7C84df9e7fe9f640afb435%7C1%7C0%7C636545934864203108=
> nFxj%2BLqwi1DLEFj3hHgpcSkBljKeHcT2AZrzNna7YSw%3D=0
> _
> Topband Reflector Archives - http://www.contesting.com/_topband
>
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Re: Topband: 1/2 wave inv L

[Charles Moizeau]

Well it is understandable.  The current maximum in the half-wave antenna is 
lifted well above ground level.  Had there been a radial system it would have 
had to employ very long radials, for most of the vertical's radiation would 
have been hitting the ground at points far away from the base of the vertical.  
It is only at those distant points that very long radial wires would be able to 
gather the radiation from the ground's surface and feed it back to the 
feedpoint.


Charles, W2SH



From: Topband <topband-boun...@contesting.com> on behalf of Mike Waters 
<mikew...@gmail.com>
Sent: Sunday, February 18, 2018 6:31 PM
To: Roger Kennedy
Cc: topband@contesting.com
Subject: Re: Topband: 1/2 wave inv L

Yup! The lack of a radial system explains why the 1/2w vertical worked
better. :-)

73, Mike
https://nam03.safelinks.protection.outlook.com/?url=www.w0btu.com=02%7C01%7C%7C45041a0e70384ee2478008d57727b9e9%7C84df9e7fe9f640afb435%7C1%7C0%7C636545934864203108=Pk6iMJXzsyQupFqxoKoeDy7Qn7WTNUF%2BOgHr40Q5n6E%3D=0

On Feb 18, 2018 4:55 PM, "Roger Kennedy" <ro...@wessexproductions.co.uk>
wrote:


Many years ago, a friend of mine used to operate on 160m with vertical
antennas suspended on a big Weather Balloon filled with hydrogen . . .

After using Quarter-wave verticals for a few months, he changed over to
Half-wave verticals . . . he found they worked much better !

He didn't have much of a radial system (due to lack of space), mainly just
earth rods at the base . . . so I suspect that's one of the reasons why.

Roger G3YRO
_
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Re: Topband: 1/2 wave inv L

[Mike Waters]

Save yourself some wire, and either search back through the Topband
archives or model your very tall vertical. :-)

Basically, it'll waste a lot of RF at unwanted high angles.

73, Mike
www.w0btu.com


On Feb 18, 2018 5:42 PM, "Charles Moizeau"  wrote:

... Now, years later, with a bit of experience in kite flying, a
not-so-distant public park with lots of open space and being a dedicated
QRPer, I'm tempted to try something larger than my 26m vertical + 21m
horizontal wire over a 2.5 km field of in-ground radials.  My thoughts are
centered on a kite-supported 7/8 wavelength vertical, the 4/8 wavelength
bottom section base fed through an LC tank circuit, decoupled from the top
3/8 wavelength section by just a capacitor.
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Re: Topband: 1/2 wave inv L

[Charles Moizeau]

Years ago I tried a a weather balloon filled with hydrogen from a hired 
canister.  The balloon's spherical shape made it highly susceptible to being 
disturbed by even a fairly mild breeze.  In my case the vertical wire was 
tilted well away from being vertical.  Fairly soon the balloon met the branch 
of what was a pretty distant tree.  Pop!  Down came the wire and the ARRL 
Topband contest which had just begun was finished (quite respectably, I should 
add) with a center-fed dipole.


Now, years later, with a bit of experience in kite flying, a not-so-distant 
public park with lots of open space and being a dedicated QRPer, I'm tempted to 
try something larger than my 26m vertical + 21m horizontal wire over a 2.5 km 
field of in-ground radials.  My thoughts are centered on a kite-supported 7/8 
wavelength vertical, the 4/8 wavelength bottom section base fed through an LC 
tank circuit, decoupled from the top 3/8 wavelength section by just a capacitor.


72 (QRP-speak for 73),


Charles, W2SH



From: Topband  on behalf of Roger Kennedy 

Sent: Sunday, February 18, 2018 5:54 PM
To: topband@contesting.com
Subject: Topband: 1/2 wave inv L


Many years ago, a friend of mine used to operate on 160m with vertical
antennas suspended on a big Weather Balloon filled with hydrogen . . .

After using Quarter-wave verticals for a few months, he changed over to
Half-wave verticals . . . he found they worked much better !

He didn't have much of a radial system (due to lack of space), mainly just
earth rods at the base . . . so I suspect that's one of the reasons why.

Roger G3YRO


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Re: Topband: 1/2 wave inv L

[Mike Waters]

Yup! The lack of a radial system explains why the 1/2w vertical worked
better. :-)

73, Mike
www.w0btu.com

On Feb 18, 2018 4:55 PM, "Roger Kennedy" 
wrote:


Many years ago, a friend of mine used to operate on 160m with vertical
antennas suspended on a big Weather Balloon filled with hydrogen . . .

After using Quarter-wave verticals for a few months, he changed over to
Half-wave verticals . . . he found they worked much better !

He didn't have much of a radial system (due to lack of space), mainly just
earth rods at the base . . . so I suspect that's one of the reasons why.

Roger G3YRO
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: 1/2 wave inv L

[Guy Olinger K2AV]

If one is not talking about ham implementations of the commercial AM
BC paradigm and their big verticals over very well done dense radial
fields, the models can do quite poorly. Go ask W7EL. But then again,
what other tools do we have to go with.

It's a little dangerous extrapolating between 80 and 160, either way.
W8JI had up a full sized 160 dipole at a half wave, which he says
rarely outperformed a high grade 1/4 wave vertical.

An 80 meter dipole at 120 feet is a really good antenna, and at NY4A a
full sized 4 element 80m wire yagi off a catenary at that height was a
true killer antenna. Been there done that! IF it was in maintenance,
it always seriously beat a well-done 4 square.

An end-fed half-wave L on 80 is a really good antenna, usually better
all around than an 80 inverted vee, apex at 76' feet at my QTH. The L
was always better on DX. Many A/B tests. The models insisted that for
many paths the Vee had a four or five dB advantage, an advantage which
I never, ever heard. This is my experiential reason for distrusting
what the models say about an end-fed halfwave L.

The problem with a big end-supported tee on 160 is all mechanical, the
distance between the supporting ends and the middle gives the weight
of the vertical wire a huge leverage advantage over the horizontal
pull at the ends, usually making it a "Y" antenna instead of a T.

This is why those kinds of top loaded antennas usually wind up
supported in the center with significantly sloping sides, appearing
like an arrow pointed up. This also reduces the effective radiation
from the top, counter-productive to the originally intended
performance of pushing RF current density, hence radiation, up high.

I would definitely top-load a T's center-supported vertical first with
a substantial coil up top and then significantly shorten the T wires.

If you actually had the means to support both the center and ends of a
160 dipole turned into a "T" with current max up top, chances are you
have the room for a good implementation of the commercial AM BC
paradigm. A good commercial quality 160 1/4 wave over dense full size
radials does not disappoint.

Personally, with a 160 3/8 wave L, up 90, out 105 for seven years, I
always thought it covered what otherwise would be holes in the
coverage for a pure vertical.

Where I finally got to with that concept was to top an L with the
electrical equivalent of ~95 feet horizontal. Call it a 65-70 degree
"topper wire".

The effect of that was to place 1/16 wave with the densest RF current
at the top of the vertical, above man-made clutter, and with a much
shorter path through RF absorbent tree tops to low angles of takeoff.
That really was what was going on with my up 90 out 105.

It also reduced the RF current in the antenna near the ground.
The 65 degree topper could be successfully used with as little as 55
feet available horizontally, by dropping down from the far end of the
horizontal as much as 40 feet, making it a sort-of inverted U. And of
course you would put up *as much vertical as was possible*. This DID
usually result in a miscellaneous feed Z that required some amount of
base feeding network.

For the I-want-to-hook-it-directly-to-50-ohm-coax-and-forget-it crowd
this is disqualifying, probably accounting for the lack of popularity.
Can't buy an end feed matcher for an L off anyone's shelf.

The far end of the L or U can be trimmed for X=0, R=whatever, losing
some of the current density up high, but possibly allowing
base-network-less operation

On Sun, Feb 15, 2015 at 5:52 PM, Richard (Rick) Karlquist
 wrote:
> On 2/15/2015 2:35 PM, Art Snapper wrote:
>>
>> I have been researching the inverted L for 160, and have received much
>> helpful information. - Thanks!
>>
>> Today I stumbled across a document regarding the 1/2 wave inverted L.
>>
>> Has anyone done a side-by-side comparison?
>> Art NK8X
>> _
>
>
> I have modeled it and the results are predictable.  About
> half your power goes into likely useless horizontally
> polarized radiation.  If you instead make a top loaded
> ("T" type) vertical where the sum of the height and half
> the top wire is a half wave, then you get a "voltage fed"
> vertical that behaves pretty much like a half wave
> vertical.  Since the drive impedance is high, you MIGHT
> get away with a much less extensive counterpoise.
> There is some controversy about this.
>
> Rick N6RK
>
> _
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Re: Topband: 1/2 wave inv L

[Richard (Rick) Karlquist]

On 2/15/2015 2:35 PM, Art Snapper wrote:

I have been researching the inverted L for 160, and have received much
helpful information. - Thanks!

Today I stumbled across a document regarding the 1/2 wave inverted L.

Has anyone done a side-by-side comparison?
Art NK8X
_


I have modeled it and the results are predictable.  About
half your power goes into likely useless horizontally
polarized radiation.  If you instead make a top loaded
(T type) vertical where the sum of the height and half
the top wire is a half wave, then you get a voltage fed
vertical that behaves pretty much like a half wave
vertical.  Since the drive impedance is high, you MIGHT
get away with a much less extensive counterpoise.
There is some controversy about this.

Rick N6RK
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