Topband: inverted L antenna match system

[sasas asasas]

Hi. I have a 500w linear amplifier at 160m band. The output is 50ohm. My antenna is an inverted L with lenght = [5*(wave lenght)]/16. I read at ARRL handbook that a variable series capacitor 0-1000pf is enought to match the transmitter with my antenna. What do you think about this? Do you have to propose anything else? (maybe a variable coil with the one point grounded and the other point connected between capacitor and linear's output)?
I have install 6 radials (2 are (wave lenght)/4 and the other 4 (wave lenght)/8)

[Mike Waters W0BTU]

> From: sasas asasas <tzitzikas_ee at yahoo.com>
> Subject: Topband: inverted L antenna match system
> ... My antenna is an inverted L
> with length = [5*(wave length)]/16. I read at ARRL handbook
> that a variable series capacitor 0-1000pf is enough to
> match the transmitter with my antenna. What do you think
> about this? ...

The formula you provide above calculates to a total length of your inverted-L of 50 meters (164 feet), if wave length=160.

My 150 foot inverted-L (vertical portion is 50 feet) has the following matching arrangement to reduce the SWR to 1:1 at the feedpoint:

approx. 350 pf series capacitor from coax center conductor to Inv-L
approx. 200 pf parallel capacitor from Inv-L(and 300 pf cap.) to ground radials.

No coils were required in my case. Both capacitors are air variables,

No ground rod was used. Coax choke at feedpoint.

Hope this helps. Your results may vary.

73 Mike

[Charles Moizeau]

Here is how I did it, along with my reasoning
behind the
design.



I have a tall ash tree and was able to achieve an 85' vertical run with
an easy
bow-and-arrow shot. I elected to build
an inverted L antenna



I knew that the current maximum in any antenna is where maximal
radiation
occurs, and that the current maximum in any antenna occurs a
quarter-wavelength
back from the wire's open end(-s). I
wanted as much radiation as possible to occur from the vertical portion
of my
antenna. With an antenna's sinusoidal
current distribution, that meant that I should make the length of the
antenna's
horizontal portion such that the current maximum would be positioned at
the
center of the vertical section.



I reckoned a quarter wavelength of #12 gauge solid copper insulated
house wire
to be about 128 feet. So with 85' up I
made the horizontal leg 85' out. Do the
arithmetic and you'll see that the current maximum occurs where I wanted
it.



I could point the horizontal leg in almost any direction, but I chose to
run it
towards the northeast. I did this so
that the antenna's horizontal radiation would be favored by a dB or so
from the
"elbow" of the inverted L towards the southwest.



I ran my 52-Ohm coax in a buried pvc conduit to the vertical portion's
base. With the antenna?s overall length of somewhat greater than 1/4
wavelength (in fact about 1/3 wavelength), there is an inductive
reactance at
the base feedpoint, so all I needed for matching was just some
capacitance
between the feedpoint and the 50-Ohm coax.
I used a husky transmitting variable capacitor. I
haven?t pulled it to measure its value,
but my eyeball guess is about 300 pF.



I have thus avoided a lossy inductor anywhere
within the
antenna, and at the shack there is no balun or antenna tuner with their
losses.



With eight in-ground radials I could adjust the capacitor to give me a
1.5:1
SWR at 1.810 mHz. I added six more
radials, readjusted the capacitor to get a 1.35:1 SWR, and then brought
that
down to 1.2:1 with 22 radials.



The antenna performs well on 160m.
Without any real effort, this past winter I worked several
European
countries with five Watts, and no QSOs occurred during contests.



If I had had only, say, a 40' vertical run, I would have adjusted the
length of
the horizontal leg accordingly. And if
I were space limited for the horizontal leg, I would have used linear
loading
to reduce the needed length by a third or so, or would have made a bend
in the
horizontal portion to fit it in the space available; i.e., do whatever
is
needed to locate the antenna's current maximum at the vertical leg's
center.



I do worry about the emerald ash borer, imported from China in the
wooden
packing crates used to pack stuff coming from there. Nothing
has yet been discovered to eradicate this pest that has
killed many thousands of ash trees in this country (including four of
mine so
far). Also, laying in radials that
range from 70 to 160 feet in length is very slow and tedious work when
extracting lots of rocks and going around tree trunks and under their
roots
near the surface.

72,



Charles, W2SH

[sasas asasas]

thank you all of you for your answers.

So more radials, means lower swr?

Do you think that the variable capacitor is all i need for low swr? If
i will not achieve swr<1.5 what do you think about to try to use a
variable coil, which will be connected between the common point (of
capacitor and 50ohm coax from transmitter) and ground. It will help to
achieve low swr?

How many uH must be this coil?

i mean something like this http://tzitzikas.webs.com/COUPLER.JPG

(without optional turns which are in series with capacitor).


--- On Sun, 5/30/10, Charles Moizeau <w2sh at msn.com> wrote:

From: Charles Moizeau <w2sh at msn.com>
Subject: Re: Topband: inverted L antenna match system
To: topband at contesting.com
Date: Sunday, May 30, 2010, 12:57 PM


Here is how I did it, along with my reasoning
behind the
design.



I have a tall ash tree and was able to achieve an 85' vertical run with
an easy
bow-and-arrow shot.? I elected to build
an inverted L antenna?



I knew that the current maximum in any antenna is where maximal
radiation
occurs, and that the current maximum in any antenna occurs a
quarter-wavelength
back from the wire's open end(-s).? I
wanted as much radiation as possible to occur from the vertical portion
of my
antenna.? With an antenna's sinusoidal
current distribution, that meant that I should make the length of the
antenna's
horizontal portion such that the current maximum would be positioned at
the
center of the vertical section.



I reckoned a quarter wavelength of #12 gauge solid copper insulated
house wire
to be about 128 feet.? So with 85' up I
made the horizontal leg 85' out.? Do the
arithmetic and you'll see that the current maximum occurs where I wanted
it.



I could point the horizontal leg in almost any direction, but I chose to
run it
towards the northeast.? I did this so
that the antenna's horizontal radiation would be favored by a dB or so
from the
"elbow" of the inverted L towards the southwest.



I ran my 52-Ohm coax in a buried pvc conduit to the vertical portion's
base.? With the antenna?s overall length of somewhat greater than 1/4
wavelength (in fact about 1/3 wavelength), there is an inductive
reactance at
the base feedpoint, so all I needed for matching was just some
capacitance
between the feedpoint and the 50-Ohm coax.
I used a husky transmitting variable capacitor.? I
haven?t pulled it to measure its value,
but my eyeball guess is about 300 pF.?



I have thus avoided a lossy inductor anywhere
within the
antenna, and at the shack there is no balun or antenna tuner with their
losses.



With eight in-ground radials I could adjust the capacitor to give me a
1.5:1
SWR at 1.810 mHz.? I added six more
radials, readjusted the capacitor to get a 1.35:1 SWR, and then brought
that
down to 1.2:1 with 22 radials.



The antenna performs well on 160m.
Without any real effort, this past winter I worked several
European
countries with five Watts, and no QSOs occurred during contests.



If I had had only, say, a 40' vertical run, I would have adjusted the
length of
the horizontal leg accordingly.? And if
I were space limited for the horizontal leg, I would have used linear
loading
to reduce the needed length by a third or so, or would have made a bend
in the
horizontal portion to fit it in the space available; i.e., do whatever
is
needed to locate the antenna's current maximum at the vertical leg's
center.



I do worry about the emerald ash borer, imported from China in the
wooden
packing crates used to pack stuff coming from there.? Nothing
has yet been discovered to eradicate this pest that has
killed many thousands of ash trees in this country (including four of
mine so
far).? Also, laying in radials that
range from 70 to 160 feet in length is very slow and tedious work when
extracting lots of rocks and going around tree trunks and under their
roots
near the surface.

72,



Charles, W2SH ??? ???????? ?????? ??? ?
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK

[Rob Stampfli]

On Mon, May 31, 2010 at 05:00:32AM -0700, sasas asasas wrote:
> thank you all of you for your answers.
>
> So more radials, means lower swr?
>
> Do you think that the variable capacitor is all i need for low swr? If
> i will not achieve swr<1.5 what do you think about to try to use a
> variable coil, which will be connected between the common point (of
> capacitor and 50ohm coax from transmitter) and ground. It will help to
> achieve low swr?

Typically, putting in radials raises the SWR, but you add them in
anyway because they make the antenna more efficient, allowing you
to radiate more signal instead of heating the ground with it. You
then add capacitors and coils to translate the antenna's native
impedence into something that will keep the coax feedline and
exciter happy. (And, to some extent, capacitors are preferred,
as they are less lossy than coils.)

Remember: A dummy load has a near perfect SWR, but doesn't radiate
worth a darn.

Rob

[Guy Olinger K2AV]

Lowering Z with more radials is the classic sign of reducing lossy
series resistance in the ground system. This is a straight power loss
to RF heated dirt which adds to the radiation resistance of the
antenna. The SYSTEM impedance is the sum of the two. The bandwidth
narrows and the Z to match lowers as additional radials lower the
ground loss.

The reason for bandwidth narrowing is that the ground loss is quite
flat with frequency, while an efficient radiator will be close to its
theoretical bandwidth as computed in models.

73, Guy.

On Mon, May 31, 2010 at 8:00 AM, sasas asasas <tzitzikas_ee at yahoo.com> wrote:
> thank you all of you for your answers.
>
> So more radials, means lower swr?
>
> Do you think that the variable capacitor is all i need for low swr? If
> i will not achieve swr<1.5 what do you think about to try to use a
> variable coil, which will be connected between the common point (of
> capacitor and 50ohm coax from transmitter) and ground. It will help to
> achieve low swr?
>
> How many uH must be this coil?
>
> i mean something like this http://tzitzikas.webs.com/COUPLER.JPG
>
> (without optional turns which are in series with capacitor).
>
>
> --- On Sun, 5/30/10, Charles Moizeau <w2sh at msn.com> wrote:
>
> From: Charles Moizeau <w2sh at msn.com>
> Subject: Re: Topband: inverted L antenna match system
> To: topband at contesting.com
> Date: Sunday, May 30, 2010, 12:57 PM
>
>
> Here is how I did it, along with my reasoning
> behind the
> design.
>
>
>
> I have a tall ash tree and was able to achieve an 85' vertical run with
> an easy
> bow-and-arrow shot.? I elected to build
> an inverted L antenna
>
>
>
> I knew that the current maximum in any antenna is where maximal
> radiation
> occurs, and that the current maximum in any antenna occurs a
> quarter-wavelength
> back from the wire's open end(-s).? I
> wanted as much radiation as possible to occur from the vertical portion
> of my
> antenna.? With an antenna's sinusoidal
> current distribution, that meant that I should make the length of the
> antenna's
> horizontal portion such that the current maximum would be positioned at
> the
> center of the vertical section.
>
>
>
> I reckoned a quarter wavelength of #12 gauge solid copper insulated
> house wire
> to be about 128 feet.? So with 85' up I
> made the horizontal leg 85' out.? Do the
> arithmetic and you'll see that the current maximum occurs where I wanted
> ?it.
>
>
>
> I could point the horizontal leg in almost any direction, but I chose to
> ?run it
> towards the northeast.? I did this so
> that the antenna's horizontal radiation would be favored by a dB or so
> from the
> "elbow" of the inverted L towards the southwest.
>
>
>
> I ran my 52-Ohm coax in a buried pvc conduit to the vertical portion's
> base.? With the antenna?s overall length of somewhat greater than 1/4
> wavelength (in fact about 1/3 wavelength), there is an inductive
> reactance at
> the base feedpoint, so all I needed for matching was just some
> capacitance
> between the feedpoint and the 50-Ohm coax.
> I used a husky transmitting variable capacitor.? I
> ?haven?t pulled it to measure its value,
> but my eyeball guess is about 300 pF.
>
>
>
> I have thus avoided a lossy inductor anywhere
> within the
> antenna, and at the shack there is no balun or antenna tuner with their
> losses.
>
>
>
> With eight in-ground radials I could adjust the capacitor to give me a
> 1.5:1
> SWR at 1.810 mHz.? I added six more
> radials, readjusted the capacitor to get a 1.35:1 SWR, and then brought
> that
> down to 1.2:1 with 22 radials.
>
>
>
> The antenna performs well on 160m.
> Without any real effort, this past winter I worked several
> European
> countries with five Watts, and no QSOs occurred during contests.
>
>
>
> If I had had only, say, a 40' vertical run, I would have adjusted the
> length of
> the horizontal leg accordingly.? And if
> I were space limited for the horizontal leg, I would have used linear
> loading
> to reduce the needed length by a third or so, or would have made a bend
> in the
> horizontal portion to fit it in the space available; i.e., do whatever
> is
> needed to locate the antenna's current maximum at the vertical leg's
> center.
>
>
>
> I do worry about the emerald ash borer, imported from China in the
> wooden
> packing crates used to pack stuff coming from there.? Nothing
> ?has yet been discovered to eradicate this pest that has
> killed many thousands of ash trees in this country (including four of
> mine so
> far).? Also, laying in radials that
> range from 70 to 160 feet in length is very slow and tedious work when
> extracting lots of rocks and going around tree trunks and under their
> roots
> near the surface.
>
> 72,
>
>
>
> Charles, W2SH
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
>
>
>
>
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK

[Charles Moizeau]

More radials will reduce losses. Crudely put, they will reduce dc losses at the base and they will also reduce rf losses by capturing some of the rf that is radiated by the antenna but splashes off the ground instead of zinging away into space, and then recycling that rf at the base feedpoint.

It is my belief that if the point of maximum radiation is made to occur higher on the vertical section of the antenna, then the rf will splash further away from the base, and this suggests the need for longer radials to gather in the errant rf.

Will more radials change the feedpoint impedance? Yes.

Will more radials change the SWR? Ceteris paribus, Yes.

Will the SWR go up or down? It can go either way, but I didn't care, for I was able to twiddle the matching device, a series variable capacitor hooked between the hot side of the feedline and the vertical radiator, and achieve a progressively lower SWR after increasing the number of radials.

Will the bandwidth be reduced with more radials? Yes, after the system is tuned for minimal SWR?

Is reduced bandwidth a problem? Not for this QRPer who hangs out close to 1.810 mHz. And if I want to go way higher in the band, I insert a high power antenna tuner located in the shack into the works and make the necessary adjustments to reduce the SWR.

What about coils? Why bother introducing their certain losses if you can do a design that avoids them?

72,

Charles, W2SH



> Date: Mon, 31 May 2010 05:00:32 -0700
> From: tzitzikas_ee at yahoo.com
> To: topband at contesting.com; w2sh at msn.com
> Subject: Re: Topband: inverted L antenna match system
>
> thank you all of you for your answers.
>
> So more radials, means lower swr?
>
> Do you think that the variable capacitor is all i need for low swr? If
> i will not achieve swr<1.5 what do you think about to try to use a
> variable coil, which will be connected between the common point (of
> capacitor and 50ohm coax from transmitter) and ground. It will help to
> achieve low swr?
>
> How many uH must be this coil?
>
> i mean something like this http://tzitzikas.webs.com/COUPLER.JPG
>
> (without optional turns which are in series with capacitor).
>
>

[Petr Ourednik]

Hello friends,

if You are looking for remote controlled antenna switch then there is
the secret sources for
the 4-positions antenna switch DTS-4 from LDG. (discontinued long time
ago)

DTS-4R (remote control unit)
http://www.cheapham.com/LDG.html

DTS-4(S) (antenna switch unit)
http://www.elix-shop.cz/store/goodsdetail.asp?strGoodsID=66246

I ordered both units today so I hope it will arrive soon.

If You will need assistance/help with ordering the DTS-4 unit as it is
Czech site then let me know.

73 - Petr, OK1RP

[k8gg]

Fellow Topbanders,

"sasas asasas" <tzitzikas_ee at yahoo.com>
wrote:

> Hi. I have a 500w linear amplifier at 160m band.
The output is 50ohm. My
> antenna is an inverted L with lenght =
[5*(wave lenght)]/16. I read at
> ARRL handbook that a variable
series capacitor 0-1000pf is enought to
> match the transmitter
with my antenna. What do you think about this? Do
> you have to
propose anything else? (maybe a variable coil with the one
>
point grounded and the other point connected between capacitor and
> linear's output)?
> I have install 6 radials (2 are (wave
lenght)/4 and the other 4 (wave
> lenght)/8)
>?

>From both modelling and actual experience I have found that a 5/16
wavelength (wl) inverted-L antenna over a good ground has a feed point
impedance Zant of approximately:

Zant = 50 + 200j ohms.

The actual dimensions we used some years back on Curacao were 85
feet up and 75 feet out with about a 20 degree down slope on the
"horizontal" part of the wire.? There were 40?radials
each about 80 feet long in the ground system over sandy rocky soils.?
We were able to tune the antenna with a series capacitor to achieve Zant =
50 +/- 0j ohms.? The capacitor was set at approximately 450 pfd on a
1000 pfd 5000 V vacuum variable.

Using only 6 radials will not
achieve the desired results as ground losses will increase and Zant will
be greater than 50 ohms.??

If the ground system is
kept as described above, then either:
1.? An L-network to bring
the impedance down to 50 ohm can be used or
2.? The antenna
length can be shortened to bring the inpedance to Zant = 50 + XXj ohms
where the XX value can be tuned out by the series capacitor.? If one
has some sort of impedance bridge this is not hard to measure on a trial
and error basis.? Don't forget that the end wire folded back on
itself will act like the fold point is the end if it is clamped tightly to
the "live end" of the antenna wire:

??????
-------------------------------=====================0? <---
insulator

I hope this helps.? GL??
73??? George?? K8GG

[sasas asasas]

Hi, and thank you for your interest post. In my case is difficult to install so many radials. You can see a drawing about my transmitter area here:
http://tzitzikas.webs.com/transmitter_area.JPG
the transmitter is about 9 meters above the ground. For ground system i have also install a ground copper rod about 2 meters vertically on ground. The distance between transmitter and this copper rod is 9 meters. Helps the copper rod to have lower ground losses, and the antenna's resictance to be near 50 ohm? How many radials i must install to have 50ohm antenna's recictance?
You can see at the above link that i can't install radials at any direction. But i can install more radials l/8 at the two directions that i have install my six radials.

--------------------------------------------------------------------- http://tzitzikas.site90.net (tzitzikas site)
http://forum.tzitzikas.site90.net (tzitzikas forum) ---------------------------------------------------------------------

--- On Wed, 6/2/10, k8gg at voyager.net <k8gg at voyager.net> wrote:

From: k8gg at voyager.net <k8gg at voyager.net>
Subject: Re: Topband: inverted L antenna match system
To: "sasas asasas" <tzitzikas_ee at yahoo.com>
Cc: topband at contesting.com
Date: Wednesday, June 2, 2010, 8:38 AM



Fellow Topbanders,

"sasas asasas" <tzitzikas_ee at yahoo.com>
wrote:

> Hi. I have a 500w linear amplifier at 160m band.
The output is 50ohm. My
> antenna is an inverted L with lenght =
[5*(wave lenght)]/16. I read at
> ARRL handbook that a variable
series capacitor 0-1000pf is enought to
> match the transmitter
with my antenna. What do you think about this? Do
> you have to
propose anything else? (maybe a variable coil with the one
>
point grounded and the other point connected between capacitor and
> linear's output)?
> I have install 6 radials (2 are (wave
lenght)/4 and the other 4 (wave
> lenght)/8)
>?

>From both modelling and actual experience I have found that a 5/16
wavelength (wl) inverted-L antenna over a good ground has a feed point
impedance Zant of approximately:

Zant = 50 + 200j ohms.

The actual dimensions we used some years back on Curacao were 85
feet up and 75 feet out with about a 20 degree down slope on the
"horizontal" part of the wire.? There were 40?radials
each about 80 feet long in the ground system over sandy rocky soils.?
We were able to tune the antenna with a series capacitor to achieve Zant =
50 +/- 0j ohms.? The capacitor was set at approximately 450 pfd on a
1000 pfd 5000 V vacuum variable.

Using only 6 radials will not
achieve the desired results as ground losses will increase and Zant will
be greater than 50 ohms.??

If the ground system is
kept as described above, then either:
1.? An L-network to bring
the impedance down to 50 ohm can be used or
2.? The antenna
length can be shortened to bring the inpedance to Zant = 50 + XXj ohms
where the XX value can be tuned out by the series capacitor.? If one
has some sort of impedance bridge this is not hard to measure on a trial
and error basis.? Don't forget that the end wire folded back on
itself will act like the fold point is the end if it is clamped tightly to
the "live end" of the antenna wire:

??????
-------------------------------=====================0? <---
insulator

I hope this helps.? GL??
73??? George?? K8GG

_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK