Elecraft

Random wires

Classic

List

Threaded

30 messages Options

bill.va3ol

Random wires

My antennas for the past few years have been Alpha Delta Dipoles (an 80/40
and a 40-10) plus an 88 foot CFZ. When I began looking for a 160 meter
antenna I came across the Balun Design website which had a 9:1 unun plus an
article on using it with a single wire for all band performance. It sounded
to good to be true and you know the old saying ...... it probably is.
Remember that I have a 125 foot run of coax to a remote antenna switch up
the hill, in my little forest so line losses due to SWR are a major
concern.

Well, I ordered their 9:1 unun and hung a 124 foot inverted L set up at 25
feet. My experience tells me that it is worth the trouble to get it up
higher once the leaves are gone. The original radial system was 8 – 10 foot
radials, 2 - 15 foot radials and 1 - 30 foot radial.

Here are my initial findings:

160 meters: less than 3:1 across the band

80 meters: less than 4:1 across the band

40 meters: less than 3.5:1 across the band

30 meters: less than 1.5:1

20 meters: between 2.1 and 1.1

17 meters: between 2.5 and 2.1

15 meters: between 1.7 and 1.5

12 meters: 1.7 across the band

10 meters: less than 1.7 across the band

The above measurements were made with a Rigexpert AA-54.

After tweeking the radials, spreading them out more and adding a few more
longer radials I used K3-EZ software to sweep each band and got very
similar results. My goal was to get access to 160 which I achieved along
with access to all of the WARC bands as a bonus. I should mention that I am
using the 5kw version to allow for the added stress of a higher than
desired SWR and an amplifier on occasion.

The BalunDesigns.com website has the article linked from this page:
http://www.balundesigns.com/servlet/the-106/9-cln-1-9-dsh-1-unun/Detail

I have no interest in the company, etc. Etc.

Bill, VA3OL
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

Barry K3NDM

Re: Random wires

Bill,
I have used/built/designed many antennas over the years. I have had
a number of favorite antennas over along ham career. My only concerns
have been line loss due to SWR and launch angle. There have been a few
minor concerns like can I really put that thing up or not.

As I read your post, I infer that at the moment you are wanting to
add 160 meters to your capability. An antenna that I have used and liked
is the Twin Lead Marconi. It's a simple, cheap, and effective antenna. I
first saw it written up by Bill Orr years ago. The premise of the design
is that a quarter wave antenna driven against ground may not be the most
efficient antenna due to low radiation resistance. Therefore, raise the
radiation resistance by using the theory of a folded dipole. The folded
element raises the radiation resistance by a factor of 4 for 2 elements
as the impedance changes as the square of the number of elements. You
will still need radials, but your ground losses will decrease.

Another antenna that I have used successfully is the center fed 80
meter dipole fed with open wire feeder. With an antenna tuner it's an
all band antenna and losses are low because you are using open wire
transmission line. A 4:1 balun located near the point where you egress
your house allows you to transition to low loss coax, like LMR-400. I
use a variant of this during Field Day where one of our runs is 370+
feet long. This works fine with QRP; look for NA3DX in the rankings when
the ARRL publishes the FD results.

73,
Barry
K3NDM

On 10/1/2013 2:35 PM, [hidden email] wrote:

> My antennas for the past few years have been Alpha Delta Dipoles (an 80/40
> and a 40-10) plus an 88 foot CFZ. When I began looking for a 160 meter
> antenna I came across the Balun Design website which had a 9:1 unun plus an
> article on using it with a single wire for all band performance. It sounded
> to good to be true and you know the old saying ...... it probably is.
> Remember that I have a 125 foot run of coax to a remote antenna switch up
> the hill, in my little forest so line losses due to SWR are a major
> concern.
>
>
> Well, I ordered their 9:1 unun and hung a 124 foot inverted L set up at 25
> feet. My experience tells me that it is worth the trouble to get it up
> higher once the leaves are gone. The original radial system was 8 – 10 foot
> radials, 2 - 15 foot radials and 1 - 30 foot radial.
>
>
> Here are my initial findings:
>
>
> 160 meters: less than 3:1 across the band
>
> 80 meters: less than 4:1 across the band
>
> 40 meters: less than 3.5:1 across the band
>
> 30 meters: less than 1.5:1
>
> 20 meters: between 2.1 and 1.1
>
> 17 meters: between 2.5 and 2.1
>
> 15 meters: between 1.7 and 1.5
>
> 12 meters: 1.7 across the band
>
> 10 meters: less than 1.7 across the band
>
> The above measurements were made with a Rigexpert AA-54.
>
>
> After tweeking the radials, spreading them out more and adding a few more
> longer radials I used K3-EZ software to sweep each band and got very
> similar results. My goal was to get access to 160 which I achieved along
> with access to all of the WARC bands as a bonus. I should mention that I am
> using the 5kw version to allow for the added stress of a higher than
> desired SWR and an amplifier on occasion.
>
>
> The BalunDesigns.com website has the article linked from this page:
> http://www.balundesigns.com/servlet/the-106/9-cln-1-9-dsh-1-unun/Detail
>
>
> I have no interest in the company, etc. Etc.
>
>
> Bill, VA3OL
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

Roger D Johnson

Re: Random wires

This is NOT true! It merely raises the feedpoint impedance...just the same as
adding a
4-1 transformer.

73, Roger

On 10/1/2013 3:10 PM, Barry LaZar wrote:

>
>
> As I read your post, I infer that at the moment you are wanting to add 160
> meters to your capability. An antenna that I have used and liked is the Twin
> Lead Marconi. It's a simple, cheap, and effective antenna. I first saw it
> written up by Bill Orr years ago. The premise of the design is that a quarter
> wave antenna driven against ground may not be the most efficient antenna due
> to low radiation resistance. Therefore, raise the radiation resistance by
> using the theory of a folded dipole. The folded element raises the radiation
> resistance by a factor of 4 for 2 elements as the impedance changes as the
> square of the number of elements. You will still need radials, but your ground
> losses will decrease.
>
>
> 73,
> Barry
> K3NDM
>
>

Vic Rosenthal

Re: Random wires

Another way to look at it is that it multiplies the radiation resistance, but does the
same for the ground resistance. So efficiency is unchanged.

On 10/1/2013 12:40 PM, Roger D Johnson wrote:

> This is NOT true! It merely raises the feedpoint impedance...just the same as adding a
> 4-1 transformer.
>
> 73, Roger
>
>
> On 10/1/2013 3:10 PM, Barry LaZar wrote:
>>
>>
>> As I read your post, I infer that at the moment you are wanting to add 160 meters to
>> your capability. An antenna that I have used and liked is the Twin Lead Marconi. It's a
>> simple, cheap, and effective antenna. I first saw it written up by Bill Orr years ago.
>> The premise of the design is that a quarter wave antenna driven against ground may not
>> be the most efficient antenna due to low radiation resistance. Therefore, raise the
>> radiation resistance by using the theory of a folded dipole. The folded element raises
>> the radiation resistance by a factor of 4 for 2 elements as the impedance changes as the
>> square of the number of elements. You will still need radials, but your ground losses
>> will decrease.
>>
>>
>> 73,
>> Barry
>> K3NDM
>>
>>
>

--
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

sfbonk

Re: Random wires

In reply to this post by bill.va3ol

There is an old W1BB drawing of a 160 L with a series capacitor which is longer than a 1/4 wave to feed it at a higher impedance point to get higher efficiency. Other neat drawing from him has an old car buried as part of the ground.

W3OU Steve

-----Original Message-----
From: bill.va3ol <[hidden email]>
To: elecraft list <[hidden email]>; qrp-l list <[hidden email]>
Sent: Tue, Oct 1, 2013 2:35 pm
Subject: [Elecraft] Random wires

My antennas for the past few years have been Alpha Delta Dipoles (an 80/40
and a 40-10) plus an 88 foot CFZ. When I began looking for a 160 meter
antenna I came across the Balun Design website which had a 9:1 unun plus an
article on using it with a single wire for all band performance. It sounded
to good to be true and you know the old saying ...... it probably is.
Remember that I have a 125 foot run of coax to a remote antenna switch up
the hill, in my little forest so line losses due to SWR are a major
concern.

Well, I ordered their 9:1 unun and hung a 124 foot inverted L set up at 25
feet. My experience tells me that it is worth the trouble to get it up
higher once the leaves are gone. The original radial system was 8 – 10 foot
radials, 2 - 15 foot radials and 1 - 30 foot radial.

Here are my initial findings:

160 meters: less than 3:1 across the band

80 meters: less than 4:1 across the band

40 meters: less than 3.5:1 across the band

30 meters: less than 1.5:1

20 meters: between 2.1 and 1.1

17 meters: between 2.5 and 2.1

15 meters: between 1.7 and 1.5

12 meters: 1.7 across the band

10 meters: less than 1.7 across the band

The above measurements were made with a Rigexpert AA-54.

After tweeking the radials, spreading them out more and adding a few more
longer radials I used K3-EZ software to sweep each band and got very
similar results. My goal was to get access to 160 which I achieved along
with access to all of the WARC bands as a bonus. I should mention that I am
using the 5kw version to allow for the added stress of a higher than
desired SWR and an amplifier on occasion.

The BalunDesigns.com website has the article linked from this page:
http://www.balundesigns.com/servlet/the-106/9-cln-1-9-dsh-1-unun/Detail

I have no interest in the company, etc. Etc.

Bill, VA3OL
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

David Gilbert

Re: Random wires

In reply to this post by Barry K3NDM

Feedpoint impedance and radiation resistance are not the same thing.
Using a folded element affects the former, but not the latter. Check
out W8JI's website.

73,
Dave AB7E

On 10/1/2013 12:10 PM, Barry LaZar wrote:

>
> As I read your post, I infer that at the moment you are wanting to
> add 160 meters to your capability. An antenna that I have used and
> liked is the Twin Lead Marconi. It's a simple, cheap, and effective
> antenna. I first saw it written up by Bill Orr years ago. The premise
> of the design is that a quarter wave antenna driven against ground may
> not be the most efficient antenna due to low radiation resistance.
> Therefore, raise the radiation resistance by using the theory of a
> folded dipole. The folded element raises the radiation resistance by a
> factor of 4 for 2 elements as the impedance changes as the square of
> the number of elements. You will still need radials, but your ground
> losses will decrease.

Barry K3NDM

Re: Random wires

In reply to this post by Roger D Johnson

Sorry roger, Roger, your analysis is not totally correct. You do raise the feed impedence from 36 Ohms as compared to using a single 1/4 wave wire over perfect ground. As most of us do not have perfect ground, there is an imperfect representation of the virtual 1/4. Because it is imperfect, you can look at this part as absorbing energy and just returning heat. By raising the radiation impedance, less energy is absorbed by ground and more is radiated. How much additional efficiency do you obtain is a matter of the ground system you put in and the ground constants under it. In my experience, it is worth the effort to build the antenna as it will outperform a similar single wire inverted L. I suggest reading Bill Orr, and others, on this antenna.

73,
Barry
K3NDM

----- Original Message -----

From: "Roger D Johnson" <[hidden email]>
To: [hidden email]
Sent: Tuesday, October 1, 2013 3:40:49 PM
Subject: Re: [Elecraft] Random wires

This is NOT true! It merely raises the feedpoint impedance...just the same as
adding a
4-1 transformer.

73, Roger

On 10/1/2013 3:10 PM, Barry LaZar wrote:

--
Remember the Liberty (AGTR-5)
http://www.usslibertyveterans.org/
http://www.gtr5.com/

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

David Gilbert

Re: Random wires

In reply to this post by Vic Rosenthal

That's a weird comment. Barry and you both have it wrong, but you are
correct that the radiation resistance is independent of the ground
resistance. The FEEDPOINT impedance, on the other hand is dependent
upon both.

The radiation resistance is NOT affected by the folded element ... the
folded element merely transforms the combination of the radiation
resistance and the ground resistance to a different value. The folded
element does NOT change the relative magnitudes of the radiation
resistance and the ground resistance, and therefore the folded element
does NOT improve the efficiency of the system at the feedpoint. It may,
however, reduce transmission line losses by reducing the SWR on the
feedline.

Seriously ... do some research first. W8JI is a good place to start but
there are others.

And by the way, Bill Orr made great contributions to antenna design, but
more than a few of his works have since been proven less than completely
accurate.

73,
Dave AB7E

On 10/1/2013 2:43 PM, Ron D'Eau Claire wrote:

> I disagree. Barry has it right. The radiation resistance of the radiator is
> independent up the ground resistance. That's why a 1/2 end fed wire with
> it's very high resistance is highly efficient against a given ground system
> compared to a 1/4 wave long or less wire.
>
> Note we are speaking of a folded full-length (i.e. 1/4 wave long) element.
> Folding short elements to make up for electrical length is something else
> entirely different. The Orr twin-lead antenna that I remember was 125 feet
> long, making it a full 1/4 wave on 160.
>
> 73, Ron AC7AC
>
> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Vic K2VCO
> Sent: Tuesday, October 01, 2013 12:44 PM
> To: [hidden email]
> Subject: Re: [Elecraft] Random wires
>
> Another way to look at it is that it multiplies the radiation resistance,
> but does the same for the ground resistance. So efficiency is unchanged.
>
> On 10/1/2013 12:40 PM, Roger D Johnson wrote:
>> This is NOT true! It merely raises the feedpoint impedance...just the
>> same as adding a
>> 4-1 transformer.
>>
>> 73, Roger
>>
>>
>> On 10/1/2013 3:10 PM, Barry LaZar wrote:
>>>
>>> As I read your post, I infer that at the moment you are wanting
>>> to add 160 meters to your capability. An antenna that I have used and
>>> liked is the Twin Lead Marconi. It's a simple, cheap, and effective
> antenna. I first saw it written up by Bill Orr years ago.
>>> The premise of the design is that a quarter wave antenna driven
>>> against ground may not be the most efficient antenna due to low
>>> radiation resistance. Therefore, raise the radiation resistance by
>>> using the theory of a folded dipole. The folded element raises the
>>> radiation resistance by a factor of 4 for 2 elements as the impedance
>>> changes as the square of the number of elements. You will still need
> radials, but your ground losses will decrease.
>>>
>>> 73,
>>> Barry
>>> K3NDM
>>>
>>>
> --
> Vic, K2VCO
> Fresno CA
> http://www.qsl.net/k2vco/
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

David Gilbert

Re: Random wires

In reply to this post by Roger D Johnson

Wrong again ... the folded element transforms the ground resistance
right along with the radiation resistance.

Look at it this way. Both the radiation resistance and the ground
resistance are present in combination at the feedpoint of a normal
monopole. Folding the element merely makes an relatively efficient
transformation of what is already there at the feedpoint. The folded
element is essentially nothing other than a transmission line, and it
has no way of knowing where that which it sees at one end came from. it
doesn't distinguish between the components.

Dave AB7E

On 10/1/2013 2:48 PM, Ron D'Eau Claire wrote:

> The important value is the resistance at the feed point of the radiator,
> independent of any matching devices used.
>
> Adding a 4:1 or other transformer is simply adjusting the impedance the feed
> line sees, like any other matching network you might use. It has no effect
> on the feed point resistance of the antenna.
>
> A 1/4 wave long folded radiator has a feed point resistance of 4x the
> typical 1/4 wavelength radiator, quite independent of the ground system.
> Hence the efficiency is higher.
>
> 73, Ron AC7AC
>
> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Roger D Johnson
> Sent: Tuesday, October 01, 2013 12:41 PM
> To: [hidden email]
> Subject: Re: [Elecraft] Random wires
>
> This is NOT true! It merely raises the feedpoint impedance...just the same
> as adding a
> 4-1 transformer.
>
> 73, Roger
>
>
> On 10/1/2013 3:10 PM, Barry LaZar wrote:
>>
>> As I read your post, I infer that at the moment you are wanting to
>> add 160 meters to your capability. An antenna that I have used and
>> liked is the Twin Lead Marconi. It's a simple, cheap, and effective
>> antenna. I first saw it written up by Bill Orr years ago. The premise
>> of the design is that a quarter wave antenna driven against ground may
>> not be the most efficient antenna due to low radiation resistance.
>> Therefore, raise the radiation resistance by using the theory of a
>> folded dipole. The folded element raises the radiation resistance by a
>> factor of 4 for 2 elements as the impedance changes as the square of
>> the number of elements. You will still need radials, but your ground
> losses will decrease.
>>
>> 73,
>> Barry
>> K3NDM
>>
>>
> --
> Remember the Liberty (AGTR-5)
> http://www.usslibertyveterans.org/
> http://www.gtr5.com/
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

David Gilbert

Re: Random wires

In reply to this post by Barry K3NDM

I suggest reading W8JI ... and others.

http://www.w8ji.com/radiation_resistance.htm

Dave AB7E

On 10/1/2013 2:53 PM, [hidden email] wrote:

> Sorry roger, Roger, your analysis is not totally correct. You do raise the feed impedence from 36 Ohms as compared to using a single 1/4 wave wire over perfect ground. As most of us do not have perfect ground, there is an imperfect representation of the virtual 1/4. Because it is imperfect, you can look at this part as absorbing energy and just returning heat. By raising the radiation impedance, less energy is absorbed by ground and more is radiated. How much additional efficiency do you obtain is a matter of the ground system you put in and the ground constants under it. In my experience, it is worth the effort to build the antenna as it will outperform a similar single wire inverted L. I suggest reading Bill Orr, and others, on this antenna.
>
> 73,
> Barry
> K3NDM
>
> ----- Original Message -----
>
> From: "Roger D Johnson" <[hidden email]>
> To: [hidden email]
> Sent: Tuesday, October 1, 2013 3:40:49 PM
> Subject: Re: [Elecraft] Random wires
>
> This is NOT true! It merely raises the feedpoint impedance...just the same as
> adding a
> 4-1 transformer.
>
> 73, Roger
>
>
> On 10/1/2013 3:10 PM, Barry LaZar wrote:
>>
>> As I read your post, I infer that at the moment you are wanting to add 160
>> meters to your capability. An antenna that I have used and liked is the Twin
>> Lead Marconi. It's a simple, cheap, and effective antenna. I first saw it
>> written up by Bill Orr years ago. The premise of the design is that a quarter
>> wave antenna driven against ground may not be the most efficient antenna due
>> to low radiation resistance. Therefore, raise the radiation resistance by
>> using the theory of a folded dipole. The folded element raises the radiation
>> resistance by a factor of 4 for 2 elements as the impedance changes as the
>> square of the number of elements. You will still need radials, but your ground
>> losses will decrease.
>>
>>
>> 73,
>> Barry
>> K3NDM
>>
>>

k6dgw

Re: Random wires

In reply to this post by sfbonk

On 10/1/2013 2:24 PM, Sfbonk wrote:
> There is an old W1BB drawing of a 160 L with a series capacitor which
> is longer than a 1/4 wave to feed it at a higher impedance point to
> get higher efficiency. Other neat drawing from him has an old car
> buried as part of the ground.

Hey! Good idea! Our little rural road seems to be a favorite dumping
ground for stolen cars ... last one was at the end of our driveway and
it was still idling. :-) If I can just find someone with a backhoe ...

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2013 Cal QSO Party 5-6 Oct 2013
- www.cqp.org

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

k6dgw

Re: Random wires

In reply to this post by Vic Rosenthal

Isn't this why AM broadcast stations, particularly 50KW clear-channel
stations, employ base-fed half-wave verticals? They still use radial
fields too I think. I recall [from years ago] that KFI's TX [650KHz]
was in Buena Park CA and the tower was around 700ft tall. BW of a stick
like that is pretty narrow, uncompensated, less than the BW of the signal.

When I saw the original post, I knew it would stimulate a reply-storm. :-)

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2013 Cal QSO Party 5-6 Oct 2013
- www.cqp.org

On 10/1/2013 2:43 PM, Ron D'Eau Claire wrote:
> I disagree. Barry has it right. The radiation resistance of the radiator is
> independent up the ground resistance. That's why a 1/2 end fed wire with
> it's very high resistance is highly efficient against a given ground system
> compared to a 1/4 wave long or less wire.

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

Lynn W. Taylor, WB6UUT

Re: Random wires

All antennas work by FM.
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

Jim Brown-10

Re: Random wires

In reply to this post by k6dgw

On 10/1/2013 3:42 PM, Fred Jensen wrote:
> Isn't this why AM broadcast stations, particularly 50KW clear-channel
> stations, employ base-fed half-wave verticals?

No, that's not the reason. The actual reason is that the vertical
radiation pattern is better than a shorter antenna.

> They still use radial fields too I think.

Yes. A radial field under a half wave antenna reduces ground losses (by
a dB or two, depending on how bad the ground is), whether the antenna is
fed against it or not. But 180 degrees is not the only popular height
for these clear channel stations -- if you peruse the FCC database,
you'll see many with vertical heights ranging from 180 to 225 electrical
degrees. Varying the height shifts the balance between low angle
radiation (for ground wave and long skip) and higher angle (for medium
distances. Making the radiator a bit taller than 180 degrees also lowers
the Z at the feedpoint, making it easier to feed.

Dave is right on -- most of those posting have confused feedpoint Z with
radiation resistance. There's a nice graph in the ARRL Antenna Book
showing radiation resistance of a vertical as a function of height.

73, Jim K9YC
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

w5tvw

Re: Random wires

In reply to this post by k6dgw

The 1/2 wave antenna has been some what of an enigma to a lot of people over
the years. I used one for years and still use one today. I work mostly the
"Low bands" (160-30) and never wanted the bother of keeping up an HF beam up
a tower! I DID go thru an extreme VHF/UHF stage when I was on 144/432 Mhz.
and contemplating some 1296 operation though. The activity down here fell
way off and I finally sold all the goodies as they became useless when the
trend towards VHF/UHF fell apart when nearly all the old timers went SK. No
use being able to run 500 watts PEP on 2 SSB when there ain't anybody to
talk to more often!

The end fed Zepp or just a "plain" end fed 1/2 wave can be big trouble when
you run a lot of power as there is inevitably the "RF in the shack" syndrome
forcing changing antenna lengths to compensate for the problem. I am
presently using a 115 end fed which is ideal for 80-30 including the 60
meter band. You can get by with a poor ground system and still radiate a
pretty decent signal with just something like a very simple "L" section
network to match it to your rig. Ground losses are much less with little or
no effect from adding counterpoise wires/grounds to suppress mostly "RF in
the shack" troubles, which are minimal on QRP and 100 watts or less.

Lots of people look upon the half wave with distain, but it can do a
remarkable job, especially in neighborhoods where beams and "visible"
antennas are frowned upon by Home Owners Associations and the attendant
"trolls" looking for "errant amateurs" to torment. The 115 wire I now have
up was used out of a hasty attempt (successful!) to get back on the air when
my XYL had a stroke which didn't mix well with my outdoor "ham shack" in the
carport building! I regularly work CW with it with 100 watts or less from
80-20 meters and also SSB in the afternoons on 40 and nights on 75 meters
with the "big boys". I'm using #26 stranded "mil spec" hookup wire for the
radiator and it works VERY well for what it is and the House wiring ground
buss for a "counterpoise"!

Don't sell the antenna short, it can and will work very well if the right
length and with a decent antenna tuner.

73 to all,

Sandy W5TVW

-----Original Message-----
From: Fred Jensen
Sent: Tuesday, October 01, 2013 5:42 PM
To: [hidden email]
Subject: Re: [Elecraft] Random wires

Isn't this why AM broadcast stations, particularly 50KW clear-channel
stations, employ base-fed half-wave verticals? They still use radial
fields too I think. I recall [from years ago] that KFI's TX [650KHz]
was in Buena Park CA and the tower was around 700ft tall. BW of a stick
like that is pretty narrow, uncompensated, less than the BW of the signal.

When I saw the original post, I knew it would stimulate a reply-storm. :-)

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2013 Cal QSO Party 5-6 Oct 2013
- www.cqp.org

On 10/1/2013 2:43 PM, Ron D'Eau Claire wrote:
> I disagree. Barry has it right. The radiation resistance of the radiator
> is
> independent up the ground resistance. That's why a 1/2 end fed wire with
> it's very high resistance is highly efficient against a given ground
> system
> compared to a 1/4 wave long or less wire.

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

w5tvw

Re: Random wires

In reply to this post by Jim Brown-10

BTW. Radiation resistance can be a tricky thing. It sometimes even
confuses even the seasoned broadcast radio engineer (in the 550-1700 Khz
region)! I worked with ship MG transmitters and antennas in the 410-512 Khz
region when ships still had radio officers. It can be very puzzling and not
follow the "normal rules" you expect! There is a lot of "empirical
engineering" that goes on that may seem to fly in the face of theory, which
can get into operation when you are dealing with wavelengths exceeding 600
meters in length!

73,

Sandy W5TVW

-----Original Message-----
From: Jim Brown
Sent: Tuesday, October 01, 2013 7:38 PM
To: [hidden email]
Subject: Re: [Elecraft] Random wires

On 10/1/2013 3:42 PM, Fred Jensen wrote:
> Isn't this why AM broadcast stations, particularly 50KW clear-channel
> stations, employ base-fed half-wave verticals?

No, that's not the reason. The actual reason is that the vertical
radiation pattern is better than a shorter antenna.

> They still use radial fields too I think.

Yes. A radial field under a half wave antenna reduces ground losses (by
a dB or two, depending on how bad the ground is), whether the antenna is
fed against it or not. But 180 degrees is not the only popular height
for these clear channel stations -- if you peruse the FCC database,
you'll see many with vertical heights ranging from 180 to 225 electrical
degrees. Varying the height shifts the balance between low angle
radiation (for ground wave and long skip) and higher angle (for medium
distances. Making the radiator a bit taller than 180 degrees also lowers
the Z at the feedpoint, making it easier to feed.

Dave is right on -- most of those posting have confused feedpoint Z with
radiation resistance. There's a nice graph in the ARRL Antenna Book
showing radiation resistance of a vertical as a function of height.

73, Jim K9YC
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

Dave-7

Re: Random wires

In reply to this post by Jim Brown-10

I don't understand the disagreement over the radiation resistance of a
folded dipole. ARRL Antenna Book, 19th edition, page 6-1, plainly
states that a folded dipole will have an impedance of approx 300 ohms.
This has been widely known for decades. This is for a folded dipole up
in the air, ran horizontally. This *is* the radiation resistance. It
is approx 4x the impedance (radiation resistance) of a regular,
unfolded, dipole.

If one were able to construct half of such a folded dipole and arrange
it vertically, it would have have an impedance (radiation resistance)
of approx 150 ohms. Again, approx 4x the radiation resistance of a
standard 1/4 wl monopole.

Modeling with EZNEC is in agreement with the ARRL Antenna Book.

So I think we can safely say that if one were able to construct a
vertical that is half of a folded dipole, the feedpoint Z, as well as
the radiation resistance, would be approx 4x that of a vertical monopole.

My question is - how do you build one of those?

In EZNEC it is easy. Just make two 1/4 wl elements closely spaced and
tie them both to MININEC ground. Place a source in the segment closest
to ground on one of the two. Bingo, a vertical that is half of a
folded dipole. Feedpoint Z is approx 150+j0 ohms.

I don't think it is quite that simple in the real world.

73 de dave
ab9ca/4

On 10/1/13 7:38 PM, Jim Brown wrote:

> On 10/1/2013 3:42 PM, Fred Jensen wrote:
>> Isn't this why AM broadcast stations, particularly 50KW
>> clear-channel stations, employ base-fed half-wave verticals?
>
> No, that's not the reason. The actual reason is that the vertical
> radiation pattern is better than a shorter antenna.
>
>> They still use radial fields too I think.
>
> Yes. A radial field under a half wave antenna reduces ground losses
> (by a dB or two, depending on how bad the ground is), whether the
> antenna is fed against it or not. But 180 degrees is not the only
> popular height for these clear channel stations -- if you peruse the
> FCC database, you'll see many with vertical heights ranging from 180
> to 225 electrical degrees. Varying the height shifts the balance
> between low angle radiation (for ground wave and long skip) and higher
> angle (for medium distances. Making the radiator a bit taller than 180
> degrees also lowers the Z at the feedpoint, making it easier to feed.
>
> Dave is right on -- most of those posting have confused feedpoint Z
> with radiation resistance. There's a nice graph in the ARRL Antenna
> Book showing radiation resistance of a vertical as a function of height.
>
> 73, Jim K9YC
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> .
>

Don Wilhelm-4

Re: Random wires

Dave,

You are equating radiation resistance to feedpoint impedance, and that
is like comparing apples and oranges, they are not the same.

73,
Don W3FPR

On 10/1/2013 9:38 PM, dave wrote:

>
> I don't understand the disagreement over the radiation resistance of a
> folded dipole. ARRL Antenna Book, 19th edition, page 6-1, plainly
> states that a folded dipole will have an impedance of approx 300 ohms.
> This has been widely known for decades. This is for a folded dipole up
> in the air, ran horizontally. This *is* the radiation resistance. It
> is approx 4x the impedance (radiation resistance) of a regular,
> unfolded, dipole.
>
> If one were able to construct half of such a folded dipole and arrange
> it vertically, it would have have an impedance (radiation resistance)
> of approx 150 ohms. Again, approx 4x the radiation resistance of a
> standard 1/4 wl monopole.
>
> Modeling with EZNEC is in agreement with the ARRL Antenna Book.
>
> So I think we can safely say that if one were able to construct a
> vertical that is half of a folded dipole, the feedpoint Z, as well as
> the radiation resistance, would be approx 4x that of a vertical monopole.
>
> My question is - how do you build one of those?
>
> In EZNEC it is easy. Just make two 1/4 wl elements closely spaced and
> tie them both to MININEC ground. Place a source in the segment closest
> to ground on one of the two. Bingo, a vertical that is half of a
> folded dipole. Feedpoint Z is approx 150+j0 ohms.
>
> I don't think it is quite that simple in the real world.
>

Dave-7

Re: Random wires

In reply to this post by Jim Brown-10

OOPs! Left off part of that vertical that is half of a folded dipole:

In the EZNEC model, those two vertical 1/4 wl elements must be shorted
at the top with a single segment wire, as well as tied to MININEC
ground at the bottom.

73 de dave
ab9ca/4

On 10/1/13 7:38 PM, Jim Brown wrote:

David Gilbert

Re: Random wires

In reply to this post by Dave-7

No ... it is *not* the radiation resistance. It is the feedpoint
resistance. They are not the same thing and nowhere in the section of
the ARRL Handbook that discusses folded dipoles does it call that 300
ohm feedpoint impedance the radiation resistance. Go read the section
on radiation resistance (section 3-2 or thereabouts) and you will note
that discussion refers only to a horizontal half wave antenna being
roughly 70 ohms and does not distinguish between whether it is a single
wire or a folded one.

Let's try another way of looking at it. Let's say you have a single
half wave wire and you feed it in the middle. The radiation resistance
is 70-some ohms and the feedpoint resistance is equal to the radiation
resistance plus any ohmic losses. If you then decide to feed the thing
several feet off center the feedpoint resistance changes but you haven't
changed the radiation resistance at all ... it's still just a half wave
dipole.

The same thing happens if you make the dipole a folded dipole. It's
still just a horizontal half wave antenna, albeit with a built in
transmission line that multiplies the original feedpoint resistance by a
factor of four. It is fundamentally no different than any other
impedance transformation scheme in relationship to the radiation resistance.

Dave AB7E

On 10/1/2013 6:38 PM, dave wrote: