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Today's Topics:
1. Re: Comments by K9YC (Dan Hearn)
2. Re: Comments by K9YC (Joe Subich, W4TV)
3. B & W Folded Dipole (Chuck Smallhouse)
4. Re: Comments by K9YC (Steve Hunt)
5. Re: B & W Folded Dipole (Jim Lux)
6. Re: B & W Folded Dipole (w5gn@mxg.com)
----------------------------------------------------------------------
Message: 1
Date: Sun, 22 Jun 2014 20:28:40 -0700
From: Dan Hearn <n5ardxcc@gmail.com>
To: "Joe Subich, W4TV" <lists@subich.com>
Cc: towertalk reflector <towertalk@contesting.com>
Subject: Re: [TowerTalk] Comments by K9YC
Message-ID:
<CAHU7KER2eVc1o+5uz2Pr_Leu2OFoMxacMJ9FZeWEebkoo=asAw@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
Thanks for your comments guys. I am very confused. There have been a
number
of things in QST saying that the current from the center conductor goes
into one half of the dipole DE and the remaining current goes partiallly
into the other half of the dipole and some of it goes down the outside
shield surface. I have never questioned that. There are commercial
antennas
which use a quarter wave line with the top near the DE and the bottom
connected to the feedline outer shield a quarter wave down the feed
line.
This should develop a high Z at the spillover point if there is one, Hi.
Here is what G0ksc says about it and he is a highly respected antenna
modeler
http://www.g0ksc.co.uk/creatingabalun.html
Frankly, I do not know what to believe. I have a rf current clamp on
meter which I may use to explore this further.
73, Dan, N5AR
On Sun, Jun 22, 2014 at 7:36 PM, Joe Subich, W4TV <lists@subich.com>
wrote:
>
> On 2014-06-22 10:12 PM, Dan Hearn wrote:
>
>> The coax saw many places on the 3 bands where the feed point
>> impedance was not 52 ohms. That will result in spill over of current
>> from the inside of the shield to the outside at the attachment point
>> and ultimately radiation which screws up the beam pattern and sends
>> rf into your shack.
>>
>
> The fact that the feedline is not working into a matched load does
*not*
> create common mode current. Common mode on a feedline is created
*only*
> when the impedance to ground is different on each leg of the antenna.
> If the impedance is the same - even if it does not match the feedline
> impedance - the current into each leg of the antenna is the same, the
> antenna is balanced and there can be no common mode current.
>
> Mosley used to connect one side of the driven element to the boom with
> a strap. Grounding one half of the driven element and connecting the
> shield of the coax to the junction of the half-element and strap is
> guaranteed to seriously unbalance the antenna, causing beam skew,
feed-
> line radiation, and common mode current. In addition, if the boom
plus
> end elements happened to be a multiple of a half wave, the 1/4 wave
> each side of the feed point along the boom could easily cause all
kinds
> of strange behavior.
>
> It is unbalance *not SWR* that causes common mode current to flow in
> a feedline. In a properly balanced system, the currents on the center
> conductor and inside the coax are equal and opposite regardless of
> their level or their phase relationship to the voltage and no current
> appears on the *outside* of the shield.
>
> 73,
>
> ... Joe, W4TV
>
>
>
> On 2014-06-22 10:12 PM, Dan Hearn wrote:
>
>> I recently sent the following to towertalk reflector. It appears
that K9YC
>> does not understand it.
>> _________________________________________________________________
>> On 6/21/2014 3:23 PM, Dan Hearn wrote:
>>
>> It is interesting to note that the Mosley claimed gain is about 2db
>>> greater than other tri band beams. They use dbd reference instead
of dbi
>>> while I think their claims would be about right if they used dbi
>>> reference.
>>>
>>> ------------------------------------------------------------
>> -------------------------------------------------
>> Maybe I should have used a few more words to explain. In the fine
Yagi
>> tests described by K7LXC and N0AX in their book on tri band
Yagis. each
>> companies reference for their gain ratings is given. Mosley gave
dbd as
>> their reference. That implies that they have about 2db greater
gain than
>> other companies who use dbi. People who do antenna modeling get
their gain
>> answers referred to dbi, an isotropic model. If this is confusing,
You can
>> go to our clubs web page, www.sdxa.org and look under Articals to
find a
>> clear discussion of dbi,dbd, and db gains.
>> ------------------------------------------------------------
>> -------------------------------------------------
>> K9YC comment.
>>
>> "Exactly the opposite. The peak gain of a dipole is 2.2 dBi. So a
gain
>> specification of 4 dBd is equivalent to 6.2 dBi."
>> ------------------------------------------------------------
>> ----------------------------------------------
>> This is true but I fail to see what it has to do with my note.
>> ------------------------------------------------------------
>> -----------------------------------------------
>>
>> My second comment
>>>
>>
>>
>>
>> I suspect if you used a good line choke at the coax feed point and
>>> subtract
>>> 2.1db from their claimed gain you would have a typical triband beam.
>>>
>>> ------------------------------------------------------------
>> ------------------------------------------------
>>
>>
>> I don't agree with that logic or that statement. A simple common mode
>> choke
>> simply reduces common mode current, which mostly prevents RF
received on
>> the feedline from filling in the nulls in the pattern.
>> ------------------------------------------------------------
>> -----------------------------------------------
>> Here I do not believe Jim understands the problem. The choke will
do what
>> he says ON RECEIVING but that is not the problem we are trying to
solve
>> with understanding the lousy test results for the Mosley tri
bander. They
>> connected the coax directly to the driven element as Mosley said.
The coax
>> saw many places on the 3 bands where the feed point impedance was
not 52
>> ohms. That will result in spill over of current from the inside of
the
>> shield to the outside at the attachment point and ultimately
radiation
>> which screws up the beam pattern and sends rf into your shack.
That is why
>> you need a good line choke at the coax attachment point.
>>
>> I have a lot of respect for Jim and his work on line chokes and
other
>> things. I have built and measured many of his designs with excellent
>> results. I do not understand why he went on such a rampage over my
post.
>> ------------------------------------------------------------
>> ----------------------------------------------
>>
>>
>> In his book, "Array of Light," N6BT shows optimized designs of
2-element,
>> 3-element, and 4-element MONOBAND Yagis. He put these IDEAL gain
figures
>> in
>> a table with the CLAIMED gains of a dozen or so competing
products. In
>> nearly all cases, the advertised gains were 2-3 dB better than the
best
>> monoband beam. In other words, they claimed impossible gains.
After the
>> first edition of "Array of Light" was published, nearly all of those
>> manufacturers revised their gain claimed downward by several dB.
>>
>> 73, Jim K9YC
>>
>> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
--
Dan Hearn
N5AR
------------------------------
Message: 2
Date: Mon, 23 Jun 2014 00:03:27 -0400
From: "Joe Subich, W4TV" <lists@subich.com>
To: Dan Hearn <n5ardxcc@gmail.com>
Cc: towertalk reflector <towertalk@contesting.com>
Subject: Re: [TowerTalk] Comments by K9YC
Message-ID: <53A7A70F.2050506@subich.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> There are commercial antennas which use a quarter wave line with the
> top near the DE and the bottom connected to the feedline outer shield
> a quarter wave down the feed line. This should develop a high Z at
> the spillover point if there is one, Hi.
Yes, the quarter wave stub (Pawsley stub) raises the impedance seen
by the "grounded" side of the antenna. It does not change the SWR
on the antenna or effect any mismatch between the impedance of the
feedline and the antenna. The only thing it does is reduce the shunt
impedance from the outside of the coax shield.
The shield of the coax is directly analogous to the grounding strap
Mosley used on one side of its antennas - it's just a little longer.
If one were to correctly model a dipole fed with coax, one would
include *a third wire* the length of the feedline running from one
side of the feedpoint to ground. With that third wire, one no longer
has a *balanced* antenna.
In fact, get EZNEC or another modeling program that will show you the
currents in each segment. Then play with the length of that third
wire to see what happens to those currents at various lengths of
wire ... what happens to "feedline radiation" and how beam patterns
can become corrupted/skewed. It's quite interesting and educational.
73,
... Joe, W4TV
On 2014-06-22 11:28 PM, Dan Hearn wrote:
> Thanks for your comments guys. I am very confused. There have been
a number
> of things in QST saying that the current from the center conductor
goes
> into one half of the dipole DE and the remaining current goes
partiallly
> into the other half of the dipole and some of it goes down the outside
> shield surface. I have never questioned that. There are commercial
antennas
> which use a quarter wave line with the top near the DE and the bottom
> connected to the feedline outer shield a quarter wave down the feed
line.
> This should develop a high Z at the spillover point if there is
one, Hi.
> Here is what G0ksc says about it and he is a highly respected antenna
> modeler
> http://www.g0ksc.co.uk/creatingabalun.html
> Frankly, I do not know what to believe. I have a rf current
clamp on
> meter which I may use to explore this further.
>
> 73, Dan, N5AR
>
>
> On Sun, Jun 22, 2014 at 7:36 PM, Joe Subich, W4TV
<lists@subich.com> wrote:
>
>>
>> On 2014-06-22 10:12 PM, Dan Hearn wrote:
>>
>>> The coax saw many places on the 3 bands where the feed point
>>> impedance was not 52 ohms. That will result in spill over of current
>>> from the inside of the shield to the outside at the attachment point
>>> and ultimately radiation which screws up the beam pattern and sends
>>> rf into your shack.
>>>
>>
>> The fact that the feedline is not working into a matched load does
*not*
>> create common mode current. Common mode on a feedline is created
*only*
>> when the impedance to ground is different on each leg of the antenna.
>> If the impedance is the same - even if it does not match the feedline
>> impedance - the current into each leg of the antenna is the same, the
>> antenna is balanced and there can be no common mode current.
>>
>> Mosley used to connect one side of the driven element to the boom
with
>> a strap. Grounding one half of the driven element and connecting the
>> shield of the coax to the junction of the half-element and strap is
>> guaranteed to seriously unbalance the antenna, causing beam skew,
feed-
>> line radiation, and common mode current. In addition, if the boom
plus
>> end elements happened to be a multiple of a half wave, the 1/4 wave
>> each side of the feed point along the boom could easily cause all
kinds
>> of strange behavior.
>>
>> It is unbalance *not SWR* that causes common mode current to flow in
>> a feedline. In a properly balanced system, the currents on the
center
>> conductor and inside the coax are equal and opposite regardless of
>> their level or their phase relationship to the voltage and no current
>> appears on the *outside* of the shield.
>>
>> 73,
>>
>> ... Joe, W4TV
>>
>>
>>
>> On 2014-06-22 10:12 PM, Dan Hearn wrote:
>>
>>> I recently sent the following to towertalk reflector. It appears
that K9YC
>>> does not understand it.
>>> _________________________________________________________________
>>> On 6/21/2014 3:23 PM, Dan Hearn wrote:
>>>
>>> It is interesting to note that the Mosley claimed gain is about
2db
>>>> greater than other tri band beams. They use dbd reference
instead of dbi
>>>> while I think their claims would be about right if they used dbi
>>>> reference.
>>>>
>>>> ------------------------------------------------------------
>>> -------------------------------------------------
>>> Maybe I should have used a few more words to explain. In the fine
Yagi
>>> tests described by K7LXC and N0AX in their book on tri band
Yagis. each
>>> companies reference for their gain ratings is given. Mosley gave
dbd as
>>> their reference. That implies that they have about 2db greater
gain than
>>> other companies who use dbi. People who do antenna modeling get
their gain
>>> answers referred to dbi, an isotropic model. If this is
confusing, You can
>>> go to our clubs web page, www.sdxa.org and look under Articals to
find a
>>> clear discussion of dbi,dbd, and db gains.
>>> ------------------------------------------------------------
>>> -------------------------------------------------
>>> K9YC comment.
>>>
>>> "Exactly the opposite. The peak gain of a dipole is 2.2 dBi. So a
gain
>>> specification of 4 dBd is equivalent to 6.2 dBi."
>>> ------------------------------------------------------------
>>> ----------------------------------------------
>>> This is true but I fail to see what it has to do with my note.
>>> ------------------------------------------------------------
>>> -----------------------------------------------
>>>
>>> My second comment
>>>>
>>>
>>>
>>>
>>> I suspect if you used a good line choke at the coax feed point and
>>>> subtract
>>>> 2.1db from their claimed gain you would have a typical triband
beam.
>>>>
>>>> ------------------------------------------------------------
>>> ------------------------------------------------
>>>
>>>
>>> I don't agree with that logic or that statement. A simple common
mode
>>> choke
>>> simply reduces common mode current, which mostly prevents RF
received on
>>> the feedline from filling in the nulls in the pattern.
>>> ------------------------------------------------------------
>>> -----------------------------------------------
>>> Here I do not believe Jim understands the problem. The choke will
do what
>>> he says ON RECEIVING but that is not the problem we are trying to
solve
>>> with understanding the lousy test results for the Mosley tri
bander. They
>>> connected the coax directly to the driven element as Mosley said.
The coax
>>> saw many places on the 3 bands where the feed point impedance was
not 52
>>> ohms. That will result in spill over of current from the inside
of the
>>> shield to the outside at the attachment point and ultimately
radiation
>>> which screws up the beam pattern and sends rf into your shack.
That is why
>>> you need a good line choke at the coax attachment point.
>>>
>>> I have a lot of respect for Jim and his work on line chokes
and other
>>> things. I have built and measured many of his designs with excellent
>>> results. I do not understand why he went on such a rampage over
my post.
>>> ------------------------------------------------------------
>>> ----------------------------------------------
>>>
>>>
>>> In his book, "Array of Light," N6BT shows optimized designs of
2-element,
>>> 3-element, and 4-element MONOBAND Yagis. He put these IDEAL gain
figures
>>> in
>>> a table with the CLAIMED gains of a dozen or so competing
products. In
>>> nearly all cases, the advertised gains were 2-3 dB better than
the best
>>> monoband beam. In other words, they claimed impossible gains.
After the
>>> first edition of "Array of Light" was published, nearly all of those
>>> manufacturers revised their gain claimed downward by several dB.
>>>
>>> 73, Jim K9YC
>>>
>>> _______________________________________________
>>
>>
>>
>> _______________________________________________
>> TowerTalk mailing list
>> TowerTalk@contesting.com
>> http://lists.contesting.com/mailman/listinfo/towertalk
>>
>
>
>
------------------------------
Message: 3
Date: Mon, 23 Jun 2014 00:32:59 -0700
From: Chuck Smallhouse <w7cs@theriver.com>
To: towertalk@contesting.com
Subject: [TowerTalk] B & W Folded Dipole
Message-ID: <20140623004903.B81DF507@sj1-dm103.mta.everyone.net>
Content-Type: text/plain; charset="us-ascii"; format=flowed
Recently I saw an ad, in maybe QST, by a company selling a dipole
that looked like the B & W one. Maybe they bought the rights from B
& W ? Does anyone recall the ad and where I saw it ? I've looked
through two or three recent QSTs and can't seem to find it .
Also two or three years ago someone wrote a not too complimentary
article, in QST, about the B & W folded dipole . Does anyone recall
what issue that was ?
Thanks & 73,
Chuck, W7CS
------------------------------
Message: 4
Date: Mon, 23 Jun 2014 10:18:26 +0100
From: Steve Hunt <steve@karinya.net>
Cc: towertalk reflector <towertalk@contesting.com>
Subject: Re: [TowerTalk] Comments by K9YC
Message-ID: <53A7F0E2.1040408@karinya.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
You can then try inserting a choke at the feedpoint in the EZNEC model
and see how it does indeed change the SWR on the feedline!
The SWR is bound to change under those conditions. If you have a low CM
impedance back along the coax braid outer surface, which is shunting one
side of the antenna to ground, the impedance "seen" at the end of the
feedline is bound to change when you then use a choke to make that shunt
CM path a much higher impedance.
Steve G3TXQ
On 23/06/2014 05:03, Joe Subich, W4TV wrote:
>
> In fact, get EZNEC or another modeling program that will show you the
> currents in each segment. Then play with the length of that third
> wire to see what happens to those currents at various lengths of
> wire ... what happens to "feedline radiation" and how beam patterns
> can become corrupted/skewed. It's quite interesting and educational.
>
> 73,
>
> ... Joe, W4TV
>
>
------------------------------
Message: 5
Date: Mon, 23 Jun 2014 11:24:55 +0100
From: Jim Lux <jimlux@earthlink.net>
To: Chuck Smallhouse <w7cs@theriver.com>
Cc: "towertalk@contesting.com" <towertalk@contesting.com>
Subject: Re: [TowerTalk] B & W Folded Dipole
Message-ID: <B46602FC-827A-40A1-84F9-2BC2E8D8845E@earthlink.net>
Content-Type: text/plain; charset=us-ascii
I doubt the B&W design is patented (or that the patent is in force)
Anyone can make and sell a terminated folded dipole
It's not inherently a bad design, although not popular for amateur
radio, which tends to put a premium on radiation efficiency, and
which doesn't do fast frequency changes and uses narrow band
signals. However, if you've got power to burn, and don't want to
fool with tuners, etc( e.g. You're doing ALE at an embassy or NGO or
doing millisecond frequency hopping) it works fairly well.
One can probably do as well with a 3 - 6 dB pad at the feed point of
a standard dipole of similar length.
73, Jim
On Jun 23, 2014, at 8:32, Chuck Smallhouse <w7cs@theriver.com> wrote:
> Recently I saw an ad, in maybe QST, by a company selling a dipole
that looked like the B & W one. Maybe they bought the rights from B
& W ? Does anyone recall the ad and where I saw it ? I've looked
through two or three recent QSTs and can't seem to find it .
>
> Also two or three years ago someone wrote a not too complimentary
article, in QST, about the B & W folded dipole . Does anyone recall
what issue that was ?
>
> Thanks & 73,
>
> Chuck, W7CS
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
------------------------------
Message: 6
Date: Mon, 23 Jun 2014 05:43:25 -0500
From: <w5gn@mxg.com>
To: <towertalk@contesting.com>
Cc: 'Jim Lux' <jimlux@earthlink.net>
Subject: Re: [TowerTalk] B & W Folded Dipole
Message-ID: <002b01cf8ecf$f803b240$e80b16c0$@mxg.com>
Content-Type: text/plain; charset="us-ascii"
I didn't write the QST article, but I did post some years ago,
probably on the Contest ListServer, about my NEGATIVE experience
when I tested the antenna on 80 meters in an NAQP Contest,
and incrementally increased my power to find that I could only
make marginal QSOs at 700 watts, but that at 1200 watts I was
getting the same success as I had with 100 watts to a 135 foot
longwire at the same elevation.
(I remember a subsequent posting about my exceeding the 100 watt
power limit in the NAQP, and I pointed out that only applied
if I had submitted my log for score - I submitted as a CheckLog.)
73
Barry, EI/W5GN
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf
Of Jim Lux
Sent: Monday, June 23, 2014 5:25 AM
To: Chuck Smallhouse
Cc: towertalk@contesting.com
Subject: Re: [TowerTalk] B & W Folded Dipole
I doubt the B&W design is patented (or that the patent is in force)
Anyone can make and sell a terminated folded dipole
It's not inherently a bad design, although not popular for amateur
radio, which tends to put a premium on radiation efficiency, and
which doesn't do fast frequency changes and uses narrow band
signals. However, if you've got power to burn, and don't want to
fool with tuners, etc( e.g. You're doing ALE at an embassy or NGO or
doing millisecond frequency hopping) it works fairly well.
One can probably do as well with a 3 - 6 dB pad at the feed point of
a standard dipole of similar length.
73, Jim
On Jun 23, 2014, at 8:32, Chuck Smallhouse <w7cs@theriver.com> wrote:
> Recently I saw an ad, in maybe QST, by a company selling a dipole
that looked like the B & W one. Maybe they bought the rights from B
& W ? Does anyone recall the ad and where I saw it ? I've looked
through two or three recent QSTs and can't seem to find it .
>
> Also two or three years ago someone wrote a not too complimentary
article, in QST, about the B & W folded dipole . Does anyone recall
what issue that was ?
>
> Thanks & 73,
>
> Chuck, W7CS
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
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------------------------------
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------------------------------
End of TowerTalk Digest, Vol 138, Issue 48
******************************************