I came across an old 2.3GHz yagi. I took the shroud — the ‘radome’ —
off to see what lay within. The matching between 50Ω coax feeder and
dipole is interesting. The feeder connects to a short length of copper
tube coaxial feeder (1). This terminates on a small tinned board. The
coaxial inner connects to the inner of a smaller diameter copper tube
feeder (2) that runs straight to one terminal of the folded dipole. The
coaxial outer of coaxial feeder (1) connects to the inner of another
smaller diameter copper tube feeder (3) that goes to the other terminal
of the folded dipole. Feeder (3) is significantly longer than feeder
(2). It looks to be somewhere between a quarter and a half wavelength
longer. The coaxial outers of feeders 1, 2, and 3 are commoned and
grounded at the small tinned board. The outers of feeders 2 and 3 are
grounded at the dipole connection points, and the inners are connected
to the dipole feed points. The dipole has a larger diameter on the arms
where the feedpoints are than on the other side. The element spacings
appear to be optimal for gain, suggesting no compromise has been made in
order to achieve better VSWR.
Does anyone have any further information or insight about the
matching/balun arrangement in use here?

Pictures
https://www.dropbox.com/sh/ehu1nlp62ut79kt/AAA0Yy0eondZlRzMe8DZoeVra?dl=0

Bill

Le 30/07/2021 à 01:24, williamwright a écrit :
> I came across an old 2.3GHz yagi. I took the shroud  — the ‘radome’ —
> off to see what lay within. The matching between 50Ω coax feeder and
> dipole is interesting. The feeder connects to a short length of copper
> tube coaxial feeder (1). This terminates on a small tinned board. The
> coaxial inner connects to the inner of a smaller diameter copper tube
> feeder (2) that runs straight to one terminal of the folded dipole.  The
> coaxial outer of coaxial feeder (1) connects to the inner of another
> smaller diameter copper tube feeder (3) that goes to the other terminal
> of the folded dipole.  Feeder (3) is significantly longer than feeder
> (2). It looks to be somewhere between a quarter and a half wavelength
> longer. The coaxial outers of feeders 1, 2, and 3 are commoned and
> grounded at the small tinned board. The outers of feeders 2 and 3 are
> grounded at the dipole connection points, and the inners are connected
> to the dipole feed points. The dipole has a larger diameter on the arms
> where the feedpoints are than on the other side. The element spacings
> appear to be optimal for gain, suggesting no compromise has been made in
> order to achieve better VSWR.
> Does anyone have any further information or insight about the
> matching/balun arrangement in use here?
>
> Pictures
> https://www.dropbox.com/sh/ehu1nlp62ut79kt/AAA0Yy0eondZlRzMe8DZoeVra?dl=0
>
> Bill

Thanks for the nice pictures.
To me it looks like a classical lambda/2 balun with the X4 impedance
rise compensated by a quarter wave symmetrical line made of 2 coaxial.
Look here:
https://www.iw5edi.com/ham-radio/files/I0QM_BALUN.PDF

On 30/07/2021 11:20, bilou wrote:
> Le 30/07/2021 à 01:24, williamwright a écrit :
>> I came across an old 2.3GHz yagi. I took the shroud  — the ‘radome’ —
>> off to see what lay within. The matching between 50Ω coax feeder and
>> dipole is interesting. The feeder connects to a short length of copper
>> tube coaxial feeder (1). This terminates on a small tinned board. The
>> coaxial inner connects to the inner of a smaller diameter copper tube
>> feeder (2) that runs straight to one terminal of the folded dipole.
>> The coaxial outer of coaxial feeder (1) connects to the inner of
>> another smaller diameter copper tube feeder (3) that goes to the other
>> terminal of the folded dipole.  Feeder (3) is significantly longer
>> than feeder (2). It looks to be somewhere between a quarter and a half
>> wavelength longer. The coaxial outers of feeders 1, 2, and 3 are
>> commoned and grounded at the small tinned board. The outers of feeders
>> 2 and 3 are grounded at the dipole connection points, and the inners
>> are connected to the dipole feed points. The dipole has a larger
>> diameter on the arms where the feedpoints are than on the other side.
>> The element spacings appear to be optimal for gain, suggesting no
>> compromise has been made in order to achieve better VSWR.
>> Does anyone have any further information or insight about the
>> matching/balun arrangement in use here?
>>
>> Pictures
>> https://www.dropbox.com/sh/ehu1nlp62ut79kt/AAA0Yy0eondZlRzMe8DZoeVra?dl=0
>>
>> Bill
>
> Thanks for the nice pictures.
> To me it looks like a classical lambda/2 balun with the X4 impedance
> rise compensated by a quarter wave symmetrical line made of 2 coaxial.
> Look here:
> https://www.iw5edi.com/ham-radio/files/I0QM_BALUN.PDF

Yes that appears to be it! Excellent detective work on your part!

Bill

On 30/07/2021 00:24, williamwright wrote:
> I came across an old 2.3GHz yagi. I took the shroud  — the ‘radome’ —
> off to see what lay within. The matching between 50Ω coax feeder and
> dipole is interesting. The feeder connects to a short length of copper
> tube coaxial feeder (1). This terminates on a small tinned board. The
> coaxial inner connects to the inner of a smaller diameter copper tube
> feeder (2) that runs straight to one terminal of the folded dipole.  The
> coaxial outer of coaxial feeder (1) connects to the inner of another
> smaller diameter copper tube feeder (3) that goes to the other terminal
> of the folded dipole.  Feeder (3) is significantly longer than feeder
> (2). It looks to be somewhere between a quarter and a half wavelength
> longer. The coaxial outers of feeders 1, 2, and 3 are commoned and
> grounded at the small tinned board. The outers of feeders 2 and 3 are
> grounded at the dipole connection points, and the inners are connected
> to the dipole feed points. The dipole has a larger diameter on the arms
> where the feedpoints are than on the other side. The element spacings
> appear to be optimal for gain, suggesting no compromise has been made in
> order to achieve better VSWR.
> Does anyone have any further information or insight about the
> matching/balun arrangement in use here?
>
> Pictures
> https://www.dropbox.com/sh/ehu1nlp62ut79kt/AAA0Yy0eondZlRzMe8DZoeVra?dl=0
>
> Bill

Looks like it has had some DIY modification. Surely no decent
manufacturer would put their name on something with all untidy goo
(araldite?) plastered all over the place?
--
Cheers,
Roger

On 30/07/2021 13:46, Roger Mills wrote:

>> Pictures
>> https://www.dropbox.com/sh/ehu1nlp62ut79kt/AAA0Yy0eondZlRzMe8DZoeVra?dl=0
>>
>> Bill
>
> Looks like it has had some DIY modification. Surely no decent
> manufacturer would put their name on something with all untidy goo
> (araldite?) plastered all over the place?

It seems to be sealant. I don't think it's DIY. I don't think anyone
without an advanced RF test facility would be able to modify such a thing.

Bill

On Friday, 30 July 2021 at 15:30:14 UTC+1, wrightsaerials@aol.com wrote:
> On 30/07/2021 13:46, Roger Mills wrote:
>
> >> Pictures
> >> https://www.dropbox.com/sh/ehu1nlp62ut79kt/AAA0Yy0eondZlRzMe8DZoeVra?dl=0
> >>
> >> Bill
> >
> > Looks like it has had some DIY modification. Surely no decent
> > manufacturer would put their name on something with all untidy goo
> > (araldite?) plastered all over the place?
> It seems to be sealant. I don't think it's DIY. I don't think anyone
> without an advanced RF test facility would be able to modify such a thing.
>
> Bill

The other thing worthy of note is that it is somewhat logarithmetic and should cover quite a wide band.

Baluns have always been a bit of a black art. I'm not sure but if you look
in some of the older uhf arrays you find all kinds of strange designs, from
tapped coils to stubs and bits of coax. I remember a ham of my acquaintance
having a 2M beam with a phasing piece of coax coming out of it to feed the
other side of the folded dipole. In the very short wavelengths mentioned,
I'd imagine all of that is easily fitted inside the insulator. I was told,
however that normal design techniques tend to be less effective the higher
the frequency is, since there is much more coupling going on.
Brian

--

This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...
briang1@blueyonder.co.uk
Blind user, so no pictures please
Note this Signature is meaningless.!
"williamwright" <wrightsaerials@f2s.com> wrote in message
news:imgrm9FqfsfU1@mid.individual.net...
>I came across an old 2.3GHz yagi. I took the shroud - the 'radome' - off
>to see what lay within. The matching between 50? coax feeder and dipole is
>interesting. The feeder connects to a short length of copper tube coaxial
>feeder (1). This terminates on a small tinned board. The coaxial inner
>connects to the inner of a smaller diameter copper tube feeder (2) that
>runs straight to one terminal of the folded dipole. The coaxial outer of
>coaxial feeder (1) connects to the inner of another smaller diameter copper
>tube feeder (3) that goes to the other terminal of the folded dipole.
>Feeder (3) is significantly longer than feeder (2). It looks to be
>somewhere between a quarter and a half wavelength longer. The coaxial
>outers of feeders 1, 2, and 3 are commoned and grounded at the small tinned
>board. The outers of feeders 2 and 3 are grounded at the dipole connection
>points, and the inners are connected to the dipole feed points. The dipole
>has a larger diameter on the arms where the feedpoints are than on the
>other side. The element spacings appear to be optimal for gain, suggesting
>no compromise has been made in order to achieve better VSWR.
> Does anyone have any further information or insight about the
> matching/balun arrangement in use here?
>
> Pictures
> https://www.dropbox.com/sh/ehu1nlp62ut79kt/AAA0Yy0eondZlRzMe8DZoeVra?dl=0
>
> Bill

Have you ever looked inside the old varicap tuners used in the older tv
sets? Glue was often used inside to stabilise the lines which were bent a
bit to increase and decrease this while tuning the tuner to a flat response
over the band, then a bit of foam was wedged in and glued to stop it moving
and any microphony that might occur.
Brian

--

This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...
briang1@blueyonder.co.uk
Blind user, so no pictures please
Note this Signature is meaningless.!
"Roger Mills" <watt.tyler@gmail.com> wrote in message
news:imialeF53bbU1@mid.individual.net...
> On 30/07/2021 00:24, williamwright wrote:
>> I came across an old 2.3GHz yagi. I took the shroud - the 'radome' - off
>> to see what lay within. The matching between 50? coax feeder and dipole
>> is interesting. The feeder connects to a short length of copper tube
>> coaxial feeder (1). This terminates on a small tinned board. The coaxial
>> inner connects to the inner of a smaller diameter copper tube feeder (2)
>> that runs straight to one terminal of the folded dipole. The coaxial
>> outer of coaxial feeder (1) connects to the inner of another smaller
>> diameter copper tube feeder (3) that goes to the other terminal of the
>> folded dipole. Feeder (3) is significantly longer than feeder (2). It
>> looks to be somewhere between a quarter and a half wavelength longer. The
>> coaxial outers of feeders 1, 2, and 3 are commoned and grounded at the
>> small tinned board. The outers of feeders 2 and 3 are grounded at the
>> dipole connection points, and the inners are connected to the dipole feed
>> points. The dipole has a larger diameter on the arms where the feedpoints
>> are than on the other side. The element spacings appear to be optimal for
>> gain, suggesting no compromise has been made in order to achieve better
>> VSWR.
>> Does anyone have any further information or insight about the
>> matching/balun arrangement in use here?
>>
>> Pictures
>> https://www.dropbox.com/sh/ehu1nlp62ut79kt/AAA0Yy0eondZlRzMe8DZoeVra?dl=0
>>
>> Bill
>
> Looks like it has had some DIY modification. Surely no decent manufacturer
> would put their name on something with all untidy goo (araldite?)
> plastered all over the place?
> --
> Cheers,
> Roger

On Sat, 31 Jul 2021 09:10:54 +0100, Brian Gaff \(Sofa\) wrote:

> Baluns have always been a bit of a black art. I'm not sure but if you
> look in some of the older uhf arrays you find all kinds of strange
> designs, from tapped coils to stubs and bits of coax. I remember a ham
> of my acquaintance having a 2M beam with a phasing piece of coax coming
> out of it to feed the other side of the folded dipole. In the very short
> wavelengths mentioned, I'd imagine all of that is easily fitted inside
> the insulator. I was told, however that normal design techniques tend
> to be less effective the higher the frequency is, since there is much
> more coupling going on.
> Brian

Strip-lines can be used as well.

Yes I'm sure they can, also of course when I used to build one channel yagis
for itv channels we were not supposed to get here, you did not really worry
about a balun at all you connected the coax across the folded dipole and
adjusted the impedance using the first director element closeness. Five
elements was almost always all you needed.
Brian

--

This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...
briang1@blueyonder.co.uk
Blind user, so no pictures please
Note this Signature is meaningless.!
"sid" <karma@home.org> wrote in message news:se3b9n$836$1@dont-email.me...
> On Sat, 31 Jul 2021 09:10:54 +0100, Brian Gaff \(Sofa\) wrote:
>
>> Baluns have always been a bit of a black art. I'm not sure but if you
>> look in some of the older uhf arrays you find all kinds of strange
>> designs, from tapped coils to stubs and bits of coax. I remember a ham
>> of my acquaintance having a 2M beam with a phasing piece of coax coming
>> out of it to feed the other side of the folded dipole. In the very short
>> wavelengths mentioned, I'd imagine all of that is easily fitted inside
>> the insulator. I was told, however that normal design techniques tend
>> to be less effective the higher the frequency is, since there is much
>> more coupling going on.
>> Brian
>
> Strip-lines can be used as well.

Le 01/08/2021 à 15:39, Brian Gaff (Sofa) a écrit :
> Yes I'm sure they can, also of course when I used to build one channel yagis
> for itv channels we were not supposed to get here, you did not really worry
> about a balun at all you connected the coax across the folded dipole and
> adjusted the impedance using the first director element closeness. Five
> elements was almost always all you needed.
> Brian
>
The main use of a balun is when you want/need The radiation
diagram to follow perfectly the theory.
This also involves polarisation of the signal.
Sometimes loosing 3dB of signal is peanuts if you gain 20 on interference.

In article <610a6ce1$0$3731$426a74cc@news.free.fr>, bilou <bilou@sfr.fr>
scribeth thus
>Le 01/08/2021 à 15:39, Brian Gaff (Sofa) a écrit :
>> Yes I'm sure they can, also of course when I used to build one channel yagis
>> for itv channels we were not supposed to get here, you did not really worry
>> about a balun at all you connected the coax across the folded dipole and
>> adjusted the impedance using the first director element closeness. Five
>> elements was almost always all you needed.
>> Brian
>>

>The main use of a balun is when you want/need The radiation
>diagram to follow perfectly the theory.

>This also involves polarisation of the signal.
>Sometimes loosing 3dB of signal is peanuts if you gain 20 on interference.
>

Blimey! Can you explain or elaborate on that a bit'!....

--
Tony Sayer

Man is least himself when he talks in his own person.

Give him a keyboard, and he will reveal himself.

tony sayer <tony@bancom.co.uk> wrote:
> In article <610a6ce1$0$3731$426a74cc@news.free.fr>, bilou <bilou@sfr.fr>
> scribeth thus
>> Le 01/08/2021 à 15:39, Brian Gaff (Sofa) a écrit :
>>> Yes I'm sure they can, also of course when I used to build one channel yagis
>>> for itv channels we were not supposed to get here, you did not really worry
>>> about a balun at all you connected the coax across the folded dipole and
>>> adjusted the impedance using the first director element closeness. Five
>>> elements was almost always all you needed.
>>> Brian
>>>
>
>> The main use of a balun is when you want/need The radiation
>> diagram to follow perfectly the theory.
>
>> This also involves polarisation of the signal.
>> Sometimes loosing 3dB of signal is peanuts if you gain 20 on interference.
>>
>
> Blimey! Can you explain or elaborate on that a bit'!....
>

Non balanced antenna has sub optimal radiation pattern. Balanced one has
something more akin to the text book. If you have a non bore sight
interferer and you want to drop it into one of the antenna’s nulls it’s
probably better to have an antenna whose radiation pattern you understand.

In article <see6b3$brq$1@dont-email.me>, Tweed <usenet.tweed@gmail.com>
wrote:
> tony sayer <tony@bancom.co.uk> wrote:
> > In article <610a6ce1$0$3731$426a74cc@news.free.fr>, bilou
> > <bilou@sfr.fr> scribeth thus
> >> Le 01/08/2021 à 15:39, Brian Gaff (Sofa) a écrit :
> >>> Yes I'm sure they can, also of course when I used to build one
> >>> channel yagis for itv channels we were not supposed to get here, you
> >>> did not really worry about a balun at all you connected the coax
> >>> across the folded dipole and adjusted the impedance using the first
> >>> director element closeness. Five elements was almost always all you
> >>> needed. Brian
> >>>
> >
> >> The main use of a balun is when you want/need The radiation diagram
> >> to follow perfectly the theory.
> >
> >> This also involves polarisation of the signal. Sometimes loosing 3dB
> >> of signal is peanuts if you gain 20 on interference.
> >>
> >
> > Blimey! Can you explain or elaborate on that a bit'!....
> >

> Non balanced antenna has sub optimal radiation pattern. Balanced one has
> something more akin to the text book. If you have a non bore sight
> interferer and you want to drop it into one of the antenna's nulls it's
> probably better to have an antenna whose radiation pattern you
> understand.

A difficulty is that using a balanced 'source' like a simple dipole via an
*unbalanced* transmission like like coax makes the system more easily
affected by intererence picked up by the screen of the co-ax. So if all
else is correct, an advantage of the balun is that it allows the coax to
screen interference as intended.

Thus it can help if you have 'local' ignition interference, etc, being
picked up on the way from antenna to tuner.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics https://www.st-andrews.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
biog http://jcgl.orpheusweb.co.uk/history/ups_and_downs.html
Audio Misc http://www.audiomisc.co.uk/index.html

In article <see6b3$brq$1@dont-email.me>, Tweed <usenet.tweed@gmail.com>
scribeth thus
>tony sayer <tony@bancom.co.uk> wrote:
>> In article <610a6ce1$0$3731$426a74cc@news.free.fr>, bilou <bilou@sfr.fr>
>> scribeth thus
>>> Le 01/08/2021 à 15:39, Brian Gaff (Sofa) a écrit :
>>>> Yes I'm sure they can, also of course when I used to build one channel yagis
>>>> for itv channels we were not supposed to get here, you did not really worry
>>>> about a balun at all you connected the coax across the folded dipole and
>>>> adjusted the impedance using the first director element closeness. Five
>>>> elements was almost always all you needed.
>>>> Brian
>>>>
>>
>>> The main use of a balun is when you want/need The radiation
>>> diagram to follow perfectly the theory.
>>
>>> This also involves polarisation of the signal.
>>> Sometimes loosing 3dB of signal is peanuts if you gain 20 on interference.
>>>
>>
>> Blimey! Can you explain or elaborate on that a bit'!....
>>
>
>Non balanced antenna has sub optimal radiation pattern. Balanced one has
>something more akin to the text book. If you have a non bore sight
>interferer and you want to drop it into one of the antenna’s nulls it’s
>probably better to have an antenna whose radiation pattern you understand.
>

It was this bit!....

Sometimes loosing 3dB of signal is peanuts if you gain 20 on interference.

--
Tony Sayer

Man is least himself when he talks in his own person.

Give him a keyboard, and he will reveal himself.

tony sayer <tony@bancom.co.uk> wrote:
> In article <see6b3$brq$1@dont-email.me>, Tweed <usenet.tweed@gmail.com>
> scribeth thus
>> tony sayer <tony@bancom.co.uk> wrote:
>>> In article <610a6ce1$0$3731$426a74cc@news.free.fr>, bilou <bilou@sfr.fr>
>>> scribeth thus
>>>> Le 01/08/2021 à 15:39, Brian Gaff (Sofa) a écrit :
>>>>> Yes I'm sure they can, also of course when I used to build one channel yagis
>>>>> for itv channels we were not supposed to get here, you did not really worry
>>>>> about a balun at all you connected the coax across the folded dipole and
>>>>> adjusted the impedance using the first director element closeness. Five
>>>>> elements was almost always all you needed.
>>>>> Brian
>>>>>
>>>
>>>> The main use of a balun is when you want/need The radiation
>>>> diagram to follow perfectly the theory.
>>>
>>>> This also involves polarisation of the signal.
>>>> Sometimes loosing 3dB of signal is peanuts if you gain 20 on interference.
>>>>
>>>
>>> Blimey! Can you explain or elaborate on that a bit'!....
>>>
>>
>> Non balanced antenna has sub optimal radiation pattern. Balanced one has
>> something more akin to the text book. If you have a non bore sight
>> interferer and you want to drop it into one of the antenna’s nulls it’s
>> probably better to have an antenna whose radiation pattern you understand.
>>
>
>
> It was this bit!....
>
> Sometimes loosing 3dB of signal is peanuts if you gain 20 on interference.
>
>

If you put the interferer in a null you can be 20dB up on it for your
wanted signal. Though 20dB is probably a bit optimistic.

On 09/08/2021 20:09, Tweed wrote:
> If you put the interferer in a null you can be 20dB up on it for your
> wanted signal. Though 20dB is probably a bit optimistic.
>
In case of locally generated interference like transmitting and
receiving on the same site you gain on both aerials and a good
balun does not involve a 3 dB loss.:-)