Feeding system name?
 

Hi

Which is the name of a feeding system in that the driven element of a
Yagi (for example) is split in two parts, and two pieces of isolated
wire are introduced in both sections of the split driven element? (to
find it in the Web)

Thank you very much in advance.

Miguel

Feeding system name?
 

In message
,
lu6etj writes
Hi

Which is the name of a feeding system in that the driven element of a
Yagi (for example) is split in two parts, and two pieces of isolated
wire are introduced in both sections of the split driven element? (to
find it in the Web)

Thank you very much in advance.

Miguel

Delta match?
http://www.ycars.org/EFRA/Module%20C/AntMatch.htm
http://www.qsl.net/pa3hbb/DeltaM1.htm
--
Ian

Feeding system name?
 

On 3 mayo, 18:29, Ian Jackson
wrote:
In message
,
lu6etj writes

Hi

Which is the name of a feeding system in that the driven element of a
Yagi (for example) is split in two parts, and two pieces of isolated
wire are introduced in both sections of the split driven element? (to
find it in the Web)

Thank you very much in advance.

Miguel

Delta match?http://www.ycars.org/EFRA/Module%20C...bb/DeltaM1.htm
--
Ian

No, no :) both wires are introduced in each driven element tubes, at
similar mode as a coaxial cable stripped of braid is introduced in a
gamma rod.

Feeding system name?
 

lu6etj wrote:

No, no :) both wires are introduced in each driven element tubes, at
similar mode as a coaxial cable stripped of braid is introduced in a
gamma rod.

It's not obvious how you'd be able to effect an impedance match with
this method. To be able to match an arbitrary impedance, you need to be
able to adjust two things which are at least partially independent. For
example, a gamma rod length and series capacitance. With this scheme,
you've got the length of the wires inserted in the tubes. What else can
you adjust? Wire diameter will give you some variability, but not an
awful lot, and it isn't easy to vary.

Roy Lewallen, W7EL

Feeding system name?
 

On 3 mayo, 19:35, Roy Lewallen wrote:
lu6etj wrote:

No, no :) both wires are introduced in each driven element tubes, at
similar mode as a coaxial cable stripped of braid is introduced in a
gamma rod.

It's not obvious how you'd be able to effect an impedance match with
this method. To be able to match an arbitrary impedance, you need to be
able to adjust two things which are at least partially independent. For
example, a gamma rod length and series capacitance. With this scheme,
you've got the length of the wires inserted in the tubes. What else can
you adjust? Wire diameter will give you some variability, but not an
awful lot, and it isn't easy to vary.

Roy Lewallen, W7EL

Thanks Roy (and Ian). Well... I thought the same thing that you and
that it is the reason of my question. Several times I heard of it and
for that reason I wanted to look for information in the Net to find
some possible explanation. I remember that years ago I neither
understood very well how the double bazooka worked :)

MIguel Ghezzi LU 6ETJ

Feeding system name?
 

Roy Lewallen Inscribed thus:

lu6etj wrote:

No, no :) both wires are introduced in each driven element tubes, at
similar mode as a coaxial cable stripped of braid is introduced in a
gamma rod.

It's not obvious how you'd be able to effect an impedance match with
this method. To be able to match an arbitrary impedance, you need to
be able to adjust two things which are at least partially independent.
For example, a gamma rod length and series capacitance. With this
scheme, you've got the length of the wires inserted in the tubes. What
else can you adjust? Wire diameter will give you some variability, but
not an awful lot, and it isn't easy to vary.

Roy Lewallen, W7EL

Does "Folded Dipole" sound right...

--
Best Regards:
Baron.

Feeding system name?
 

lu6etj wrote in
:

On 3 mayo, 18:29, Ian Jackson
wrote:
In message
,
lu6etj writes

....
No, no :) both wires are introduced in each driven element tubes, at
similar mode as a coaxial cable stripped of braid is introduced in a
gamma rod.

I have not seen it done, and can't imagine wide application.

The technique presumably is to insert a (lossy) capacitive reactance in
series with the feedpoint, and such that the reactance decreases with
freqeuency, thus exacerbating the natural feedpoint impedance change.

Owen

Feeding system name?
 

"Owen Duffy" wrote in message
...
lu6etj wrote in
:

On 3 mayo, 18:29, Ian Jackson
wrote:
In message
,
lu6etj writes

...
No, no :) both wires are introduced in each driven element tubes, at
similar mode as a coaxial cable stripped of braid is introduced in a
gamma rod.

I have not seen it done, and can't imagine wide application.

The technique presumably is to insert a (lossy) capacitive reactance in
series with the feedpoint, and such that the reactance decreases with
freqeuency, thus exacerbating the natural feedpoint impedance change.

Owen

I think it was Mosley that used it in their Classic 33 beam. I don't recall
exectally how it was made, but the driven element was in two insulated
pieces. Then a piece of coax (it may have been just the center part with
the braid stripped off) was placed in the driven element. Part ran inside
one element side and the other part ran the other way I don't think there
is any direct connection to the driven element.

Feeding system name?
 

On 5/4/2010 3:58 PM, Owen Duffy wrote:
The technique presumably is to insert a (lossy) capacitive reactance in
series with the feedpoint, and such that the reactance decreases with
freqeuency, thus exacerbating the natural feedpoint impedance change.

Owen

I am curious about your statement. You say "insert a (lossy) capacitive
reactance in series". Why would a braidless piece of coax inserted in a
tube have significantly different loss than the intact coax of that length?

I've made matches made that way for decades that ran at full or near
full legal limit on 6m. I'm pretty sure that any significant loss would
have shown up as dripping plastic. The matches when taken apart after
years of use show no sign of heating.

tom
K0TAR

Feeding system name?
 

tom wrote in
t:

On 5/4/2010 3:58 PM, Owen Duffy wrote:
The technique presumably is to insert a (lossy) capacitive reactance
in series with the feedpoint, and such that the reactance decreases
with freqeuency, thus exacerbating the natural feedpoint impedance
change.

Owen

I am curious about your statement. You say "insert a (lossy)
capacitive reactance in series". Why would a braidless piece of coax
inserted in a tube have significantly different loss than the intact
coax of that length?

I've made matches made that way for decades that ran at full or near
full legal limit on 6m. I'm pretty sure that any significant loss
would have shown up as dripping plastic. The matches when taken apart
after years of use show no sign of heating.

Tom,

My use of "lossy" was to remind readers that capacitive reactance
obtained by using such a transmission line element is a relatively lossy
'capacitor'. For example. an o/c stub of RG213 for a reactance of -10
ohms at 144MHz has a resistance of about 0.1 ohms, or a Q of about 100.
That is not a huge loss, but quality capacitors achieve much higher Q
than that.

So, I don't know why one might use such a thing in a driven element,
introducing say 0.2 ohms of resistance which consumes about 0.4% of the
power if it was a R=50 feedpoint, when a similar reactance could be
obtained by a slight shortening. The purpose is probably not for
frequency compensation, it works the wrong way.

Is the loss significant, not really in this case, and it won't melt the
PE, but TL derived capacitors are relatively lower Q.

Owen

Feeding system name?
 

On 5/4/2010 6:39 PM, Owen Duffy wrote:

Tom,

My use of "lossy" was to remind readers that capacitive reactance
obtained by using such a transmission line element is a relatively lossy
'capacitor'. For example. an o/c stub of RG213 for a reactance of -10
ohms at 144MHz has a resistance of about 0.1 ohms, or a Q of about 100.
That is not a huge loss, but quality capacitors achieve much higher Q
than that.

So, I don't know why one might use such a thing in a driven element,
introducing say 0.2 ohms of resistance which consumes about 0.4% of the
power if it was a R=50 feedpoint, when a similar reactance could be
obtained by a slight shortening. The purpose is probably not for
frequency compensation, it works the wrong way.

Is the loss significant, not really in this case, and it won't melt the
PE, but TL derived capacitors are relatively lower Q.

Owen

I'll take the .4%. I'll take 4%. It's a bulletproof easy way to make a
gamma match. I've never had one fail, and I've made quite a few.

And you need to define where you think lossy starts, because nothing
that we can afford to use isn't, and true room temperature
superconductors still aren't available.

tom
K0TAR

Feeding system name?
 

On 5/4/2010 8:17 PM, tom wrote:
On 5/4/2010 6:39 PM, Owen Duffy wrote:

Tom,

My use of "lossy" was to remind readers that capacitive reactance
obtained by using such a transmission line element is a relatively lossy
'capacitor'. For example. an o/c stub of RG213 for a reactance of -10
ohms at 144MHz has a resistance of about 0.1 ohms, or a Q of about 100.
That is not a huge loss, but quality capacitors achieve much higher Q
than that.

So, I don't know why one might use such a thing in a driven element,
introducing say 0.2 ohms of resistance which consumes about 0.4% of the
power if it was a R=50 feedpoint, when a similar reactance could be
obtained by a slight shortening. The purpose is probably not for
frequency compensation, it works the wrong way.

And I forgot to address this.

Because .4% is meaningless and the change to a slightly less lossy feed
method would contribute nothing useful for the effort.

Because the effort with your method is that I would have to trim an
element clip by clip instead of simply sliding things at the match.

tom
K0TAR

Feeding system name?
 

On 5/4/2010 6:39 PM, Owen Duffy wrote:
wrote in
t:

On 5/4/2010 3:58 PM, Owen Duffy wrote:
The technique presumably is to insert a (lossy) capacitive reactance
in series with the feedpoint, and such that the reactance decreases
with freqeuency, thus exacerbating the natural feedpoint impedance
change.

Owen

I am curious about your statement. You say "insert a (lossy)
capacitive reactance in series". Why would a braidless piece of coax
inserted in a tube have significantly different loss than the intact
coax of that length?

I've made matches made that way for decades that ran at full or near
full legal limit on 6m. I'm pretty sure that any significant loss
would have shown up as dripping plastic. The matches when taken apart
after years of use show no sign of heating.

Tom,

My use of "lossy" was to remind readers that capacitive reactance
obtained by using such a transmission line element is a relatively lossy
'capacitor'. For example. an o/c stub of RG213 for a reactance of -10
ohms at 144MHz has a resistance of about 0.1 ohms, or a Q of about 100.
That is not a huge loss, but quality capacitors achieve much higher Q
than that.

So, I don't know why one might use such a thing in a driven element,
introducing say 0.2 ohms of resistance which consumes about 0.4% of the
power if it was a R=50 feedpoint, when a similar reactance could be
obtained by a slight shortening. The purpose is probably not for
frequency compensation, it works the wrong way.

Is the loss significant, not really in this case, and it won't melt the
PE, but TL derived capacitors are relatively lower Q.

Owen

Sorry, but I thought of another comment. :)

Length for length, a 50 ohm feed yagi has already lost much more than
..4% when compared to a well designed yagi on the same boom in the 20 to
25 ohm range.

I'm speaking of .6 to .8 lambda and up yagis.

tom
K0TAR

Feeding system name?
 

On 4 mayo, 20:39, Owen Duffy wrote:
tom wrote .net:





On 5/4/2010 3:58 PM, Owen Duffy wrote:
The technique presumably is to insert a (lossy) capacitive reactance
in series with the feedpoint, and such that the reactance decreases
with freqeuency, thus exacerbating the natural feedpoint impedance
change.

Owen

I am curious about your statement. *You say "insert a (lossy)
capacitive reactance in series". *Why would a braidless piece of coax
inserted in a tube have significantly different loss than the intact
coax of that length?

I've made matches made that way for decades that ran at full or near
full legal limit on 6m. *I'm pretty sure that any significant loss
would have shown up as dripping plastic. *The matches when taken apart
after years of use show no sign of heating.

Tom,

My use of "lossy" was to remind readers that capacitive reactance
obtained by using such a transmission line element is a relatively lossy
'capacitor'. For example. an o/c stub of RG213 for a reactance of -10
ohms at 144MHz has a resistance of about 0.1 ohms, or a Q of about 100.
That is not a huge loss, but quality capacitors achieve much higher Q
than that.

So, I don't know why one might use such a thing in a driven element,
introducing say 0.2 ohms of resistance which consumes about 0.4% of the
power if it was a R=50 feedpoint, when a similar reactance could be
obtained by a slight shortening. The purpose is probably not for
frequency compensation, it works the wrong way.

Is the loss significant, not really in this case, and it won't melt the
PE, but TL derived capacitors are relatively lower Q.

Owen- Ocultar texto de la cita -

- Mostrar texto de la cita -

Could it simply be a capacitive coupling method without any matching
property ?

Feeding system name?
 

lu6etj wrote in
:
Could it simply be a capacitive coupling method without any matching
property ?

That depends what you mean by "without any matching property".

If the o/c stub is less than an electrical quarter wave (as it seems from
the description, it must introduce some series capacitive reactance, and
loss resistance, the longer it is, the higher the loss resistance.

It is not at all obvious why they would do what you described (and for
Tom's benefit, I am not talking about a gamma match).

Owen

Feeding system name?
 

On 6 mayo, 19:20, Owen Duffy wrote:
lu6etj wrote :

Could it simply be a capacitive coupling method without any matching
property ?

That depends what you mean by "without any matching property".

If the o/c stub is less than an electrical quarter wave (as it seems from
the description, it must introduce some series capacitive reactance, and
loss resistance, the longer it is, the higher the loss resistance.

It is not at all obvious why they would do what you described (and for
Tom's benefit, I am not talking about a gamma match).

Owen

Hi Owen

I mean "any matching property" in the sense that we give to a coupling
condenser in electronic circuits.

Another possibility could be that it was a method to trim the resonant
frequency easily from the center of the structure without to cut the
tube neither to make it telescopic making the element a little more
longer. I don`t know, I hoped to obtain a correct answer looking for
it in the Web.

At worse, maybe that system never existed. I only remember sometimes
heard speak about it in the eter or a mailing list :)

Thank you very much for your helping

Miguel LU6ETJ

Feeding system name?
 

On 8 mayo, 15:13, lu6etj wrote:
On 6 mayo, 19:20, Owen Duffy wrote:

lu6etj wrote :

Could it simply be a capacitive coupling method without any matching
property ?

That depends what you mean by "without any matching property".

If the o/c stub is less than an electrical quarter wave (as it seems from
the description, it must introduce some series capacitive reactance, and
loss resistance, the longer it is, the higher the loss resistance.

It is not at all obvious why they would do what you described (and for
Tom's benefit, I am not talking about a gamma match).

Owen

Hi Owen

I mean "any matching property" in the sense that we give to a coupling
condenser in electronic circuits.

Another possibility could be that it was a method to trim the resonant
frequency easily from the center of the structure without to cut the
tube neither to make it telescopic making the element a little more
longer. I don`t know, I hoped to obtain a correct answer looking for
it in the Web.

At worse, maybe that system never existed. I only remember sometimes
heard speak about it in the eter or a mailing list :)

Thank you very much for your helping

Miguel LU6ETJ

Another speculation...

Increasing dipole length radiation resistance increases. Could be a
method devised to take advantage of that effect using the condenser to
take the antenna to resonance again

Will it compensate the increase in the radiation resistance the higher
losses in coaxial condenser?

Miguel