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

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

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.

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

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

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.

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

"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.

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

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