HI,

The KGD antenna of qrpproject is no longer sold.
I would like to build one and I am looking for infos about it : Coil,
capacitor and connections.
(The manual didn't say anything about that)

Thank you for your help

bern

On Thu, 6 Aug 2009 14:57:43 +0200, "Brobin"
wrote:

HI,

The KGD antenna of qrpproject is no longer sold.
I would like to build one and I am looking for infos about it : Coil,
capacitor and connections.
(The manual didn't say anything about that)

Thank you for your help

bern


Hi Bern,

No information, a manual that isn't helpful, aside from that, what
makes it so good?

In other words, why not build an antenna that suits your needs? As
far as that goes, what about the KGD antenna was appealing? There is
nothing particularly remarkable about gracing it with a term like QRP.

73's
Richard Clark, KB7QHC

No information, a manual that isn't helpful, aside from that, what
makes it so good?

In other words, why not build an antenna that suits your needs? As
far as that goes, what about the KGD antenna was appealing? There is
nothing particularly remarkable about gracing it with a term like QRP.

Hello...
Richard, you are right ! This antenna isn't a special case. It is only a
very short dipole with a capacitor which adapt the impedance of the antenna
at the coaxial line. Nothing very new or even miraculous! (I do not believe
in miracles ;o).
I just want to make a comparison between several types of antenna (including
a miraculous o).
I do not therefore wish to innovate in the miracle, but simply to replicate
some in order to compare them (without spend to many money ;o)

72

"
hmmm, sure you don't mean inductor?



Yes ;o) it is why I would like to try that antenna...
Here is the link you could find more info about it :
http://www.qrpproject.de/UK/kg-dipole.htm

On Thu, 6 Aug 2009 18:01:48 +0200, "Brobin"
wrote:

This antenna isn't a special case. It is only a
very short dipole with a capacitor which adapt the impedance of the antenna
at the coaxial line.

The combination of "very short" with capacitor does not lend itself to
a match.

I do not therefore wish to innovate in the miracle, but simply to replicate
some in order to compare them (without spend to many money ;o)

Save ALL your money, aside from heating effects (which I doubt you
could measure anyway), there won't be wit of difference.

73's
Richard Clark, KB7QHC

Hmmm. It looks to me as if this may be a sort of L-match.

The basic antenna is a dipole, with each arm being inductively loaded
at its base with a coil wound from magnet wire. The inductive loading
would allow the relatively short dipole (which would have a very low
radiation resistance, and a high capacitive reactance) to resonate
properly on the 40-meter frequency.

Even when resonated, and even with the relatively high losses in the
coils, the antenna's feedpoint impedance would probably be on the low
side. If I'm understanding the German manual correctly, it's on the
order of 20 ohms.

It sounds to me as if the antenna uses an L-match arrangement to raise
the feedpoint impedance. This would be done by:

- Lengthening the tuning rods at the end slightly (or adding a turn or
two more to the coils than would be required for resonance). This
would increase the resistive portion of the feedpoint impedance
very slightly (trivially), and would add some inductive reactance
in series with the resistance. With the correct adjustment, the
feedpoint impedance would be equivalent to 50 ohms resistive, in
parallel with some amount of reactance.

- Place a shunt capacitor directly across the feedpoint, with the
capacitor's value chosen to have a capacitive reactance equal in
magnitude (but opposite in sign) to the antenna's parallel
reactance. The two reactances would add, resulting in a zero
reactance, and thus a feedpoint impedance of 50 ohms resistive.

A similar matching arrangement is sometimes used with mobile HF
antennas such as screwdrivers and bug-catchers.



Yes it is.
I found the description on my old ARRL Handbook (1994 p33.22)
Thanks a lot...that was simply but I had some difficulties to find the start
of the trail...

Brobin wrote:
Hello...
Richard, you are right ! This antenna isn't a special case. It is only a
very short dipole with a capacitor which adapt the impedance of the antenna
at the coaxial line.


hmmm, sure you don't mean inductor?


- 73 de Mike N3LI -

On Thu, 6 Aug 2009 19:05:42 +0200, "Brobin"
wrote:

Yes ;o) it is why I would like to try that antenna...
Here is the link you could find more info about it :
http://www.qrpproject.de/UK/kg-dipole.htm

Hmmm, I was wrong. With those tightly wound coils handy, you can
measure the heat loss.

73's
Richard Clark, KB7QHC

hmmm, sure you don't mean inductor?



Yes ;o) it is why I would like to try that antenna...
Here is the link you could find more info about it :
http://www.qrpproject.de/UK/kg-dipole.htm

Hmmm. It looks to me as if this may be a sort of L-match.

The basic antenna is a dipole, with each arm being inductively loaded
at its base with a coil wound from magnet wire. The inductive loading
would allow the relatively short dipole (which would have a very low
radiation resistance, and a high capacitive reactance) to resonate
properly on the 40-meter frequency.

Even when resonated, and even with the relatively high losses in the
coils, the antenna's feedpoint impedance would probably be on the low
side. If I'm understanding the German manual correctly, it's on the
order of 20 ohms.

It sounds to me as if the antenna uses an L-match arrangement to raise
the feedpoint impedance. This would be done by:

- Lengthening the tuning rods at the end slightly (or adding a turn or
two more to the coils than would be required for resonance). This
would increase the resistive portion of the feedpoint impedance
very slightly (trivially), and would add some inductive reactance
in series with the resistance. With the correct adjustment, the
feedpoint impedance would be equivalent to 50 ohms resistive, in
parallel with some amount of reactance.

- Place a shunt capacitor directly across the feedpoint, with the
capacitor's value chosen to have a capacitive reactance equal in
magnitude (but opposite in sign) to the antenna's parallel
reactance. The two reactances would add, resulting in a zero
reactance, and thus a feedpoint impedance of 50 ohms resistive.

A similar matching arrangement is sometimes used with mobile HF
antennas such as screwdrivers and bug-catchers.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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