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Hello
Stefan,
Thank you for the
response. I hope to increase the "C" with top wires?
The coil I have
calculated is very large as you say.
Using one of Reg Edwards programs, it appears
that a coil 1.2 meters tall, .6 meters in diameter, using #21 wire, .76 MM dia
would result in a 545 mHy inductor.
It would take
1500 turns, have a dc res. of 110 ohms and consist of 9300' of wire for a total
of 23 lbs of copper. I chose #21 because of the its larger than the .46
MM you uses and hopefully would yield
a higher "Q"
and because I found a 50 LBs spool in
possession already helps also. :>)
The predicted "Q" of the inductor is
300.
I have to read more about tophat/wires at 9 KHz, but
anything that would reduce the size of the coil would be
helpful.
PauLC
W1VLF
-----Original Message-----
From:
Stefan Schäfer [mailto:[email protected]]On Behalf Of
Stefan Schäfer
Sent: Saturday, March 27, 2010 7:23
PM
To: [email protected]
Subject: AW: LF:
Question about ground impedance at 8.97 KHZ
**UPDATE
Paul, the values you
measured seem to be realistic for me. Especially the measured antenna C does
not really differ very much between 137kHz and 9 kHz. It is a good value that
allows you to dimension your needed L. The needed L is nearly independent
from the earth losses. I generally recommend a variometer part of 1...5% of
the fixed L to compensate all effects that influence the antenna C. But
think about if it is possible to increase the antenna C instead of building a
very huge coil that causes further losses.
Good luck and have fun with building up!
:-)
73, Stefan/DK7FC
Von: [email protected] im
Auftrag von Paul A. Cianciolo
Gesendet: Sa 27.03.2010
22:01
An: [email protected]
Betreff: RE: LF:
Question about ground impedance at 8.97 KHZ **UPDATE
Hello Folks,
Thank you for all the help with measuring
my antenna impedance.
Let me explain further what I was using to
measure with and then add some updates.
The homebrew bridge I was using was
built as the one in the following link.
The diagram at the very bottom of
the page is the schematic I used.
http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=2285
This
really my first venture into things LF and I had really no idea of what to
expect for numbers
After posting my results here, and talking to W1VD, he
forwarded me a link to Alan and Finbar's bridge experiments here
http://www.alan.melia.btinternet.co.uk/aelossbr.htm
Basically
I duplicated that design, making sure that the transformer had 100 mHy of
inductance to work at 10 KHz.
Sure enough the bridge worked, and balance
with my antenna, but would not balance with my antenna simulator
load.
The simulated load is 2 X 390 ohm .1% resistors in series with a
500 pf silver mica.
Reading on Alan talks about stray
capacitance.
"The problem with the usual trifilar wound transformer is
that if driven from an unbalanced source the secondary suffers unbalanced
strays to ground. This would mean that if you were to swap the components on
the arms of the bridge the balance would be different"
With that in
mind I built another transformer to balance the drive to the bridge.
After doing this the bridge will now balance with the simulated load and the
antenna.
See the following numbers for results:
Measurments were
taken 10Khz
The "R" and "C" "known" side of the bridge were then measure
measured
Sim load = 780 Ohms and 507 PF on LCR
meter
Sim load = 940 Ohms and 460 pf on the
bridge.
Antenna = 1111 Ohms and 330 PF on
bridge
Antenna also measured at 137 KHz
Antenna = 85 ohms and
340 pf @137 Khz.
I think these are more in line with what I should
be reading????
What do you folks think?
Thank you to everyone
who responded to this post and helping me get started.
PauL
C
W1VLF
-----Original
Message-----
From: [email protected]
[mailto:[email protected]]On
Behalf Of Johan H. Bodin
Sent: Friday, March 26, 2010 4:32 PM
To:
[email protected]
Subject: Re: LF: Question about ground
impedance at 8.97 KHZ Stefan.
Hi Paul,
it sounds like your
impedance bridge is measuring the absolute impedance
(that is Z = (R^2 +
X^2)^0.5 where R is the real part, resistance, and X
is the imaginary part,
reactance). R is probably a 10 to a few hundred
ohms, most of it is ground
resistance - it can be neglected - the major
part of your impedance is the
capacitive reactance of the antenna (Xc).
At 9 kHz, where C =
1/(2*Pi*9000*Xc), 70 kOhms means 253pF which is in
the ballpark for your
170' wire (about 5pF/m).
73
Johan SM6LKM
----
Paul A.
Cianciolo wrote:
>
> Hello All,
>
> Below is a quote
from the Stefan's web page concerning his latest "Dreamers Band" DX contact
Congratulations again Stefan.
>>From this information alone is it
possible to calculate or know the antenna system
impedance.
>
>
>
>
> "100m Vertical wire
antenna, coil/antenna voltage was abt 15kV rms, average antenna current about
480mA, giving up to 1,7mW ERP. Applied power was up to 250W."
>
>
Pertaining to the coil "Technical and mechanical data: L=553mH, Q=82,
R(DC)=283 Ohm; 0,4mm diameter enameled copper wire, about 1200 turns! Average
diameter 0,55m, height abt 0,5m. So, about 2000m wire!
:-)"
>
>
>
> I have built a small impedance bridge
that operates at 10 KHZ and shows my sloping 170' wire as 70K Ohms. I can also
see approx 500 PF that can be nulled out using the bridge?
>
> Can
the 70K value possibly be correct? (3) 6' ground rods about 6'
apart are the ground... plus the electrical ground of the
house.
>
> I am hoping to attempt a local transmission on
9KHZ
>
> Any information would be helpful.
>
> Thank
you
>
> Paul
>
>
W1VLF
>
>
>
>
>
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