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Yes... That coil inductance number was what I
calculated based on a guess of what the "C" would be.
Now that I can
read the capacitance... the inductance would be higher.
Sadly.
My next step is
to see how much the "C" can be increased through the use of several
parallel radiators.
Here is my
situation for the antenna.
170' (55
meters) meters of #12 (2 mm) dia
wire. The wire is terminated near the top of a 40 meter tall tower.
There is a ceramic
insulator 6" long at the
top, and the wire is suspended away from the tower after that by
rope.
The wire runs to a point near the shack 2 meters about
the ground.
The antenna forms a 45 degree angle with the
earth.
So currently
there is measured 340 pf in the antenna.
Next test is to
run another wire, 1 meter spaced from current wire in parallel and remeasure the
amount of "C"
This is an easy
test to do as I have a rope and pulley at the top of the
tower.
If this works out
I can use 3 wires spaced 1meter apart and test.
Not sure how to
implement a tophat yet.
Most important is
to get my "C" up and the need for "L" down.
Normally used for
a rain barrel. I will check them out tomorrow for suitability in coil
building.
PauLC
W1VLF
Hello Paul,
Addition: If your C is
340pF and you want to resonate at 8,97kHz, your 545mH coil is to small! You
will need L = 926mH!
GL, Stefan/DK7FC
Von: [email protected] im
Auftrag von Paul A. Cianciolo
Gesendet: So 28.03.2010
20:27
An: [email protected]
Betreff: RE: LF:
Question about ground impedance at 8.97 KHZ **UPDATE
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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