Hi Paul,
My loading coil is also on a water barrel and it works fine and has the
necessary stability and not to much mass. Also the ratio between diameter and
lenght is optimal and it is the cheepest one can get for that.
A 2mm wire is good to increase the partial discharge inception level. My wire
has just abt 1mm and it works -proven- up to 16kV rms and hopefully more ;-)
The ceramic insulator could be a little small. Those devices are normally
constructed for 50/60 Hz and will get stressed a bit more on 9 kHz. But you
will see. It will not melt or burn, like a plastic insulator..
Try to put an insulator between the rope and the wire as well. Otherwise it
could become a problem for the rope, especially when it is wet. In my opinion,
Teflon is a good material that can help you here (if weight is a question).
73, Stefan/DK7FC
________________________________
Von: [email protected] im Auftrag von Paul A. Cianciolo
Gesendet: Mo 29.03.2010 02:43
An: [email protected]
Betreff: RE: LF: Question about ground impedance at 8.97 KHZ **UPDATE
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.
Possible former is here http://hartford.craigslist.org/for/1659831822.html
Normally used for a rain barrel. I will check them out tomorrow for suitability
in coil building.
PauLC
W1VLF
-----Original Message-----
From: Stefan Schäfer [mailto:[email protected]]On Behalf
Of Stefan Schäfer
Sent: Sunday, March 28, 2010 7:48 PM
To: [email protected]
Subject: AW: LF: Question about ground impedance at 8.97 KHZ **UPDATE
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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