This is one way to start but maybe the 50Hz and it's harmonics could cause 
problems to the soundcard? Maybe it is useful to apply a simple LC-bandpass 
and/or a resonated antenna (wire, L and parallel C, stepped L or separate 
primary winding) in a circuit, active or passive...

Stefan/7fc

________________________________

Von: [email protected] im Auftrag von M0FMT
Gesendet: Do 25.02.2010 11:38
An: [email protected]
Betreff: Re: LF: RE: Re: VLF_8.79 kHz


Ken.
Why not just stick an antenna wire into your Sound card mic socket and install 
either Argo Spectran or Spec lab FFT application. You then have DC to 48kc/s 
VLF coverage with the ability to detect very very weak signals. Using SDR 
software you can then record the result in real time spectrum allowing it to be 
processed by others. 

This type of set up is used by many people to copy SAQ on 17.2kc/s.
 
It is the method we are using here for some simple tests on 7.8125kc/s and or 
9.765625kc/s depending upon xtal used. 
 
You are about 11km from this location if you are keen on this exercise I can 
let you know when my setup is working. Now that the weather is getting better I 
will be able to get out working on the antenna.
 
Two arrangements will be tried a vertical loop up abt 12/13m and an earth 
electrode method. I have no real idea of how to load these antennas because my 
best calculations say if I use a kW the coil about 1 Henry will dissipate most 
of the power which means it be getting very very hot and probably fail and need 
over 2 km of wire. Totally impractical! Some ideas have been kicked around on 
the is reflector and off list there may be something I can try.

73 es GL petefmt

--- On Thu, 25/2/10, Ken <[email protected]> wrote:



    From: Ken <[email protected]>
    Subject: LF: RE: Re: VLF_8.79 kHz
    To: [email protected]
    Date: Thursday, 25 February, 2010, 10:05
    
    
    Hi Jim.
    I think I could knock up a quick 9kHz RX here in Luton over the weekend if
    that would help. I have been following this thread with interest, could you
    put up some diagrams etc of your parallel capacitor and other antenna
    configurations and formulae.
    
    73.
    Ken
    M0KHW    IO91TV
    
    -----Original Message-----
    From: [email protected] 
<http://uk.mc281.mail.yahoo.com/mc/[email protected]>
 
    [mailto:[email protected] 
<http://uk.mc281.mail.yahoo.com/mc/[email protected]>
 ] On Behalf Of James Moritz
    Sent: 24 February 2010 21:14
    To: [email protected] 
<http://uk.mc281.mail.yahoo.com/mc/[email protected]> 
    Subject: LF: Re: VLF_8.79 kHz
    
    Dear LF Group,
    
    A couple of years ago I did some measurements of Rloss of the 10m high, 40m 
    long inv-L antenna at my home QTH, and also a near-identical antenna set up 
    in the middle of a field away from trees and buildings. The attached graph 
    shows Rloss plotted against frequency over the range 10kHz to 600kHz for 
    both antennas. At all frequencies, the loss resistance of the open-field 
    antenna is much lower than the home QTH antenna, which is surrounded by 
    numerous small trees. The ground in both cases was 4 x 1m ground rods, close
    
    to the feed point of the antenna. The actual ground around both antennas was
    
    very similar - a waterlogged clay soil.
    
    At 10kHz, the open  field antenna has Rloss of 50R, against 380R for the 
    home QTH antenna. Both antennas show a decreasing Rloss with frequency - 
    this suggests dielectric losses are dominant (the antenna voltage increases 
    at lower frequencies for a given current) in both cases. The text books say,
    
    for electrically small antennas, that dielectric losses will dominate at low
    
    frequencies, while at high frequencies the skin effect will eventually cause
    
    resistance to start increasing - in the case of the open field antenna, a 
    turn-over point might have been reached at a few hundred kHz.
    
    The 50R figure suggests that antenna efficiency might actually be higher at 
    9kHz than people are expecting - at least in an open field site. A suitable 
    loading coil would be a problem. The antenna capacitance was around 350pF - 
    in these experiments I used a ferrite-cored coil of around 0.7H with a Q of 
    about 150, but this had a loss resistance of about 300R. If you tolerated 
    loosing half the TX power in the loading coil, a similar inductance with a Q
    
    of around 1000 would be needed. Increasing the top-loading capacitance of 
    the antenna would definitely be useful...
    
    Cheers, Jim Moritz
    73 de M0BMU
    
    
    

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