[Linrad] Delta 44 vlf rx

[Jeremy Alexander <w7eme.org; jeremy@xxxxxxxxxxxxxxxx>]

Mahalos Leif,

I am going to look at some of these different audio preamp chips, many offer the type of parameter you suggest.

I have a couple different selective voltmeter and vlf receivers here, so should at least be able to see what the D44 is detecting.

Pardon me on the lowfer thing, yes I meant in the D44's bandwidth.

I am still considering adding the HF converter to my WSE setup, Leif. Was however looking really to see what I could use the left over break-out box from the sound card for...hi. And you know, the 1/4" audio jacks come right out and BNC fits right in their place. Pleanty of room in the box for the preamps and imp matching on the big pcb.

I'll report back at some future time and let everyone know what I can receive with the d44 stand alone rx.

73 for the hints...Jeremy w7eme



--- On Mon, 3/30/09, Leif Asbrink <leif@xxxxxxxxxx> wrote:

> From: Leif Asbrink <leif@xxxxxxxxxx>
> Subject: [Linrad] Re: off subject Delta 44
> To: linrad@xxxxxxxxxxxxxxxx
> Date: Monday, March 30, 2009, 11:56 AM
> 
> Hi Jeremy,
> 
> > I am curious about using the delta 44 and the Linrad 
> > for lowfer listening. What precautions should I follow
> 
> > before connecting antenna to input of the sound card.
> 
> You mean listening in the range 5 to 45 kHz or so?
> (Wikipedia says lowfer is at higher frequencies than
> that...)
> 
> > Also I am sure someone is doing this, what kind of 
> > success would one have with this setup over say a 
> > commercial selective voltmeter type receiver? 
> It could make a tremendous difference. It depends on what
> you want to hear.
> 
> At low frequencies your antennas will be very small
> compared
> to the wavelength so they will always have a dipole
> pattern.
> Electric dipole for E field sensors and magnetic dipole
> for
> H field sensors. The E field and the H field are coupled
> in
> free space, E/H=300 Ohms but in the near field they are not
> 
> coupled (much) and ratio between the E field and the H
> field
> may deviate very much from 300 ohms. A fluorescent light
> might give a very strong E field (high voltages) but a low
> H field (small RF current in the plasma) while the
> transformer
> in an old TV might leak strong magnetic fields at the line
> frequency and its overtones.
> 
> Make yourself two antennas. One magnetic. Could be a coil
> with a diameter of a couple of meters. It is very important
> that
> it is not capacitively coupled to anything. Connect a low
> impedance amplifier through a low capacitance transformer.
> High permeability so you can place the windings on opposite
> 
> sides of the core. It will be a magnetic loop and if you
> place 
> it vertically you will have a nice figure 8 radiation
> pattern.
> 
> Also make a magnetic antenna. Maybe a 5 m vertical tube. 
> You will need a low capacitance fet amplifier and
> presumably
> a good (high Q) inductor to balance stray capacitances
> and make the impedance very high.
> 
> Place the two antennas at a good distance away from noise 
> sources and connect both of them to Linrad. If the gain is
> set
> to make the signal level similar for stations in the lobe
> of the magnetic loop you will linrad splits the received
> signal into two groups, backwards and forwards because
> the phase relation in the two directions differ by 180
> degrees.
> 
> All that might be fun, but you could equally well do it
> on 80 meters. It is the same as 80m fox-hunters do:-)
> 
> Now, what is more intreaguing is that you can adjust
> gain and phase to make the pol indicator in Linrad
> say the polarization is always left or right circular
> for forward or backward. Then you can move the cables
> and send the signal from one antenna into I and the other
> into Q of Linrads channel 1. Now running in I/Q mode
> you will see two spectra. Negative frequencies are 
> forwards and positive frequencies backwards or vice 
> versa.
> 
> Having two more channels you can of course do the 
> same thing once more:-) You may place sensors of any kind
> in a way that makes them pick up the local qrm that
> might enter your antena and use Linrad to phase out the
> QRM by setting pol adjustment to manual.
> 
> > The dual antenna thing is curious to me at LW and
> wonder 
> > who is doing it.
> I have been waiting a long time for HF operators to
> discover
> what they can do. I have even made the RXHFA available
> with
> a hope it would be found to be a useful tool at e.g. 160
> m.
> 
> I had no feedback or comments on this issue from anyone
> before 
> and yet I honestly believe the potential is much bigger
> than in
> 144 MHz EME. Two channels will give +3dB at maximum in a 
> white noise background, but when it comes to interference 
> suppression the limit is set by the phase stability of
> the signals from the interferer. Local signals should
> be extremely stable and I would guess one can attenuate
> by 40 dB at least. Linrad does not have routines to
> suppress
> a particular signal (yet?) To look at ways of doing it
> well
> I need recordings of typical cases. 
> 
> 
> 
>    73
> 
>    Leif / SM5BSZ
> 
> > 
> 

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