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[Linrad] Re: off subject Delta 44

At 10:56 AM 3/30/2009, you wrote:

>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
>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.

Interesting ideas.  I am setting up my station for 160m and 600m 
operations.  930-foot BOG (Beverage on Ground) made from coax cable 
and a 45x130x45 foot EWE for transmitting.  No tx for 600m but using 
SDR-IQ as receiver.  On 160m I will use FT-847+2x3-400zPA and SDR-IQ 
running several different programs including Linrad.  This a project 
in works for this summer with Rx to be done, first.

Current work is getting the 4.9m dish going on 23cm-eme and building 
up a 300w sspa (W6PQL).  I will squeeze in getting Linrad and MAP65iq 
going and getting my new Rubidium Ref set up for locking the 1296 xvtr.

Thanks for all the good info on Linrad.  I have made up a notebook to 
keep a library of postings.

73, Ed - KL7UW              BP40iq, 6m - 3cm
144-EME: FT-847, mgf-1801, 4x-xp20, 8877-600w
1296-EME: DEMI-Xvtr, 0.30 dBNF, 4.9m dish, 60/300W  (not QRV)
http://www.kl7uw.com       AK VHF-Up Group
NA Rep. for DUBUS: dubususa@xxxxxxxxxxx

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