Re: Portable SWL setup with Airspy HF+ and GPD Win #hardware #airspyhfplus #swl #shortwave


Leif Asbrink
 

Hello LS,
 
https://www.youtube.com/watch?v=oRzJE3LAxDk

GPD Win is similar to other Atom-based tablets in terms
of the huge amounts of interference it injects into the
antenna part of the system. I have to use a Bluetooth
speaker or plug in a pair of headphones, as when the
built-in speakers are active, the sound card produces
huge spurs on the spectrum (the louder the sound, the
bigger the spurs!). I've managed to reduce the remaining
RFI by using Bonito's GI300 isolator, as seen in the
video, but I'm wondering if other users have found more
effective ways of doing this.
This does not look right to me. I think the advice
from Bonito to place the isolator very near the radio
is not a good idea. If you want to eliminate all
interference completely I suggest you look at these 4
videos:
1) http://www.youtube.com/embed/ItLkn8r4s3E (24 min)

2) http://www.youtube.com/embed/zsZTX7MQSGQ (47 min)

3) http://www.youtube.com/embed/kgMbaJDFu9M (55 min)

4) http://www.youtube.com/embed/C65u7Pmz7a0 (21 min)

At the end of #2 you can see how interference suppression
is much better with the isolator at some distance from
the radio. The mechanism is that the cable from the
antenna to the isolator has a very high impedance
at the point where it ends (for common mode) in the
isolator. It is extremely sensitive to electric fields.

Put the isolator halfway between antenna and rx. It is good
if you supply a ground point on the screen towards the
antenna at the isolator - but leave the screen towards the
radio ungrounded. It should be grounded at the radio.

For grounding you might use half a square meter of
sheet metal lying on the ground (you can see in the video
that the whip antenna is grounded that way.) You might also
stick some kind of metal rod into the ground.

The video should explain if you have the patience to see
all of it.


73

Leif

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