LF: TA Grabber modifications

[markusvester@aol.com]

Dear LF,

 

many thanks to Wolfgang and Jean-Pierre for their hints on optimizing SpecLab settings for improved TA reception. I have now adopted the fast AGC following a 50 Hz wide filter, which seems to handle QRN quite a bit better than the original wideband noise blanker.

 

It looks like I also finally managed to get some aerial directivity. I have used a second pair of large loops and combined their signals in a small goniometer, sitting on the desk. It consists of two closely spaced ferrite rings having two windings across them, without going through the core hole (see pic). The weighted combination is then added in phase to the E-field signal, at about 80% amplitude. This results in a rotatable cardioid pattern with ~ 19dB F/B ratio. As this addition does not introduce a phase term (at least not in theory), the RDF principle should still work, even near the back of the beam.

 

Steering northeast now, I seem to get a significant reduction of QRN, as well as some relief from the Budapest stuff. And here comes a signal on 137779.85 - looks like XGJ who started at 23:10.

 

73 and best of luck

 

Markus, DF6NM
http://members.aol.com/df6nm/Grabber.htm

 

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