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G8JNJ
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- G8JNJ
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Home Brew Broadband Magnetic Loop
Hi Ron,I think the loop is still unbalanced.The split is to avoid a continuous 'screen' (Faraday screen to minimise E-Field pickup) around the loop. But if one end of the center conductor is connected to ground you may have a problem.Check signal levels with the loop normal and 180 degrees as suggested previously.A 1:1 transformer on the loop input may help improve balance. Try six bifilar turns through a BN73-202 core as a starting point. One winding as the (balanced) loop input (primary) the other as the output (secondary) unbalanced connected to the amplifier input, with one end of the winding connected to ground. This will also provide galvanic isolation.You can also try a few more turns on the secondary as an experiment as this may improve reception on the LF bands.If you made a balanced loop amplifier with a much lower value of input impedance (LZ1AQ or Wellbrook copy) you wouldn't need the loop outer screen to minimise E-Field pickup.Regards,Martin - G8JNJ -
Broadcast database application with control of WEB SDR
Hi John,I recently found a broadcast database application that allows control of various receivers (including the Twente WEB SDR).Although it's a bit of a pain to setup, it does have some 'interesting' features that may be of interest for KiWi admins and users.Regards,Martin - G8JNJ -
Some things I have noticed [problems with a large DX/label database]
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v1.161: FSK/RTTY extension
Hi John,Quite a few 170Hz / 100bd FSK signals I've heard (but not decoded) turn out to be "Digital selective-calling system for use in the maritime mobile service" using a ten-bit error-detecting code.All of the code structure is defined in https://www.itu.int/dms_pubrec/itu-r/rec/m/R-REC-M.493-14-201509-I!!PDF-E.pdfDSC calling frequencies- 2.1875 kHz
- 4.2075 kHz
- 6.312 kHz
- 8.4145 kHz
- 12.577 kHz
- 16.8045 kHz
Regards,Martin - G8JNJ - 2.1875 kHz
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Home Brew Broadband Magnetic Loop
Hi Ron,I think that the problem is almost certainly loop imbalance.You can check this by rotating the loop to peak a known station. Note the signal level then rotate the loop 180 degrees and note the signal level of the peak in that direction.If the loop is properly balanced the signal levels should be the same. If it isn't the peaks will be different as the imbalance means that it is now configured as an Aperiodic loop.Which are often used for phased receive arrays like this commercial version.I found that the LZ1AQ design was easier to build than the 'Wellgood' (Wellbrook copy) and performed slightly better.I fed mine with coax and left out the input filter network and voltage regulator (works OK on 13.8v)The Wellgood and ZL1AQ work OK up to about 10MHz then run out of steam. if you want better performance on the HF bands the only solution is to make a 'fatter' loop or connect multiple loops in parallel in order to reduce the loop inductance.Lots of notes here http://www.lz1aq.signacor.com/ and here http://active-antenna.eu/amplifier-kit/technical-documentation/More stuff about loops etc. on my active antennas webpage http://www.g8jnj.net/activeantennas.htmRegards,Martin - G8JNJ