Hello all,
since some months I am listening to the 136KHz band with a Icom IC761,this
is a good HF tranceiver but on longwave it has some intermodulation problems
with local broadcasting stations on 675KHz and higher.To solve this I build
a narrowband preamp,also suitable for a whip antenna.Enclosed the circuit,a
picture of the filter shape follows.
B-3 dB : 3 KHz
B-60dB : 28 KHz
No more IM problems on any receiver I use.To compensate for the gain on the
50 Ohm input I use the 20 dB attentuator on the IC761.
Greetings,
Victor
PA3FNY
preamp.png
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