Dear Henryk, et. al.,
The low pass filter schematic I sent out from the 1985 ARRL Handbook have
series resonances of 680 KHz for C5-L1, 1311 KHz for C6-L2 and 1168 KHz for
C7-L3 with the values given. If one has an AM radio station nearby, one can
adjust the resonance slightly by spreading or compressing the turns of wire on
the torroidal cores. Using a radio with AM band and an S-meter one can tune
the coils for nulls near these frequencies. I am also told one could add a
turn or raise the capacitor C6 if a strong AM station was well below 1100 KHz
and well above 700 KHz. Since the nearby station here is on 930 KHz, I did use
a larger value of L3 to make a better null on one Hi-Pass filter at that
frequency, which lowers the rejection in the 1100 - 11200 KHz range. Our next
strongest station is on 1400 KHz, so the C6-L2 circuit was adjusted for a
highest null at 1400 KHz. It has not seemed to attenuate the bottom end of 160
meters.
73 George K8GG
----- Original Message -----
From: Henryk Majcher
To: gmguerin@voyager.net
Sent: Sunday, April 06, 2003 12:05 PM
Subject: HPF
Hi George
Many thanks for quickly mailing.
Fortunately, I have few T 50-2 at home, also good LCR
bridge. I am going to built HPF. Another thinks is preamplifier, I will look
web sites You send.
73! Henryk SP3E
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