LF LISTENING FILTER
This filter is connect between a selective meter or a receiver and antenna, it protect from overload the input stage of a selective meter over 450 Khz, were there are the medium wawe commercial broadcasting.
The CAD project and prototype of this filter was made by Adamo IK2SBB ex IK1, the final measurement was made by Pietro I2BUM, he has confirmed to me and Adamo what the software said.
The software is the:"AADE Filter Design and Analysis" free download in this site: http://www.aade.com/download.htm
It's impedance is 50 Ohm, pay attention when you use it do not exchange input with output, the inserition of this filter had improve the signal-noise ratio with my hf groun plane.
I have try on air the filter on 20th july 2008 at around 12 am when i heard on 414 Khz a little signal from VEEN, i don't know anything about it at the moment when i wrote theese notes.
Without filter on my selective voltmeter with increasing of the sensibility i dont heard anything !!!
It's alluminum case measure: 30 x 37 x 110 millimeters the toroids are AMIDON T 68-3 gray, and the wire is 0.5 mm of diameter.
This is the scheme with L and C value .
This is the roll off response, made by software.
This is the roll off response, made by I2BUM lab's.
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This is the prototype closed . |
This is the prototype open |
The filter in action at 900 khz !!!