Topband: BC filters and inductance calculations

[Jeff Blaine]

Paul,

K8ZOA makes exactly what you want.  I have tested it on the bench here and 
it puts the hammers of hell on the BC stuff.  Far better than my W3NQN set 
does.  The filter has 90 db of attenuation on 1.2 Mhz and below.

See the test results here:

http://www.ac0c.com/main/page_antennas__homebrew_clifton_labs_z10022a.html

73/jeff/ac0c
www.ac0c.com
alpha-charlie-zero-charlie

-----Original Message----- 
From: N1BUG
Sent: Thursday, January 05, 2012 5:18 AM
To: Topband
Subject: Topband: BC filters and inductance calculations

Two unrelated questions:

A recent improvement to my station has brought other issues to the
forefront. I am going to need a serious filter to keep AM BC
stations out of my preamp. I had been thinking bandpass filters, but
none I am aware of roll off quickly enough below 1.8 MHz. I am now
investigating high pass filters. The W3NQN filters sold by Array
Solutions look very impressive. Is there anything else (maybe a
little cheaper) anywhere near this or are these in a class by
themselves? This will be a receive only application.

I am also looking for a better formula for calculating inductance of
single layer air core coils. Although I have done well enough over
the years with the "simplified formula" from ARRL Handbooks which
gives a "close approximation" I now wish for something better.
Ideally I would like something accurate for coils of any length to
diameter ratio, including very short coils. A free downloadable or
online calculator would be great, but a plain old formula is fine
too. I have found several on the internet but which ones to trust?
Any guidance would be appreciated.

Thanks, 73, & HNY!

Paul N1BUG

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UR RST IS ... ... ..9 QSB QSB - hw? BK