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