Hi Larry You are correct in the thinking of a higher Q (more C less L) however it is very important the lower L factor be made of larger wire with proper spacing (a high Q type coil). There are special dimensions and wire spacing to be considered for a high "Q" coil assemblies. I won't go into that here as there are probably more expert coil winders available here on the list than I am. But I do know that it makes a difference. The whole thing will need to be put in a shielded box else coil assembly may act as an antenna for the 1500KHZ
As I recall, 100pf and 100uh resonates at around 1590KC but you may want higher C yet? Another thing to consider: You might use an antenna tuner but not the pi-net type with the series coil as these are low pass circuits. Instead the seldom seen pi-net with two coils to ground and a series capacitor making a hi-pass network would be real good but doing two adjustable coils would be a pain. So the old fashioned link coupled parallel tank is best for this application. Perhaps some of the modern "T" nets might be good also I don't know. Perhaps the trap and a tuner together would work well. Good Luck John, WA5BXO -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Larry Szendrei Sent: Friday, August 08, 2008 7:09 PM To: Glowbugs; AM Reflector Subject: [AMRadio] 1500 KHz trap for NC-156 However, the IF in the NC-156 is 1500 KHz, and as you might expect there is bleed-through of broadcast stations on or near that frequency, especially on the 160M band, and especially at night, when there is sky-wave propagation there. The undesired signals are so strong that it makes operation on 160M totally impossible. I first tried a series-resonant circuit from ANT to GND, and it was totally ineffective, probably because the source impedance of the antenna is low. Then I reconfigured my L and C as a parallel resonant circuit in series with the ANT at the receiver, and I was able to totally eliminate the 1500 KHz +/- interference. But, 160M signals are highly attenuated also (although S/N, if you will, where N is the the 1500 KHz interference, is much better). Also WBZ on 1.3 MHz is very noticibly attenuated. My trap consists of a 140pf air trimmer at ~40% mesh (= ~56 pF) in parallel with 200µH. I'm thinking a higher Q circuit (more C and less L) will sharpen the peak and I'll have less attenuation 300 KHz away from the resonant frequency of the trap. Or is there a better way to eliminate the 1500 KHz QRM? 73 es Tnx, -Larry/NE1S ______________________________________________________________ Our Main Website: http://www.amfone.net AMRadio mailing list Searchable Archives: http://www.mail-archive.com/amradio@mailman.qth.net/ List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net To unsubscribe, send an email to [EMAIL PROTECTED] with the word unsubscribe in the message body.