[AMRadio] 1500 KHz trap for NC-156

John Coleman jc at pctechref.com
Mon Aug 11 14:54:39 EDT 2008

Good work Larry:
	I have just a quick suggestion and it may not be even noticeable. 
When tuning for the 1500KC null on the trap start tuning from the low end
(maximum capacitance) stop tuning when you get enough attenuation even if it
is not centered on 1500KC.  You may find that you can reach enough
attenuation of the unwanted 1500KC when the trap is actually resonating at a
much lower frequency.  This will bring the gain back up a little on the 160
meter band.
	It may not work but it won't take long to find out.
John, WA5BXO

-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of Larry Szendrei
Sent: Monday, August 11, 2008 12:54 PM
To: Jim Tonne; Discussion of AM Radio in the Amateur Service; Glowbugs
Subject: Re: [AMRadio] 1500 KHz trap for NC-156

Hi Jim,

Apologies if my post was confusing.

Yes, I'm attempting to reject 1500 KHz, which is the IF frequency.

The receiver covers 0.3 - 1.2 MHz, and 1.7 - 17 MHz, skipping a band
approximately centered about the IF frequency. Therefore, the ideal (and
impossible) filter would be a brick wall stopband from 1.2 - 1.7 MHz, with
zero attenuation outside of that range.

I mentioned 80M only to comment that I noticed no attenuation that far
removed from the filter center frequency.

Yes, I wanted minimal attenuation at 160M as well. There were no signals
on that band when I was playing with this last night around 7PM local time
to use for reference, which is why I didn't quote attenuation for 160M.
However I was hearing plenty of static crashes on 160M with and without
the filter. I imagine the attenuation on 160M will be somewhat similar to
what I saw at 1.13 MHZ, roughly 12 dB - nothing to write home about, and
hardly optimized, but good enough considering the time and effort I care
to invest in this particular project.


----- Original Message -----
From: "Jim Tonne" <tonne at comcast.net>
Sent: Mon, August 11, 2008 13:33
Subject:Re: [AMRadio] 1500 KHz trap for NC-156


Let me jump in on that trap thing for just a

You are trying to reject what frequency / frequencies?

And you want to pass what frequency / frequencies?

Reading your last mail here leaves me confused as to
what you wanted to do.  I thought you wanted to
reject 1500 or so and still pass 160 meter band but
you just now mentioned 1100 and the 80 meter band.

- JimT

----- End of original message -----

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