Topband: AM Broadcast Filter recommendation

[Jim Brown]

On 12/5/2023 1:19 PM, Steve Muenich wrote:
> I'm looking for a recommendation for an AM Broadcast filter for my receive
> only input.
> Unfortunately I live 2 miles form 910 khz AM so their 2nd harmonic wipes
> out 1820.

It's important to figure out where that harmonic is being generated. If 
it's in their transmitter, nothing you can do will help -- you'll have 
to lean on them to fix it. Some questions.

Is the harmonic present on all of your antennas? The Hi-Z array? The 
Beverage? Is there a preamp for the Beverage? If so, at the feedpoint or 
in the shack?

Is the harmonic present on a much shorter wire?

A good filter will help with that harmonic if it's being generated 
somewhere in your RX chain -- those preamps, and/or the front end of 
your RX. If it's being generated in one of the preamps, it must be ahead 
of the preamp (that is, between the antenna and the preamp).

I've owned more than a half-dozen ICE filters over the years, and 
measured their performance. I also found serious QC issues with a couple 
of them purchased new -- poor alignment, resulting both in poor 
rejection and excess loss in the passband. One of the BCB filters I 
owned measured 58 dB down at 1 MHz, which is where I started the sweep.

If you don't have to transmit through the filter (using it ahead of a 
preamp, or at if your rig has patch jacks for RX in and RX out), the 
data sheet for a receive-only preamp like the AS-1.8HPF-RX that Array 
Solutions sells for $79 shows more than 50 dB of attenuation around 900 kHz.

73, Jim K9YC