Topband: BCB Filter Recommendation?

[Jeremy Maris]

Hi Rick,

Thanks for that - good point about Inverse chebyshev. and the toroids were dust iron…
We’re fortunate in not having mega strong signals near the top of the MW band here.

Jeremy



> On 17 Apr 2020, at 05:24, Richard (Rick) Karlquist <richard at karlquist.com> wrote:
> 
> 
> 
> On 4/16/2020 2:45 PM, Jeremy Maris wrote:
>> Make your own!
>> Use this site to design your filter.
>> http://www.iowahills.com/9RFFiltersPage.html
>> Attached are the values I used back in 2016 when the G4AQG FT-1000MP had intermod problems with a new Beverage.
>> I built a 9 pole Chebyshev high pass filter, designed with the excellent RF filter design package from Iowa Software, and used an LC meter to get the capacitor and inductor values correct. Caps were made from polystyrene and inductors wound on small ferrite torroids..
>> Difficult to see from the (ancient!) spectrum analyzer picture but the filter response was almost exactly as the design showed.
>> No labels for stop-band but it was 10dB down at 1579kHz, 50dB down at 1000kHz and at 693kHz was in the noise, at least 70dB down, almost undetectable compared to 60dB over S9 or more without the filter, and the  intermod was gone.
> 
> The good filters use INVERSE Chebyshev designs,
> made with mica or C0G capacitors, and powdered iron cores.
> 10 dB down at 1579 kHz is not good enough for many QTH's.
> I have a very strong local station at 1700 kHz,
> for example, and another at 1530 kHz.
> 
> Rick N6RK

Jeremy Maris
140 Edward Street, Brighton BN2 0JL
jeremy at maris.plus.com