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 <[email protected]> > 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 [email protected] _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
