Well,
Now that I have some life in my Minima, I need to remake the 15MHz Low Pass Filer. You may remember the sweep I did originally:
There is a bit too much attenuation at the 14-15MHz frequency range - this will result in a very deaf radio on the 20M band!
So I used the QUCS tool to design an 11th Order filter with a cut off at 15MHz, I then changed the capacitor values to "real world" numbers and ended up with this:
I then made the filter and after winding each toroid I measured the value and carefully spaced the turns to get as close to the required value as I could.
The physical construction looks like this - all the toroids are T50-6s:
and when I sweep the filter on the Spectrum Analyser I see this:
So this looks much more like what we need - I will use this and replace the one in the radio right now.
Good, egh?
Now that I have some life in my Minima, I need to remake the 15MHz Low Pass Filer. You may remember the sweep I did originally:
There is a bit too much attenuation at the 14-15MHz frequency range - this will result in a very deaf radio on the 20M band!
So I used the QUCS tool to design an 11th Order filter with a cut off at 15MHz, I then changed the capacitor values to "real world" numbers and ended up with this:
The physical construction looks like this - all the toroids are T50-6s:
and when I sweep the filter on the Spectrum Analyser I see this:
So this looks much more like what we need - I will use this and replace the one in the radio right now.
Good, egh?
I see the schematic has the higher value inductors in the 3 center positions but the picture of the filter shows the 13 turn toroids on the right 2 positions and the second from the left- did the values just work out that way or can you elaborate. I would have thought that the 13 turn cores would have all been in the center positions.
ReplyDelete73, Gord
Very interesting observation! I guess it has to do with the winding spacings; I measured each one before I used it - the filter scans are of the filter you see photographed.
ReplyDelete