As was mentioned, you need to add the missing capacitor in parallel. 47pf in the QDX HB. IIRC this is all the parts Hans shows in his example of the LPF modeling in the QDX manual. I did my modeling for 50 ohm impedances, but knowing that it's not what happens in reality. But using the "tune part" function in Elsie, I could easily see what the relative effect was of changing inductances or capacitor values.?
I modeled this LPF for the QDX using values that Hans put in the manual for inductance. (Which, is what it was modeled with I believe, probably using the earlier T37-10 toroids.)? ?That one used 290 and 250nh for inductor values for the 15/17m LPF. If I leave the one at 290, and shift the other to less ,like 220nh, my -3db frequency increases by about 1 Mhz.
For this LPF, try reducing the inductance on Part #4 in your model.??
If you mess around with the inductance of part 2, you'll see in the plots it wildly affects the SWR...which is another component of filter design that makes it more tricky! Reducing Part #4 inductance seems to be favorable, SWR wise, and still moves the cutoff frequency up.?
-Nate
N8BTR
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