Re: QRP Labs Low Pass Filters
|
kees,? these filters are very fickle about the exact impedances at both ends. i hope you measured them with strong 50 ohms source and termination
- f
On Sat, Mar 18, 2017 at 5:17 PM, Steve Hunt <steve@...> wrote:
Mike,
I did the same using RFSim99, so the shift in the measured frequency
response must be down to capacitor tolerances, inductor values being
out, or, conceivably, stray capacitance added by the PCB.
It's surprising just how much variation there can be in the inductor
values. In addition to the Al tolerance of +/-10%, the winding
spacing makes a big difference. In Micrometals application note they
show the inductance of 10 turns of #20 wire on a T50-17 varying
between 0.22uH and 0.39uH depending on how the turns are spaced!
Also I note in the QRP labs table that at least two different
required inductor values are realised with the same number
of turns on the same core, so that introduces another
"approximation factor".
Steve G3TXQ
On 17/03/2017 22:25, K5ESS wrote:
Steve,
I just entered the L and C values
that QRP Labs lists for the 20 meter LPF into AADE filter
Design.? The analysis shows only a .03 dB loss at 14.5 MHz
and doesn¡¯t exceed 1.5 dB until above 15.5 MHz.? I suspect
you¡¯ll have to measure and tweek your toroids to get close
to the values that QRP Labs calls out for their 20 meter
filter.
Mike
K5ESS
?
|
