Hybrid Low Pass filter, part 1
Thanks to Mikael SJ2W I started to play with hybrid LP filters. Why? Because it is easy design, high power ready, low insert loss and UFB notch.
What is it about... There are two coax stub filters, lambda/4 on notch frequency and inductor between. The stubs work as capacitor in the classic PI LP filter design. Look at the results:
Hybrid LP filter for 20m, notch on 10m:
Design: 2x coax abt 2,2m H1000, L is 4,5turns on 30mm
Design: 2x coax abt 4.5m H1000, L is 7turns on 30mm
Hi ..I'm trying to replicate the 40m filter, what is H1000 coax, we dont have this in the UK .. Could capacitors be used in place of coax?
ReplyDeleteJim M0CKE
Hi Jim. It is Belden H1000, but you can use any cable. Just cut 1/4 * k on notch frequency. Or better , cut it longer, two the same coaxes and tune it than in LP filter. The capacitance is not critical, just use one turn more on inductor and tune it on VNA.
ReplyDeleteThanks for fast reply, so using something like RG213 with a vf of 0.66 and 100pf/m then we cut the stubs for 14.200, and adjust the coil fit min loss or max null??
ReplyDeleteI am using RG-213 too: http://ok2zaw.blogspot.cz/search/label/Filters
ReplyDeleteFor sere, cut it longer, for example for 13,9MHz and than you can just fine-tune it. You can also cut one to CW and second to SSB part if you want. There will not be so high null, but wider.
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ReplyDeleteHi again, the stubs are open or shorted ?
ReplyDeleteHi, yes open. Open lambda/4 * k for null freq. (20m) in 40m filter.
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