Topology of Bitx40 bandpass filter

cove37 All Messages By This Member #24390 Does anyone know what it is? ?It has remarkable characteristics. ?I've extrapolated it to make equally performing filters for all the other bands (confirmed with Elsie) but would like to know what I'm making... ..thanks Burton Ison W5IAC
Noel All Messages By This Member #24392 I'd be curious to make a similar topology HIGH pass filter, for when I put my BitX onto the higher bands.. -- 73 de Noel, ZL1NC
cove37 All Messages By This Member #24393 I'm planning to use these for both rx and tx on the 40-20-15m bands...retloss never rises above -13db, that's good enough for this market
Ken All Messages By This Member #24397 You can read about double tuned and tripled tuned BPF in EMRFD page 6.76. 73 Ken VA3ABN toggle quoted message Show quoted text On Sun, Apr 2, 2017 at 4:45 PM, Noel <08004us@...> wrote: I'd be curious to make a similar topology HIGH pass filter, for when I put my BitX onto the higher bands.. -- 73 de Noel, ZL1NC
cove37 All Messages By This Member #24401 Hm, appears to be a cross between a double and a triple tuned...5 poles, but no separate Cmid value Burton Ison W5IAC
Ken All Messages By This Member #24402 The series resonant version does have Cmid. 73 Ken VA3ABN toggle quoted message Show quoted text On Sun, Apr 2, 2017 at 5:41 PM, cove37 via Groups.Io <cove37@...> wrote: Hm, appears to be a cross between a double and a triple tuned...5 poles, but no separate Cmid value Burton Ison W5IAC
cove37 All Messages By This Member #24405 No, not to nitpick, the filter in the bitx40 schematic, does not have a separate Cmid value, the series capacitors, all 3, are of the same value On Sunday, April 2, 2017 6:24 PM, Ken <chase8043@...> wrote: The series resonant version does have Cmid. 73 Ken VA3ABN toggle quoted message Show quoted text On Sun, Apr 2, 2017 at 5:41 PM, cove37 via Groups.Io <cove37@...> wrote: Hm, appears to be a cross between a double and a triple tuned...5 poles, but no separate Cmid value Burton Ison W5IAC
Ken All Messages By This Member #24409 C3 and C5, 1000 pf are the mids. See EMRFD Page 6.77 Fig 6.135 73 Ken VA3ABN toggle quoted message Show quoted text On Sun, Apr 2, 2017 at 8:55 PM, cove37 via Groups.Io <cove37@...> wrote: No, not to nitpick, the filter in the bitx40 schematic, does not have a separate Cmid value, the series capacitors, all 3, are of the same value On Sunday, April 2, 2017 6:24 PM, Ken <chase8043@...> wrote: The series resonant version does have Cmid. 73 Ken VA3ABN On Sun, Apr 2, 2017 at 5:41 PM, cove37 via Groups.Io <cove37@...> wrote: Hm, appears to be a cross between a double and a triple tuned...5 poles, but no separate Cmid value Burton Ison W5IAC
cove37 All Messages By This Member #24413 Ok. ?They work, whatever they are. ?If anyone's interested, just divide all component values by 2 for 20m, divide by 3 for 15m, etc. ?They look great on Elsie.
Ashhar Farhan All Messages By This Member #24418 This is cohn topology. here are some more for you guys. i'd really appreciate someone digging deeper into these. i worked the values out by plugging these into the gpla program that comes on EMRFD. -f toggle quoted message Show quoted text On Mon, Apr 3, 2017 at 8:27 AM, cove37 via Groups.Io <cove37@...> wrote: Ok.? They work, whatever they are.? If anyone's interested, just divide all component values by 2 for 20m, divide by 3 for 15m, etc.? They look great on Elsie.
Ken All Messages By This Member #24423 Hi Farhan I also used GPLA at first and then switched over to LTSpice. On my BITX I stripped all the BPF components from the board and used headers to solder external BPF board to with RG174. I am testing the same 40m BPF as the stock and a 20 BPF using values from EMRFD. I am finding that the 20m BPF is not 50 ohms 73 Ken VA3ABN toggle quoted message Show quoted text On Mon, Apr 3, 2017 at 12:56 AM, Ashhar Farhan <farhanbox@...> wrote: This is cohn topology. here are some more for you guys. i'd really appreciate someone digging deeper into these. i worked the values out by plugging these into the gpla program that comes on EMRFD. -f On Mon, Apr 3, 2017 at 8:27 AM, cove37 via Groups.Io <cove37@...> wrote: Ok.? They work, whatever they are.? If anyone's interested, just divide all component values by 2 for 20m, divide by 3 for 15m, etc.? They look great on Elsie.
cove37 All Messages By This Member #24424 Thanks for that link, exactly what I was looking for. Thanks also for your work on the filter, I haven't seen an LC filter with such steep characteristics and low loss before. ?The 20m and 15m extrapolations I entered into Elsie model great, I'll? build a couple and see how they stand up to the spec analyser. Burton Ison W5IAC
Ken All Messages By This Member #24425 Hi Burton Let me know what kind of i/p and o/p imperdance you get with the 20m BPF? 73 ken VA3ABN toggle quoted message Show quoted text On Mon, Apr 3, 2017 at 9:18 AM, cove37 via Groups.Io <cove37@...> wrote: Thanks for that link, exactly what I was looking for. Thanks also for your work on the filter, I haven't seen an LC filter with such steep characteristics and low loss before.? The 20m and 15m extrapolations I entered into Elsie model great, I'll? build a couple and see how they stand up to the spec analyser. Burton Ison W5IAC
cove37 All Messages By This Member #24426 Unfortunately my program doesn't show complex impedances (or I just don't know how to make it do that) but according to the passband/retloss charts, plus the Smith chart (after 40 years, still trying to get my head around that one) it appears to be 50 in/out...might want to plug the values into your program and see what you get. ?I just halved the component values and a nice pattern appeared centered on 14mHz...all the hard work has already been done designing the original filter.? PS I've found that tinkering with the input/output capacitor values (moving them up slightly higher than 50 ohms) seems to give you a much better return loss curve.

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Topology of Bitx40 bandpass filter