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Paul Burridge wrote in message ... Hi all, I need a simple design for a BPF with a centre frequency of 17.2Mhz., corner frequencies one Meg or therabouts either side of that and a reasonably good shape factor (nothing critical here). I don't mind having to do a bit of tweaking of values myself if anyone has something close to that they can post. Passive L/C combinations only, please. (assume the usual 50R nominal Zs.) Thanks, p. -- The BBC: Licensed at public expense to spread lies. The simplest filter that'll get you by, is this one. (a couple of tuned circuits with a bit of top-coupling :-) ... ___ ||C1 -|_R_¦------.----.-------||-------.----.-------, O/p Source |L2 |C2 || |C2 |L2 | I/p | | | | .-. C| --- --- C| | |load R C| --- --- C| |R| C| | | C| '-' | | | | | === === === === === GND GND GND GND GND F1=16.2e6 'lower limit MHz F2=18.2e6 'upper limit MHz R=50 'Ohms source and load impedance Pi=3.142 C1 = (F1+F2) / (4 x Pi x F1 x F2 x R) C2 = F1 /(Pi x F2 x (F2-F1) x R)/2 L2 = 2xR /(4 x Pi) x (1/F1 - 1/F2) The inductors end up being quite small but a couple of loops of wire cost nothing. At 25megs the output is down to about 3% , which is not bad. This particular style is the "3 element" design and from the traditional "Constant K" filter stable. The pleasantly simple to design "constant K's" and associated "M derived" filters, can be easily and freely used for most day-to-day electronics work. Exact Filter design, or 'synthesis' as they nowadays prefer to call it, can be a nightmare if you're coming in from scratch. Even using a filter design programme requires a good knowledge of filter types/performance/spec's before data can begin to be entered. If not using a prog' you move onto the more vexing method of having to design an initial (prototype) low-pass filter, either via precalculated tables or computing the required co-efficients, then mathematically transforming the low-pass values into a bandpass (etc) design. For higher order filters it can be ball-acheing drudgery and even then inductor resistance has a nasty habit of spoiling that pristine work of art. (not a problem with DSP filters). I can't suggest a decent book, as the general purpose books seem over complicated and destined to be written by maths people for maths people. (The old GPO line-comm's manuals have useful notes on the 'K and M ' filters). regards john |
Go to Alt Binaries Schematics -
bg Paul Burridge wrote in message ... Hi all, I need a simple design for a BPF with a centre frequency of 17.2Mhz., |
Go to Alt Binaries Schematics -
bg Paul Burridge wrote in message ... Hi all, I need a simple design for a BPF with a centre frequency of 17.2Mhz., |
John Jardine wrote:
I can't suggest a decent book, as the general purpose books seem over complicated and destined to be written by maths people for maths people. I'd suggest Temes and LaPatra, "Circuit Synthesis and Design." Now out of print, but occasionally you can find a cheap old copy used. I'd also suggest the original poster does a couple of the exercises (he might have already), doing what you describe with building a low frequency prototype filter and then transforming it to a different type and frequency range, but just for, e.g., a second order filter. There's not much to be gained by doing the 'drudgery,' as you say, for a higher order filter other than proficiency in aithrmetic. ---Joel Kolstad |
John Jardine wrote:
I can't suggest a decent book, as the general purpose books seem over complicated and destined to be written by maths people for maths people. I'd suggest Temes and LaPatra, "Circuit Synthesis and Design." Now out of print, but occasionally you can find a cheap old copy used. I'd also suggest the original poster does a couple of the exercises (he might have already), doing what you describe with building a low frequency prototype filter and then transforming it to a different type and frequency range, but just for, e.g., a second order filter. There's not much to be gained by doing the 'drudgery,' as you say, for a higher order filter other than proficiency in aithrmetic. ---Joel Kolstad |
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On Fri, 05 Mar 2004 16:18:32 +0000, Paul Burridge wrote:
On Fri, 05 Mar 2004 11:28:51 GMT, Active8 wrote: He already has a book with a fair amount of tables and all the explainations on how to go about the design. I'm wondering WTF here. Hey paul. wtf? Fair point. I just wondered if anyone had a design similar to requirements *already* lying around they might post it, that's all. Save me a bit of scrawling and button-pushing. I didn't wish to put anyone out. Thanks to all who responded, BTW. Some very useful steers. Yes. I had to check my disorganized drive to make sure I'd been to all those links. BTDT. I like having tools like that around to compare what they say with what I figgered out on paper. -- Best Regards, Mike |
On Fri, 05 Mar 2004 16:18:32 +0000, Paul Burridge wrote:
On Fri, 05 Mar 2004 11:28:51 GMT, Active8 wrote: He already has a book with a fair amount of tables and all the explainations on how to go about the design. I'm wondering WTF here. Hey paul. wtf? Fair point. I just wondered if anyone had a design similar to requirements *already* lying around they might post it, that's all. Save me a bit of scrawling and button-pushing. I didn't wish to put anyone out. Thanks to all who responded, BTW. Some very useful steers. Yes. I had to check my disorganized drive to make sure I'd been to all those links. BTDT. I like having tools like that around to compare what they say with what I figgered out on paper. -- Best Regards, Mike |
On Thu, 04 Mar 2004 23:43:21 +0000, Paul Burridge
wrote: Hi all, I need a simple design for a BPF with a centre frequency of 17.2Mhz., corner frequencies one Meg or therabouts either side of that and a reasonably good shape factor (nothing critical here). I don't mind having to do a bit of tweaking of values myself if anyone has something close to that they can post. Passive L/C combinations only, please. (assume the usual 50R nominal Zs.) Thanks, Since your too lazy to do this, here, have a few designs. You can run these on LTSpice. What is reasonably good shape factor? Mark Butterworth, pi-input, 1st-order low-pass prototype Vin 1 0 AC 2.0000V Rin 1 2 50.000 L1 2 0 26.899n C1 2 0 3.1831n Rout 2 0 50.000 ..AC DEC 396 253.58kHz 1.1667GHz ..PROBE ..END Butterworth, pi-input, 2nd-order low-pass prototype Vin 1 0 AC 2.0000V Rin 1 2 50.000 L1 2 0 38.041n C1 2 0 2.2508n L2 2 3 5.6270u C2 3 4 15.216p Rout 4 0 50.000 ..AC DEC 792 5.7378MegHz 51.560MegHz ..PROBE ..END Butterworth, loose coupled, 2nd-order low-pass prototype Vin 1 0 AC 2.0000V Rin 1 2 50.000 C1 2 0 2.0654nF L1 2 0 38.046nH C2 2 3 185.01pF C3 3 0 2.0654nF L2 3 0 38.046nH Rout 3 0 50.000 ..AC DEC 792 5.7378MegHz 51.560MegHz ..PROBE ..END Butterworth, pi-input, 3rd-order low-pass prototype Vin 1 0 AC 2.0000V Rin 1 2 50.000 L1 2 0 53.798n C1 2 0 1.5915n L2 2 3 7.9577u C2 3 4 10.760p L3 4 0 53.798n C3 4 0 1.5915n Rout 4 0 50.000 ..AC DEC 1188 10.224MegHz 28.937MegHz ..PROBE ..END Butterworth, loose coupled, 3rd-order low-pass prototype Vin 1 0 AC 2.0000V Rin 1 2 50.000 C1 2 0 1.4607nF L1 2 0 53.798nH C2 2 3 130.84pF C3 3 0 1.3299nF L2 3 0 53.798nH C4 3 4 130.84pF C5 4 0 1.4607nF L3 4 0 53.798nH Rout 4 0 50.000 ..AC DEC 1188 10.224MegHz 28.937MegHz ..PROBE ..END Butterworth, loose coupled, 8th-order low-pass prototype Vin 1 0 AC 2.0000V Rin 1 2 50.000 C1 2 0 511.07pF L1 2 0 137.94nH C2 2 3 109.63pF C3 3 0 457.95pF L2 3 0 137.94nH C4 3 4 53.121pF C5 4 0 527.60pF L3 4 0 137.94nH C6 4 5 39.985pF C7 5 0 543.91pF L4 5 0 137.94nH C8 5 6 36.809pF C9 6 0 543.91pF L5 6 0 137.94nH C10 6 7 39.985pF C11 7 0 527.60pF L6 7 0 137.94nH C12 7 8 53.121pF C13 8 0 457.95pF L7 8 0 137.94nH C14 8 9 109.63pF C15 9 0 511.07pF L8 9 0 137.94nH Rout 9 0 50.000 ..AC DEC 3170 15.208MegHz 19.453MegHz ..PROBE ..END |
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