Passive filter design software using preferred component values - Page 1
Forum section: electronics / projects

author: perdrix
author_rank: Frequent Contributor
timestamp: March 03, 2018, 01:04:18 pm
content: Hi folksLooking to build a 10MHz bandpass filter to convert a square wave to a sine.I would like to find some desing software for this that doesn't propose totally unobtainium component values - it's anot as iff I have any 229.76uH inductors lying around or even ordereable.Hence the wish to use preferred value parts - I'll quite happily accept a wider bandpass for this trade off.I tried "Elsie" but AFAICT that doesn't have any option to tell it to use only preferred values - but I could easily have missed it.David

author: Benta
author_rank: Super Contributor
timestamp: March 03, 2018, 01:27:17 pm
content: At that frequency you'll have so many parasitic effects that using calculated values is hopeless anyway.I don't know your signal levels, but a possibility could be using 10.7 MHz adjustable IF coil sets. Cheap and easy to find. Or you could scavenge them from an old FM radio.Edit: they're actually called "IF transformers".

author: Mechatrommer
author_rank: Super Contributor
timestamp: March 03, 2018, 01:42:16 pm
content: any spice simulation will do.. tina-ti? ltspice?

author: orbanp
author_rank: Regular Contributor
timestamp: March 03, 2018, 02:04:16 pm
content: Quote from: perdrix onTodayat 12:04:18 AMHi David,Looks like you missed it!On the "Design" page there is a "Nearst 5%" button, as well as a "Specify L" button, those let you tune the component values.DISCLAIMER:I have not updated "Elsie" for a while, my version is Student Edition 2.77, from 2016.Newer versions might behave differently.Do check the help pages!Good luck, Peter

author: perdrix
author_rank: Frequent Contributor
timestamp: March 03, 2018, 02:34:56 pm
content: Yes, you are right it was a separate tab, and I was looking for a tick box or similar.ThanksDavid

author: G0HZU
author_rank: Super Contributor
timestamp: March 03, 2018, 02:40:33 pm
content: QuoteAre you sure about that? The centre frequency is only 10MHz.

author: Benta
author_rank: Super Contributor
timestamp: March 03, 2018, 02:50:16 pm
content: Quote from: G0HZU on March 03, 2018, 02:40:33 pmIt's been my experience, at least. For the caps you're down in the pF range, for the coils uH. Layout and wires start playing quite a large role.

author: mc172
author_rank: Frequent Contributor
timestamp: March 03, 2018, 02:53:17 pm
content: Iowa Hills "RFFilter"http://iowahills.com/9RFFiltersPage.html

author: G0HZU
author_rank: Super Contributor
timestamp: March 03, 2018, 03:24:15 pm
content: Quote from: Benta on March 03, 2018, 02:50:16 pmIf you were correct, Coilcraft would have gone out of business years ago. It's possible to model and build decent BPFs up towards a GHz or so using fixed inductor values from Coilcrafthttps://www.coilcraft.com/prod_smind.cfm

author: Benta
author_rank: Super Contributor
timestamp: March 03, 2018, 03:37:47 pm
content: I don't question building filters up to 1 GHz with fixed inductors. I do question the modeling, though. But I've only done it a few times, and my calculations were always off compared to the measurements afterwards.

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: March 03, 2018, 03:40:23 pm
content: If you want to turn 10Mhz square into sine only a low-pass filter is needed--you just need to suppress the higher harmonics which are all in the 20MHz and up range. A bandpass filter takes more components than equivalent LPF.

author: rhb
author_rank: Super Contributor
timestamp: March 03, 2018, 03:44:50 pm
content: I suggest trying this:http://www.tonnesoftware.com/svcdownload.htmlIt designs filters using Standard Value Components. Tonne Software have quite a few other programs besides Elsie.

author: Kalvin
author_rank: Super Contributor
timestamp: March 03, 2018, 04:01:55 pm
content: A crystal-based passive bandpass filter is simple and requires very few components in addition to the crystal(s) itself. The Q-value is very high compared to equivalent LC-filter, so you will required only few stages.https://hackaday.com/2016/03/13/designing-a-crystal-ladder-bandpass-filter/

author: G0HZU
author_rank: Super Contributor
timestamp: March 03, 2018, 04:48:19 pm
content: Quote from: Benta on March 03, 2018, 03:37:47 pmAt 1GHz it's best to use a VNA to take an s2p model of the inductor when it is mounted on the correct PCB material. The other alternatives are to use Coilcraft's own s2p files or try using the Modelithics range of models (expensive). Even then, at 1GHz you also have to model the PCB layout to get a sensible overall model of the complete filter.But at 10MHz I think things are a lot easier.

author: mc172
author_rank: Frequent Contributor
timestamp: March 03, 2018, 10:07:46 pm
content: I would agree - at 10 MHz the layout is hardly important. As long as the coils aren't touching each other, and you aren't looking for 50+ dB of rejection, it isn't going to be a problem whatever you do.

author: David Chamberlain
author_rank: Frequent Contributor
timestamp: March 03, 2018, 10:48:07 pm
content: Quote from: mc172 on March 03, 2018, 02:53:17 pmAlso came to say Iowa Hills one. On the download page 'RF Filter Designer Ver. 2.2'It has an option for 'std LC Values'