15MHz and 50MHz Low pass filter - Page 1
Forum section: electronics / projects

author: xzswq21
author_rank: Frequent Contributor
timestamp: December 14, 2017, 08:02:23 pm
content: Helloin my project I need to have some 15MHz and 50MHz SMA Low pass filters.I wanted to buy from mini-circuits but the freight charge is only 135$!is there any ways to realize such filter?6 or 7 order LPF is better.I want to put it at the input of ADC.I could design it with some softwares but you know the behavior is completely dependent to the inductors and capacitors.Best Regards

author: danadak
author_rank: Super Contributor
timestamp: December 15, 2017, 12:43:00 am
content: This might help -https://www-users.cs.york.ac.uk/~fisher/lcfilter/http://www.tonnesoftware.com/elsie.htmlRegards, Dana.

author: darrell
author_rank: Regular Contributor
timestamp: December 16, 2017, 12:19:18 am
content: Qucs has a built in filter synthesis tool. It's on the tools menu. Run it and then paste to your schematic. Then simulate and add plots of S11 and S21.http://qucs.sourceforge.net/download.htmlLoss will be mostly from the inductors. Look for high Q, low DCR, high SRF. I download S Parameter models from the inductor manufacturer and put that into the Qucs simulation in place of the ideal inductor. Caps should be NP0/C0G, but you don't need special RF ones.Also, if you want to buy ready made, Crystek makes filters similar to Minicircuits and Digikey carries them.

author: cdev
author_rank: Super Contributor
timestamp: December 16, 2017, 02:06:07 pm
content: I usually use a very useful piece of abandonware called RFSIM99 . I downloaded my copy from a community college engineering professor's web site in San Diego California. It runs fine under Wine and its very easy to use for all kinds of filters, and its free. It does the math and plots curves and can even figure out the worst case examples due to component variations, and work with S-parameters.Once you get the hang of it you can bang a multi-pole filter out in a couple of minutes, solder it together, and poof, it works.Total cost, almost nothing.

author: Neganur
author_rank: Unknown
timestamp: December 16, 2017, 08:21:53 pm
content: That can’t be right. Freight charge if 135$ ? You sure you’re not under their minimum order amount or something?

author: xzswq21
author_rank: Frequent Contributor
timestamp: December 16, 2017, 09:12:39 pm
content: Quote from: Neganur on December 16, 2017, 08:21:53 pmtry it!choose only one filter and then order it!Mini-circuits has some representatives in other countries.for example there is one seller in Australia but the seller has to sell minicircuits products within Australia and New Zealand!https://www.cseonline.com.au/SXLP-16.htmlthere is no way...I'm contacting with some dealers in other countries, some of them said me you should buy 10 pieces at-least!finally I found a good dealer! this is a good achievement in my project!

author: Gerhard_dk4xp
author_rank: Frequent Contributor
timestamp: December 17, 2017, 12:48:54 am
content: I have bought MCL stuff at Industrial Electronics near Munich.Some transformer and ERA-* kits, the price was reasonable.(has been some years since)Just don't expect them to break out into jubilee mode when theyget a 15% markup from $20 for half an hour of man power.Bying kits gives them at least the illusion of seeding for the future.regards, Gerhard.

author: Neganur
author_rank: Unknown
timestamp: December 17, 2017, 11:26:05 am
content: Quote from: xzswq21 on December 16, 2017, 09:12:39 pmYou have to set the warehouse location to UK or else you will be faced with a hefty shipping surcharge.

author: cdev
author_rank: Super Contributor
timestamp: December 17, 2017, 09:01:40 pm
content: Somebody would have to be nuts to pay that much for some filters they could bang together in a few minutes.The ones they made by hand would almost certainly work better, too.For that much money I could buy a nice LC meter.Then I could measure inductor values precisely and never have to guess at their values from a formula.Although I would miss the push and pull on the coils until the thing works just right, actually.That's kind of a fun process. I enjoy it.

author: basinstreetdesign
author_rank: Frequent Contributor
timestamp: December 18, 2017, 03:06:42 am
content: This from a calculator I have, FWIWYou didn't say if passband ripple was to be avoided or any other specs, so this Butterworth is the default but is the worst filter to build. A Cauer would reduce the 5-6th order number significantly.

author: cdev
author_rank: Super Contributor
timestamp: December 18, 2017, 02:36:58 pm
content: To make your own filters you need to have a material to build them on. I usually use scraps of PCB materials and regular wire (if its insulated, use wire that's got low loss insulation. )The best way to do it through hole is by using very short lengths of mini-coax. For HF and low VHF I usually use SMA connectors but instead of mounting them on the end I mount them on the surface so the transmission line runs along the surface. The solder connection points then end up being at the ideal point just a bit above the PCB. I then usually just twist and then solder through hole the components for an HF filter keeping the leads short. For inductors it works best if you situate nearby inductors at right angles to one another unless they are intended to interact.OP, are you all set up for your design, then?Is this for an up-converter for an RTLSDR? Just curious.Quote from: xzswq21 on December 14, 2017, 08:02:23 pm