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Hmm wouldn't a Q =3D ~5 high pass filter at 10 MHz followed by a Q =3D ~5 Low pass filter at 50 MHz do it? Of course it would be relativly flat in between.

(Or is that too simple?)

George H.

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That might work. Post a schematic!

The ideal clock-input-reference filters have narrowband responses around the input frequency, as narrow as parts tolerances allow, to reject as much non-ref crud as possible. You want to be operating on the flat part of the frequency response curve, so's not to convert any amplitude or temperature effects into phase shift... so too much Q is bad too. That suggests higher-order filters in extreme cases.

At 10 MHz, we usually use a simple R-L-C with a Q around 5. That also allows ugly inputs, like square waves that ring and whatever.

John

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That DOES NOT need to be the five hours it usually takes...

On odd element microwave ones, short the Inner element. Adjust the outer ones for SWR as desired, open up the inner one.

Dishal's method.... The guy wrote a brilliant paper on it..

Steve

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Ah found it:

Dishal, M., =94 Alignment and Adjustment of Synchronously Tuned Multiple- Resonant- Circuit Filters,=94 Elec. Commun., pp. 154-164, June, 1952.

Also see Hayward, =94 Introduction to Radio Frequency Design,=94 ARRL, 1994, pp95-101.

Steve

Steve, Many of us have no access to either of those articles (I have only 1981 and 1999 ARRL Handbooks).

Can you post, or provide a link where IEEE rears their ugly head ?:-)

Thanks! ...Jim Thompson

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

I can scan in the snippet out of Hayward tonight if no one else already has a PDF of it...

Googling on....

"Alignment and Adjustment of Synchronously Tuned Multiple-Resonant-Circuit Filters" -ieee -wipo -patent -portal

Give two returns, one in some oriental script, the other just a reference :-( ...Jim Thompson

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

This one will get you some of the flavor of the technique:

I've tried this at 70cm, and while it works, if you just have a bunch of, e.g., capacitor-coupled LC resonators on FR4, it still requires some hand-tweaking in that you're already getting to the point where there's a little bit of coupling through "opens" and a slightly noticeable little bit of impedance through "shorts."

---Joel

Thanks, Joel!

If no one comes forth with the actual paper in the next few days, could you scan the snippet out of Hayward?

Thanks again! ...Jim Thompson

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

Sure thing, will do.

---Joel

Dishal works best with high-Q filters--it relies on the fact that detuned series sections look like open circuits and detuned parallel sections like shorts. You use a return-loss test setup, start from the end you're measuring, and get all the bumps in the calculated spots.

Also it doesn't matter what you put in parallel with a series section--in the limit of high Q, you can't move its resonance.

Works well for Q >~ 20 IME, but not as well at lower Q since the approximations don't hold as accurately.

The thing to watch out for is the temptation to make the filter look nice but with a slightly too-narrow bandwidth: "There's no way to get there from here."

Cheers

Phil Hobbs

I was thinking of using it for simulation tools ;-) ...Jim Thompson

If you already know where the section resonances should go, that'll work fine, although I'm not sure what problem you're trying to solve.... Generally what makes filter tuning hard is that you're adjusting L and C, whereas you really want to adjust f_0 and Q, and simulators don't have that problem.

Cheers

Phil Hobbs

network

Every once in a while I have to demonstrate a filter made from RLC's (but in PSpice) that meets the clients needs.

_Possibly_ this method will allow me to "fake" some real filters ;-) ...Jim Thompson

In the end it's like what I have seen at an auto shop in Italy. Alfa Romeo, hot edition with four independent carburtors, needed adjusting. "O mama mia, only Giuseppe can do those, you'll have to wait until he gets back".

I had a friend with a Spider. To reach the points, working around the hard fuel-injection lines, it helped to first break your arm about 1/3 of the way up. But it was sinful to drive.

John

Oh yeah, and the design is really slick, too. This one was a Julietta but with four carbs, each having as "air filter" nothing but a stretched piece of cloth above the throat.

They made a lot of very sporty cars down there. Except they rusted like crazy, at least in the 80's.

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Ouch, sorry John, I was speaking theoretically. I never designed any RF filters. I=92ve only been mucking about at audio frequencies where with opamps it would be dead easy.

George H.

Jim Thompson a écrit :

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You could have a look at spice opus. It's free and has quite a rich optimization algorithms set.

It's been a while since I used it and I don't know whether they've included a GUI or not, so it might bring you back to the good editor/netlist old days, but for a few RLCs filters this is pb OK. (my spice being a 3F5-Xspice based one I could use it straight with some hand written added commands for the spice opus unsupported specific commands)