Re: Prototyping?

Joel Koltner wrote:
Hi Joerg,

"Joerg" <notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote in message news:WHIWi.2552$yV6.1654@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Really steep resonances are frowned upon because now you rely on things such as cleanliness of surfaces, board materials and stuff, and that becomes dicey. Better increase the number of filter stages.

OK, let's just call it Butterworth -- how's that? That asks for far less out of the resonators (with the inductor of course being the generally lousy component -- getting Q>>100 is hard if you're after both "small" and "cheap"...).

Same offer to you as with John: Let's design a, say, 5th order Butterworth filter, 430-440MHz using something like (free) AADE filter designer and then simulate/tweak a bit using (free) LTspice to get to standard component values. I can do a layout from a sketch/description, cut a board, and measure its response... and I claim the result is most likely to have band edges that are off at least, say, 5% from the simulated result. Whaddaya say?


As I said, you can't get 5% out of catalog parts if this gear has to be affordable by folks other than the Rockefellers. If you have to be that accurate there is no way around trimming. Preferably a uC or some other computing device has to do that, meaning you'll need a test signal mux in most situations unless you can use your regular signal.


If you expect tweaking you can provide either varicaps or PIN diodes and have them under host control. I try to stay away from any hand-trimming.

The idea was that you hand-tune using trimmers to get the response right, then replace them with decent accuracy fixed caps that you then crank out in production quantities.


Decent accuracy caps in production -> top Dollar.

I don't like to take that approach, too expensive. A friend of ours is a tech who works in the >10GHz field and she does this kind of trimming all day long. But even there she said they are mulling to automate that.

One method that has almost fallen from grace for some reason is active laser trimming. I loved it. You design everything low, then the stuff gets loaded into a laser and ... phsssst ... a minute later there is a part with the perfect frequency response coming out the other side of the laer box. One design ran about 30k units/year and at night there was only the guard with his German Shepherd in the huge facility. All fully automated.


There are excellent books in the ham radio community on how to built UHF and microwave gear that actually works right off the bat.

Quick survey of a couple books on my shelf...

"Experimental Methods in RF Design" (Hayward/Campbell/Larkin) -- Doesn't bother with filters >3rd order. For frequencies above ~400MHz, they suggest going with transmission line filters (and discuss how to do so).


Hey, John, did you write that? Or a relative?


"Practical RF Design Manual" (DeMaw, R.I.P.) -- "For operation above 200MHz it is more convenient to adopt the [transmission line filter] approach..."


Doug has passed away? I didn't know.


"ARRL Handbook (2007)" -- Goes through plenty of theory, with the usual data tables and implication that, sure, go ahead, build yourself a 9th order filter at 800MHz -- just use these component values here! Actual projects are 3rd or less for VHF filters.

...

I'm telling you, higher-order UHF filters using lumped elements are a little tricky and not just a trivial "Crank out the design from tables, simulate/tweak in LTspice, build the board, results match simulation."


Well, I just opened my "UHF Unterlage" at an arbitrary page. Fell open on page 461 and whoopdidou, a filtered three-stage RF amp for 2.3GHz with layout and all. Followed by lots of others including a power amp. Most of this book assumes two-layer because that's all hobbyists can do at home.

The intro part of this book explains in great detail all kinds of microstrip and other structures, including how to build them with a modest set of tools.


Totally OT now: Are you guys up there also having a wood pellet shortage?

We have a regular wood stove and we're still working on a couple of cords that we purchased last year, so I'm not certain about wood pellet availability. I'll ask around and see...


We have a wood stove upstairs. Blew through four cords last, technically ran out but then the weather turned warmer. So now we've got five cords plus whatever we collected here and there. Almond, the good stuff (but lots of ash).

--
Regards, Joerg

http://www.analogconsultants.com/
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