Re: Prototyping?

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?

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.

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

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...

---Joel


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