Re: Matching a monolithic xtal filter

On Sep 11, 1:51 pm, Joerg <notthisjoerg...@xxxxxxxxxxxxxxxxxxxxx>
wrote:
Tom Bruhns wrote:
On Sep 11, 11:15 am, Joerg <notthisjoerg...@xxxxxxxxxxxxxxxxxxxxx>
wrote:

Tom Bruhns wrote:

...

how much you can do. At a 45MHz center frequency, without going
really overboard with the LC filter, you probably will end up with a
3dB bandwidth at least a couple MHz wide. To do much better while
keeping the filter loss low requires coils with high Q, which get
physically large.

That's where the old concept of the Q-multiplier comes in. After that it
only boils down to how good you are able to control the CF of a resonant
circuit up front. But shhht, don't tell anyone. The younger lads out
there don't have the foggiest idea what that is.

Ouch! Not around my designs, thank you. :-(

[For the uninitiated: just stay away from them.]

What made you gun-shy here? Got hurt by them? Nowadays you can create
nice gain controlled amps and in most of my cases this is under full
computer-control. That was way different when I started as a teenage
hobbyist where the price tag of an Apple II would make you cringe. Now
you can buy a uC for a buck.

Baaackk iiinnnn theeee oolldddd ddaaaaysss wwhhhhheenn IIII
wwwwwwwaaaaaaaaasssssss yyoouuuunnnggg, I had the bright idea to add
negative resistance to improve the Q of an otherwise passive bandpass
circuit, since the coil was limiting the performance due to its Q. An
experienced engineer told me not to bother trying for commercial grade
equipment that had to operate across a wide temperature range. I never
revisited it.

So you've had luck with this technique at RF? Seems more a ham/garage
thing to me.

.

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