Tuned Circuit Selectivity

Not IME. But people's perceptions vary and I accept that.

??? I think you're confusing me with someone else, Jan. I only ever use heavyweight PB equipment for such purposes. God knows I have enough of it!

Don't sweat it, John. We've established it's primarily a coupling issue so I can now move on with it. Thanks all the same.

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Okay, you're getting close. For parallel resonance, the drive is ideally a current source, and for series resonance it is a voltage source.

I got close before you did.

Drives for parallel/series resonant crystal operation are a common application of that principle.

On a sunny day (Mon, 6 May 2019 15:32:25 -0000 (UTC)) it happened Cursitor Doom wrote in :

Oh, Ok, though I did see a header raspberry pi as signal generator, I use that sometimes. I also use a shortwave SSB radio to measure some frequencies, works perfectly. The only BIG thing I have is my old Trio analog scope. Oh and the cryo coooler and the TX set and computahs .. but Things are getting more and more nano...

There are good ones and bad ones. The Heathkits are junk. The Measurements 59 Megacycle Meter is a thing of great beauty--I have three of them (two HF/VHF and one UHF). They give a good-sized dip with very weak coupling, so that the measurements are pretty accurate.

I measured the dial calibration accuracy of one of them, and it's still within 2% througout all ranges.

Cheers

Phil Hobbs

Very well. I suggest you try AMDX (MikeK) component values. And put the capacitor in series with the source. You will see much higher Q and, in fact the voltage across the inductor is a measure of Q.

Good luck.

Proximity, to a grid-dip meter, used as directed (that is, start with fairly close coupling, and move the meter probe away until you just barely get a dip - less pulling that way).

Then, without changing the grip-dip meter settings from your best dip point, hold it near a loop antenna connected to a sensitive frequency counter and get a reading.

They should have called it the Magnificent Measurements 59 Megacycle Measuring Meter

You might suggest that to their marketing department. ;) It would be less hyperbolic than some names I've seen.

They later changed their name from Measurements Corp. to Boonton Radio Corp. and then got bought by HP. They made a lot of good stuff--Q meters, dip meters, true-RMS AC voltmeters, and so on. I especially like their three-terminal capacitance meters, the Boonton 72 series.

Cheers

Phil Hobbs

I think I still have an old Heathkit frequency meter somewhere. IIRC it looked rather well-made. Performance wise I've no idea; it may have sucked donkey arse for all I know.

I have got so many old wavemeters still lying around collecting dust. I really must do something with them at some stage. Maybe there's some old- timer on the other side of the planet who is constantly scanning Ebay looking for one and I might be able to help him out. :-/

I got my eye on a HP 4192A impedance analyzer as my next major lab purchase, they seem to go for between 1k-2.5k now depending on condition and calibration situation.

I need some boat anchor in my life

They're great for LW and medium-wave stuff if you have a hand truck to ca rt them around. For microwave work, well, don't.

IME the problems most people have with them is down to poor construction practice, specifically not paying attention to HF wiring discipline. Too ma ny pF to the wrong thing and whoosh, your readings are all over the place. Try taking readings holding one in different places. Seriously- if it coupl es to your hand differently one way it will show up instantly. Unshielded c ases often look just like shielded ones...

I built one decades ago (with replaceable coils, ooh) from ARRL plans whi ch assumed you knew about good wiring practices. I didn't, and eventually t ore it apart and rebuilt it with every new lesson I learned. Wish I still h ad it.

Mark L. Fergerson

I have several 72's and I love them. They are ancient and none has ever broken.

Well, one did fail when an intern connected a couple KV to the bias terminals. Ex-intern.

Here's my Q meter. The voltmeter is a 0.2 pF SD14 sampling probe.

It uses series voltage boosting, from a very low impedance source. Q calculated from -3 dB frequencies.

That *is* impressive. I've got one of these instead:

It's very precise, but the lowest C FSD range is 100pF. I *was* perfectly happy with it - until you posted yours. :(

Like I've said before, you're far too charitable iro the people you hire.

I have a rebuilt Heathkit IT-11, the magic eye doesn't give particularly accurate results but it's for testing/re-forming high voltage caps that a DMM won't test properly.

Been there, done that! I've just had a rummage through my many rooms of old test gear and discovered I have a Boonton GDM I'd forgotten all about! This is actually a valve one, by the look of it, with about a dozen plug-in coils. THIS is one I've never tried. Maybe it could rescue my perception of GDMs! (if it doesn't, it and all the others will be heading for the reclycling facility.)