Tuned Circuit Selectivity

[Cursitor Doom]

On Mon, 06 May 2019 09:03:02 -0500, amdx wrote:

> So what type of inductor? Is there a good way to couple to it?

Air-core single solenoid - and yes.

> Sometimes I just hang a clip lead from the generator near the coil.

That might just do the trick...




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[Cursitor Doom]

On Mon, 06 May 2019 14:20:39 +0000, Jan Panteltje wrote:

Yes a bit tricky to use, oh what is large,
in the few MHz range and lower it works.

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

> With your raspi as signal generator

??? 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!



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[Cursitor Doom]

On Mon, 06 May 2019 09:07:40 -0500, John S wrote:

> Are you wanting the loaded or unloaded Q of your network?

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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On Monday, May 6, 2019 at 9:59:24 AM UTC-4, John Larkin wrote:

On Mon, 6 May 2019 13:13:35 -0000 (UTC), Cursitor Doom
curd@notformail.com> wrote:

On Sun, 05 May 2019 16:59:19 -0700, John Larkin wrote:

How are you coupling the signal gen into the resonant tank? Are you
using a 10x probe on the scope?

Yes, 10x/1x switchable. And directly coupled.


A Q of 50 should be easy at that frequency, and that would make a very
sharp peak.

I'd have thought so, yes.


What are your L and C values?

33uH & 385pF


Here's my LC program.

I find it's easiest just to use the full features of a programmable
scientific calculator, TBH. YMMV of course.


Xc = Xl = 292 ohms at 1.4 MHz. If you connect a 50 ohm signal
generator across that parallel tank, Q is about 0.16. Not much of a
resonant bump. Couple gently from the generator into the tank, with a
big resistor or a tiny cap, or just proximity.

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

--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Jan Panteltje]

On a sunny day (Mon, 6 May 2019 15:32:25 -0000 (UTC)) it happened Cursitor
Doom <curd@notformail.com> wrote in <qapk29$52e$6@dont-email.me>:

On Mon, 06 May 2019 14:20:39 +0000, Jan Panteltje wrote:

Yes a bit tricky to use, oh what is large,
in the few MHz range and lower it works.

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

With your raspi as signal generator

??? 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!

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...

 

[Phil Hobbs]

On 5/6/19 9:18 AM, Cursitor Doom wrote:

On Mon, 06 May 2019 07:28:29 +0000, Jan Panteltje wrote:

A grid dip meter was a useful instrument long ago:
https://en.wikipedia.org/wiki/Grid_dip_oscillator
Build one once.

I still have a selection of them and I built one once. NEVER had any luck
with *any* of the damn things for some reason! I suspect they're only
useful if you are testing really physically large combinations of C and L.

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

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[John Larkin]

On Mon, 6 May 2019 08:42:08 -0700 (PDT),
bloggs.fredbloggs.fred@gmail.com wrote:

On Monday, May 6, 2019 at 9:59:24 AM UTC-4, John Larkin wrote:
On Mon, 6 May 2019 13:13:35 -0000 (UTC), Cursitor Doom
curd@notformail.com> wrote:

On Sun, 05 May 2019 16:59:19 -0700, John Larkin wrote:

How are you coupling the signal gen into the resonant tank? Are you
using a 10x probe on the scope?

Yes, 10x/1x switchable. And directly coupled.


A Q of 50 should be easy at that frequency, and that would make a very
sharp peak.

I'd have thought so, yes.


What are your L and C values?

33uH & 385pF


Here's my LC program.

I find it's easiest just to use the full features of a programmable
scientific calculator, TBH. YMMV of course.


Xc = Xl = 292 ohms at 1.4 MHz. If you connect a 50 ohm signal
generator across that parallel tank, Q is about 0.16. Not much of a
resonant bump. Couple gently from the generator into the tank, with a
big resistor or a tiny cap, or just proximity.

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.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

On Monday, May 6, 2019 at 11:51:17 AM UTC-4, John Larkin wrote:

On Mon, 6 May 2019 08:42:08 -0700 (PDT),
bloggs.fredbloggs.fred@gmail.com wrote:

On Monday, May 6, 2019 at 9:59:24 AM UTC-4, John Larkin wrote:
On Mon, 6 May 2019 13:13:35 -0000 (UTC), Cursitor Doom
curd@notformail.com> wrote:

On Sun, 05 May 2019 16:59:19 -0700, John Larkin wrote:

How are you coupling the signal gen into the resonant tank? Are you
using a 10x probe on the scope?

Yes, 10x/1x switchable. And directly coupled.


A Q of 50 should be easy at that frequency, and that would make a very
sharp peak.

I'd have thought so, yes.


What are your L and C values?

33uH & 385pF


Here's my LC program.

I find it's easiest just to use the full features of a programmable
scientific calculator, TBH. YMMV of course.


Xc = Xl = 292 ohms at 1.4 MHz. If you connect a 50 ohm signal
generator across that parallel tank, Q is about 0.16. Not much of a
resonant bump. Couple gently from the generator into the tank, with a
big resistor or a tiny cap, or just proximity.

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.

--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[John S]

On 5/6/2019 10:34 AM, Cursitor Doom wrote:

On Mon, 06 May 2019 09:07:40 -0500, John S wrote:

Are you wanting the loaded or unloaded Q of your network?

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.

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.

 

[Dave Platt]

In article <b6f0delff10il9e92u061jmb7m0g4htvk9@4ax.com>,
John Larkin <jjlarkin@highlandtechnology.com> wrote:

Xc = Xl = 292 ohms at 1.4 MHz. If you connect a 50 ohm signal
generator across that parallel tank, Q is about 0.16. Not much of a
resonant bump. Couple gently from the generator into the tank, with a
big resistor or a tiny cap, or just proximity.

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.

 

[bitrex]

On 5/6/19 12:31 PM, Phil Hobbs wrote:
> Measurements 59 Megacycle Meter

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

 

[Phil Hobbs]

On 5/6/19 3:37 PM, bitrex wrote:

On 5/6/19 12:31 PM, Phil Hobbs wrote:
Measurements 59 Megacycle Meter

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

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Cursitor Doom]

On Mon, 06 May 2019 12:31:55 -0400, Phil Hobbs wrote:

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

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. :-/




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[bitrex]

On 5/6/19 5:52 PM, Phil Hobbs wrote:

On 5/6/19 3:37 PM, bitrex wrote:
On 5/6/19 12:31 PM, Phil Hobbs wrote:
Measurements 59 Megacycle Meter

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 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

 

[nuny@bid.nes]

On Monday, May 6, 2019 at 6:18:16 AM UTC-7, Cursitor Doom wrote:

On Mon, 06 May 2019 07:28:29 +0000, Jan Panteltje wrote:

A grid dip meter was a useful instrument long ago:
https://en.wikipedia.org/wiki/Grid_dip_oscillator
Build one once.

I still have a selection of them and I built one once. NEVER had any luck
with *any* of the damn things for some reason! I suspect they're only
useful if you are testing really physically large combinations of C and L..

They're great for LW and medium-wave stuff if you have a hand truck to cart 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 many 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 couples to your hand differently one way it will show up instantly. Unshielded cases often look just like shielded ones...

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


Mark L. Fergerson

 

[John Larkin]

On Mon, 6 May 2019 17:52:11 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 5/6/19 3:37 PM, bitrex wrote:
On 5/6/19 12:31 PM, Phil Hobbs wrote:
Measurements 59 Megacycle Meter

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

https://www.dropbox.com/s/7k57wicymctj3s0/boonton-72.jpg?dl=0

1 pF full scale! With a bias input for making C-V curves.

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


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[John Larkin]

On Sun, 5 May 2019 22:13:25 -0000 (UTC), Cursitor Doom
<curd@notformail.com> wrote:

Gentlemen,


I'm just trying a number of combinations of L and C to find the right
values for resonance at around 1.35Mhz. The problem I'm having is that
the resonance point is far from clear. It's as if the Q of the components
is very low (even though they actually aren't). I'm trying to think of a
way to make it more 'peaky' on the oscilloscope display to take the guess
work out of finding that sweet spot.
ATM the two components are in parallel, but I'm thinking maybe I'd have
more luck if I wired them in series and increased the Zo of the signal
generator by placing a highish value resistor into the genny's central
output pin and feeding the tank via that.
Would that work or has anyne got any better ideas?

CD

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.

https://www.dropbox.com/s/ycd8ya9kwit8o0y/Q-meter.jpg?dl=0

https://www.dropbox.com/s/b4xwf1g2ldk0bfl/Q.JPG?dl=0


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Cursitor Doom]

On Mon, 06 May 2019 23:41:42 -0700, nuny@bid.nes wrote:

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

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.)



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[bitrex]

On 5/7/19 10:05 AM, John Larkin wrote:

On Mon, 6 May 2019 17:52:11 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 5/6/19 3:37 PM, bitrex wrote:
On 5/6/19 12:31 PM, Phil Hobbs wrote:
Measurements 59 Megacycle Meter

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

https://www.dropbox.com/s/7k57wicymctj3s0/boonton-72.jpg?dl=0

1 pF full scale! With a bias input for making C-V curves.

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

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.

<http://tubularelectronics.com/Heath_Manual_Collection/Heath_Manuals_IT-NE/IT-11/IT-11.pdf>

 

[Cursitor Doom]

On Tue, 07 May 2019 07:05:38 -0700, John Larkin wrote:

1 pF full scale! With a bias input for making C-V curves.

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

https://tinyurl.com/y68p9g3e

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

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

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



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