Re: Concluding comments on Heathkit QM-1 Q-Meter
Jeff,
If your QM-1 is 10% to 20% off you may want to take a closer look at the components and calibration.? I am typically seeing about 2% to 3% accuracy between calculated values and measured when designing coils.? Once it is calibrated to a standard it is pretty accurate in relation to the values of the standard.
I recently made a few coils to see how accurate it tracked between a web coil design program and the actual measurements. I have two coils I made to see how identical I could get them. Calculated they should have a Q of 160. One is 161 (0.625%) and one is 166 (3.75% off, but has a ferrite bead on one leg).? I made another much larger diameter coil with large wire and calculated it should be 452. It measures 462 (2.2% high) on my QM-1.
The biggest gripe I am have with my QM-1 is that the range is only up to a Q of 500.? I can cheat a little and lower the signal to give me an X3 or X4 (X4 is at 45 on the meter scale) multiplier but still that would top out at a Q of 1000 best case. I need to make some higher Q coils to confirm the accuracy near 1000. I suspect the accuracy will drop as the multiplier goes up due to the inability to read the cal point and reading markings accurately on an analog meter. The second problem/gripe is that I wish the frequency range went down just under 100Khz and above 18Mhz, toward 30Mhz.? I could use an external frequency source but have not tried that yet.? I have low expectations that it will just work by turning up the frequency, and it will hit some limit very quickly.
It is not real bad at reading L but will not substitute for a more modern L meter. The pointer and scale method leaves a bit to be desired.? I set my frequency to 7.900Mhz, using a freq counter, and my 5.3uH coil looks like it is 5.7uH on the scale. An 8.2uH indicated 8.2uH but a 25.7uH shows as 27uH (though my DE5000 indicates the coil is 26.6uH). A 131uH coil reads about 134uH at 790Khz. You must have a frequency counter in order to get readings anywhere close to these.
If you decide to add a BNC on the front for a frequency counter, I have had luck with a 3.3k resistor to the cathode of the oscillator tube. Connect when setting the frequency but disconnect when setting the Q cal level since the freq counter will load down the oscillator a bit.? Using an amp to drive the BNC is a better design so you can leave the freq counter connected when measuring Q.
You might want to do some further tweaking on the Q meter to see if you can reduce the level of error you are seeing to under 10%. As a hobbyist device, the QM-1 is not really that inaccurate once it is restored and calibrated. It is not bad compared to a Boonton within the 18MHz range. If you just need to design a coil and see if the L and Q are close to the design values, the QM-1 should work ok, within the limits of the frequency range and Q maximum range. Most handheld digital meters top out at 10KHz to 100KHz so even though they might be more accurate for those frequencies, how often do you wind a coil for 50Khz?? If you need an accurate measurement of high Q values and much higher frequencies, get a Boonton or some more modern LCRQ meter/VNA.
I am a bit of a restoration nut and have a bunch of HP, Tek, Heath, LeCroy, Fluke and other equipment. Not sure why we chase precision Q measurements other than it is one of the harder ones to nail down. Voltage, current, resistance and frequency measurements are pretty easy to build accurate equipment for but building an accurate wide range Q meter is like wrestling a greased pig.? I don't think the intent of this group is to get super accurate readings, such as Q to three decimal points, but rather to get a method/device that has a higher frequency and Q value range than the Boonton and HP gear we currently have, and reduce the sources of inaccuracy/uncertainty that plagues Q meters and Q measurements.
It is great you have saved another QM-1. Have fun.
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Re: Concluding comments on Heathkit QM-1 Q-Meter
I'm into radio, SWL
& ham, but haven't needed to make a Q measurement since
leaving Southcom International about 1970.? Have a 160 and QM-1
somewhere in the garage.? QM-1 meter badly marred by spilled Q
Dope.? I've long been fascinated by Q meters and am a nut about
various precision measurements, even my daily body temperate.
John?? KK6IL
On 11/12/2022 8:10 AM, Jeff Green
wrote:
toggle quoted message
Show quoted text
The Heathkit
102 QM-1 Q-meter is clearly nowhere near as accurate as a
Boonton, but it a great beginners tool.
?
I’ve found a
better assembly and use manual:
?
And this is
some additional information:
?
An EE friend
talked me through restoring the QM-1. I replaced all the
electrolytic capacitors, measured each resistor and changed
all of them for newer metal film resistors. Most of the the
carbon composition resistors had increased in value, putting
them well out of tolerance, I removed the solder from some
questionable connections, tested all the tubes, then put the
voltage regular and applied power to the unit through a series
120 100W incandescent light bulb.
?
The logic
being any short would cause the bulb to glow brightly. My EE
friend has a special test rig with an Edison light bulb
socket, an AC input power switch, light bulb bypass switch,
and a NEMA 15-5R power socket. He uses different wattage bulbs
for different tests.
?
I’m guessing
all the calibration coils are 250uH with a Q of 110.
?
On the VNA
my calibration coil read 251.4 and the q was 108. Pretty good
for a product older then I.
?
At least I
now have a nice variable RF oscillator that covers 150kHz to
18MHz, or 150kc to 18mc.
?
The case was
actually in much better shape then it initially looked. A lot
of TLC by my artistic inclined wife and the unit looks pretty
snazzy. She used home made soap, warm water, a soft brush,
sponge, and a lot of care. I’m guessing here, but I suspect
she spent 5 hours cleaning the case.
?
The OD3
voltage regulator produced 153 volts, well within tolerance.
All of the tubes (Valves to our British cousins) checked near
perfect for emission.
We replaced the 2 conductor power cord and 2 prong power
connector with a 3 conductor and a NEMA 15-5P 3 prong power
connector and added an internal fuse for safety.
?
It has been
educational to wind coils using various winding schemes.
?
My unit was
compared to a VNA in the EE Instrumentation and measurement
practical lab and, within its limits, it is within 10 to 20%.
?
This is an
overview of using a VNA.
?
Note, I did
not do the measurement! The TA in charge of the lab did that.
They aren’t silly enough to let “sort of freshmen dilatants”
touch the expensive test equipment.
?
My next goal
is to get matching knobs for the controls.
?
We replaced
the missing rubber feet with stick on plastic feet.
All in all
this has been a great practical learning experience.
I think I've covered all the major points.
If I might ask a question, "Why the fascination and
determination to make precision measurements of Q?"
Are y'all into radio?
?
?
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Thanks Jeff, those are good ideas.
My current bench-top setup is working well for my 'limited' requirements.
Meanwhile, yesterday I tried replacing the "speaker" with a fairly cheap 1.5" headphone element from about 30 years ago. The thought was: "If it sounds good playing music right next to my ear, then it should be good for my close-coupled testing." -- Right?
Wrong! The response turned out to have two very large peaks, with a valley in between at about 3500 Hz. It basically implements a "Loudness Contour" response, to make low/moderate volumes sound more 'balanced'.
So I went back to the 1" dynamic mic element, which works OK.
Pete
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Re: Concluding comments on Heathkit QM-1 Q-Meter
Congrats on a successful QM-1 job!
Steve
On 11/12/2022 9:10 AM, Jeff Green
wrote:
toggle quoted message
Show quoted text
An EE friend
talked me through restoring the QM-1. I replaced all the
electrolytic capacitors, measured each resistor and changed
all of them for newer metal film resistors. Most of the the
carbon composition resistors had increased in value, putting
them well out of tolerance, I removed the solder from some
questionable connections, tested all the tubes, then put the
voltage regular and applied power to the unit through a series
120 100W incandescent light bulb.
?
All in all
this has been a great practical learning experience.
|
On Sun, Sep 25, 2022 at 03:29 AM, Alan wrote:
Impact of 100M ohm
A simple work around is to measure Q of a coil then to add 100M ohms in parallel then retune and take a second Q reading then calculate out the 100M ohm first reading. However most? measurements don't need such a process because the 100M ohm loading is <1% Q reduction.? If you have an excellent 100uH inductor? Xl=628 ohms at 1MHz, so for a Q=2000? the parallel loss will be 1.26M ohm . Adding 100M ohm in parallel to 1.26M produces 1.2443, a 1.26% drop from Q=2,000 to 1975.? In reality a large coil near to the metalwork of a Q meter will read low Q because of eddy currents, in my experience the Q drop due to eddy currents is often far greater than 1%!
? Has anyone tried the above? I did, but used a 10MΩ.
?I set up an inductor and measured Q at 1MHz, the Q is 1092, the reactance is of the tuning capacitor is 1,053Ω.
So, ?Rp = Q times X =1092 x 1053 = 1,149,876Ω =Rp.
Then I put a 10MΩ Metal Film ? W resistor in parallel with the tuning capacitor.
?The Q is reduced to 882. Making the resistor Rp = 928,746Ω
i.e. Q times X = 882 x 1053 = 928,746Ω
The parallel combination 1,149,876Ω and 4,280,00 gives a Q of 882.
The parallel combination of a 1,149,876Ω and 10MΩ is 1,031,290Ω.
Meaning the should have dropped to a Q of 979, not 882.
?I have a theory, but I'd like to see what others say.
?
Thanks, Mikek
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Update to my original post (thanks for all the comments):
The following setup is working rather well:
- The "speaker" is a modern (but inexpensive) dynamic mic cartridge, driven with a signal in the range of about 100-300 mV RMS.
- The "test chamber" is a few inches of 2" ABS pipe, with a cap on one end to enclose the "speaker".?
- The mic to be tested is mounted on the end of a length of 1/2" pipe, then rolled up in a length of fleece fabric, then inserted into the 2" pipe.
- The distance between the "speaker" and the DUT is short - about 1cm.
- The setup was confirmed to be "good" by using a small, modern electret that is known to be very flat across the whole range (an audio-nerd friend sent it to me). This mic is my "calibration standard".
- I've been able to roughly duplicate frequency response curves for two mic types that I have datasheets for (one is a small dynamic from the 60's, the other is an electret hearing-aid mic from the 70's).
SO, one takeaway is that it is certainly NOT required to have a large anechoic chamber to do reasonable and useful measurements of this type. I'm not trying to establish directionality patterns and such.
I originally planned to do the whole experiment using only 1960's-vintage technology. That still is possible, but I don't happen to have a vintage "speaker" (dynamic cartridge) that is very good for this purpose. So I'm "cheating" and using some more modern stuff for now.
Pete
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I work with ferrite loop antennas and filters for low frequency RF.
The "Q-Multiplier" is a fun circuit.? The basic idea is that a high Q tuned circuit is necessarily loaded down by the following stage, which can significantly hammer the Q. If you design to maximum power transfer maybe for a bipolar transistor amp, then the antenna impedance is matched by the amplifier impedance, and the Q is of course dramatically reduced. A high impedance amplifier (FET based) puts minimum loading on the circuit, not so much "drawing power to turn on the transistor" as "observing the voltage on the tank and amplifying it". A crystal radio is a great example, the headphone impedance very much affects the Q of the tank.
Ben Tongue (of Blonder-Tongue) has done a lot of work on this.
When you look at the parameters for a crystal, the Q values are insanely high, but it totally makes sense. The main feature is that they run at basically one frequency as long as the circuit is designed properly. Most people seem to overlook the fact that all crystals have both parallel and series modes which of course are on different frequencies, and using the wrong circuit will result in an oscillator that cannot run at the desired frequency, only at one that's "pretty close".? With the correct loading caps, a garden variety crystal circuit can be built in production quantities with only a very small variance in frequency.? If it's not running within the PPM error spec, you've got the wrong circuit or the wrong loading caps.
DSP filters are wonderful.? Unlike analog they don't store energy, and they can look forward and backward in time. :) However.. If you don't want your ADC to get hammered or have signals aliasing down into the passband, you're going to need some analog filtering except in very special cases.
My EE friend has explained Q to me, how the “ultimate” Q in a practical tuned circuit is a crystal filter. He also shared some articles from a now vanished crystal radio webpage that showed too much Q in an AM circuit can be too narrow.
I understand the logic behind ‘counting cycles as they decay,’ but I’m a long way from the knowledge having any practical use in my hobbies.
?
My antennas are intentionally broadbanded, 15kHz to 20MHz. I read about a loop antenna with built in “Q-multiplier” that might be nice for separating closely space European MW (AM BCB) stations from American stations. Europe uses 9kHz channel spacing and some European station are between the 10kHz American spacing.
?
He also showed me his first decent SW receiver, a Heathkit GR-64 with a Q-multiplier input. He’s restored the SW receiver and Q-multiplier and it was interesting to see how a signal could be peaked or nulled.
?
I’m learning a lot by reading this thread. Mainly, just how dedicated (or fanatical) some people are in the pursuit of their goals.
?
In a way our daughter deals with Q in the audio domain. She’s an MD who has specialized in hearing and balance issues caused by the inner ear. Some of her diagnotistic equipment has what my EE friend calls brick wall filters “With impossibly steep skirts with no ringing.”
?
Of course her equipment converts everything to digital signals and plays high level math wizardry to achieve the impossible.
?
In an ideal world, our SW receivers, or audio processing chain, would break the incoming audio into two bands, one for vowels the other for consonants and throw everything else away.
?
Modern hearing aids are marvelous, they accomplish near magic DSP with very lower electrical power.
-- K1FZY (WA4TPW) SK? 9/29/37-4/13/15
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I'm receiving several emails asking about purchasing the Ringdown Q meter.
As I understand it, there is a limited amount being built, (22). The first shipment was 10,
?I don't know if all those were sold or when the next 12 will arrive.
?If you look in the files section, there is a folder, "DIY Ringdown Method Q Meter Kit'
if you open that folder, it has 4 files, one is 'Enhanced Version Diy Q Meter Kit'
In that file is an email address for the seller Ming Mak. Send him an email and ask if there are any
available or if you can get on the waiting list.
?To MR, for some reason all my emails sent to @hotmail bounce, otherwise I would have emailed you.
They take a week to bounce, I thought I was going to miss out because Ming's email is a @hotmail.
I had a friend send in my request.
--
Thanks, Mikek
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On Thu, Nov 10, 2022 at 02:04 AM, tgerbic wrote:
I think the big problem with these circuits is that once the Q or frequency gets very high the problem of accurately detecting and counting the rings gets a little fuzzy. Some attempt to look at the slope of the decay in ring down to estimate the smaller or finer spaced rings instead of attempting to actually measure them directly. Some use a much faster processor to sample the smaller faster rings. In the end the basic ring down process suffers from many of the problems and uncertainties other methods run into with higher frequencies and higher Qs.
?The? meter kit I'm building measures Qs to 2500, it's max frequency 9.2MHz.
Do you need a more detailed explanation of how ring down circuits work or just this specific one?
There is some ring down info in the files section. ? -- Thanks, Mikek
|
People have been using the ring down method for decades, manually with scopes or with dedicated measuring circuits. Lots of DIY circuits out there, most these days with microprocessors to do the work. The principal is pretty simple where the number of rings for a change in voltage level times a constant will give you the Q, while the period of the rings gives the frequency which can be backed into determining the unknown L or C.?
I think the big problem with these circuits is that once the Q or frequency gets very high the problem of accurately detecting and counting the rings gets a little fuzzy. Some attempt to look at the slope of the decay in ring down to estimate the smaller or finer spaced rings instead of attempting to actually measure them directly. Some use a much faster processor to sample the smaller faster rings. In the end the basic ring down process suffers from many of the problems and uncertainties other methods run into with higher frequencies and higher Qs.
Do you need a more detailed explanation of how ring down circuits work or just this specific one?
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On Wed, Nov 9, 2022 at 01:09 PM, Ray, W4BYG wrote:
Mikek,
I think it came to me via the listserver. Sorry if I wasn't supposed to see it.
Ray, ?I don't know what you mean. I sent a private message about how to contact the seller of the Ringdown Q meter. ?I got no response, so I'm asking you on the group if you received the private message on where to get the ringdown Q meter. ?If you did, great. If you didn't send me an email. I'm under Mikek in the directory. ?I've been working at putting the kit in an enclosure this morning, here's a picture of the bits going together.  -- Thanks, Mikek
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Mikek,
I think it came to me via the listserver. Sorry if I wasn't
supposed to see it.
73,
Ray, W4BYG
On 11/9/2022 10:48, Mikek wrote:
On Tue, Nov 8, 2022 at 07:40 AM, Ray, W4BYG wrote:
Where did you purchase the"Ringdown Q meter kit"? I
did a search online and didn't see any useful results.
Ray, W4BYG
Hi Ray,
?Just wondering if you got my private message about the Ringdown Q
meter?
Thanks, Mikek
--
"If you want to build a strong house, I'll give you my engineer's number.
If you want to build a strong life, I'll introduce you to my carpenter."
Lebron and Heather Lackey
|
Mike
National and myriad others such as Motorola, Siliconix etc
published both, data books for their products and application notes that frequently shared circuit schematics.
Case in point, National's Linear IC Data Book has a schematic
for using Op Amps in a Gyrator based bandpass audio filter.
You can find that same schematic in their book of Application
Notes.
Heaven knows I carbon copied a lot of those 'Recommended
Circuits' in designs over the last 50 years. After a particularly
disastrous budgetary creative attempt, I learned the valuable
lesson of avoiding NIH.
NIH in the lab means, "Not Invented Here". That lesson is right
up there with, "Don't spend NRE (Non-recurring engineering)
funds to duplicate someone else's work."
Regards
Chuck WD4HXG
On Nov 9, 2022, at 10:43 AM, Mikek <amdx@...> wrote:
On Tue, Nov 8, 2022 at 05:33 PM, John Kolb wrote:
The circuit comes from National Semi AN-32
I thought it was from a linear book, but it's the best I have so far.
?
--
Thanks, Mikek
|
On Tue, Nov 8, 2022 at 07:40 AM, Ray, W4BYG wrote:
Where did you purchase the"Ringdown Q meter kit"? I did a search online and didn't see any useful results.
Ray, W4BYG
Hi Ray, ?Just wondering if you got my private message about the Ringdown Q meter? Thanks, Mikek
|
On Tue, Nov 8, 2022 at 05:33 PM, John Kolb wrote:
The circuit comes from National Semi AN-32
I thought it was from a linear book, but it's the best I have so far. ? -- Thanks, Mikek
|
The circuit comes from National Semi AN-32 (TI SNOA620),
attached, where an NPN symbol is labeled 2N3644.??? The 2N2222
would be a good choice for a NPN, little higher hFE and fT.
John?? KK6IL
On 11/8/2022 4:40 AM, Pete_G4GJL wrote:
toggle quoted message
Show quoted text
Mike,
Im reading the bipolar transistor to be 2N3644, though the
diagram is a little indistinct.?
2N3644 is a PNP transistor, though the diagram show an
NPN one.
Ill probably get around to building the amp to compare
results with the Millivac MV828 and other homebrew amps Im
playing with here.? 2n3644's are obsolete,although PN3644's
are available.? 2N3643 would be an equilevent NPN choice for
the circuit
Pete
G4GJL
On Tue, Nov 8, 2022 at 12:31
PM Mikek < amdx@...>
wrote:
I
thought I had posted this schematic of a high input impedance
amp, but I don't find it.
? I have built it, and after adding back an underside
groundplane I had etched away, it is flat from 50kHz to 30Mhz.
?Before I added back the groundplane it had a 15% level peak
at 29MHz. I also added a bead on the FET gate?
because of an intermittent 200MHz oscillation. Looks like the
bead solved that problem.
Here's a picture showing level at ~1MHz and 30MHz. 30Mhz is up
0.2db. It doesn't go 3db down until 105MHz.
I'm sure the circuit could be made much smaller, (it's 2.3" x
4") but I find even though I know about strays, I'm not good
at minimizing them.
I have another, 3 transistor high input impedance circuit to
try, but I want to get back to building the Ringdown Q meter
kit I have. So that's back burner for now.
??????????????????????????????????????????????????????? Mikek
???????????????????????????????????????????????????
--
Thanks, Mikek
|
On 11/8/2022 07:31, Mikek wrote:
... but I want to get back to building the Ringdown Q meter kit I
have. So that's back burner for now.
Where did you purchase the"Ringdown Q meter kit"? I did a search
online and didn't see any useful results.
Ray, W4BYG
??????????????????????????????????????????????????????
???????????????????????????????????????????????????
--
--
"If you want to build a strong house, I'll give you my engineer's number.
If you want to build a strong life, I'll introduce you to my carpenter."
Lebron and Heather Lackey
|
On Tue, Nov 8, 2022 at 04:41 AM, Pete_G4GJL wrote:
2N3644 is a PNP transistor, though the diagram show an NPN one.
Yes, The number is wrong, I used a NPN MPSH10, But I suspect it would work with a transistor having a lower Ft. I just tried a BC548C, I didn't work, zero output, I thought it should at least work at lower frequencies. -- Thanks, Mikek
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Mike, Im reading the bipolar transistor to be 2N3644, though the diagram is a little indistinct.? 2N3644 is a PNP transistor, though the diagram show an NPN one.
Ill probably get around to building the amp to compare results with the Millivac MV828 and other homebrew amps Im playing with here.
Pete G4GJL
On Tue, Nov 8, 2022 at 12:31 PM Mikek < amdx@...> wrote: I thought I had posted this schematic of a high input impedance amp, but I don't find it.
? I have built it, and after adding back an underside groundplane I had etched away, it is flat from 50kHz to 30Mhz.
?Before I added back the groundplane it had a 15% level peak at 29MHz. I also added a bead on the FET gate?
because of an intermittent 200MHz oscillation. Looks like the bead solved that problem.
Here's a picture showing level at ~1MHz and 30MHz. 30Mhz is up 0.2db. It doesn't go 3db down until 105MHz.
I'm sure the circuit could be made much smaller, (it's 2.3" x 4") but I find even though I know about strays, I'm not good at minimizing them.
I have another, 3 transistor high input impedance circuit to try, but I want to get back to building the Ringdown Q meter kit I have. So that's back burner for now.
??????????????????????????????????????????????????????? Mikek
???????????????????????????????????????????????????
--
Thanks, Mikek
|
I thought I had posted this schematic of a high input impedance amp, but I don't find it.  ? I have built it, and after adding back an underside groundplane I had etched away, it is flat from 50kHz to 30Mhz. ?Before I added back the groundplane it had a 15% level peak at 29MHz. I also added a bead on the FET gate? because of an intermittent 200MHz oscillation. Looks like the bead solved that problem.  Here's a picture showing level at ~1MHz and 30MHz. 30Mhz is up 0.2db. It doesn't go 3db down until 105MHz.  I'm sure the circuit could be made much smaller, (it's 2.3" x 4") but I find even though I know about strays, I'm not good at minimizing them. I have another, 3 transistor high input impedance circuit to try, but I want to get back to building the Ringdown Q meter kit I have. So that's back burner for now. ??????????????????????????????????????????????????????? Mikek ??????????????????????????????????????????????????? -- Thanks, Mikek
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John Kolb
saipan59 (Pete)
Ray, W4BYG
Pete_G4GJL
