A gadget that I built a couple of years ago.?
The purpose is to compare an unknown freq to the output of a GPSDO, so that the unknown can be tweaked to match.
It's only useful when the unknown's freq is rather close to a known value.
The circuit does an AND of the GPSDO output with the unknown, thus "mixing" the two signals, then a small MCU measures the difference freq.
Pete
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I use one source to trigger a scope. Other source goes into vertical. Tweak until sine wave quits moving.Using this technique I had a sine wave take all day to get 10 divisions.
Idea is from NBS or NIST nowdays.
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On Tue, Aug 2, 2022 at 05:16 PM, John Griessen wrote:
On 8/2/22 12:55, Group Notification wrote:
> Hello,
>
> Welcome to the [email protected] group at Groups.io
>
Is this set up right?
[email protected]
or
[email protected]?
--
John Griessen
I see the group up in 1999 as [email protected]?but never used it. I decided to repurpose it, so renamed it. Did you get an announcement under the old name in the last 24 hours? If so, something is wrong. However, if you got the message more than a day ago, ,then it's understandable. I decided to repurpose an old group, rather than create a new one, as there are more generous allowances on the older groups; If one sets up a new group, one is limited to 100 members, whereas the old ones have no limits. Dave
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I got the technical-radio-UK one as a welcome, looking at my groups indicates the correct group.
Haven't gotten about UK style radios (no longer a ham....)
Harvey
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I got notified this morning on the old names. I was going to mentioned this tonight after I got back to the lab and a computer
Though I do agree the 100 member limit from seems a bit dumb.
Eric
On Tue, Aug 2, 2022, 8:28 PM Harvey White < madyn@...> wrote: I got the technical-radio-UK one as a welcome, looking at my groups
indicates the correct group.
Haven't gotten about UK style radios (no longer a ham....)
Harvey
On 8/2/2022 2:57 PM, John Griessen wrote:
> On 8/2/22 12:55, Group Notification wrote:
> > Hello,
> >
> > Welcome to the [email protected] group at Groups.io
> >
> ? Is this set up right?
>
> [email protected]
> or
> [email protected]?
>
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On 8/2/22 18:23, Dr. David Kirkby, Kirkby Microwave Ltd wrote: Did you get an announcement under the old name in the last 24 hours? Yes, Monday PM. -- John Griessen -- building lab gear for biologists Albuquerque NM blog.kitmatic.com
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On Wed, Aug 3, 2022 at 10:23 AM, Dr. David Kirkby, Kirkby Microwave Ltd wrote:
Did you get an announcement under the old name in the last 24 hours?
Yes. It was the new member welcome message. You need to adjust it, and any other files of this nature left over from the old group. ? -- EJP
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On Tue, Aug 2, 2022 at 06:08 PM, EJP wrote:
On Wed, Aug 3, 2022 at 10:23 AM, Dr. David Kirkby, Kirkby Microwave Ltd wrote:
Did you get an announcement under the old name in the last 24 hours?
Yes. It was the new member welcome message. You need to adjust it, and any other files of this nature left over from the old group.
?
Thank you. I have updated that welcome message. Unfortunately several hundred members have received the wrong message; I'll have to see if there's anything else that needs adjusting.
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Simple Voltage and Current reference for meter testing.
Sometimes simple is all you need. Based on a cheaply available AD584 module with some mod's to capacitor values and the addition of an Opamp to counteract? the shunt voltage (burden) of the meter being tested for the current ranges.? I could have added trimming for the reference , current setting resistors, and opamp offset, but all should be within about 0.1% from data sheets. I felt that it was better to have it close enough and stable rather than introducing other possible items to drift just to get some more zero's. There are probably better opamps out there, but I used what I had, minimal/stable offset voltage and input current probably most important parameters. The BAT48 is to protect the opamp input from potential over voltage when no meter is attached to the current outputs.? I used ten 10K 0.1% resistors in parallel for the 1K because I had a box of them. Comments, suggestions for improvements, etc. invited. Paul McMahon VK3DIP  
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On Tue, Aug 2, 2022 at 08:29 AM, saipan59 (Pete) wrote:
A gadget that I built a couple of years ago.?
The purpose is to compare an unknown freq to the output of a GPSDO, so that the unknown can be tweaked to match.
Is the output of the GPSDO just 10 MHz like mine, or is it programmable??
I recently wanted to adjust a 10 MHz OXCO? in a 40 GHz frequency counter. The approach I took was to set my highest frequency signal generator (20 GHz) to 20 GHz, with that locked to the GPS frequency reference. The 20 GHz was then fed into the frequency counter. The fact the signal generator was producing a frequency 2000 x higher than its reference standard meant that any difference between undisciplined OCXO and the GPSDO were magnified 2000 x. So I adjusted the OCXO until the frequency counter read 20 GHz.
I do have a few HP 5370B time-interval counters. One would start the counter with one oscillator and stop it with another. Then if the two signals are at the same frequency, the delay between them stays constant. However, this does not work too well for sine-wave inputs, as the triggering is not consistent enough. Of course, it's easy to convert a sine wave to a square wave .but not so easy to do it whilst not causing jitter of more than the 20 ps resolution.
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On Tue, Aug 2, 2022 at 07:59 PM, Dr. David Kirkby, Kirkby Microwave Ltd wrote:
Is the output of the GPSDO just 10 MHz like mine, or is it programmable??
Programmable. The 4 buttons on the front panel talk to the MCU, which allows setting the GPSDO freq. As I recall, it is settable from something like 1 KHz to 30 MHz. The little "square wave" on the display is a representation of the difference freq - basically a simple o-scope display, with a sweep speed of 30 seconds. So, when the freqs are very close, only 1 or 2 cycles are displayed in 30 seconds. >I use one source to trigger a scope. Other source goes into vertical. Tweak until sine wave quits moving. Using this technique I had a sine wave take all day to get 10 divisions. Yes, like the classis Lissajous pattern. I have several o-scopes, and an HP 5345A counter, which is mostly a better way to go, but it's not much "fun", eh?. In part, I wanted to prove to myself that I could make an AND gate function as a Mixer, but with digital signals. It works fine! I'm thinking I should add a tiny speaker to the difference signal, so that there is audible feedback to make it easy to tune. Pete
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Isn't classic mixer an XOR gate followed by an LPF?
Leo
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Hello all
As a check that it is really me, I always send E-Mails in this format.
I am a new member, and have been a civilian Telecoms repair mech in the 50's and 60's and after that an Instrument mech on a Nuclear Power station. Now long retired
73 de Rob M0LYD
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For at-a-glance monitoring of
frequency/phase differences between my Rubidium, DOCXOs and GPSDOs
at 10 MHz and 100 MHz I use AD8302 log amp/phase comparator chips
to drive edge-reading centre-zero moving coil meters.? With a gain
control and 10 turn offset control and a precision op amp, I can
see the phase changes caused by a frequency difference of less
than 1 mHz very easily.? It's as sensitive as using a dual channel
scope with the gain turned up high to watch the phase difference,
but a lot more convenient and runs all the time, sitting in a 1U
rack case. It has DC outputs from the phase signal so I can watch
the levels on an external meter.? I suppose I could fit a
microcontroller with ADCs and e-ink display and maybe an ethernet
connection so I could monitor the phase outputs, but the simple
analogue meters and electronics are easy on the eye and the unit
doesn't cause any radio noise. If I want to monitor the outputs to
look for GPS phase glitches and diurnal/temperature changes, I
just connect my Fluke 8845A to the output and log the output from
that.
I sometimes use a similar approach to
Dave's method, using a receiver at? around 10 GHz to monitor a
harmonic from a 10 MHz source using a x4 multiplier and bandpass
filter, then a x3 multipler and filter to 120 MHz, then use that
to drive a snap-recovery diode comb generator. I combine that with
a harmonic from my HP E4433B which I lock to whatever reference I
want to compare the 10 MHz source with.? The beat note between the
two harmonics gives me a very fast way to adjust the frequency of
the 10 MHz source to within a few Hz, which represents a few mHz
at 10 MHz. That audible feedback means I don't need to watch a
meter, so it makes the process of trimming a little more
ergonomic.
I'm considering adding an analogue
voltage to frequency chip and speaker/headphone socket to the
analogue phase comparator so I can get that same hands-free audio
feedback as a tone.? Using the same voltage that drives the meter,
I would get the advantage of the offset and gain controls so a
change of 10 mV per degree phase difference can be mapped to a
change of perhaps 100 Hz per degree of the tone. I can check for
DC drift in the comparators by using the same signal at both
inputs, although it's also amusing to use the same signal to each
input but with different cable lengths, then watch the wobbles and
shifts as you manipulate the cable or warm it up.
Definitely still a work in progress. I
must make a video about it one day before my Rubidium source wears
out and dies.
--
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Re: Simple Voltage and Current reference for meter testing.
I have personally never made anything like this - instead just comparing values to a 6.5 digit multimeter. But recently I bought a cheap(ish) 20,000 count Chinese multimeter, and wanted to check it. On DC around a few volts and resistance it was excellent. However, I wanted to check AC volts and amps too. That brings a whole lot of challenges. The AC mains is not stable enough, so comparing a 20,000 count multimeter with a 6.5 digit HP 3457A is totally impossible.?
I actually bought a 100 W Tandy PA amplifier from eBay, that was designed to run into 4 ohm speakers. My plan was to put that into a high voltage transformer to allow me to generate AC that should be more stable than the 50 Hz mains. Other projects go in the way, so I never got around to testing the multimeter properly on AC.?
You can expect any multimeter to be most accurate on DC voltages around its reference voltage, so most are probably going to be mist accurate on a 3 V or 10 V DC scale. To do a proper check, one really needs to test at high and low voltage DC too.?
You could consider adding AC calibration.
Fluke multifunction calibrators are extremely expensive. There’s probably a lot of work into making some produce a wide range of voltages and currents.?
Dave
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Re: Simple Voltage and Current reference for meter testing.
If you can find a HP3245A - they can be had for about $1000 if you are lucky - you can can use it as a source for DC volts, DC current, AC volts and AC current (up to 1MHz). The main drawback is it's limited to 10V output unless you have the elusive 002 option which takes it to 100V. It's not intended as a calibrator but then it's not $25k like a Fluke 5720.
- Keith
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On Wed, Aug 3, 2022 at 03:13 AM, Leo Bodnar wrote:
Isn't classic mixer an XOR gate followed by an LPF?
I'm no expert on the theory, but "intuitively" I think both XOR and AND works. I can say for certain that AND works... Pete
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Yes, indeed. Although, as Leo said, an XOR is a classical mixer,
pretty much anything that's not strictly linear and time-invariant
will perform mixing of some kind. And "some kind" is often good
enough. I've even used a CMOS inverter (74C04) as a mixer. It's not
a great mixer, but it mixes.
--Tom
--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
On 8/3/2022 06:38, saipan59 (Pete)
wrote:
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Show quoted text
On Wed, Aug 3, 2022 at 03:13 AM, Leo Bodnar wrote:
Isn't classic mixer an XOR gate followed by an LPF?
I'm no expert on the theory, but "intuitively" I think both XOR
and AND works.
I can say for certain that AND works...
Pete
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Here is my take on XOR versus Inverter as a mixer. The XOR, with two digital inputs (for example divided down from RF signals) will act as a phase detector. The output will be zero when two, 50% duty, digital inputs are exactly out of phase. Okay to be clear, an XNOR will be zero – a XOR will have flat positive output. As the two inputs deviated from that phase and/or frequency, it will generate pulses that can be averaged using and RC or integrator to give you an analog representation of the phase difference. I had seen these in PLLs for example, since that uses a phase detector. ? To use an inverter as a mixer, I am guessing you would do the trick where you bias it up as a linear gain block (two large series resistors from OUTPUT to INPUT, with maybe a bypass cap to ground at the miid-point). This creates a very high gain (analog) amplifier, so when you combine two input signals and apply to the input, it will bang rail to rail, basically it’s a nonlinear gain block, and you get that square law behavior that is the classical mixer: (SinA + SinB) ^2 which expands to the sums and differences (and some DC). ? I once measured a CD4049 inverter, biased as an amplifier, at 10.7MHz, and was amazed that it was >50dB, and I believe it consumed about 10mA. ? Dan
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saipan59 (Pete)
Dr. David Kirkby, Kirkby Microwave Ltd
