Re: QMX High swr into 50 ohm dummy load
It has to be lived with. When I built a multi-band Quad antenna, the phenomenon was still present.
Frameworks influence each other. Therefore, tuning takes longer.
--
Gyula HA3HZ
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Re: QMX T501 Primaries Crossed - is this a problem?
Hi Sandy
Not a problem. Proceed regardless!? 73 Hans G0UPL
On Sat, Oct 21, 2023, 7:08 AM Sandy < mac3iii@...> wrote: I noticed after all the excitement of the really twisted sisters transformer 12 volt style I ended up with the two primary leads crossed over into holes opposite from the opening of the T501 transformer. Is this a problem that I need to correct before proceeding? Sandy KB3EOF
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I found this thread very useful as I have had a very similar experience. My newly built QMX was connected to a PSU at 7V limited to 200mA as suggested in the documentation. As soon as I pressed the left encoder button, the PSU started to current limit. I spent hours looking for solder bridges but found nothing.?
I eventually tracked the problem down to a faulty Q107, which appears to have a fixed low resistance (my peak DCA75 says "no component detected") and effectively keeping the SMPS transistor Q109 turned on and allowing the "12V" to the VDD line. I hope that the Zener was enough to protect the MCU. There appears to be no other faults on the board.?
Many thanks to Chris, G5CTH, for his PSU board test procedure. I would have struggled without it.
Using his test at the very end of his post, with the PSU set to current limit at 20mA, I determined that the Zener diode, D109, limits the voltage to 4.0 volts. Is this adequate? Does it too need to be replaced?
I have ordered some BSS123 transistors and I am anxious to see if the MCX has been saved by the Zener diode!
73
Ellis, GM4GZW
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QMX T501 Primaries Crossed - is this a problem?
I noticed after all the excitement of the really twisted sisters transformer 12 volt style I ended up with the two primary leads crossed over into holes opposite from the opening of the T501 transformer. Is this a problem that I need to correct before proceeding? Sandy KB3EOF
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Re: QMX suffers zero negative impact from deleting L401 (with measurements)
Clocked switching itself is linear so that approach/assumption is valid. What cannot be concluded is the mixer's dynamic range or the degree of effects/benefits of having a BPF since all the real life nonlinearity are omitted from the simple model.
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Re: QMX suffers zero negative impact from deleting L401 (with measurements)
Ryuji,? Yes, it is correct that the spectral roll off of the Dirac approximation must be considered when viewing these results.
Regarding other means of seeing the input impedance of the Tayloe, recall also that any LTSpice swept frequency analysis is based on a linearization of the simulated circuit. The complicated action that results from clocked switching is lost in that and results can be quite bizarre.
JZ
On Fri, Oct 20, 2023, 6:29 PM Ryuji Suzuki AB1WX < ab1wx@...> wrote: I see. So what I suggested earlier, dividing the voltage by the current and plot as a complex number would solve the problem... not? (Or you could take magnitude of Fourier transform of the raw fake impulse and divide, but it is less preferable...)
Does that also mean that the true asymptote on the high frequency side is also different from what's shown in the graph?
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Re: QMX suffers zero negative impact from deleting L401 (with measurements)
I see. So what I suggested earlier, dividing the voltage by the current and plot as a complex number would solve the problem... not? (Or you could take magnitude of Fourier transform of the raw fake impulse and divide, but it is less preferable...)
Does that also mean that the true asymptote on the high frequency side is also different from what's shown in the graph?
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Re: QMX 60-10m mod last remaining issue: RX deep notch at 25MHz
I changed the inductors in my LPF wound on T27-17 to give a bit extra space between the cores, and in fact I made one of them extra millimeters of leads so that I can move it around. Just moving the inductor a bit makes significant differences in the receiver RF sweep traces. It makes significant impact above 20MHz but particularly on 12/10m (and 11m if you care). My receiver sensitivity is within 10dB of the 20m sensitivity, with image rejection > 30dB, on all 8 bands now.
I still have a couple of annoying phenomena that I want to defeat over time, but all the major mysteries are now resolved.
I know vast majority of textbooks say toroidal cores are a closed magnetic circuit and their leakage flux is negligible. I don't know of any real RF engineer that believes any of that... be careful with textbooks...
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Re: QMX suffers zero negative impact from deleting L401 (with measurements)
Ryuji,
Remember that my Dirac spike is an approximation.? A true Dirac Delta would be flat over the entire spectrum. The approximation does not possess that property. It's spectral response is part of what you are seeing.
Over the last few months I have played with a number of attempts at modeling the Tayloe circuit. Sadly, no LTSpice model for the mux chip exists. I started. by using BS123 models run at low frequency. That was interesting but it had its limitations. Later I tried the chip-level NMOS models in LTSpice, the ones in which you specify device width and channel length. I had some success with that, too. but still parasitics, and especially clock feedthrough to the input were complicating things. I decided to go with the utterly clean and parasitic free switches to best understand the tracking-filter property of the Tayloe circuit. That clarified many things.
JZ
On Fri, Oct 20, 2023, 5:56 PM Ryuji Suzuki AB1WX < ab1wx@...> wrote: JZ, indeed. I'm deeply in LPF/BPF/amp area and I don't know if I want to pick up another project. Well, mixer is related to BPF issue but I'd rather see all the right questions reported here :-)
So, are you saying that input Z is inductive where f < f_LO, and capacitive otherwise? But then your first trace goes up as f goes below 100k. Isn't that capacitive??
Real transformers have coupling coefficient < 1 and trifilar on a FT50-43 is not leakproof, and that transformer has a lot of magnetizing inductance. So, I would expect the real mixer to have some leakage inductance, especially at higher frequencies. Then there is winding capacitance. So, I would expect the mixer input impedance to be also signal frequency dependent not just relative to the LO frequency. I did note that you made a caveat that parasitics were omitted, but the real simulation needs parasitics...
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Re: QMX High swr into 50 ohm dummy load
This is no longer speculative. Toroids on QMX boards have some magnetic coupling (most significant on 12/10m). When I made my LPF inductors with several millimeters of leads to move around, the behavior changes in the upper passband depending on how I arrange the inductors. Winding two inductors in the opposite directions also have a different effect. If your QMX is working fine no need to worry but if anyone is only getting weak output power on 20m or 40m while getting good outputs on 30 and 60m, giving the LPF inductors a bit of a space may be worthwhile trying. When people start building high band version, this may be even more significant.
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Re: QMX suffers zero negative impact from deleting L401 (with measurements)
JZ, indeed. I'm deeply in LPF/BPF/amp area and I don't know if I want to pick up another project. Well, mixer is related to BPF issue but I'd rather see all the right questions reported here :-)
So, are you saying that input Z is inductive where f < f_LO, and capacitive otherwise? But then your first trace goes up as f goes below 100k. Isn't that capacitive??
Real transformers have coupling coefficient < 1 and trifilar on a FT50-43 is not leakproof, and that transformer has a lot of magnetizing inductance. So, I would expect the real mixer to have some leakage inductance, especially at higher frequencies. Then there is winding capacitance. So, I would expect the mixer input impedance to be also signal frequency dependent not just relative to the LO frequency. I did note that you made a caveat that parasitics were omitted, but the real simulation needs parasitics...
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Re: QMX suffers zero negative impact from deleting L401 (with measurements)
Lastly, the coupling coefficient I used is 1.
On Fri, Oct 20, 2023, 5:22 PM Ryuji Suzuki AB1WX < ab1wx@...> wrote: JZ,
Is n002 an input node with a purely resistive constant impedance to the ground? Why not divide with the input current and plot in the polar or re/im coordinates?
What's the coupling coefficient of the input transformer in your model?
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Re: QMX suffers zero negative impact from deleting L401 (with measurements)
Hi Ryuji,
The Tayloe input impedance is complex, with a response similar to a high Q parallel LC circuit, and it moves about with the clock frequency.
I have used several different schemes to illuminate the behavior of the Tayloe input, including direct ratios, injection of wide band noise from a behavioral voltage or current source, and finally the Dirac Delta function approach. The last produces the best results. The others are computationally burdened or otherwise compromised.
If you are interested I can send you my sim deck.
I am delighted to see the elevation of technical discussion that is taking place on this forum!
JZ KJ4A?
On Fri, Oct 20, 2023, 5:22 PM Ryuji Suzuki AB1WX < ab1wx@...> wrote: JZ,
Is n002 an input node with a purely resistive constant impedance to the ground? Why not divide with the input current and plot in the polar or re/im coordinates?
What's the coupling coefficient of the input transformer in your model?
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Re: QMX suffers zero negative impact from deleting L401 (with measurements)
JZ,
Is n002 an input node with a purely resistive constant impedance to the ground? Why not divide with the input current and plot in the polar or re/im coordinates?
What's the coupling coefficient of the input transformer in your model?
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Re: QMX suffers zero negative impact from deleting L401 (with measurements)
Thanks John. Appreciated.?
Peter
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Re: QMX suffers zero negative impact from deleting L401 (with measurements)
Peter,
In my morning I will DM you a .asc file for that simulation. Have fun with it!
The literature regarding the input impedance of the Tayloe circuit is nil it seems, as is that for optimum clock phase waveforms/overlap. These are important issues that are not well considered.? Simulation may help clear that up.
JZ KJ4A?
On Fri, Oct 20, 2023, 3:07 PM Peter Ayearst < ve3poa@...> wrote: John,
Lately I've been thinking about the Tayloe Detector and setting up a LTspice simulation.? Could you post a clearer picture of your schematic?? I'd be most interested in seeing what you have done.
73, Peter ve3poa?
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Re: QMX PC Connect, Anyone?
Hi Jim
Yes it was MLDX's log which clearly showed the issue with the QMX responding as a terminal, which can only happen if it gets a carriage return character.?
It is great that MLDX had that log available. Then subsequently once proper CAT comms were established the use of the AG command could be seen in the QMX log.?
It all highlights the usefulness of logs in troubleshooting. I'm glad to hear it is all resolved now! And that the MLDX developer was so responsive. Great support from him.?
FYI, technically the QMX volume control IS a number from 0 to 255. But this is interpreted on dB and clearly a gain of anywhere near 255 is massive overdrive. How this sounds on a QMX can be as a sudden decrease in volume, since digital signal processing and SDRs do do this scenario, overload causes sudden catastrophic effects unlike analog systems where the deterioration is often more gradual.?
The gain control issues which many people interpret as suddently getting quieter and louder are, I believe, actually the symptoms of DSP going into overload. It does sound like misbehaving volume levels.?
Generally this needs fixing urgently. And the AGC situation.?
On Fri, Oct 20, 2023, 7:13 PM Jim Bennett / K7TXA via <w6jhb= [email protected]> wrote: It was a struggle because there was a NO log file to show. The logging program never made the connection until a day or so ago, thus nothing in the QMX CAT log file. Once the MLDX developer changed his program to not send a carriage return, QMX was able to connect and a log was available. Didn't take too long after that to see why audio went down the tubes. Anyway, water under the bridge now. QMX working pretty well (NEEDS AGC!) - lots of CW contacts and several FT8, including VK2LAW (20 M) and 5W1SA (30 M) a few minutes ago - both with my flagpole vertical!
--
Jim / K7TXA
Eagle, ID
SKCC 10447C
BUG 301
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Re: QMX suffers zero negative impact from deleting L401 (with measurements)
John,
Lately I've been thinking about the Tayloe Detector and setting up a LTspice simulation.? Could you post a clearer picture of your schematic?? I'd be most interested in seeing what you have done.
73, Peter ve3poa?
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Re: QMX / QCX Mini New Feet?
I got these for my mini and they work great.
--
Wayne S.
KF7RCM
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Re: QMX suffers zero negative impact from deleting L401 (with measurements)
I thought it might be useful to post the sim results for detection of
a 1.001 MHz signal vs the 1.000 MHz clock. The Cacc waveforms are
beautiful, representing a 1KHz beat note with I and Q and their
complements present.
Enjoy!, JZ KJ4A
toggle quoted message
Show quoted text
On Fri, Oct 20, 2023 at 12:10?PM John Zbrozek <jdzbrozek@...> wrote:
Stephan, you had asked for some simulation results.
I couldn't resist ;-)
The LTspice simulation below shows some of the fascinating properties
of the Tayloe detector.
The simulation uses ideal voltage controlled switches to perform the
MUX function of the detector. This avoids complications with
parasitics and device performance.The switch model also has an
optional internal resistance. Since the switches change state 'hard'
at defined voltage points, the four phase clock system can simply be
four sine generators staggered by phase. I used 2 X 4 just to keep the
visual clutter down. As shown, the clock is running at 1MHz.
The input signal is a single sharp spike, an approximation to the
Dirac Delta function, which produces a very wide spectrum.
The simulation output is selected as the voltage at the input winding
of the balun. As you might expect, it is also a single sharp spike.
The voltage at that node can be taken as a surrogate for the input
impedance of the detector.
The real treasure of the simulation is the FFT spectrum at that node,
shown. You can clearly see the intrinsic bandpass behavior of the
Tayloe circuit, as well as its receptivity at odd clock harmonics. As
the clock frequency changes, the response curve follows it. As the
Cacc parameter alters the values of the accumulating capacitors, the
bandwidth changes.
JZ KJ4A
On Fri, Oct 20, 2023 at 3:17?AM Alan G4ZFQ <alan4alan@...> wrote:
On 19/10/2023 16:35, Rod Smith via groups.io wrote:
does this link work for you?
<>
Rod,
Yes, thanks.
An impressive project for it's time. Some parts can be improved and
simplified by modern developments.
The designers certainly believed in good filtering, no compromises.
73 Alan G4ZFQ
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HA3HZ
Ryuji Suzuki AB1WX
Peter Ayearst
