Just a thought, what frequency are you trying to receive on? Same as the u3s or +1500hz? double check.
I can see your spots so you are getting out OK. Can't be much wrong.
Andy
--
The universe is made up of Protons, Neutrons, Electrons but contains only one M0RON.
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I assume it’s not uncommon to receive QRP labs bits in separate consignments? I received a box and some pots, etc. but no circuit board (VFO order)?
I ask because there was nothing in the package to say it was part of a consignment; or anything at all!
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Thanks all: dummy load it is! And point taken about blowing Mosfets; I am paranoid about that!
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Re: Ultimate 3S reciever question
Whilst it may be good practice to have a band pass filter for each band I have found that it is not strictly necessary with the receiver module although I am only using an indoor aerial and have no high power transmitters nearby.
As far as the relays are concerned somewhere in the U3S documentation is the comment that two relays can be switched directly because of their low current consumption. This may not of course apply to other relays.
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Regards
Ian
G3VAJ
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Oddly now others can decode my 17m WSPR transmissions but I can't. I have looked for a setting in WSJT-X but can't see a 'don't decode my own' box.?
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Hans,
Thank you for your most excellent explanation of the reasons the historic U4B antenna works the best.
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Tom
K1FQY
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Thanks for the replies, the screen shows WSPR on the second line of the screen and the call is GW4SYI, my callsign. The U3S uses a QLG1 GPS device for the timing. Is any other info required?
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Lucien
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Re: QMX, one of op-amps self-oscillates at 25 MHz (or picks up the system clock?)
Hi Adam
I watched your new video, thanks.?
I don't think it is possible for the IC202 output to produce that kind of signal, which looks so perfectly like 25MHz at one timebase then 833 Hz at the other. Note that the frequency measurement in the bottom right of your screen indicates 25MHz also, which would probably not be the case if there was some kind of interruption going on.?
I think Stan has it correctly identified as a red herring, an artefact of the measurement procedure (the 'scope). And also 833Hz doesn't match the symptomatic 100Hz noise either.?
I think I am inclined to suspect a partially damaged MS5351M chip. Not the 25MHz TCXO.
Hans Summers via <hans.summers=[email protected]> wrote:
> Downstream of IC202 there isn't any "almost", this is the very reason why
> IC202 is there. You will have a 3.3Vpp output at IC202 output.
I do. The scope shows some overshoots, but probably the probe needs to be
calibrated.
> Can you take a similar video please for the signal at IC202 output?
Yes -- posted below.
> I'm still having trouble trying to convince myself that the 25 MHz TCXO is
> at fault here rather than - sorry to say it - some weird artefact
> introduced by the measurement itself (at the TCXO output / gate input).
Don't be sorry -- in the realm of high frequencies I'm not sure of
anything :) HF never fails to find ways to surprise me.
BTW, I find this frequency weird as well. It's very low, compared to the
nominal frequency of the TCXO. It's probably way too low to result from
some stray capacitances or inductances.
It might be some weird artefact. But the oscilloscope never had such
artefacts before (I have it for 14-15 years), and symptoms (intermittent
CLK0 and CLK1 at 100 Hz, precisely the frequency of the buzzing both
audible in the speaker and visible in WSJT-X's spectrum view) fit.
Here's a new video with:
1. Output of the IC202 gate at various time bases
2. Signal from the TCXO with C203 (capacitor coupling TCXO with the gate)
removed -- so it's a signal on unloaded TCXO
3. VDD after L201 (so the power line of the clocking subsystem: TCXO,
gate, synth chip), showing some very minor ripple of the same frequency (I
suspect it's the effect of the problem, not the cause of it, but at this
point I'm not sure of anything)
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Re: QMX, one of op-amps self-oscillates at 25 MHz (or picks up the system clock?)
Feedback from a CMOS gate output to its input will result in oscillation at some frequency unique to each chip. It’s impossible to predict the oscillation frequency but in general, yes, it will typically be a high frequency. This is not good practice but if you want to bias a logic gate, you should use a pull-up and pull-down resistor at the input to create a half-supply bias. How is this different than using the feedback resistor? Well, the gate won’t oscillate continuously without feedback. Rather, thermal and/or electrical noise present at the input will cause the output to randomly toggle (no fixed frequency) or it may just get stuck high or low.
Using a CMOS logic gate as a high-gain amp is a risky practice. Logic gates are designed to be switches, not amplifiers for low voltage input signals. Running a 1V p-p signal into a logic gate powered at 3.3V or 5V will probably work but the totem pole input stage will carry switch-through current and may spend too much time in the linear region. This can cause unwanted high-frequency oscillation during each state transition. This is why logic gates have a maximum rise-time and fall-time spec - to minimize time spent in the linear region so the gate won’t oscillate during transitions.
A better way to implement this would be to use a Schmitt trigger biased at half supply using its positive feedback to rapidly pass through the linear region. Still, I’ve never seen a CMOS gate wired with a feedback component in my 45 years of engineering. In fact, doing such a thing would absolutely prevent passing design reviews.
I see nothing wrong with the use of the circuit in this way in this application. Without any input signal, the circuit will indeed oscillate in the VHF region. However this is not the situation; the 25MHz TCXO signal is always present and the circuit is always locked onto it. Unwanted high-frequency oscillation during state transitions would require a many orders of magnitude lower input signal frequency with therefore very much slower rise/fall times than the 25MHz TCXO signal. No unwanted high frequency oscillation is possible during the state transitions at 25 Mhz which are much too short to cause any instability.
Every single microcontroller on the planet uses an inverter gate with a resistor across it to put it in linear mode, as the? amplifier of its clock oscillator circuit. It's called the Pierce oscillation configuration which is really a development of the Colpitts topology. Before we had microcontrollers and we had CPUs requiring an external clock, we used to do it with 74LS TTL. Before that, they even had resistor-feedback inverter gate oscillators clocking the CRAY 1 supercomputer.?
Many manufacturers have app notes on the topic; examples: - ? - note, most of the app note is about unbuffered inverters, it does mention buffered can be used too, but are less stable and more sensitive to parameter changes.?
- Plenty of interesting reads on Google search term "inverter gate feedback resistor"
This circuit works reliably in QMX and QDX transceivers. I don't think there's a problem here...
73 Hans G0UPL
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Hello Hans
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I am a bit concerned as to whether my e-mails are getting to you? Sent 2 recently but not seen any replies?
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73
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Ian G4GIR
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Re: Ver 1 vs Ver4 QMX...going bonkers
Thanks again Stan...regardless of how I measure, with power applied, or after hitting the on push button, all I see is supply voltage of 11.94 where the red probe is pointing and maybe 11.83 for the black--nothing at all on the 6 pin plug--no voltage at all.
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Scott
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Re: question 50 watts amp
I'm reading now what you have written.
Thanks.
hanz
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Has anyone tried using a GPS antenna as used on the Traquito just on leg of 1" that works very well on a U4B?
This type of antenna is a monopole antenna, like a 1/4-wave vertical. And like a 1/4-wave vertical, it also needs a groundplane (radials etc). Firstly 1" would?be 25.4mm which would not be the right length; at 1575 MHz L1 GPS a 1/4-wave antenna would need to be about 45mm (something like). The groundplane is formed by the groundplane of the tracker (Traquito in that case).?
However:?Traquito is a much larger tracker than U4B. Approximately 3x the weight?and 3x the board area. Therefore U4B would be an even less effective groundplane than Traquito.?
The antenna Dave VE3KCL used on the test flights, and I also used successfully, consists of a full-size dipole made from the same 0.33mm wire used in all the QRP Labs kits. Each arm of the dipole is 45mm long. Then make a "feedline" (and balun) by tightly twisting the wire for a distance of about 3-4cm (not critical). The result looks like a T with a shorter trunk than its arms; the vertical section is the twisted wire part, soldered to the U4B (ground and GPS Ant pins) at the bottom end, with the two horizontal arms of the dipole pointing left and right at the top.?
Furthermore Dave found that the performance is further improved by bending the dipole arms towards each other so that they are at 90-degrees. Now the antenna looks like a Y. Presumably improves the impedance match.?
I think this kind of dipole antenna outperforms most other types of passive antenna system. You see a lot of GPS ceramic "chip" antennas. These are a compromise, designed for when very little space is available. Your smartphone is a good example. That poor thing has to have a GPS antenna, WiFi, Bluetooth, Cellular, NFC, who knows what else... all crammed into a tiny case alongside a relatively huge screen, relatively huge battery, and tons of electronics. Having the space for a full-size dipole is a very nice luxury to have.
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Re: Ver 1 vs Ver4 QMX...going bonkers
Scott, I would make some voltage measurements.
These can all be done with just the bottom cover of the QMX removed, via the 8-pin and 6-pin power supply connectors you soldered in.? You just need to carefully identify which pin is which.
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[the 8-pin connector]
1) Vin (JP102 pin 5) - should be the same voltage as your power source
2) 12V (JP102 pin 6) - should be 0V until you push the PWR_ON button, when it should immediately switch to the same voltage as your power source, minus a couple of tenths of a volt.
3) VCC (JP102 pin 4) - should stay at 0V until firmware is loaded, otherwise about 1/2 sec after you press PWR_ON, it should change to 5V.
[the 6-pin connector]
4) VDD (JP103 pin 4) - should be 0V until you push the PWR_ON button, when it should immediately rise to about 3V.? This is what powers the processor on to initialize the USB so you can load your firmware.
5) LIN_REG_EN (JP103 pin 3) - should start at 0V then immediately go to about halve the value as the 12V line measured above.
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One of those is probably not working as described, which can lead us to the next troubleshooting step.
Stan KC7XE
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Re: question 50 watts amp
Many thanks Jushua,
I have build the qmx plus for 9 volts.
For the cae not to use attenuators i am building now a variable output poeer supply based on a lm317 wiith a 2n3055.
Many for the points of attention.
73 hanz
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Ver 1 vs Ver4 QMX...going bonkers
I have to say I have never had such grief with a build--ever. Including my own homebrew design.?
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Having blown out the earlier qmx V1 a couple weeks ago I ordered some new boards and another QMX (v4). Being over paranoid I have constructed it meticulously...I am no Hans, but no stranger to solder smoke either. That said, I have once again fallen short.
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Now before i go any further, and this is a faint hope, I am hoping someone will tell me the V1 Display and control board are not compatible with V4. I simply used those after building the new V 4 board as they are known to work fine--on my orig build, and on a friends QMX.
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So, to the matter at hand. On power up sequence, nothing. No current draw at all, no recognizing the usb, no sounds, (no smoke) absolute silence). I have searched the questions here and have found some places to start when there is at least usb recognition , but this is truly ground zero.?
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Scott
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Re: QMX+ with ~1000 tone on 12M & 6M
Is this an issue related only to Version 1 of the board???
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Ludwig, I was very careful inspecting the board, but it's perfectly possible that is the situation.? I will reinspect and make sure I can locate all 10 caps.??
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Thanks & 73
Dick
W4PID
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I chose the 60-15m QMX for SOTA, as 40, 20, 15 meters are the bread and butter bands that are most likely to support SOTA activity.? 60m and10m are there for the ride but sketchy supporting SOTA water holes.? YMMV.
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Brien - KE7WB
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Qrper.com - words and video?
-Mike/w1mt
Any suggested article available online?
73!? de Bekir TA2RX
10 Oca 2025 Cum 02:42 tarihinde Ivica - YU1QRP via <yu1qrp= [email protected]> ?unu yazd?: On Thu, Jan 9, 2025 at 07:13 PM, Ed Kwik wrote:
Go to YouTube. Search on ham radio sota
Or simply read a good article in 30 minutes instead of loosing time watching 3 hours of videos, same ammount of info and no forced ads.
?
?
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Any suggested article available online?
73!? de Bekir TA2RX 10 Oca 2025 Cum 02:42 tarihinde Ivica - YU1QRP via <yu1qrp= [email protected]> ?unu yazd?:
On Thu, Jan 9, 2025 at 07:13 PM, Ed Kwik wrote:
Go to YouTube. Search on ham radio sota
Or simply read a good article in 30 minutes instead of loosing time watching 3 hours of videos, same ammount of info and no forced ads.
?
?
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M0RON
Chris G7LQX
hanz YL3JD
Richard Hattaway
Brien - KE7WB