Re: QMX+ back up clock accuracy
Hello Mark
Fixing the accuracy of the RTC is again something on my to-do list. The RTC runs from the 32.768 kHz crystal and like any uncompensated uncalibrated crystal they can be off. I will include some kind of software calibration to use the 25 MHz TCXO or GPS (if available) to fix this.?
Right now my priority is on SSB... I've got the SSB modulation working very well (see attached 700/1900 two tone test with excellent IMD3 performance) and now moving on to tackle the microphone audio processing, filtering and compression.?
But I will get to this RTC accuracy issue in due course. It's nothing wrong with your radio. So just wait a little please...
73 Hans G0UPL
I'm using a QMX+ with the CR2032 installed and "QMX+ RTC" selected.
The problem is with the accuracy of the clock when the unit isn't switched on.
AFAICT, it's pretty accurate when the radio is operating in WSPR mode: it can run happily for several days at a time without any GPS input. However, if the unit's not powered up, the clock goes fast very quickly - I put the radio away for a few days and find the clock is several minutes fast, roughly 30 seconds a day. :-(
The 25MHz reference oscillator is virtually spot on: I've checked it using Hans's 20m WSPR tools (checked with both tx and rx), tweaked it a tiny bit (7Hz) and now everything's almost perfect.
Similarly, I've checked the CR2032's connections, cleaned the contacts and that seems well: the cell gives 3.15 volts measured at the PCB (healthy enough, surely?).
I find the on-screen time display helpful for logging purposes - I don't want to have to connect up the GPS or manually set it every time I leave the rig unused for a few days. What's up? How can I improve the accuracy?
73 Mark G?OIW
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QMX+ back up clock accuracy
I'm using a QMX+ with the CR2032 installed and "QMX+ RTC" selected.
The problem is with the accuracy of the clock when the unit isn't switched on.
AFAICT, it's pretty accurate when the radio is operating in WSPR mode: it can run happily for several days at a time without any GPS input. However, if the unit's not powered up, the clock goes fast very quickly - I put the radio away for a few days and find the clock is several minutes fast, roughly 30 seconds a day. :-(
The 25MHz reference oscillator is virtually spot on: I've checked it using Hans's 20m WSPR tools (checked with both tx and rx), tweaked it a tiny bit (7Hz) and now everything's almost perfect.
Similarly, I've checked the CR2032's connections, cleaned the contacts and that seems well: the cell gives 3.15 volts measured at the PCB (healthy enough, surely?).
I find the on-screen time display helpful for logging purposes - I don't want to have to connect up the GPS or manually set it every time I leave the rig unused for a few days. What's up? How can I improve the accuracy?
73 Mark G?OIW
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Re: Still no output on QMX
On Sun, Sep 22, 2024 at 05:25 AM, James wrote:
winding T501? 12V or 9V?
James, there are pros and cons for both. Searching through the forum you will find some discussion.
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I wish you success for your work and hope to read good news from you.
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73, Ludwig
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Re: Still no output on QMX
On Sat, Sep 14, 2024 at 11:03 PM, @Ludwig_DH8WN wrote:
On Sat, Sep 14, 2024 at 04:26 AM, James wrote:
The Gate and the source voltage remains the same at 8.0V during all three "No Key", "P", "T".
If I read the tester display right, Q507 seems to be ok.
To be clear, it looks like Q507 is ok but I'm not sure because
But why is the voltage at G the same as at S?
So Q507 maybe not ok or something around Q507 is wrong. If voltage at G and at S are the same, across a well working Q507 no current is flowing and no voltage at the PA like for your QMX.
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My suggestion:
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Please check schematics and trace from gate of Q507 to R506 and collector of Q514. Check voltage of both sides of R506 and voltage at base of Q513 (signal DAC from the controller). Check also R507 for the right value and no short.
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Normally a current should flow across R506 in each situation. When "no key" and "P" depressed this current is low and the gate voltage is a bit below the source voltage but not the same. When "T" depressed the signal DAC from the controller (B of Q513) is going from nearly 0 V to more than 1 V. This results in an increase of the current across R506 and the gate voltage of Q507 drops more. This lowers the source drain resistance of Q507 and a current is flowing to T501 and the BS170. This should be.
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So you have to find why not for your QMX.
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73 Ludwig
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Re: Removing flux. Is it necessary? Yes/No
I use 99.9%? IPA (not the beer!) and an old medium toothbrush to dissolve the flux away. While the area is still wet I lay two layers of kitchen roll over it and rub over the top of that with the same toothbrush. It's a fairly gentle method, doesn't leave and debris and the boards come up minty-fresh every time.
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Ronan
MM0IVR?
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Re: Still no output on QMX
Hi Paul, I initially built the 9V version of the QMX.?All my power sources are either 13.8V or 12.8V. My thoughts were building the 9V version with a voltage regulator inline of a dedicated power cord. ?My only concern, and honestly I'm not knowledgeable to know, but I was thinking that the extra voltage would be dissipated in heat, and the hotter the regulator would get, the more amperage it would draw. I was going to inquire about this theory, but then actually getting any output at all out of the rig became the major concern. In the middle of all that, I rebuilt it to the 12V arrangement. Right now I'm not sure why I'm not getting any output so like I said, I will reassemble the rig and run the test that Ludwig was suggesting and go from there. Thank you for your input. After I tackle the output problem, I'll check into your suggestion. I'll try to find some information on which is better, boosting up to 9V, or regulating down from 12V.?
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James
KA9TII??
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Hi I have used this but CW only, The KX3 has superb power control
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73
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Andrew
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Re: qmx with tiny lcd display
Just curious, why would you replace it with a smaller one? Are you trying to make space for something else by shrinking the LCD?
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Re: 180pf (181) Capacitor Needed
Hi Amazon do leaded capacitor kits, build up some stocks.
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73
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Andrew
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Re: BS170 Heat flow experiment with results (Updated)
It’s all interesting?
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The trouble with assuming temperature = heat flow
is that actually temperature is just heat and without knowing the magnitude of the flow is a bit of a dead end?
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There is a better inference to be had with standardised significant heatsink areas as (ambient temp being equa) extra hot = more heat flow
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Re: QMX (not-plus) power issue
I agree with Stan's assessment. When I had a blown PA transistor in my QMX, the rig (12v) was drawing over 200mA during receive.?
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I didn't have to remove the Heat-sink washer to find the bad one. It was quite obvious which one was bad, but it likely helps to remove it to see if any are warmer than others. Start with a cold radio, and don't transmit at all.?
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Stating the obvious, you have an extra 35mA going somewhere. Is that constant, or does receive current draw change by band??
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Hopefully someone else can jump in and help you with diagnostics.?
--
73
de Roy - KI0ER
Littleton, Colorado USA
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Re: QMX+ High Current and Self Start
Based on the post’s you referenced, I’m going to perform a “sanity check” on the LPF considering that L507 was found open.?
I can now invision a path through Q507 and the BS170’s with there being a shorted capacitor.?
I haven’t employed it yet until the simple things have been checked first. I suppose we are there! I have a 200MHz 4-ch DPO and a bench top power supply. I’ll clear the build space and stage the equipment.?
Before your last response, I was headed down the random clock signal to the gates “rabbit hole”. I see the logic in the LPF and it’s probably the culprit. There is a very good chance I have some high end RF rated capacitors and inductors in storage.?
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You will need a high band QMX+ with 6m to do transverting up to 2m and 70cm.? Failing that 10m had been popular in the past. There are many reasons you won't want yo go lower. When I played with them in the past I have always used the SBL-1 type diode mixers RF fets and MMICs. You will need good quality crystals for the LOs. Lot's of such circuits around. Auto r/f detect T/R switching is the norm. I would start with a 1 or 2W output unit, get it working before boosting the power further up.?
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Re: QMX crashes on RF filter sweep (and other anomalies)
Hi Greg et al
John VA7JBE's description is also what is happening with the QMX+ I have just completed.? This is my second QMX+ as the first one didn't work due to faulty ic's in both the tx and rx chains.? IC407, PCM1804 and IC503, 74ACT08D both failed.? I was able to replace both and the QMX+ is operating very well.? However I ordered a second kitset (without the case) as I was unsure if I could actually desolder and replace the PCM1804.? I now find the second kitset does not receive at all - there is no audio output from the receive chain but there is a harsh sidetone when the cw key is pressed.
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On top of this, when using the terminal programme (PUtty), the diagnostic screen shows everything works fine except the tx power and swr, which show nix.? The QMX draws the correct current (~90mA) when switched on and when keyed with the Terminal 'T' key the transmitter draws current.?
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I used the oscilloscope across the dummy load to measure the tx output and it is ok on all bands but the tx remains on and the unit becomes unresponsive until the power supply is removed. Replacement of the power just leads to the same cycle again.
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After pressing the cw key? the harsh sidetone turns on but the transmitter is not turned on and the QMX becomes unresponsive to any inputs - either from the keyboard or front panel controls.? It leads me to think there may be a problem with the microprocessor.?
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It's a bit beyond me and my fault finding abilities.? Although I do have a functioning QMX+ I really don't know where to go from here.? It may pay me to get in touch with Jeff W1NC to see if it's worth sending the board for repair.? I don't know of anyone in NZ who would be capable of diagnosing and fixing the problem.
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Any input would be appreciated.
Regards
Greg
ZL4GW
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Re: Still no output on QMX
I think it mainly depends on what you want to use for a power
source. 9V will use ~1.3A in transmit, 12V will be under an amp
(working from memory here!) 12V is tempting to use a nominal 12V
source, but fully charged it will be more than that (13V or more!)
So you'd need (read: should have!) a regulator to limit it to 12V
anyway...
There's been discussion here that swr and other factors can push
the voltage limits of the BS170's. Hans thinks he's got that under
control, in the QMX, FWIW.
At this point, I might consider building for 9V and then use a
Buck/Boost converter with output set to 9V, to adapt to the
voltage that's actually available. Downside is possible noise from
the converter, and a slight loss of power efficiency. Upside is
the operating voltage of the BS170's will be more stable, and
maybe more safety margin on the voltage. (Maybe not, too-- Lower
voltage should mean more current being switched off, which could
translate into a larger di/dt spike! :-( )
I like the idea of 9V/Buck-Boost because it strikes me as
relatively foolproof, re: supply voltage.? I don't know if anyone
has compiled BS170 failures for QMX vs 9 or 12 volts...
Good Luck!
73, Paul -- AI7JR
On 9/21/24 20:25, James via groups.io
wrote:
Well I'm back;
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Ludwig, since we determined that Q507 was good (until I broke
the legs off), is there anything else that I need to pay
particular attention to, to determine why there is no output
power. I was going to wait to reinstall the parts that I
uninstalled to avoid damaging while I removed Q507, but I think
I will assemble everything and reference your last message you
sent with the voltage information of some surrounding parts.
What is your recommendation as far as winding T501? 12V or 9V?
Is one more successful than the other as far as you can tell? If
I need to rewind T501 back to 9V, I'd rather do it now while
that portion of the board is partially empty.
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As always, thank you and the others so much for the input
and help to get this radio working.
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73
James
KA9TII?
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--
Paul -- AI7JR
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Re: Still no output on QMX
Well I'm back;
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Ludwig, since we determined that Q507 was good (until I broke the legs off), is there anything else that I need to pay particular attention to, to determine why there is no output power. I was going to wait to reinstall the parts that I uninstalled to avoid damaging while I removed Q507, but I think I will assemble everything and reference your last message you sent with the voltage information of some surrounding parts. What is your recommendation as far as winding T501? 12V or 9V? Is one more successful than the other as far as you can tell? If I need to rewind T501 back to 9V, I'd rather do it now while that portion of the board is partially empty.
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As always, thank you and the others so much for the input and help to get this radio working.
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73
James
KA9TII? ?
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Re: BS170 Heat flow experiment with results (Updated)
Tony,
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? ? I wasn't sure if you were measuring the active device, so higher temps meant poorer transfer *to* the heatsink, or measuring the heatsink meaning higher temps might mean better heat transfer *away* from the active device.? Thanks for clearing that up.
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Bill?
W2EB
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Re: 180pf (181) Capacitor Needed
This looks like the one, Nate -- thank you !??
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Bill? W3WJ
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Re: J201 USB -c connector solder photo
Mine looked like that too. ?I couldn’t get a reliable connection to my pc until I resoldered those pads. ?Just used a fine tip iron and took my time. ?
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There's no free lunch.?
Power out < Power in
V*I out < V*I in
The 12V battery would need to sustain high current for the buck converter to achieve 20V at the current required to amplify the signal to from 5W in to 50W out.
So at the recommended 20V @5A, you would need more than 20*5/12 = 8.3A sustained from your 12V battery.
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73, Mike KK7ER?
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Mark Palmer
James
Andrew Lenton
Willem VA2WLM
Bruce Akhurst
F4WCV
Paul - AI7JR
Adam N0ZIB