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I installed one of Hans' new AGC boards in my 20m QCX classic.? It works as advertised on receive.? But now my sidetone is distorted.? The first dit or dah is badly clipped and the remainder of the characters seem "muffled" a bit.? Turning the AGC off doesn't affect this.? Any suggestions?? I'd like to resolve this before I install the AGC boards in my other two QCX classics.?
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73/72,
Dean K5DH
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I just installed a AGC board in a QCX Classic yesterday and it works as advertised and does not affect the sidetone in any way. Maybe you have it set up too tight ... ie too far counterclockwise on the trimmer... Ron
I installed one of Hans' new AGC boards in my 20m QCX classic.? It works as advertised on receive.? But now my sidetone is distorted.? The first dit or dah is badly clipped and the remainder of the characters seem "muffled" a bit.? Turning the AGC off doesn't affect this.? Any suggestions?? I'd like to resolve this before I install the AGC boards in my other two QCX classics.?
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73/72,
Dean K5DH
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I guess I should have included more detail in my original post.? I upgraded to firmware 1.08 via a new chip purchased from QRP Labs to allow the AGC to be selectable via the menu.? It does not matter where the AGC threshold pot is set (literally anywhere across its range), or if the AGC is Off or On in the menu.? The sidetone still behaves badly.? As I stated originally, on receive, the AGC functions as advertised.? I'll disconnect the AGC board from the circuit and see if the sidetone performance improves.?
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73/72,
Dean K5DH
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Well, poop.? I removed the AGC board, and the sidetone is still messing up.? I either broke something, or something failed.? Suggestions??
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73/72,
Dean K5DH
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Are you having this issue when using a dummy load? If you were using an antenna, go ahead and try it on a dummy load and see if the problem persists. The Mini does sometimes get a messed up sounding sidetone when RF sneaks into it from an antenna.?
Well, poop.? I removed the AGC board, and the sidetone is still messing up.? I either broke something, or something failed.? Suggestions??
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73/72,
Dean K5DH
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Ronald,
The sidetone issue is the same whether I'm on the antenna or a DL.? Another note on the sidetone: it's sudenly very "clicky" in addition to the first dit or dah being badly clipped and all of the characters being "muddy".? I listened to the QCX's transmitted signal on my K3, and it sounds fine, so the problem must be with the sidetone circuit rather than the transmitter.? Apparently I messed something up when I was installing the AGC board.? Rats!?
As a side note... I installed the AGC boards into my 30m and 40m QCX Classics today, and they both work fine.?
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73/72,
Dean K5DH
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Dean, one thing you can check is a test of the muting circuit. If it is no longer muting the receiver on transmit, the sidetone will be very distorted. Connect your ohm meter between the center pin of the volume pot and ground. Key the transmitter (with load attached of course) and the resistance should drop to a very low value like just a couple of ohms. If it isn't then check the gate of Q7. It should go to 5 volts on key down. If it is doing that, then Q7 is bad. Good luck .. Ron
Ronald,
The sidetone issue is the same whether I'm on the antenna or a DL.? Another note on the sidetone: it's sudenly very "clicky" in addition to the first dit or dah being badly clipped and all of the characters being "muddy".? I listened to the QCX's transmitted signal on my K3, and it sounds fine, so the problem must be with the sidetone circuit rather than the transmitter.? Apparently I messed something up when I was installing the AGC board.? Rats!?
As a side note... I installed the AGC boards into my 30m and 40m QCX Classics today, and they both work fine.?
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73/72,
Dean K5DH
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Good morning!? I just saw this post and did not look at the circuit but to the best of my knowledge I believe it is not a good idea to measure resistance on an active, powered up circuit.? The ohm meter actually applies power to the circuit when measuring resistance.? 73 Steve KY4GX.
Glory to God in the highest, and on earth peace, good will toward men. Luke 2:14
On Tuesday, December 21, 2021, 06:27:53 PM EST, Ronald Taylor <wa7gil@...> wrote:
Dean, one thing you can check is a test of the muting circuit. If it is no longer muting the receiver on transmit, the sidetone will be very distorted. Connect your ohm meter between the center pin of the volume pot and ground. Key the transmitter (with load attached of course) and the resistance should drop to a very low value like just a couple of ohms. If it isn't then check the gate of Q7. It should go to 5 volts on key down. If it is doing that, then Q7 is bad. Good luck .. Ron
Ronald,
The sidetone issue is the same whether I'm on the antenna or a DL.? Another note on the sidetone: it's sudenly very "clicky" in addition to the first dit or dah being badly clipped and all of the characters being "muddy".? I listened to the QCX's transmitted signal on my K3, and it sounds fine, so the problem must be with the sidetone circuit rather than the transmitter.? Apparently I messed something up when I was installing the AGC board.? Rats!?
As a side note... I installed the AGC boards into my 30m and 40m QCX Classics today, and they both work fine.?
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73/72,
Dean K5DH
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In this particular case the test point is DC isolated from the rest of the circuit and doesn¡¯t cause an issue. I tested it and it works. I should have mentioned that in the post because normally you are correct. Thanks?
Ron
Good morning!? I just saw this post and did not look at the circuit but to the best of my knowledge I believe it is not a good idea to measure resistance on an active, powered up circuit.? The ohm meter actually applies power to the circuit when measuring resistance.? 73 Steve KY4GX.
Glory to God in the highest, and on earth peace, good will toward men. Luke 2:14
On Tuesday, December 21, 2021, 06:27:53 PM EST, Ronald Taylor < wa7gil@...> wrote:
Dean, one thing you can check is a test of the muting circuit. If it is no longer muting the receiver on transmit, the sidetone will be very distorted. Connect your ohm meter between the center pin of the volume pot and ground. Key the transmitter (with load attached of course) and the resistance should drop to a very low value like just a couple of ohms. If it isn't then check the gate of Q7. It should go to 5 volts on key down. If it is doing that, then Q7 is bad. Good luck .. Ron Ronald,
The sidetone issue is the same whether I'm on the antenna or a DL.? Another note on the sidetone: it's sudenly very "clicky" in addition to the first dit or dah being badly clipped and all of the characters being "muddy".? I listened to the QCX's transmitted signal on my K3, and it sounds fine, so the problem must be with the sidetone circuit rather than the transmitter.? Apparently I messed something up when I was installing the AGC board.? Rats!?
As a side note... I installed the AGC boards into my 30m and 40m QCX Classics today, and they both work fine.?
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73/72,
Dean K5DH
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As Steve points out, I didn't want to insert an Ohmmeter into a live circuit.? That is poor practice.?
I switched to straight key mode and measured the voltage at Q7's gate.? It did go to 5 V on TX.? The sidetone was still wonky in straight key mode, too.?
The circuit description in the manual indicates that muting is achieved by essentially grounding the wiper of the volume pot through the FET.? I grounded that point using a clip lead, in other words, always muted.? There was no change in the sidetone's performance.?
I did some more general experimenting.? I noted earlier that the problem is present whether I'm connected to my station DL (a 2 KW Drake air-cooled unit) or my antenna (a well-matched dipole -- VSWR about 1.2:1 -- and the same antenna I always use).? But it's much more pronounced on the antenna.? Wondering if there was a problem in the station's coax connections somewhere, I connected the QCX directly to the antenna feedline.? No change.?
I then connected a small commercial-grade 25 W DL directly to the QCX.? The problem cleared up!? Switching back and forth between the small DL and the normal station connections produced repeatable results... for a few minutes.? Then the problem showed up on the small DL!? It was not as pronounced as on the station DL, but obvious nonetheless.?
I continued experimenting for a few more minutes, and I noticed that the problem became significantly worse under all circumstances.? Maybe something is failing, and I need to stress it enough to cause it to give up?? Connect a DL, lock the paddles in dit mode, and let it run for a while??
This is aggravating.?
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73/72,
Dean K5DH
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Maybe try the rig in practice mode (menu item 4.7) to rule our any problems due to RF.
Steve G4EDG
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I had a somewhat similar problem with sidetone and it turned out being a leaky C21 (or C22). The Classic QCX used 10mF caps. Recent versions use 1mF I believe.?
Sidetone is a PWM square wave generated in the microcontroller and it needs the DC blocking action of those two caps.
Hope it helps!
--Al
WD4AH
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Steve G4EDG:? Practice mode sounds perfect.?
Al WD4AH:? I replaced C21 and C22.? No improvement.?
But... Al's suggestion got me thinking.? What about C24?? I recall reading that later QCX versions replaced this 10 uF cap with a 470 uF cap to reduce "thump".? So I replaced C24 with a 470 uF cap from the parts bin, and that did the trick!? My sidetone is fixed!? I can only assume the original C24 was leaky.?
Thanks for all of the help, guys!? This group is very helpful!? I hope I can somehow return the favor someday.?
Merry Christmas and Happy New Year from The Republic of Texas!?
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73/72,
Dean K5DH
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Dean,
Glad to hear you got it fixed!!
Even Happier Holidays, now!!
--Al
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Hello Al
I need to clear up some misunderstanding here.?
The sidetone is injected much earlier than C21 and C22, in fact before the CW filter. Which is intentional to make it sound nice (turn it into a nice 700Hz sinewave). C21 and C22 are not involved in DC blocking of the sidetone.?
The sidetone is generated at ultrasonic frequency, 42kHz. It is indeed a squarewave whose duty cycle is modulated at a rate of 700Hz in order to create the 700Hz tone. Regardless of the sidetone volume, the average DC voltage of the sidetone signal is always 2.5V. This is the same as the DC bias at that point in the circuit, which is carried all the way from the phase-splitting T1 secondaries through the QSD, baseband pre-amps, and audio phase shift circuits. No DC blocking is required since both the existing audio signal and the sidetone do have the same DC bias level theoretically, and in practice also close enough.?
C21 blocks the 5V DC bias at the IC9 output, so that only AC audio is handled by the volume control potential divider. C22 blocks the DC bias from IC10 which is at midrail, for example 6V if the supply voltage is 12V.?
73 Hans G0UPL http://qrp-labs.com
-------- Original message -------- From: Al Holt <grovekid2@...> Date: Wed, Dec 22, 2021, 6:51 PM To: [email protected]Subject: Re: [QRPLabs] QCX classic -- sidetone distorted after installing AGC board I had a somewhat similar problem with sidetone and it turned out being a leaky C21 (or C22). The Classic QCX used 10mF caps. Recent versions use 1mF I believe.?
Sidetone is a PWM square wave generated in the microcontroller and it needs the DC blocking action of those two caps.
Hope it helps!
--Al
WD4AH
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YES!....exactly what Hans said...  Happy Holidays everyone! Rich KQ9L
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Dean said:
"But... Al's suggestion got me thinking.? What about C24?? I recall reading that later QCX versions replaced this 10 uF cap with a 470 uF cap to reduce "thump".? So I replaced C24 with a 470 uF cap from the parts bin, and that did the trick!? My sidetone is fixed!? I can only assume the original C24 was leaky. "
I just had a problem with the same capacitor in my new QCX+ on 20 meters. In my case I spent a few days trying to chase down a fault which messed up the side tone horribly, turning it into a loud buzz, and also allowed strange noises from the logic chips to half drown the receive audio. On my QCX+ the problem was erratic. It would come and go and seemed at first to be related to using the programing buttons on the front of the rig. Then I noticed that tapping part of the board with a plastic probe while the radio was receiving, I could make the fault appear and disappear, so it was clear we had a bad joint of some sort.
In my case, the cause was that c24 had one wire NOT actually soldered to the pad and plated through hole. I didn't build this rig, and the builder had seemingly trimmed the capacitor lead a bit short, before inserting it, and then soldered the pad, but the wire wasn't actually soldered and had intermittent contact. The problem didn't even show itself until I had been using it for about a? week. I only found it because I was re flowing all the joints in the part of the board where I thought the problem was. As I slid the iron into the joints, I always came up against the stub of the component lead inside the joint - until I came to the negative lead of C24. Then the iron slid right across the hole and further inspection revealed that I could tilt C24 on the upper side of the board.?
Now rectified and performing very well.
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Ronald Taylor