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Output power problem #qcxmini
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Amaury - F4IKG
Hi everyone, I have a problem that I can't solve myself,
I've just finished building my QCX mini 20m, everything works great except TX. When I keyed down, I've read 1.8W output (on 12V supply). But after a series of key down, the output drops out to 0W. I removed the 3 yellow toroids and rewound them with new enemal wire and the same thing happens. about 1W output then after a few presses : 0W. Does anyone has an idea of what I did wrong ? |
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Hello Amaury (please put your name in the signature line so we don't have to look it up :-)
First, you take a good approach, but you might not be doing anything wrong. In fact, with that behavior (power dropping to zero) it is likely that there is a component problem, like capacitor C29, for example, or one of the capacitors in the LPF. Next, I assume you have some basic tools like a DVM; do you have an oscilloscope available? And how are you measuring output power? Now, can you check the voltage at the connection between L4 and the collector of Q6 upon key-down? It should be very close to your supply voltage, and not droop during key-down. What we are looking for, in general, is some change in voltage somewhere in the transmitter path that corresponds to the change in output power. Lastly, feel for anything getting hot during key-down. Let us know what you find. -- Julian, N4JO. |
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Roger Hill
Hi It could also conceivably be a weak power supply that droops... 73 Roger 8P6RX ---
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Roger Hill *************************** On 2022-03-02 11:57, Julian N4JO wrote:
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Sure could be... I had inferred from "after a series of key down" that it took more time that would be typical of a soft power supply; maybe that was an incorrect assumption.
-- Julian, N4JO. |
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Amaury - F4IKG
Hello Julian,
First I updated my display name! I am sorry I don't have an oscilloscope handy, but I do have a DVM and I am measuring my output power with an ATU-100 that usually works well as a meter. I have checked the voltage between L4 and Q6, I'm getting between 1V and 3V on key down. Nothing seem to get warm on key-down also. For my power supply I am using a 12V, 3Ah Liion battery as I don't have a proper power supply. I've also tried with a 9V battery as the transceiver is supposed to work on that voltage too but I have the same result. The thing I don't understand is that I have the same fault avec totally rewinding all the toroids. Thank you for your help, I hope I can solve this case one day ahah. 73. |
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howard winwood G4GPF
What prompted you to rewind the toroids?
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Amaury - F4IKG
The first time I wound them, they were to spread out, so I just redid it so they would be tighter this time.
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On Thu, Mar 3, 2022 at 11:51 AM, Amaury - F4IKG wrote:
I have checked the voltage between L4 and Q6, I'm getting between 1V and 3V on key down.OK, that's definitely bad: we need to find out why. (Note for the other fault-finders here: my plan is to work on the droop first, and in doing so finding out if the cause of the droop and the lower power are related. We know that the 20m usually needs a couple of turns taken off L3, but I want to make sure the basic circuit is good first. So Amaury, can you do Roger's suggested check to make sure your 12V (nominal) supply stays good during key down? If the L4/Q6 node is drooping, we should first check the incoming supply on the board. You could check at the regulator input terminal first, but if that is good then the next point would be the Q6/R41 node if you can find it and reach it. Again, please test both key down and key up. If the 12V supply stays good during key-down, but L4/Q6 droops to 1 to 3V, then the next point to check is the Q6/R42 node and the Q4/R42 node. They should go down to almost zero volts on key-down. Lastly, if you have a means to measure DC current change between key-up and key-down, that would be helpful. -- Julian, N4JO. |
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