Re: 20 meter QCX-- 1/2 watt output

Alan G4ZFQ
 

Input voltage is 10V, current draw is 108mA receive, 240mA key down.
Michael,

Going back to your first post.
10V is not going to give so much power, but more than 0.5W. Possibly 2W but your current increase of ~130mA is not enough for that.

The output of the next NAND gate, on Pin 3 is a 3.3V square wave on key-down--it should be a 5V square wave.
If you are absolutely certain of this then is pin 14 5V?
I guess it is possible a faulty BS170 could cause this to be low. Check pin 6, this should be 5V square wave.

The next step is to check the drain voltage on Q1-3: it was 15.5V.
Presumably RF?

The power output at L1, using the onboard power meter: .55 watts.
Power at the BS170 drains: 5.2 watts.
Note that power readings will be nothing like correct except at the output. If all the extra TX current is converted to RF that is ~130mA @ 10V =1.3 Watts.

The usual remedy is to reduce LPF coil turns first. But is the PA working correctly?

As Andrew says in a few cases certain capacitors in the LPF have been found faulty. But not all, look back if you really decide any need changing, you will not need to change them all. The normal symptoms have been an increase in power on key down but you are running at low input voltage so that would be more difficult to notice.


The suggestion at this point is that the fault is in the low pass filter. ("If you see power output at the BS170 drains, but not at the overall transceiver RF output, then this means the fault likes in the Low Pas Filter. Check the soldering and the enamel situation on those toroids.", p 131).I measured the continuity of the toroids. It was good. I double-checked the values of the filter capacitors (C25 and 26, C27 and 28); they were correct. The coils had the right number of turns.

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