Re: Unexpected measurements

Peter Russell <peter.russell@...>
 

My power supply is home brew 5A with a big capacitor and a LM338.
I've done a bit more work and It seems that the problem was the factory setting of the drive preset.
I've just acquired a rather nice oscilloscope - OWON DS7102 - so I put it to use measuring the voltage at the output bnc connector (into 50 ohms).
Not having used a 'scope for about 20 years, I fell into the obvious trap of measuring the peak - peak voltages and calculating from that! Oh dear, I really should have known better.
Anyway, once I realised my mistake and did it properly, that led me to adjusting the drive level. I've now got it to a point where all bands are happy ( except top band, but who cares about that).
Measured values are now .....

3.5Mhz 6.05W
5 1.88
7 2.4
10 5
14 4
18 1.7
21 5
24 1.03
28 0.85

5Mhz and 21Mhz are a bit of a puzzle, but I'll delve a bit further and see what the drive levels are like.(Could this be a filter thing? I'm not sure what the bandpass filters are tuned to.)

Back to the workbench!

Peter G8FWY


On 17/01/2019 17:14, Curt via Groups.Io wrote:
I agree this seems weird.  You did not mention the type of power supply used nor its current, but perhaps its a good low noise supply used with your other rigs?
Of course to make more power, which is typical at lower frequencies, it must draw more DC current (and dissipate a bit less in heat perhaps).  I have no issues using my uBITX on 160m, into a dummy load or my decently matched vertical with a 3 amp supply made for ham radio use.
I would definitely checking the wiring for both RF and audio interfaces.  Make sure you don't have the ground connection on the board connected to the center pin of the antenna connector.  Please note there are 2 power supply connections - one is segregated to feed only the PAs - of course both need to be connected to your power supply.  I would look to see that audio ground is going to the expected place on the headphone jack.  Use very light audio gain for your testing, maybe 5 or 10% of the volume control should produce headphone audio of the sidetone.
The only other thing I can think of for buzzing is to inspect for any broken or missing capacitors.
As I write doing my own debug - its part of the journey.
Curt WB8YYY
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