[AMRadio] Transformer help

[Donald Chester]

>From: Gary Schafer <gschafer at mediaone.net>
>

>I wonder if you have ever looked at your hv supply voltage with a scope 
>when
>keying the transmitter on cw? That would be a vary wide swing in load 
>current.
>According to Rich Measures you get a momentary dip in the output (then it 
>comes
>back up) when applying the load. (poor transient response because of the 
>choke)
>There must be some critical value of filter cap needed to compensate.
>
>73
>Gary  K4FMX

Gary,

I check my cw waveform on the monitor scope.  I once tried reducing my 
filter capacitance from 30 mfd to 6 mfd to see what happened.  The waveform 
looked atrocious (however you spell that - translate: it looked like shit).  
I looked at an article on power sppplies from the old GE Ham News.  Their 
scope pattern looked exactly like mine.  With 30 mfd, I get a much better 
pattern (not perfect).  I tried 100 mfd, and it looked almost perfect, but I 
had to pre-charge the capacitor to keep from blowing a fuse whenever I 
turned on the power supply.  With some kind of step-start I could use that 
much capacitance and get a near-perfect pattern, but the degradation at 30 
mfd is not enough to worry about.

With plate modulated AM, if you use a separate power supply for the 
modulator, you have exactly the same situation that you have with SSB or CW. 
You need to increase the capacitance until the time  constant is 
considerably below the syllabic rate or cw keying rate.  With the low values 
of capacitance (1-6 mfd) the time constant is about the s ame the syllabic 
rate on voice and keying rate on cw, and the voltage bounces all over the 
place, even though the meters show good regulation.  The best indication, of 
course, is to put the scope right on the power supply output and what what 
happens to the voltage.  You can see the same effect by monitoring  the 
envelope pattern of the signal on cw.

Don K4KYV

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