[hpsdr] Janus Alpha #2

[Lyle Johnson]

> I note that there are seven parts that are still TBD - C66, C72, R13,
> R14, R27, R35, and R36. When are these to become D

During Alpha testing.

>, how and by whom?

I suspect Phil H will be taking the lead.

Four of the parts (R35, R36, C66, C72) are the PWM filter, they'll be 
pretty easy to quantify.  If this output is going to be used for IF 
(e.g., the lowest frequency is likely to be on the order of 8 kHz or so, 
the RC constant would be about ((10 * 1)/8 kHz =) 1.25 msec.  With 0.1 
uF caps, this would imply a series resistance of 12.5K; a resistance 
value in the range of 10K to 20K ought to be fine to start with.

If it is to be used for audio, then you'd want maybe 1 uF and 100K at 
least, and a time constant even slower would be better.

Two of the parts (R13 and R14) are only used if you need to reduce the 
gain of the input amplifiers.  They are otherwise bypassed by JP3 and 
JP4, and coul otherwise be replaced with 0-ohm jumpers, I suspect.

The final part, R27, is the mic bias resistor, and its value probably 
depends on your microphone. It is for electret mics, so the value is 
probably not to critical.  I'd suggest putting a 4.7K resistor in that 
position and testing it.  I may be that 10K is better, or that 3.3K is OK.

73,

Lyle KK7P


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