[hpsdr] Pennywhistle completed at last

[Chris Smith]

Hi John & Phil

I've spent a rather sleepless night thinking about this problem and have 
fired up the computer early (0500) to see what has been said.

Thanks for your valuable input. While lying awake I realised a) that the 
o/p transformer misconfiguration loss is 2dB not the figure I originally 
quoted and b) I was worried that Penelope would be only using a few bits 
of the D/A to produce full output. I have to admit that I hadn't thought 
of this in terms of a degradation in S/N ratio.

I reckon the easiest, long-term solution is to make use of the input 
attenuator pads on Pennywhistle and seriously under-run it. I only need 
50mW at the input of PW for 100W out of the AN762. So I calculate that I 
need an 8dB attenuator and leave the o/p transformer alone or a 10dB 
attenuator and correct the o/p transformer. This way Penelope will be 
pushing out  in the region of 300+ mW and I've got some head-room in the 
amplifier chain.

Now where was that posting regarding the input attenuator ...

Many thanks again.

73

Chris
G4NUX


On 21 Mar 2010, at 04:43, John Petrich wrote:

> ***** High Performance Software Defined Radio Discussion List *****
> 
> Phil,
> 
> Your comment on Penelope's output S/N ratio got me thinking.
> 
> In your post to Chris, under the "Pennywhistle completed at last" thread you made reference to Penelope's output S/N ratio.  What exactly do you mean "output S/N ratio?  In the CW mode I see a clean coherent signal with no noise pedestal down to at least -70 dBc.  On SSB, I'm guessing, that there is a residual broadband audio noise about -32 dBc or less with the microphone disconnected.  Maybe the S/N ratio that you are talking about is not readily measured using classical spectrum analysis methods?
> 
> In response to your post I added enough input attenuation to my PA such that Penelope is now delivering 300+ MW at the desired PA output level.  Prior to the addition of the attenuation, Penelope was putting out 76 MW for that same PA output.  Haven't really looked at the output spectrum yet.
> 
> A penny for your thoughts,
> John Petrich, W7FU 
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