[hpsdr] Questions re internal and external LPF on Penelope, Penny Lane and Hermes

[John Marvin]

  So I tried the experiment, and it appears that you can use the two 
receiver version of PowerSDR to do this.  I'm not sure I was doing 
everything right, and I only tested at one point in each band, but it 
appears that the harmonics (I only checked up to the 5th harmonic) were 
always at least 50 db down, and in many cases significantly less than 
that. I'll probably explore this in more detail in the coming weeks.

John

On 11/7/2012 3:20 PM, John Marvin wrote:
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>
> Kjell,
>
> Wow, no need to be sorry! Thanks so much for looking into this 
> further. It would seem that with the right software one could actually 
> do the measurements on a single hermes with the transmit output 
> connected to the receiver (with the 20db attenuator enabled). As 
> already mentioned in the VNA setup documentation, it might be better 
> to use a 6db external attenuator when connecting output to input, not 
> so much for the attenuation but to ensure that a proper impedance is 
> seen by the transmitter.
>
> I haven't played with the two receiver mode of PowerSDR. What does it 
> do when transmitting? Is the second receiver still enabled during 
> transmit (I seem to remember that on older versions of PowerSDR the 
> main window switched to a transmit view while transmitting). 
> Potentially you could send the two-tone test and use the second 
> receiver to move around the spectrum looking at the various possible 
> harmonics. But there may be something that prevents that since I 
> haven't tried it. I'll look into that tonight. Since PowerSDR doesn't 
> support the wide bandwidth view I would likely miss anything non 
> harmonically related.
>
> Of course, using Hermes to measure itself could have a variety of 
> issues, so that such measurements may not be completely trustworthy. 
> But it still seems like an interesting exercise to me, given that I 
> have no other way of doing such a measurement.
>
> Thanks,
>
> John


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