[hpsdr] Further Information: Help Needed: PowerSDR TX FrequencyInaccuracy

Joe Martin K5SO k5so at valornet.com
Sat Jan 12 10:34:13 PST 2013

…when I mention 3.530 000 in my previous post I mean 3.530 000 MHz.  And, the measurements I made this morning for this test used Hermes running the latest Hermes_v2.2 firmware and Doug W5WC's latest RX2 PowerSDR software. 

73,  Joe K5SO

On Jan 12, 2013, at 11:28 AM, Joe Martin K5SO wrote:

> ***** High Performance Software Defined Radio Discussion List *****
> Hi Tokio, 
> The absolute frequency accuracy issue has been discussed here previously.  As Dave mentioned, the finite size CORDIC steps in the firmware necessarily result in less-than-perfect frequency output for some frequency selections and this is highly dependent upon the exact frequency specified.  Some frequencies are essentially perfect whereas others suffer somewhat, just as you indicate.  However, I have never found any frequency more than 1Hz off here, with most frequency selections yielding errors of less than a few tens of milli-Hertz absolute error.  
> The specific frequency of 3.530 000 you mention yields only a -0.000 000 030 MHz error (-30 milli-Hertz error) here on my system when running with a Rb-vapor frequency standard into the 10 MHz ext 10MHz clock port on Hermes (and properly selected via J20 on Hermes, of course!), as measured using an HP-5345A counter locked to a second Rb-vapor frequency standard.  
> If, on the other hand I do not use the ext 10 MHz input ref clock but use the on board 10 MHz osc on Hermes, I observe a +2.903 Hz error at 3.530 000 Tx; not surprisingly, certainly.  
> I don't observe any unreasonalble/unexpected behavior at all with frequency accuracy here.  
> 73,  Joe K5SO
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