[Fwd: LF: Frequency stability]

Andre' Kesteloot akestelo@bellatlantic.net
Sat, 30 Jan 1999 17:24:41 -0500

M. Bruno wrote:

> At 08.15 31/01/99 +1300, Bob ZL2CA wrote:
> >
> >Which perhaps raises another matter .....   How good is the "timebase"
> >in each of the PC based spectrum displays?  Each must rely on some
> >internal oscillator or bus data for reference, and it is probably an
> >oscillator with other than a tight specification.  I have used GRAM
> >(uses a SB card) for some audio checks, and it seems to be agreeably
> >"correct" from a general point of view, but I do not know the actual
> >tolerance.  No doubt there are readers who can fill in the gaps on this
> >....
> >
> >Bob ZL2CA
> >
> Hello Bob,
> the audio board may have it's internal clock or use the bus clock at 14.318
> kHz.
> Both should be within about 50 ppm, that is, the tolerance of a commercial
> crystal. The error will only affect the sampling rate of the board, and
> since we use it to process audio signals, the error is 50 ppm at your beat
> frequency. If you use a BFO at 800 Hz the error may be +/- 0.04 Hz or so.
> The main frequency error source is the LO in the receiver. Suppose that the RX
> has a first IF at 40 MHz. Then 1 ppm error is a 40 Hz shift. If the second
> LO is derived from the same reference that may largely cancel out. It all
> depends from the conversion scheme / LO generation in your RX.
> 73 - Marco
> Marco Bruno - IK1ODO
> spin@inrete.it
> SPIN Electronics - www.spin-it.com