In message <[email protected]>, Bob Camp writes:
>Do you have any idea how 'clean' your 200 MHz signal is? The manual >suggests getting it to -65 dbc for subs using a spectrum analyzer. That's >pretty far down. I seem to recall the adjustment process being a bit tedious >(lots of back and forth). My estimate is that all harmonics are at least -50 and most probably -60 down. The 10MHz is probably the worst. My Lab is not really set up for RF work, so this is probably an area where one of the hams could do lot more competent job than me. I've attached a plot of one of the runs yesterday, beause things are more complicated than I initially thought. The vertical bars are AVG +/- STDDEV of 1000 sample TI on a 10MHz from my HP3336 in start-com mode. The X-axis is the phase offset set on the HP3336 in degrees, and represents the phase difference between the ext-ref and start+stop signals on the HP5370 plus some arbitrary offset due to cables etc. Obviously, the phase difference has no systematic meaning for the red bars, since it is free running on the OCXO at some frequency offset from the input signal. Yet, it is quite evident that there still is a periodicity in the data, which peaks around 0, 5, 10 and 15 degrees. The green bars however... The initial artifact I noticed when I just plotted the STDDEV is still there, around 9 degrees where both the average and the stddev take a hop. But that blib is peanuts relative to the 3-degree periodicity for which I have absolutely no explanation, and the equally evident 18-degree periodicity. The 3-degree periodicity cannot be a simple harmonic, it it were it would be a 1.2 GHz signal. (360/3 * 10 MHz = 1200 MHz) But what then ? As in a canonical scientific paper, I have to conclude that more research is clearly needed, and I'd really love to see what results other people might get. In the meantime, run you 5370 on internal clock, and rely on the law of big numbers. Poul-Henning -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 [email protected] | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.
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