[evlatests] WIDAR wobbles vs. time, contd.

[Vivek Dhawan]

This is mostly to correct my previous comments - Thanks, Michael.


>> c. The periods do change over an hour, but I see no way to relate them to
>>    the corresponding fringe rate changes.
> 
> By how much do they change?  10s of %, factors of 2, factors of 100?  Do
> wobbles vanish or just move around?

factors of 2 change in period, little change in magnitude.

> 
> 
>> d. There is no differential in the wobble across the band = it is _not_
>>   a delay change = there is no delay jitter associated with the wobbles.
> I'm confused by this plot.
> 
> It looks to me like the blue shows a smaller version of the wobble seen 
> in the red.
> 
> If blue= phase(channels 129-256)-phase(channels 1-128), then this
> means that there *is* a difference between the low and high channels.
> 
> Help!

OK - I guess there is a (much smaller to my eye) delay wobble. but I expect
the delay change in 500ns steps or not at all. This is closer to not at all.
> 
> 
>> e. The noise-diode switching at 9.6Hz is seen at ~few % in the autocor
>>    and is at about 0.1-1% of the cross-correlation amplitude on most
>>    baselines. Assuming 30K Tsys, 3K noise injection, that is ~30Jy, so
>>    the f_shift is suppressing the noise diode by a factor of >100 (1000
>>    on most baselines), else it would be comparable to 3C273.
> 
> I'm confused by this argument (have you noticed that I'm confused a lot? 
> ;).
> Should the noise tube correlated between antennas?  or are you thinking
> leakage of an antenna's noise tube through the sidelobes of its neighbor?
> In either case how do you know how much of any suppression is due to 
> fshift?

Sorry - thus was a bogus argument on my part - the leakage between antennas
is NOT removed by shift at all. This morning's brain thinks I expect a
1% modulation of the noise on each antenna, thus the normalization changes
by about 1%, not the correlation coeff itself. We see 0.2 to 1%; is that
close enough?