[evlatests] ea28 reflection

[Ken Sowinski]

On Thu, 10 Oct 2019, Rick Perley via evlatests wrote:

>     A short test was run yesterday, to check the status of the strong 
> reflection on ea28, on the RCP side.  The reflection is there, although 
> perhaps not as bad as during some of my recent observations.
>
>     Attached are three .eps bandpass plots, showing the severity of the 
> problem.  The spectral resolution is 500 kHz.  Ringing, with a period of 10 
> ch = 5 MHz, is seen in all spectral windows, although the effect is much 
> reduced in the highest frequencies. this frequency corresponds to a 
> (free-space) distance between reflection points of 30 meters.
>
>     Plot 1 shows the lower eight spectral windows, plot 2 the upper eight, 
> and plot 3 is spw11 alone (this is the SPW with the strongest effect).
>
>     No other antenna shows anything close to this.  For those interested, I 
> can provide plots for any, or all, other antenna.
>
>     Because this high frequency ringing is highly time variable, these 
> oscillations cannot be easily calibrated out (likely, not at all).  My 
> opinion is that this problem needs to be adequately addressed, or the 
> monitor should be disconnected.

A reminder, mostly for Dan, that this effect is easily seen in
autocorrelation and so can be looked at in real time.  When we
last poked at this a few years ago it was easy to see the changes
as Dan fiddled with components at the antenna.

Ken