[evlatests] ea28 reflection

[Dan Mertely]

OK.  Thanks Rick.  As a result of your test results I disconnected
the W8mon tap today (Thursday, 10 October) at around 4 PM MDT.

I left the -10 dB directional coupler in-line with the RCP output
of the L-band FE, but disconnected the W8mon amp & coax.  I then
terminated the directional coupler tap with a commercial quality
50 Ohm RF load.  (I didn't remove the directional coupler for
fear of messing with delays.)

I think I will try using a -30 dB directional coupler + a high-
isolation amp next time.  TBD.
-Mert

On 10/10/2019 9:43 AM, 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.
> 
>      Rick
> 
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