[evlatests] ea28 reflection

[Ephraim Ford]

We also discussed rebuilding the cable run as it is showing its age and could likely be rebuilt more consistently, too.

-----Original Message-----
From: evlatests <evlatests-bounces at listmgr.nrao.edu> On Behalf Of Dan Mertely via evlatests
Sent: Thursday, October 10, 2019 4:16 PM
To: evlatests at listmgr.nrao.edu; Tyler Mobraten <tmobrate at nrao.edu>; Dan Mertely <dmertely at nrao.edu>
Subject: Re: [evlatests] ea28 reflection

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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