[evlatests] Antenna 14 FRM interference

[Dan Mertely]

Hi Frank.  Thanks for the investigation.

I'm a bit confused.  In the AC14_FRM_on.ps plot the strong (RFI?)
signals at 54.75 &  77.4 MHz are > 100.  On the AC14_FRM_on_zoom.ps
plot the same signals are < 20.  Shouldn't they be the same amplitude
& just go off the scale (since you zoomed in on the vertical scale)?

We are familiar with the problem and probable cause.  One (very
temporary) solution is to set-up the scripts to (or to have the Op
manually) turn off the FRM during the data collection portion of
observing.  This would only be for the purpose of allowing 4m
testing to continue until the problem is fixed.  Is that possible?
-Mert





On 6/2/2016 4:31 PM, Frank Schinzel wrote:
> Hi everyone,
>
> We did today a test today to verify the extend of the FRM interference
> from antenna 14 at 4 band. We observed Cas A at low elevation with the
> antennas facing West. We did one 5 min scan with the FRM off and another
> one with the FRM on. The interference clearly shows up. What surprised
> me the most is that cross-correlation products in IF6 show this as
> correlated interference present across the entire B array (see attached
> config.pdf).
>
> For your enjoyment I have made comparison plots across the band for XY
> auto-correlations of antenna 14 (AC14_FRM_off.pdf, AC14_FRM_on.pdf, and
> AC14_FRM_on_zoom.pdf).
>
> I also added an example of two cross-correlation plots with FRM on and
> off just showing IF6 XY (XC_FRM_off.ps and XC_FRM_on.ps). Those are for
> two baselines one between 14 and the neighboring antenna 23 and one
> where I didn't see strong interference in the cross-correlation between
> antennas 14 and 22.
>
> It would be great if we could address this issue in the near future
> before we take some more 4-band data.
>
>       Frank
>
>
> _______________________________________________
> evlatests mailing list
> evlatests at listmgr.nrao.edu
> https://listmgr.nrao.edu/mailman/listinfo/evlatests
>