[evlatests] Serious C-Band RFI: Gray Hill C-band table

[Dan Mertely]

Hi Rick.  Here in one place is a list of the C-band
microwave data links into and out of the Gray Hill
electronic transmitter site (just off of the east arm,
north of E64/EA8):

Gray Hill to  Magdalena-1 = 6345.490 +/-30 MHz @ +66.8 dBm
Magdalena to  Gray Hill-1 = 6093.450 +/-30 MHz @ +66.7 dBm

Gray Hill to  Magdalena-2 = 6315.840 +/-30 MHz @ +66.8 dBm
Magdalena to  Gray Hill-2 = 6063.800 +/-30 MHz @ +66.8 dBm

Gray hill to Mangus Mtn-1 = 6375.140 +/-30 MHz @ +69.3 dBm
Mangus Mtn to Gray Hill-1 = 6123.100 +/-30 MHz @ +69.2 dBm

Gray hill to Mangus Mtn-2 = 6404.790 +/-30 MHz @ +69.3 dBm
Mangus Mtn to Gray Hill-2 = 6152.750 +/-30 MHz @ +69.2 dBm

Gray hill to Datil/Bagley = 6615.000 +/-5  MHz @ +64.4 dBm
Datil/Bagley to Gray hill = 6775.000 +/-5  MHz @ +64.4 dBm


This generates the following frequency map for C-band data
in-to and out-of the Gray Hill Electronic site:

IN:
MG2GH2:   MG2GH1:   MM2GH1:   MM2GH2:            DB2GH:
6048-6078 6078-6108 6108-6138 6138-6168          6612-6618

OUT:
GH2MG2:   GH2MG1:   GH2MM1:   GH2MM2:            GH2DB:
6301-6331 6330-6360 6360-6390 6390-6420          6772-6778


Of those, the RFI table at:
https://science.nrao.edu/facilities/evla/observing/RFI/C-Band
highlights those thought to be most detrimental to EVLA observing.
I'll probably put them all in there eventually.

-Mert


Rick Perley wrote:
>     The new 'spectral sweep' of our entire 1 -- 50 GHz has emphasized 
> the challenge we have before us to operate in S and C bands. 
> 
>     In S-band, the problems have not changed:  Two extremely strong 
> interferors, spanning 2180 -- 2200 MHz, and 2310 -- 2360 (this is 
> Digital Satellite Radio).  The spectral densities (in 125 kHz 
> resolution) are typically 40 dB above the noise floor.   The power from 
> these signals completely  dominates the total system power.   Rob Long 
> has today inserted stop band filters into two antennas to test if these 
> give sufficient isolation while preserving the rest of the band for 
> science. 
> 
>     In C-band, a new RFI signal has appeared, and it is strong.  Between 
> 6.0 and 6.7 there are three quite strong interfering signals -- I 
> believe all three are microwave links running overtop the VLA):  6.11 -- 
> 6.17 GHz, 6.36 -- 6.42 GHz, and 6.612 -- 6.618 GHz.  The spectral 
> densities within these are 15, 25, and 25 dB above the noise floor.  
> Integrated together, these three contribute a power about 12 times (11 
> dB) above the noise power within the 2 GHz IF..  The middle one of these 
> (6.36 -- 6.42) is the new one -- it was absent last spring, but present 
> last September. 
>     We were pointed at the NCP during this test -- perhaps the signals 
> are weaker in other directions, but nonetheless, we have a serious 
> problem for wideband observing in C-band.  The 3-bit samplers are not up 
> to the task of handling such strong signals (2 bits are needed just to 
> span the RFI power).   We're going to have to think seriously about 
> using more than 3 bits if we are to cover the entire span of C-band. 
> 
>    
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