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

[Rick Perley]

    Dan:

    Thanks for this. 
    We don't see the links to/from Magdalena, but the others are all 
easily visible, including the Datil/Bagley to Grey Hill at 6775 MHz 
(this one is rather weaker, so I didn't include it in my list sent 
yesterday ...). 

    This information needs to be put where users can easily see it. 

    Rick

Dan Mertely wrote:
> 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.
>>    _______________________________________________
>> evlatests mailing list
>> evlatests at listmgr.cv.nrao.edu
>> http://listmgr.cv.nrao.edu/mailman/listinfo/evlatests