[evlatests] L-Band Frequencies

[Dan Mertely]

A few extra notes & comments on Rick's overview:

One of the "narrow slots" between 1524 MHz (the low end of
the INMARSAT downlink band) and 1640 MHz (13 MHz above the
IRIDIUM downlink band) mentioned by Rick is actually quite
clear most of the time, and important for OH- observing:
The frequency region from the top of the GLONASS top channel
(#06 @ 1605.375 MHz) up to the bottom end of the IRIDIUM
downlink band (currently 1618 MHz, but occasionally 1616 MHz
during emergencies) is generally clear, except for GLONASS
sideband splatter during near approaches to our main beam.
During those occasional near main beam "hits" our monitor
detects sidebands extending up to the OH- line at 1612.231
MHz, but only once or twice per day, and only for a few minutes
at a time.

I concur with Rick about problems with the high end allocation.
Over the past couple of years we have been watching the increasing
RFI between 1930 & 1990 MHz from PCS cell phone base stations
along I25 & from Albuquerque (T-Mobile, AT&T, Sprint).  Although
no "local" PCS (1.9 GHz) cell services exist along the US60
corridor, the bleed-over from the noisy valley is getting bad.
Since there is currently no PCS service along US60, the hand-held
uplink band of 1850.0–1910.0 MHz is still rather quiet.

The RFI seen in the 1683 - 1698 MHz region is due to GOES and
PEOS weather satellite image downlinks.  They are intermittent,
and seen (to the sensitivity of our non-integrated, 35 deg K L-band
monitor) around 3-4 times a day, for 1-2 hours at a time.  As
future generations of meteorological satellites are brought into
operation (GOES-R), the duty cycle of the downlinks will become
greater.  1670-1680 MHz should continue to be used for about 2
hours twice daily as airport around the world launch weather
balloons with L-band temperature transponders.  These launches
are @ 0000 and 1200 UTC.

-Mert







Rick Perley wrote:
>     All:
> 
>     I've reviewed the L-band RFI spectrum, using the high-resolution, 
> full-band spectra produced during WIDAR0 testing.  Some results and 
> recommendations:
> 
>     A)  'Low' end:  The satellite RFI begins abruptly at 1524 MHz -- 
> from there until 1640 MHz, essentially all is lost (except for a few 
> narrow slots).   There are strong emitters (as many of you have found) 
> from 1244 to about 1260 MHz, which lies within the current low default 
> setting.
>     I recommend that for the adjacent low-end tunings we move the 
> defaults up by about 20 MHz -- i.e. to center at/near 1328 and 1456 
> MHz.  This puts the lower edge of the lower subband at 1264 MHz, and the 
> upper edge of the upper subband to 1520 MHz.  This will avoid the worst 
> of the signals, but still leaves in the ABQ radars, and the GPS L3 link 
> (which is very occasional, so not a big issue).  Not perfect -- but hey, 
> it's a rough neighborhood...
> 
>     B) 'High' end:   I learn with surprise that for the adjacent high 
> frequency pair we have selected centers at 1820 and 1948 MHz.  A bad 
> decision, for which I take full responsibility.  The problem is that 
> between 1930 and about 1980 MHz lies a multitude of emission, which I 
> think are from cell phones. 
>     I recommend, for this pair, center frequencies of 1860 and 1732 
> MHz.  This will avoid the cell communications, but overlaps some RFI at 
> 1680 MHz (strong) and 1690 MHz (weak).  However, as I believe these are 
> due to meteorological broadcasts, perhaps there is hope these are 
> intermittent?  Perhaps Dan Mertely can shed light on this...
> 
>     C) There is no need to change the current 'separated' pair 
> frequencies (1436 MHz and 1810 (?) MHz) -- these lies in quite safe zones. 
> 
>     Rick
> _______________________________________________
> evlatests mailing list
> evlatests at listmgr.cv.nrao.edu
> http://listmgr.cv.nrao.edu/mailman/listinfo/evlatests