# cb az swings, 5ghz rfi  13jan16

#### last updated 15jan16

Azimuth swings were done with the cband  receiver on 13jan16.
The setup was:
• az 270-630 and back at +/- .35deg/sec
• clear weather, data taken in the afternoon
• dome at za=18deg
• mock spectrometer with 7 boxes covered 4200 to 5200 mhz, 150 Mhz spacing
• 172MHz bw, 8192 channels per box
• 1 sec sampling
The data processing for each board
• input the data averaging to 1 second
• average pola and b.
• interpolate az positions to center of data records.
• For dynamic spectra
• compute median band pass, divide this into all spectra
• find rfi free section of band, compute median value  for each spectra and then divide each spectra by these values
• For rfi bands:
• looking at the dynamic spectra:
• find the center and bandwidth of each rfi band
• also find the non-overlapping portion of the rfi band (many rfi bands were overlapping).
• compute the total power in each rfi band using the non-overlapping portion of the rfi band.
• plot this total power vs az for the CW and CCW az swings.

## Dynamic spectra:

The images show the dynamic spectra for the Clockwise (CW)  az swings for the 4950 and 5100 Mhz mock bands.
• 4950 Mhz band azswing (.gif)
• the 20 Mhz bands at 4930 and 4950 have been reported by chris  salter.
• these look like u-nni band transmissions.. which would make them illegal
• 5100 Mhz band azswing (.gif)
• the u-nni band starts at 5150 Mhz. everything below that is illegal.
• You can see that lots of the 20 Mhz rfi's overlap each other in frequency.

## Birdie power vs azimuth.

I also plotted the rfi power vs az position for the non-overlapping portion of each rfi (.ps) (.pdf)
• Each rfi was plotted in a different color with an offset for display purposes
• For each rfi, the CW and CCW az spins were overplotted
• The CW and CCW swings were spaced by at least 20 minutes...
• most of the rfi bands show a repeatable azimuth dependence.
• This means that the rfi is coming from a stationary azimuth direction
•  (not necessarily the azimuth of the peak since the scattering into the dome can be complex).
• Some of the rfi's look to have similar azimuth peaks.. that means they are probably coming from the same tower
• many of the rfi's have unique azimuth peaks.
• I wonder if some of these are coming from people's houses.. which would be spread in azimuth.
The table shows the rfi bands that were found:
Frequencies with common colors, have similar  azimuth dependence

 center Freq bandwidth notes not intermod 4930 20 verified 4950.00 20 verified 4977.50 5 4985.08 10 4995.15 10 5030.00 10 verified 5044.99 20 verified 5065.03 20 verified 5084.43 20 5109.88 20 verified 5124. 20 verified 5149.94 20 verified 5160.02 20

## Are we seeing intermods in our receiver?

Is it possible that some of the separate rfi's we see are being created as intermods in our receiver.
To test this, i took 300 seconds of data (15jan16) with the frequencies shifted..
If these are intermods, then the frequency location of the rfi's will shift as the lo's are shifted:

The setups were:

• data taken 13jan16:
• rf cfr of band: 4650
• individual band centers: 4950, 5100
• az swings 270 to 630 ,za=18deg
• data taken 15jan16
• rf cfr of band: 4630 (shifted down by 20 Mhz)
• individual band centers: 4940, 5090 (shifted down by 10 mhz)
• telescope sitting az=200, za=18 degrees, 300 1 second spectra
the dynamic spectra show the results

After changing the lo's all of the visible rfi's showed up at the same frequency

• The 15jan16 data was at a fixed azimuth, so not all rfi's peaked up...
• The rfi's that were seen at the same frequency are labeled verified in the not intermod column of the table.

## Summary

• The 5 ghz rfi's are not intermods in the system
• The rfi's repeat in azimuth (spaced by  over 20 minutes). So they are coming from a fixed azimuth location (they are not just time variable.
• a number of the rfi's have similar rfi dependence.. these are probably coming from the same towers.
• others have unique azimuth dependence. I wonder if they are coming from internet emanating from peoples houses (the uplink to the tower).

processing: x101/160113/azswing_cbinp.pro, azswing_cbplot.pro, and similar routines in 160115.

rfi measurements home
home_~phil