rdr harmonics in galspec spectrometer

28mar11

Sections:

29nov09:Galspec rfi during basketweaving.
28mar11: dynamic spectra of galspec and mock spectrometers while sitting.
28mar11: aligning galspec rfi with the radars.
Table of radar 1st lo intermods when rfCfr=1375
Table of galspec 2nd lo intermods from radars when 2nd lo = 188.97
Summary.

PLOTS:

Galspec rfi 29nov09.. basketweaving

Galspect users (using alfa) have reported rfi that was fixed in declination (za) while nodding in za at the meridian (basketweaving).
An example is seen in dynamic spectra taken on 29nov09 (file:galfa.20091129.a2124.0014.fits).

The img is made from beam 5, polB.
The azimuth was at 360 degrees (looking south) while the dome moves from 6.5 to 19.6 deg za (for this file).
dynamic spectra time vs frequency (.gif)
dynamic spectra Za vs frequency (.gif)
The rfi of interest is

1419.0 to 1419.2
1422.0 to 1422.2
It has a 12 second periodicity --> it's from a radar
It is stronger in polB and is in all beams.
there are places in za where the 1422.2 rfi remains visible for an entire 12 second rotation.

za=14.3. This is a dec of about 4.degrees.
The rfi appears continuous at dec=4 since the rfi is always present when we pass that za.
For other za's the radar will appear only if the radar is pointing at AO at that instant of time.

The 200 KHz width matches the bandwidth of the 1270,1290 remy radar as well as the 1330,1350 faa Radar.

There is also rfi at:1417.9 and 1422.7.

this only appears in beam 5
It is not symmetric about Dc

28mar11: rfi sitting at za=6.4 degrees.

On 28mar11 data was taken with the galspect spectrometer as well as the mock spectrometers using alfa.
The setup was:

Telescope:

Sitting at az=360,za= 6.4 deg (dec=11.9 deg)

alfa:

1375 MHz center frequency mixed down to 250 MHz.

galspec:

lo2: 188.97 MHz, digital mix: -15.625 MHz

Mock:

2 172 MHz bands each with 8192 channels. Centered at 1300 and 1450 MHz.
spectra sampled every .1 seconds

Dynamic spectra were made (time vs freq) from the galspec and mock data:

The data was aligned to cover the same time period.
Dynamic spectra from galspec (.gif)

The 1419.1 and 1422 MHz radar rfi is visible
1420.6 looks to have occasion rfi that is probably radar based.

Looking carefully you can also see it in the mock 1450 band.

There is also something at 1420.8 drifting to lower freq.

Dynamic spectra from mock 1300MHz band (.gif)

this shows all of the radars:

1330, 1350: faa radar
1270: remy radar.
1246,1262 : aerostat radar. Looks like it started to turn off towards the end of the scan.
1232,1242,1247,1257: punta salinas radar (in modeA)
the mocks use complex sampling so there are images of the radars symmetric about DC (1300 MHz).

1330 and 1270 are equidistant about DC so the have images on each other.

There are intermods that show up from the radars (1360,1372,1375,1392..)

Dynamic spectra from mock 1450 MHz band (.gif)

There are a few radar intermods (1375, 1475,1480, and maybe 1420.5)
The 1419.1 rfi that galspect sees is not visible.
The radar rfi close to 1420 is visible.

Aligning galspect rfi with the radar pulses:

The radar Tp vs time shows where the 1319,1422 rfi comes from (.ps) (.pdf):

The frequency channels covered by the radars were averaged as well as the 1419.1, 1422 rfi from galspec.
The data was plotted vs time to align the plots.
TOP: Radar power vs time:

black,red : aerostat 1246,1261.

you can see where the aerostat blanks in the AO and Airport directions.

Green:Remy 1270 radar
blue,purple: FAA 1330,1350 radar.

A dotted purple line is drawn at the FAA peaks.

Bottom: galspec 1419.1 (black) and 1422.0 (red) rfi

The dashed purple line shows the FAA radar peaks
The 1419.1 and 1422 galspect rfi align with the FAA radar.

Where the rfi comes from:

The idl routine intermods.pro was used to compute where the intermods for all of the radars landed in the
galspect band assuming:

1st lo mixes 1375 to 250Mhz (1st IF)
2nd lo = 188.97 complex mixes 1436.03 to DC

The tables show:

intermods created by the first mixer
intermods created by the 2nd mixer when 2nd lo set to 188.97

ALFA CFR=1375 Radar Intermods with 1st mixer
Radar	Radar Freq	order 1st Lo	order RdrFreq	IF Freq	Sky Freq
Punta Salinas	1232.6	4	5	337.0	1288.0
		6	8	110.8	1514.2
		7	9	281.6	1343.4
	1241.7	4	5	291.5	1333.5
		6	8	183.6	1441.4
		7	9	199.7	1425.3
	1247.6	3	4	115.4	1509.6
		4	5	262.0	1363.0
		6	8	230.8	1394.2
		7	9	146.6	1478.4
	1256.7	3	4	151.8	1473.2
		4	5	216.5	1408.5
		6	8	303.6	1321.4
Aerostat	1241.7	4	5	291.5	1333.5
		6	8	183.6	1441.4
		7	9	199.7	1425.3
	1246.2	3	4	109.8	1515.2
		4	5	269.0	1356.0
		6	8	219.6	1405.4
		7	9	159.2	1465.8
	1256.7	3	4	151.8	1473.2
		4	5	216.5	1408.5
		6	8	303.6	1321.4
	1261.2	3	4	170.0	1455.0
		4	5	193.8	1431.2
		6	8	340.0	1285.0
		8	10	387.5	1237.5
Remy	1270.0	3	4	205.0	1420.0
		4	5	150.0	1475.0
		8	10	300.0	1325.0
	1290.0	3	4	285.0	1340.0
		5	6	385.0	1240.0
		7	9	235.0	1390.0
		8	10	100.0	1525.0
FAA	1330.0	4	5	150.0	1475.0
		5	6	145.0	1480.0
		8	10	300.0	1325.0
	1350.0	4	5	250.0	1375.0
	1350.0	6	7	300.0	1325.0

Intermods created in the 2nd mixer:

ALFA CFR=1375 Radar Intermods 2ndmixer. Band=1314.0 (189 IF)
Radar	Radar Freq	IF Freq	order 2ndLo	order Radar	baseband Freq	skyFreq +	skyFreq -
Punta Salinas	1232.60	392.40	2	1	-14.5	1450.5	1421.6
			4	2	-28.9	1465.0	1407.1
			6	3	-43.4	1479.4	1392.7
	1241.70	383.30	2	1	-5.4	1441.4	1430.7
			4	2	-10.7	1446.8	1425.3
			6	3	-16.1	1452.1	1419.9
			8	4	-21.4	1457.5	1414.6
			10	5	-26.8	1462.8	1409.2
	1247.60	377.40	2	1	0.5	1435.5	1436.6
			4	2	1.1	1435.0	1437.1
			6	3	1.6	1434.4	1437.7
			8	4	2.2	1433.9	1438.2
			10	5	2.7	1433.3	1438.7
	1256.70	368.30	2	1	9.6	1426.4	1445.7
			4	2	19.3	1416.8	1455.3
			6	3	28.9	1407.1	1464.9
			8	4	38.6	1397.5	1474.6
			10	5	48.2	1387.8	1484.2
Aerostat	1241.70	383.30	2	1	-5.4	1441.4	1430.7
			4	2	-10.7	1446.8	1425.3
			6	3	-16.1	1452.1	1419.9
			8	4	-21.4	1457.5	1414.6
			10	5	-26.8	1462.8	1409.2
	1246.20	378.80	2	1	-0.9	1436.9	1435.2
			4	2	-1.7	1437.8	1434.3
			6	3	-2.6	1438.6	1433.4
			8	4	-3.4	1439.5	1432.6
			10	5	-4.3	1440.3	1431.7
	1256.70	368.30	2	1	9.6	1426.4	1445.7
			4	2	19.3	1416.8	1455.3
			6	3	28.9	1407.1	1464.9
			8	4	38.6	1397.5	1474.6
			10	5	48.2	1387.8	1484.2
	1261.25	363.75	2	1	14.2	1421.8	1450.2
			4	2	28.4	1407.7	1464.4
			6	3	42.6	1393.5	1478.6
Remy	1270.00	355.00	2	1	22.9	1413.1	1459.0
	1270.00	355.00	4	2	45.9	1390.2	1481.9
	1290.00	335.00	2	1	42.9	1393.1	1479.0
			7	4	-17.2	1453.2	1418.8
			9	5	25.7	1410.3	1461.8
FAA	1330.00	295.00	3	2	-23.1	1459.1	1412.9
			6	4	-46.2	1482.2	1389.9
			8	5	36.8	1399.3	1472.8
	1350.00	275.00	3	2	16.9	1419.1	1452.9
			6	4	33.8	1402.2	1469.9
			10	7	-35.3	1471.3	1400.7

SUMMARY:

galspect sees FAA radar intermods at 1419.1 and 1422 from the 2nd mixing stage.

the 2nd lo was set to 188.97

The mock spectrometer does not see these intermods since they are generated in galspects 2nd lo.

1419.1 is 2*275(IF of 1350rdr) - 3*188.97 (2ndlo)

I'm not sure how the 1422 rfi is generated from the FAA radar frequencies.

The rfi Appears at a constant dec in the final maps.

there are certain zenith angles were the radar is strong enough to be present for an entire 12 second radar rotation. This guarantees that it will be present in any scan that passes through this za.
At other za's, the rfi is only present if the radar points at AO while the dome passes that za. Averaging multiple scans will then smear the rfi out at these za's.

The first mixing stage contributes radar rfi at:

1270 radar --> 3*1625 - 4*1270 -> 205. This is 1420 On the sky.

changing the 2nd lo moved the 1419,1422 intermods out of the band.
on 30mar11 the galfa users moved the 2nd lo to 195.22. This moved these two rfi's out of the band.

A strong radar rfi was visible at 1420.6 Mhz
Looking with the spectrum analzyer, the remy 1270 radar was actually at 1269.84 Mhz so the 1420.0 intermod should show up at 1420.6.. This is coming from the 1st mixer. It is seen in the mocks and the galspect data.exit

processing: x101/110328/galfarfi.pro, galfarfi_2009.pro

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