Rfi list by freq

last mod 25sep08

This is a working list of rfi found at the observatory. It should eventually get merged into the rfi page (when i figure out how to modify it). Each entry in a list has a link to any further info. The dates are when we (me) became aware of the birdie, not when when it first appeared. A birdie in the list means that it was here at one time. It may have gotten fixed (many of the beeper harmonics). It stays in the list in case in pops up again. The status column is filled in for the birdies that i'm sure about. The column being blank reflects my ignorance.

By frequency:

430Mhz birdies
327Mhz birdies
lband birdies
birdies above lband

Combs

327 Mhz birdies

The table below comes mainly from azimuth swings done on 28oct05 (more info). If a birdie varies with azimuth, then it is coming from outside of the dome.

327 birdies (top)

freq

date

stat

Comments

308.352

05oct

This was the strongest signal (1600*Tsys).
It was less then 1 frequency channel wide.
It was time variable in time: on for 1 second (may have been shorter than 1 second).
It repeated every 18.6 seconds.
It was present for the first 55 minutes and then turned off.
It was not causing the set of frequencies that looked like intermods since they continued after it turned off

308.7
309.9
311.07
313.1
314.3
317.5
318.9

05oct

These signals were time variable and got stronger/weaker together.
317.5 was heard to be the FM station 107.3 (on the radio). This may mean that all the others are related to 107.3 (see 321.9/317.5 below).
308.7 is the 3rd harmonic of 102.9. On the whip antenna this is the 2nd strongest fm station (after 107.3).
There may be an out of band birdie that is causing all of this birdies to increase?
The common frequency difference is about 1.2 Mhz.

312.3

05oct

This the 3rd harmonic of 104.1. We heard the radio station when we listened to the 312.3 birdie in the 2nd IF.

321.9
317.5

05oct

321.9 :This is the 3rd harmonic of 107.3 It is the strongest fm station at AO. The music was heard in the IF using the radio.
317.5:

This was heard (with the radio) to be 107.3.
It is 4.4 Mhz below 321.9 Mhz.
4.4 Mhz is the fundamental difference between 107.3 and 102.9. These are the two strongest fm stations.

320.9
328.1

05oct

These came from the alfa motor controller. Turning of the controller made them go away. Look at 28oct05 swing 1. gif at the bottom. The motor controller was on and then turned off around an az of -50.

309.66
317.04
323.18
330.01*
331.78

324.41
325.64

05oct

Birdies coming from the azimuth encoder comb (more info).
They all share the same azimuth dependence (although 324.41 and 325.64 look a little different). The strongest is 324.41 at 1.6 Tsys in a 24 Khz resolution bandwidth.
The encoder comb is spaced at 614.368 Khz (where 1 freq is 320.719). The table below shows the frequencies for the comb in the 327 band. The resolution in the step is probably hz. The resolution in the offset is 10 to 20 Khz (determined by the rbw):

**azimuth enc comb freq in 327 band**
308.431	309.046	309.660	310.275	310.889	311.503	312.118	312.732	313.346	313.961
314.575	315.190	315.804	316.418	317.033	317.647	318.261	318.876	319.490	320.104
320.719	321.333	321.948	322.562	323.176	323.791	324.405	325.019	325.634	326.248
326.863	327.477	328.091	328.706	329.320	329.934	330.549	331.163	331.777	332.392
333.006	333.621	334.235	334.849	335.464	336.078	336.692	337.307	337.921	338.536

319.5

05oct

showed repeateable az dependence. This is the 3rd harmonic of 106.5. It is the 5th strongest fm station on the whip antenna. It is also close to the azimuth encoder comb frquencies.

319.93
320.00
320.06

05oct

Same azimuth dependence.

312.3
312.5
313.99
324.00
325.00
327.51

05oct

These all showed unique azimuth dependence.

**430 MHZ BIRDIES (**top)
FREQ Mhz	BW	DATE	STAT	COMMENTS
408.6145	<.003	oct02		(more info)
410.5249	<.003	oct02	active	Coming from 1000 foot navy tower in aguada.(more info)
410.8118	<.003	oct02		(more info)
418.75 423.5 427.75 432.25 435.75		mar03	fixed jan05	tv chn14,22 intermods moreInfo 2f1Video-f2Audio 2f1Video-f2Video 2f1Audio-f2Audio 2f1Audio-f2Video alias of 423.5 using 12.5 mhz digital filter jan05-low loss filters to notch out tv stations inserted in front of dewar. (moreinfo)
422.72 423.18 423.25 423.46 -- 429.89 430.31 430.38 430.48 -- 432.67	30 Khz	dec05	active	These birdies have 1 minute periods (more info).
424.03 420.096 429.550		aug99		dome camera birdies at 430 mhz when the iflo cabinet door was open. Note seen when the door was closed. (more info)
425-440	6	aug01	radar	Airborne radar. customs or navy. Usage decreased since war games at rosy rodes stopped. Can tune to a 6 mhz band between about 420 to 440 Mhz. Easily seen on the hilltop rfi monitoring plots. (more info)
426.25	lt 12.5 Khz	jun03	active	az swing peaks at -59 az. When this signal was baseband samled, it looked like a phase lock loop that was sweeping back and forth thru its input bandwidth as if it was out of lock. The sweep time took 12 seconds to repeat. moreInfo
429.16 433.32 427.48 430.11 430.49	<.001	aug99		Power meter in dome (429.16,433.32). 433.32 is strongest Multimeter in dome (427,430) They were first placed in the shielded iflo rack in the turret room (birdie_Strength) The power meter and 1 multi meter was then placed in an rfi shielded box within the iflo rack. The 2nd multi meter is still in the iflo rack.(more info)

**LBAND BIRDIES (**top)
FREQ Mhz	BW	DATE	STAT	COMMENTS
1090				secondary surveillance radar (SSR) and air borne collision avoidance systems (ACAS). Seen in hilltop monitoring system.
1215 to 1400 1232/1247 modeA 1241/1256 modeA	1.15 .625	feb00	active radar	Punta salinas frequency hopping radar. 12 sec rotation. short and long pulse lengths: 51.2 and 409.5 usecs. When we request, they will sit in mode A rather than hop thru the entire band. (freqList)
1227.60	tone	apr99		gpsL2 measures ionsphere delay.
1241.75 1244.6 1256.5 1261.25	1.67	jan97	active Radar	Aerostat radar ballon in lajas. dual freq or quad freq modes. 160 usec per pulse, chirped. Rotation rate 11.59 secs. Blanks toward AO. (see aerostat info)
1270/1290	.2	feb02	active Radar	Remy Radar at the end of the runway .(fps20-93a). 12 sec rotation rate, single ipp of 2781. Runs in 1270 or 1290 mode (not simultaneously). (see radar info)
1287.5/1299.84 1300,1399.83 1400 1411.52 1412.5	<.025	jan01 apr02		Distomat birdies. Occur every 2 minutes for a few seconds. Az dependent.Distomats have a 27 Mhz clock. Data was measured in jan01 (before shielding work) Data was remeasured in apr02 (after some shielding work). The window was changed
1330/1350	.2	jan97	active Radar	FAA airport radar.12 sec rotation, 5 ipps about 2.5 ms,5 usec pulse, 1350 then 1330 pulse sent each ipp. (radar info)
1366.2/1382.66 1324/1340 1387.3/1371.0		feb01	Radar	Radars with 1.94 sec rotation rates. ( more info). These radar were probably associated with military ship practices. Fast rotating radars are needed when objects move far within 1 rotation (planes near aircraft carriers,etc..)
1381.05	1	sep91	active	GPS L3 downlink. (more info)
1388.55	.024	98		beeper harmonic (3rd of 462.85)
1388.6	.024	93		beeper harmonic (3rd of 462.875) (borinquen beepers)
1388.858 1417.495	<190 (hz)	may02		dome camera birides. part of a comb of 14.3185 Mhz. (more info).
1390.8	.024	feb93		beeper harmonic (3rd of 463.6 (mr. beeper)
1407	.3	apr01	fixed	tvChan20 arecibo. Drifted around with time. They were having trouble with their transmitter. (more info)
1422.5				tvChan54 2nd harmonic
1525-1545		aug03		Inmarsat stdBC ship,portable earch downlinks Inmarsat stdM ship downlinks
1525-1559		aug03		Inmarsat stdF ship, stdM portable earth downlinks
1530-1559		aug03		Inmarsat airborne downlink
1535.0 -1543.5		aug03		InmarSat stdA downlink. RHC xmitted. 339 channels. chan1=1535.025, chn339=1543.475. chn spacing 25Khz. signal bw 12 Khz. FM modulation. chan110 is call announcments. position tracking carriers at 3947.0 / 3949.4 / 3950.6 /3953.0. Info 06aug03
1575.42	1.			GPS L1
1602+.562n		aug98	active	GLONAS n=1 to 24. shutting down soon?? but leaving n=12,21,22,24??
1621.35-1626.5			active	iridium communications satellites. 66 sat, 6 planes, inclined at 86.4deg to pole. 3*16 beams per sat. 90 millisec rep rate. 8 8.29 ms tdma slot. 4 uplink, 4 downlink. band protect guard time of 22.48 ms interframe guard times:.1ms upl, .28 ms downlink delay sat to ground: about 2.6 millisecs 120 fdma chan in 5.15 Mhz. Each chan 31.5Khz Within each fdma chan there are 8 tdma chan (4upl,4dwnl).
1626-1646.5		aug03		InmarSat stdBC ship earth station, portable mobile earth InmarSat stdM ship earth station uplinks
1626-1660.5		aug03		Inmarsat stdF ship earth station uplink Inmarsat stdM portable earth mobile station uplink Inmarsat airborne uplink
1636.5-1645.0				InmarSat standardA uplink

**Birdies above lband (**top)
FREQ Mhz	BW	DATE	STAT	COMMENTS
1990-2110	17Mhz 12Mhz			bas(Broadcast aux serv), LTTS(local television transmission serv), cars cable television relay service. Moving from 17 Mhz chan to 12 Mhz chan (2005).
2700		may96		Faa radar 1350 2nd harmonic (seen in rfi monitor.. probably our system).
2900-3100			radar	pico del este sps-48 9 distinct freq. (more info)
3600-3621		aug03		Inmarsat downlinks LHC (*a)
3945.5		aug03		marisat trackin beacon LHC (*a)
3947.0		aug03		inmarsat tracking beacon LHC (*a)
3947.5		aug03		intelsat tracking beacon RHC (*a)
3949.4		aug03		inmarsat tracking beacon LHC (*a)
3950.6		aug03		inmarsat tracking beacon LHC (*a)
3952.5		aug03		intelsat tracking beacon RHC (*a)
3953.0		aug03		inmarsat tracking beacon LHC (*a)
3952.5		aug03		marisat tracking beacon linear??(*a)
4188.72		aug03		marecs satellite tracking beacon LHC(*a)
5610		sep08		Terminal Doppler Weather radar at punta salinas.
9186.2	narrow	nov04	fixed	this had sidebands spaced by 85 Khz. It sounded like the dewar refrigerator when plugged into the radio. Turned out to be an oscillation in the sbw dewar (1 channel). By retuning the bias, it went away.
94100		sep08		mayagueaz weather radars.

Information sources.
INMARSAT *(a)**	http://ourworld.compuserve.com/homepages/pjmarsh/inmarsat.htm . may be a bit old L to C and C to L transponders. Tracking beacons at 39xx Mhz. geostationary satellites. Path loss to earth 188.5 db. Mainly describes stdA

**Combs (**top)
COMB SPACING	IN RCVR	DATE	STATUS	NOTES
1,2 Mhz	327	jul02	resolved	This was coming from the power meter on the roof of turret room that reads the power for the 430 Mhz xmter. It is in a huffman box. The edges of the box used a metallic gasket to improve the contact. This gasket contained silver and stopped working do to oxidation. 'resolution: We switched to another gasket material. (more info)
372Khz 744Khz (odd harmonics)	327	nov03	resolved	This comb was coming from the sb tx rack in the sband tx room above the turret room. The filters and doors of the enclosure were shot. There was also some problems with some of the cables going into the cabinet. These were fixed. (more info).
375/750 Khz 40Khz	327,430	apr06	resolved (again)	This was the sband console in the dome again. Inside the cabinet are some covers that need to be screwed in place to increase the shielding. They had been left unscrewed because of some maintenance work that was going on. (more info)
				Alfa motor controller
16Khz	327	apr05	resolved	saw in 327 rcvr. resolved oct05. coming from the alfa motor controller. It is a modulation on top of the 40 Mhz comb from the controller. Resolution is to turn off the motor controller for low frequency work. (more info)
40 Mhz	327	oct05	resolved	saw at 320 Mhz. This is from the alfa motor controller. The 16khz comb is center on this harmonic. (more info)
2 Khz	327	oct05	resolved	This is from the alfa motor controller. This comb is centered on the 40 Mhz comb harmonics. (more info). To get rid of it turn off the alfa motor controller.
				Dome AC units
1 Mhz	327 430	oct05	src found	This comb was seen at 327 and 430. It can wander by up to 30Khz in and hour. The birdie width is about 1 hz. It is coming from the AC units in the dome. There are actually 2 combs, 1 from each ac unit. The birdie is coming from the digital communications portion of the ac unit. Turning off the ac unit with the remote does not make it go away. You need to turn the power off to the ac unit. There is a switch downstairs for the old ac unit. The new ac unit can not be switched off. ( more info).
614 Khz	327	sep06	resolved	a 614 khz comb in the 327 Mhz receiver. Each element was about 1-3 Khz wide. It showed an az and za dependence. The comb was coming from the azimuth 2 (ch side) encoder. This was a new type of encoder that was installed on 02aug06. The old type of encoder was re=installed (more info).

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