430 MHz rfi with 10 sec period

17mar14

data taken on the telescope
checking old x111 data
looking for the birdie out in the field
summary

Intro:

The atmospheric radar run on 08mar14 saw strong chirped rfi at 430 MHz with a 10 second period.

Resolution:

20mar14: this birdie is coming from the fm tower site in utuado (102.9,104.1, and the smaller tower belonging to tua)

The engineers from 102.9,104.1 went to the site on 20mar14. They both agreed that the birdie was coming from the smaller tower (to the east) belonging to tua. (see tower locations)

21mar14: tua went to his tower and started turning off equipment.

The problem was coming from a motorola repeater that was supposed to be working at 460 Mhz.
He replaced the repeater.

data taken on the telescope:

Data was taken on various days using the dome 430 receiver and the mock spectrometers. The setup was normally

30 seconds of data. this should catch 3 10 second cycles
the sampling time varied from .2 to .6 millisecs per spectra
different bandwidths were used on different days.
Normally A/D dc was shifted up by 5 mhz and then shifted back down in the digital mixer of the mocks. this was to get rid of the dc spike and other problems at dc.

The table below shows the dynamic spectra for various days:

date	3 images spaced by 10 secs	Notes
10mar14	img1 (.gif) img2 (.gif) img3 (.gif)	3.2 MHz bw, .6 millisecond spectral average, img resolution .6 millisecs no pulses were seen 5mhz away pulse lasted about 180 millisecs 16 bit spectra
14mar14	img1 (.gif) img2 (.gif) img3 (.gif)	34 MHz bw, .19 millisec spectral avg. img resolution 1.4 millisecs last two imgs have 2nd birdie 5 mhz below 430 birdie starting .5 secs after 430 birdie starts. The birdie at 440 MHz is the mock mixer image of the 430 birdie (DC was at 435 MHz). 16 bit spectra
14mar14	img1 (.gif) img2 (.gif) img3 (.gif)	26 MHz bw, .19 millisec spectral avg. img resolution 1.4 millisecs no birdies offset by 5 mhz. The birdie at 440 MHz is the mock mixer image of the 430 birdie (DC was at 435 MHz). 32 bit spectra
15mar14	img1 (.gif) img2 (.gif) img3 (.gif)	26 MHz bw, .19 millisec spectral avg. img resolution 1.4 millisecs birdie seen 4 mhz below 430 birdie, .4 sec before 430 birdie. The birdie at 440 MHz is the mock mixer image of the 430 birdie (DC was at 435 MHz). 32 bit spectra,

checking old x111 data:

Looking at the x111 data from sep13 - jan14 (very little x111 data taken during the beam repair).

A 10 sec periodic birdie was first seen 17dec13.
It was close to 426 MHz
no periodic birdie was seen at 430 MHz
is was seen most times 430 was looked at.

17-30dec13,... 06jan14-13jan14, and 22feb14

looking for the birdie out in the field

We spent some time with the log periodic antenna looking for the birdie from out in the field:

from 12meter hill

Clear strongest signal coming from utuado. bearing 137.3 east of true north
it was 6 db lower looking at yiyi's tower

from platform.

It was difficult to get a direction for the maximum (too much metal?)

14mar14 field trip (oil pressure sensor breaks..)

route 10 scenic overlook.

strongest direction was pointed at yiyi's tower.

about 1 mile from yiyi's tower

There was not 430 birdie visible at all
there was a hill north (behind us).. but we had a clear view of the tower.

the line from the observatory to utuado and the line from route 10 overlook to yiyi's tower cross somewhere near the boyscout camp off route 10

the directionality probably has lots of error since it is hard to peak up with the log periodic's wide beam.

see x101/140317/rfibearings.dat for the lat,long for these locations (taken from google maps).

18mar14: field trip (high center at route 10 overlook..)

We used the log periodic antenna, compass, and spectrum analyzer to measure the signal strength versus azimuth from various locations during the 18mar14 field trip.. The spectrum analyzer setup was:

1 Mhz span (default rbw), peak hold chan b.

The table shows the locations and the readings vs magnetic and true direction (mag = -12.7 deg from true north (west of north)

looking at google maps and the compass readings, it looks like the directions may have been off by more than the -12.7 degrees mag-> true

locations	az (Magnetic)	pkHold dbm
route 10 overlook 18.37937,66.68618 src.. tua's tower: 18.290332,66.65682	130	-96
	160	-83.4
	190	-83.4
	220	-83.4
	250	-96
most way up mountain to fm station towers (looking south). parking lot of colmado. foundation of house hanging out over the mountain 18.2857,66.6894 src: tua's tower: 18.290332,66.65682	160	-97
	195	-90
	230	-88.5
	270	-83
	300	-81.5	hills blocking
	330	-82
	0	-88
at bar parking lot west of fm towers 18.2874,66.66187 src: tua's tower 18.290332,66.65682	0	-60
	40	-70
	70	-51	104.1 tower 18.2895,66.6604
	80	-48	102.9 tower 18.2886,66.6606
	100	-51
	110	-48	short tower belonging to tua. 18.290332,66.65682
	130	-52
	160	-57.5
	190	-73
	220	-60.5
	250	-61.5
	280	-62
	310	-65
	330	-66
drove to east of towers 18.28702,66.65926 src: tua's tower 18.290332,66.65682	pnt at towers	-53
	pnt 180 deg from towers	-83

Summary:

periodic birdie near 430 MHz.
It slews in freq for the first 10'2 of miliseconds.
sometimes a companion birdie 5 mhz below in frequency is seen

1 day the offset was 4 MHz.
it appears .5 secs before or after the start of the 430 birdie

The peak value of the 430 birdie:

50 kHz channel width, 1.3 millisec average
10e3 to 20e3 times Tsys.

the peak value for the offset birdie (in time and freq) is about 10 times Tsys.

processing: x101/140317/doall.pro

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