WP06_AntennaIF

equalizer bandpass filter

bandpass filter

equalizer

equalizer bandpass filter

spare

detector

a/d

RFNitro NBB-300

dewar

alternate location for bandpass filter

thermoelectric temperature regulation(if needed)

microcontroller

laser power monitor, laser temp monitorCANbus

SP4Tswitch

80-116 GHz

210-270 GHz

28-36 GHz

CARMA I.F. block diagram v. 2.1Dick Plambeck, 13 Sep 2002

eq

atten 0-30 dB eq

atten 0-30 dB eq

bias tee

DC bias

0 dBmlaser trx

HMC 424

amplifier module

WP06_AntennaIF3 principal modules

• switch

• amplifier (= ATA ‘PAM’)– includes attenuators (0-60 dB), power detector, and bias

tee for the laser transmitter– integrate with CANbus controller?– aluminum box; mount flange to temperature regulated

plate, or if necessary to separate thermoelectric cooler

• laser transmitter (= ATA ‘OTX’)

WP06_AntennaIF: amplifier module = ATA post-amp module

• frequency range 500 MHz – 10 GHz• gain flat within ±3 dB across band• input noise temp < 1200 K• input pwr level –50 dBm to +10 dBm (!)• linearity better than 1%• gain stable to 1 part in 103, if temperature

regulated to 0.1 C

WP06_AntennaIF:prototype ATA PAM

WP06_AntennaIFprototype PAM; gain ~ 50 dB

amplifier module: gain compression ~ 1% at 1.5 dBm output power

output pwr

gain, .02 dB/div

input pwr swept from –60 dBm to –45 dBm

WP06_AntennaIFtemperature dependence of gain

0.3 dB / 20 C 0.4% / C

gain stability of 10-3 requires ±0.1 C temp regulation

high freq ripples due to poor output match

WP06_AntennaIF: optical transmitterNEC NX8560LJ

1550 nm DFB laser + electroabsorption modulator + TEC

WP06_AntennaIF: laser transmitter = ATA OTX module

• includes:– NEC NX8560LJ

• laser• EA modulator• thermoelectric cooler• photodiode power monitor• thermistor

– TEC controller (5 V, ~ 1 amp)– laser current supply– modulator DC bias (bias tee located in amplifier module)

• Photonics Inc will build 700 modules for ATA; cost approx $2.5 K each

WP06_AntennaIFopen questions

• will detector on amplifier module be used for beamswitched continuum measurements?

• if so, will switched-power demodulation be done at the IF CANbus node? how will mirror position be transmitted?

• power supply: requires ~ 1 amp at 5 V; is it necessary to get this from 24 V dc-dc converter

• can RF power damage the electroabsorption modulator; how to protect without compromising linearity?

WP02_LOreference key features

• distributes two reference frequencies (1100-1260 MHz tunable, 10 MHz fixed) from control building to antennas via singlemode optical fiber

• linelength system continuously monitors electrical delay through each fiber to an accuracy of ~0.1 picosec, approx 8° phase at 230 GHz

• 1 pps tick distributed to antennas, as a missing pulse on the 10 MHz reference

• allow for 3 subarrays operating with different reference frequencies

WP02_LOreference:current BIMA system

Agere 3540AAgere 2510B

Agere 2510B

linelength rcvr

NI 6031EI/O

Wavetek synth

8662synth

1100-1260 MHztunable

Ortel 3120A-101-102

10 MHz TTL

f_ref

f_ref+ 10 MHz

1310 nm laser

-20dB

-10dB

1310 nm laser

Agilent HFBR2316T

photoreceiver

10 MHz cleanup osc

4-way opticalpwr splitter

+1 dBm

9.99995 MHzfixed

offsetosc

computer

a/d converter

fiberoptic coupler

10 MHz

10 MHz

missing pulse generator

1 pps tick1 pps tick

10 MHz

1100-1260 MHz

50 Hz sine wave

LO distribution and linelength systems

Dick Plambeck, 8 June 02

pwr splitter12-way optical

WP02_LOreferencephase noise vs optical pwr

optical pwr rms

coax 6.3°

-2 dBm 6.65°

-6 dBm 7.05°

-9 dBm 8.31°

WP02_LOreferencecurrent BIMA fiber distribution

splice tray

weathertight box on

portable stand

az wrap

elev wrap

umbilical

weathertight box on side of

antenna

underground cable

patch panel

rcvr

echo

LO ref out

antenna fiber

lab

FC/APC connector

approx 135 feet (200 nsec) of fiber exposed to outdoor air temp

linelength monitor via roundtrip phase

• 135’ of fiber at outdoor air temp ( = 200 nsec)

~ 2 psec/C

~ 180°/C at 230 GHz

WP02_LOreferencelinelength options

TRX

RX

CPL TRX

RX

CPL

1. echo on 2nd fiber

do fiber lengths track each other?

2. echo on same fiber

temperature coefficients of circulators?

reflections from bad connectors?

optical circulators

WP02_LOreference: 3-fiber test

echo from 1 antenna coupled back on 3 separate fibers: 3 independent measurements

WP02_LOreference: 3-fiber test

0.2 psec glitches during slew

1 psec long term drifts due to cabin temp change

example of linelength correction

raw data linelength-corrected

3c454.3, 86 GHz, baseline 2-8, through sunrise

thermal tests of 10 MHz fiber link from ‘good’ antenna

thermal tests of 10 MHz fiber link from ‘bad’ antenna

slow/fast thermal ramp – phase structure remains the same

probable explanation

fiber photodiode

1. gap acts like Fabry-Perot cavity; increasing temp expands gap, causes periodic variation in laser power at photodiode

2. laser power affects diode capacitance or resistance, hence changes phase of RF signal

substituting APC connector seems to cure the problem

WP02_LOreference

• short term: with 10 MHz thermal problem fixed, reinstall on BIMA in November

• longer term:– test optical circulators?– one laser/antenna to make subarrays easier?– convert to 1550 nm NEC lasers?