Use of the system for wide channel bandwidth very long base interferometry is described. System requirements, description, and implementation plans are given

Chaney, W. D.

English

NASA Technical Reports Server

N82' 3 2 a' 3 2 
The DSW VLBI System 
MayandJune 1982 
Mark IV-86 
W. 0. Chaney 
TDA Engineering 
This article describes thhp DSN VLBI System Mark IV-86, Wide Channel Bandwidth 
(Block 11). It covers the system requirements, description and implementation phns, 
Narrow Channel Bandwidth VLBI (Block I )  was described in prei 'us articles (Refi. 1,2). 
1. Introduction 
The DSN Very Long Baseline Interferometry (VLBI) 
System Mark 1V-86 will be implemented to provide the radio 
source catalog and baselines maintenance for Galileo delta 
differential one-way range (defta DOR). The primary stations 
to be used for radio source catalog maintenance are the 34-m 
deep space listen-only stations that are planned for Goldstone, 
California, and Canberra. Australia. However, the 64-m deep 
space stations at each complex can also be used for Wide Chan- 
nel Bandwidth (WCB) VLBI. 
Thc Galileo precision requirement for radio source cata- 
log is 25 nannradians (15 cm). and 30 cm for baseline deter- 
mination. 
11. System Description 
A. Definition 
Tte Deep Space Communications Complex (DSCC) VLBI 
System is the assemblage of various subsystems at a specific 
complex which form an instrument for receiving and obtain- 
ing necessary VLBI data in conjunction with at least ant other 
complex and,  together with elements involved with the moni- 
toring and control and data processing fnnctions, comprise 
the DSN VLBI System. 
6. Description 
Functionally, the DSN VLBI Systcm (Fig. 1) comprises the 
DSCCs, which individually receive the RF signal and down- 
convert segment bandwidths of the RF spectrum to videoband 
frequencies, which are then digitized and formatted by @tal 
equipment. The digital data is then recorded on wideband 
recorders and shipped to the JPL/Caltech Correlator Facility 
for processing. Many of the functional blocks in Fig. 1 are 
common to both the Wide Channel Bandwidth (Block 11) and 
the Narrow Channel Bandwidth (Block I) versions of the VLBI 
System. (See Refs. I and 2 for Block I description.) 
The Antenna Subsystem is pointed to the appropriate signal 
source at the proper time by the Antenna Pointing Subsystem, 
which obtains pcinting information (predicts) from the Net- 
work Data Processing ArLa (NDPA) of the Network Opera- 
tions Ccntrol Center (NOCC) via the DSS Monitor m d  Control 
Subsystem (DNC) and the Ground Communications Facility 
(GCF). 
The Antema Microwave Subsystem (W) receives the 
signal flux gathered by the antenna. APer amplification by 
the FET or TWM. the signal is sent to the Receiver-Excit.; 
Subsystem, which heterodynes this signal to an intermediate 
frequency (IF). 
16 
https://ntrs.nasa.gov/search.jsp?R=19820024656 2020-03-21T06:16:08+00:00Z
The WCB system Lotifiguration will have 14 channels of 
7 pairs (expandable to 28 of 14 pairs) of adjacent lower and 
upper sideband spectra selPable from 0.25- to 2.0-MHz band- 
widths. These paired c;.mnels may be allocated as desired 
between S- and X-band ,'requcneies, and each channel may be 
individually set to any place within the bandwidth, limited 
only by the front end amplifier and RF-IF downcnnverter. 
These frequencies arc further downconvert. from IF to video 
for the final acquisitim and recording processes. 
The Frequency and Timing Subg stem (FTS) provides the 
station local clock, sing a very stable hydrogen maser as the 
primary standard. Reference freqilencies and timing signals 
xe derived from the clock for distribution to other subsys- 
tems. Similarly, a reference signal from the coherent refer- 
ence generator (CRG), which distributes the reference sig- 
nals, will drive phase calibration generators (pee) as part of 
the Frequency and Timing Subsystem (FTS) via a coaxial- 
cable, phase-stabilization assembly which effectively trans- 
lates the station's clock frequency stability to the comb gener- 
ators in the PCG. The comb generator provides comblike, 
phasestable, line spectra S- and X-band microwave frequen- 
cies, which are injected into the respective Microwave Sub- 
systems prior to the input circuitry of the FETs or TWMs. 
These phasestable reference signals are amplified by the 
receiver a d  are down-converted simultaneously with the 
received slgnals. These reference signals will be used to cali- 
brate out phase variations (which occur within the rtaiver, 
down converter. and digital subsystem) during the cross- 
correlation and data processing procedure. Since the comb 
signal encounters the received s . g a l  for the first time at the 
injection point, this point is established as the instrument's 
RF reference i p -  .nt for the DSCC VLBI System. This is the 
point at which the cross-correlation and postcorre!ation esti- 
mation calcu'otions refer the resultant Earth parameters, 
station lxation and clock offset and rate information relative 
to the other instruments. 
The reference is u,sed to relate other station references such 
as h e  station's location reference point (intersection of 
antenna axes or equivalent) and the Epoch reference point at 
the M S  CRG output located within the control room. The 
cabl. stabilizer effectively translates these points with ii known 
t h e  delay for interstation clock synchronization purposes. 
The clock Etoch reference point in turn will function as the 
reference for ail subsystems and assemblies within thc respec- 
tive staticns. 
T!w dat:i acquisition and recording subassembly records 
the data a t  rates up t c  112 Mbitslsec. The tapes generated are 
shipped to the JTL/Caltcch correlation facility for processing. 
The sample of data from each radio source is transmitted 
via GCF wideband data line to the NOCC VLBI Processor 
Subsystem (WS) for validation of fringes from the baseline 
pair of stations. The results are displayed to the Network 
Operations Control Team, and ah0 transmitted to the sta- 
tions for displ~y. 
'Ihe Deep Space Communic~~tions Compkx (DSCC) MoN- 
tor and Control Subsystem @MC) sends coctrol and config- 
uration information to the DSCC VLBI Subsjestem @VS) 
from data received from NOCtJ via the GCF. It ai20 collects 
various calibration and configuation data wX& IS provided 
t3 the DVS for recdwding with the VLBl data ma ;?a the X F  
for monitoring. 
At NOCC (Fig. 1). the ND,PA we ita i Jr real-time 
monitorinpiisplay functions in the .,ark Operations 
Control Area (NOCA). The NOCA provides thc contiil infor- 
mation to the DSCC, via the GCF, to the DMC. 
The JPL/Caltech VLBI Prmesor receives tapes and per- 
forms the cross-correlation 0;' the data from the observing 
stations and, with further postcorrelation and estimation 
processing, radio source catalag &ita and baseline data am 
generated. 
111. Implementation 
A. General 
Implementation of Wide Ch.mnel Bandwidth (WCB) VLBI 
will provide a ccpability to mantain the radio source catalog 
and baseline distances. The WCB VLBl supplements the Nar- 
row Channel Bandwidth (NCB) VLBI. The NCB VLBI is used 
for direct navigation suppDrt in determining relative clock and 
clock rate offsets, Universal Tine 1 (UTJ), polar motion (PIG) 
and delta differenced one-way raige (delta DOR). 
A simplified block diagram of WCB VLBI is shown in 
Fig. 1. The WCB VLBl will be implemented on a 34-m listen- 
only mterma subnet. Effective t andwidth will be 400 MHz at 
X-band m d  100 MHz at S-band. Sampling rates and recording 
will be at 14 Mbits/sec to : 12 M W s e c .  Tapes will be shipped 
to the JPUCaltech correlalor for processing. 
8. Functional Performance Requirements 
S-bmd Parameter X-bac! 
System temperature 60 K SO K 
Bandwdth 400 MHz 100 MHz 
Frequency range 8200-&iOO MHz 2200-2300 MHz 
- ---- - 
17 
Parameter X-band S-band 
~ ~ -- ~ 
No. of channels 
Cliannel bandwidth 2 M!-L 
No. of tones/channel 3 (minimum) 
No. o! samphg rate 
14 (expandable to 28) 
14-1 12 Mbits/sec 
C. Moditications for WC6 VLBl 
Modifications to a standard 34-m Iisten-only Front-End 
Area (FEA) rnd Signai Processing Center (SPC) to pruvide 
WCB VLBI are given below. 
1. Minowave. Widaband field effect transistors (FET) at 
both S- and X-band freqlr,.icies will be added w'.th a band- 
width of 100 ar! * 400 MHz, respectively. System tempera- 
ture will be less than 50 K at S-band and 60 K at X-band. 
The frequency range will be at least 100 MHz at S-band from 
2200-2300 Mtlz and 40G MHz at X-band from 8200- 
8600 MHz. 
An inrertion port for both S-band and X-band will be sup- 
plied as far forward in the microwave as possible in order to 
insert calibration tones for VLBI system calibration. 
2. Receiver. An EF-to-IF conversion assembly will be 
added fcr both S- and X-band. The S-band will have d band- 
width > 100 MHz z d  range of 2200-2300 MHz. The X-band 
will have a baridwidth 2400 MHz and a range of 8200- 
P60C MHI. 
3. Phase calibration generators (PCC). A KG assembly 
wll be added that will  transfer the stability of the hydrogen 
maser frequency standard to the anteni ..icrowave (LWY). 
At the UWV a coherent comb generator subassenibiy generates 
a comb o f  frequencies across the frequency range. This comb 
fiequency divisor is selected so that at least thiw tones are in 
o.ie 3-MHz VLBI hannel. 
4. WCB VLBl Data Acquisition Assembly. The Data 
Acquisition Assembly is located in tile SM: dnd provides the 
following functions: 
( I \ Selects the IF signal. 
( 2 )  Selects frequency synthesis channels. 
(3 )  Providcs It-vidco ccnversioii 
(4) Provides i i inpe  rCJCc!lOll aid low r':ss filtering. 
( 5  Provides data sanl:)liiig. formatting and recording. 
(6) Pruvidcs sclcctive data Iiansniissioii via WBDL for 
validat io ! i .  
Initially the Data -4cquisition Assembly will provide 14 
channels of 7 pairs of adjacent upper ard lower sideband 
spectra, selectable from 0.25 to 2.0 NIHZ. The number of chaw 
neb will be expsrldible to  28 channds of 14 pairs. 
Data sampbg and recording will be at 14 to I12 Mbi&ix. 
Thc format for ,word;* *g will be compatible with the Mark 111 
Haystack Ooservatory. Data transfer w J l  be magnetic tapes 
shipped to the P U C V  correia+or facility. 
5. Water Vapor Radiome::. '.W f i e  WIR measur i 
water vapor content along the hie of sight in order t o  calibrate 
the V U 1  drta for this error source. The AdvancedSystenis 
W V R  rrmiels will be upgraded and integrated into the DSCC 
technical faciiities. Data w i l l  t: relayed from the technical 
facilities subsystem to the DSCC VLBI subsystem for incorpo- 
ration into the VLBl data stream. These data will be used b) 
the Block I1 correlator t o  calibrate VLBI observables for water 
vapor content along the line of  sight. 
The WVR meawes the brightness temperature at two 
frequencies - 20.7 and 3 1.4 GHz. These brightness tempera- 
tures are used to determine the water vapor conted along the 
h e  of sight. The WVR is dued with the main antenna; and 
periodic calibration is done by dipping in elevation at each 90" 
in 3 z i i i l . h  
6. Block I1 correlator. The Blcck 11 VLBi correlator is a 
joint JPLICaitech implementaticn with th? correlator located 
at the Caltech campus. 
The Block 11 correlator will be implemented for the corre- 
lation and pos!correlation for 3 stations sirnultanmuly 
(expandable to 7 stations). Data correlption will be to the 
rate of data acquisition. Data input will be VLBl data tapes. 
In order to calibrate the VLBl data, known tone ;@nais 
of constant frequency are injected in the microwave subsystem 
during a VLBl observation. DL.ring correlation, the correlator 
assembly will generate (with a local model) this same fre- 
quency and (by compariso? .a the injected constant fre- 
quency) measure phase chanf;e due to phase instabilities in 
('le microwave and receiver scbsysteins. 
Given a sc't uf parametm, the software model calibrates the 
pliase to within IO-' cycle if frmge. Also, a record of the cal- 
culations along with their results are kept with a precision of 
IO-' cycle of fringe. Output IS availabk in both delay and fre- 
quency domain. 
The softwa;e model constantly updates its computat.,n of 
the requircd geometric time delay lag due to the Earth's rota- 
tion. tight instantaneous lags (four preceding and fcur f(Jll0W- 
ing the noininal geometric delay) will be provided to deter- (1) Compute natural radio source and tone phase. 
mine the gomtk delay. The maximum equivalent (2) C&bmte phw for statim bm- 
ment error. error of the VLBl Block ll processor tracking the model delay 
(the error in keeping constant the pOmi of maxinium cone- 
lation) will be 0.01 lag. (3) Compute calibrated natural radio source delay. 
(4) Resolve cycle ambiguities. 
( 5 )  Calibrate for transmission media effects. 
(6) Solve for natural radio source locations and baseline. 
(7) Update radio source catalog and baselines. 
The JPUCaltech VPS will be able also to process data col- 
lected and recorded by Coddard Space F w t  Center (GSFC)/ 
Haystack Observatory Mark 111 VLBl System. 
Postcorrelation functional requirements are as follows: 
I .  Chmey. W. D.. and Ham, N. C.. “DSN VI51 System MK 1-80.” TDA hgress Report 
2. Chaney. W. D.. ‘The DSN VLBI System Mark IV-85.” TDA Prvgress Report 42-64. 
42 56. Jet Propulsion Laboratory. Pasadena, Calif., April IS. 1980. 
Jet Propulsion Laboratory, Pasadena. Calif., August IS. 1981. 
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The DSN VLBI System Mark IV-86

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