A set of measurements performed by the Michigan Tech Sensing and Signal Processing Group on the analog receiver built by the Virginia Polytechnic Institute (VPI) and the Jet Propulsion Laboratory (JPL) for propagation measurements using the Olympus Satellite is described. Measurements of local oscillator (LO) phase noise were performed for all of the LOs supplied by JPL. In order to obtain the most useful set of measurements, LO phase noise measurements were made using the complete VPI receiver front end. This set of measurements demonstrates the performance of the receiver from the Radio Frequency (RF) input through the high Intermediate Frequency (IF) output. Three different measurements were made: LO phase noise with DC on the voltage controlled crystal oscillator (VCXO) port; LO phase noise with the 11.381 GHz LO locked to the reference signal generator; and a reference measurement with the JPL LOs out of the system

Campbell, Richard L.

Sweeney, Dennis

Wang, Huailiang

English

NASA Technical Reports Server

N91-11960
OLYMPUS RECEIVER EVALUATION AND PHASE NOISE MEASUREMENTS
Richard L. Campbell and Huailiang Wang
Sensing and Signal Processing Laboratory
Department of Electrical Engineering
Michigan Technological University
Houghton, MI 49931
Dennis Sweeney
Satellite Communications Group
Department of Electrical Engineering
VPI and State University
Blacksburg, VA 24061
This paper describes a set of measurements performed by the Michigan Tech
Sensing and Signal Processing Group on the analog receiver built by VPI and
JPL for propagation measurements using the Olympus Satellite. Measurements of
local oscillator (LO) phase noise were performed for all of the LOs supplied
by JPL. In order to obtain the most useful set of measurements, LO phase
noise measurements were made using the complete VPI receiver front end. This
set of measurements demonstrates the performance of the receiver from the RF
input through the high IF output. Three different measurements were made: LO
phase noise with DC on the VCXO port; LO phase noise with the 11.381 GHz LO
locked to the Reference signal generator; and a reference measurement with the
JPL LOs out of the system.
INTRODUCTION
The Olympus satellite has three beacon frequencies, all derived from a common
high stability oscillator. If an earth station receiver is phase or frequency
locked to any one of the beacons, the local oscillator frequencies for the
other two beacons may be obtained. In the Virginia Tech Olympus receiver, the
12.5 GHz receiver frequency locks to the Olympus 12.5 GHz beacon. The local
oscillator signals for the 20 and 30 GHz beacon receivers are then derived
from the locked 12.5 GHz receiver. In this way, the 20 and 30 GHz receivers
can remain locked even during deep fades of the 20 and 30 GHz signals. Phase
noise on the earth station local oscillators is important for three reasons:
the frequency locked loop (FLL) will be unstable if the phase noise is poor;
received signals are modulated by the local oscillator phase noise; and the
minimum receiver predetection bandwidth and hence sensitivity is limited by
the short term fluctuations of the receiver local oscillator.
PREPARATION
The measurements were made at Virginia Tech the week of January 22 to 27,
1990. During the week before the trip, the 1296 IF system, Reference and PCM
audio recorder were set up and calibrated at Michigan Tech. The system was
then broken down and packed for shipping, along with a set of adapters and
cables to connect the Michigan Tech and Virginia Tech systems.
54
https://ntrs.nasa.gov/search.jsp?R=19910002647 2020-03-19T20:11:38+00:00Z
TRAVEL TO VPI
The 1296 IF system, Reference oscillator and other critical components were
taken as carry on baggage. The PCM recorder (Toshiba DX 900) was too large to
be carried on, so it was packed in its shipping box and checked.
SET UP AT VPI
Tuesday, January 23, the 1296 IF system was connected to the VPI receiver with
the assistance of Dennis Sweeney, as shown in Figure 1. . The system was
allowed to stabilize overnight while Dennis reviewed the current status of the
receiver system.
JANUARY 1990 STATUS OF OLYMPUS RECEIVER
As of the end of January 1990, the analog receiver was working in breadboard
form. Dennis was still working on minor modifications to the frequency locked
loop dynamics before committing the design to a PC board layout. The system
was capable of receiving the 12 GHz Olympus beacon signal, but an on-the-air
test was not practical due to the high feedline loss between the outdoor
antenna and the bench where the breadboard receiver was located. In final
form, the receiver front end will be located in an outdoor cabinet near the
dish feed.
Dennis demonstrated capture, lock and tracking of a weak CW signal from the
HP 8673 signal generator. The system is capable of tracking any changes in
beacon frequency over the life of the satellite. Since day to day variations
will be much smaller, it is possible to improve loop stability by reducing the
range of the tracking loop and providing a front panel manual adjustment with
a zero center meter to compensate for long term variations.
PHASE NOISE MEASUREMENTS
Three different types of measurements were made:
1. Measurements of downconverted LO phase noise, using the apparatus
shown in Figure 1. These measurements were made on all three analog
receiver front ends, using both the primary and spare LOs. The VCXO
frequency change terminal was grounded for these measurements. In
order to insure that the dynamic range of the measurement system was
not exceeded, two measurements were made on each LO: the first
measurement was made with the signal level adjusted 10 dB lower than
the maximum input to the digital audio recorder; and the second
measurement was made with the signal level 20 dB lower than the
maximum to the digital audio recorder. Since the dynamic range of
the digital record is 86 dB, this provides two records, one with the
signal 76 dB above the digital tape recorder noise floor and one
with the signal 66 dB above the noise floor. The no signal receiver
output was adjusted so that it just indicated on the recorder
output. Either of these measurements has sufficient dynamic range
to see the close-in phase noise on the LO and verify that it is
within specifications at 100 Hz separation.
55
2. A measurement of the phase noise of the 11.381 GHz LO was made with
the LO locked to the HP 8673 signal. This measurement was made with
the signal downconverted to 10 kHz using the breadboard VPI receiver
system. The downconverted signal was recorded on the right channel
of the digital audio recorder, and the 10 kHz reference was recorded
on the left channel. This permits not only a phase noise analysis
of the locked LO, but a measurement of loop behavior by doing a
cross-spectrum between the locked LO and the reference. This
measurement also demonstrates direct digital audio recording of the
10 kHz IF signal which can be used to obtain data during propagation
events with rapid fluctuations, as in thunderstorms.
3. The third measurement was made to determine the phase noise of the
measurement system itself. As shown in Figure 2, the 576 MHz
reference from the 1296 MHz IF receiver (derived from a 5 MHz
Vectron CO-203 oscillator) is multiplied by 4 in a Campbell
multiplier board. The 2304 MHz signal is then multiplied by 5 in a
harmonic mixer (Mini-Circuits ZFM-4212) to 11.520 GHz. The HP 8673
is adjusted to 11.6641 GHz. The output of the harmonic mixer is
then 144.1 MHz, which is downconverted to 1024 Hz using the low IF
receiver as in the first set of measurements.
Table 1 shows the time, frequencies, levels and tape counter indications for
all the measurements.
PROCESSING OF PHASE NOISE DATA AT MICHIGAN TECH
The lab was set up to process the recorded IF signal as shown in Figure 3.
All of the data at 1024 Hz IF was processed, but the 10 kHz data (measurement
"a" in Table 1) has not been processed.
The power spectra for the JPL LOs were obtained by playing the 1024 Hz
recorded IF signals as analog audio into the HP 5451C Fourier analyzer. For
each spectrum plot, 100 sequential 1024 sample time records were Hanning
windowed, Fourier transformed, converted to a power spectrum and averaged to
obtain a 500 Hz wide spectrum with 1.5 Hz noise bandwidth and 1 Hz spacing
between frequency domain points.
The JPL LO phase noise plots are shown as Figures 5-14. All of these plots
have phase noise at the 100 Hz points that are very close to the Olympus LO
specification shown schematically in Figure 4. These LOs meet the
specifications set at the beginning of the receiver development program. The
± N x 60 Hz noise sidebands are discussed in the next section.
PHASE NOISE MEASUREMENT SYSTEM CALIBRATION
In order to prove that the phase noise being measured was actually that of the
JPL LOs rather than the measurement system, a measurement was made of a very
low phase noise microwave LO built by R. Campbell. Unfortunately, the output
of the Campbell LO was contaminated by 60 Hz noise on the bench at Virginia
Tech. This may have been 60 Hz noise transmitted over the power supply lines
56
or it may have been magnetically coupled from a nearby power transformer into
the ovenized crystal oscillator in the Campbell LO. It would have been easy
to remove the 60 Hz noise from the reference LO by running it on a different
power supply and moving it away from any nearby magnetic AC devices, but the
60 Hz contamination was not suspected at the time of the measurements.
In any case, Figure 15 demonstrates that the phase noise measurement system
used to measure the JPL LOs has a phase noise floor at least 10 dB below the
best JPL LO within 50 Hz of the carrier and at least 5 dB better at + 100 Hz
from the carrier.
APRIL 1990 STATUS OF THE OLYMPUS RECEIVER AT VIRGINIA TECH
As of April, 1990, the 12.5 GHz beacon receiver and radiometer are on the air
at Virginia Tech, as discussed in the companion paper by Warren Stutzman. The
signal was first received with a carrier to noise ratio of 30 dB in March
1990. The FLL locks from -115 to -150 dBm. Three additional IF systems are
now under construction for the 20 and 30 GHz receivers.
57
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TABLE 1
Run LO Freq.
# and SN
1
2
3
4
5
6
7
8
9
a
b
c
d
e
f
g
h '
Tape
* 2
Notes
10.3819
SN 35267
same
same
same
same
10.3819
SN 35268
same
4. 4640
RLC LO
10.3819
SN 35268
HP 8673 HP 8673 Record Start Start Stop Stop Notes
freq. level level time count time Count
GHa dBm dB EST EST
12.678006
same
same
same
same
same
same
5.7601
12.5019
-40
-30
-30
-40
-40
-30
-80
28.535684 29.831784
SN 35270
same same
18.650456 19.946492
SN 35273
same same
18.650456 same
SN 35272
same same
-64
-74
-64
-74
11.520 11.66410
reference
same
: 1.
2.
3.
4.
5.
6.
7.
8.
same
-15
0
0
-15
-15
0
' 0
0
-10
0
0
-10
0
-10
0
0
11:21
2:51
2:54
3:08
3:20
3:26
3:42
4:03
4:45
5:02
9:57
10:09
10:30
10:41
11:11
11:37
0615
1670
1713
2290
2716
2926
3219
3365
3633
4240
4619
4945
5121
5464
5640
0020
11:36
3:04
3:16
3:25
3:45
4:09
5:00
5:12
10:07
10:14
10:30
10:46
1:00
1665
1713
2290
2714
2926
3219 -
3367
3629
4237
4620
4945
5121
5464
.5632
1
2
3
4
5
6
7
8
Data is at 1024 Hz unless otherwise noted.
Runs 1, 2 and 3 were setup runs. Don't use.
Aborted run 4 to ground VCXO terminal .
"0" and "-15" on recorder are approximate from LED bar graph
Diagnostic measurement of free running 5th OT Butler oscillator
Measurement of locked 11.381 GHz LO. Data is at 10 kHz
Run h aborted -- end of VHS tape.
Tape #2 is 1.5 hours of 1024 Hz reference sine wave downconverted
from 11.6641 GHz
60
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Olympus receiver evaluation and phase noise measurements

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