Document text
UNCLASSIFIED
AD 4
DEFENSE DOCUMENTATION CENTER
FOR
SCIENTIFIC AND TECHNICAL INFORMATION
CAMERON STATION, ALEXANDRIA, VIRGINIA
UNCLASSIFIED
NOTICE: When government or other drawings, speci¬
fications or other data are used for any purpose
other than in connection with a definitely related
government procurement operation, the U. S.
Government thereby incurs no responsibility, nor any
obligation whatsoever; and the fact that the Govern¬
ment may have fonnulated, furnished, or in any way
supplied the said drawings, specifications, or other
data is not to be regarded by implication or other¬
wise as in any manner licensing the holder or any
other person or corporation, or conveying any rights
or permission to manufacture, use or sell any
patented invention that may in any way be related
thereto.
/l/ <5
US ARMY
ELECTRONICS
RESEARCH & DEVELOPMENT
ACTIVITY
INTERPRETING THE IRIG STANDARDS FOR PAM/FM TELEMETRY
BY
ROBERT C. BARTO
USA ERDA-23
MAY 1963
V* * .
I
!.
t ■'
J
WHITE SANDS MISSILE RANGE
NEW MEXICO
INTERPRETING THE IRIG STANDARDS FOR PAM/FM TELEMETRY
BY
ROBERT Co BARTO
USA ERDA-23
MAY 1963
DA Project 1-G-2-50206-D241
INSTRUMENTATION DEPARTMENT
Uo S„ ARMY ELECTRONIC RESEARCH AND DEVELOPMENT ACTIVITY
WHITE SANDS MISSILE RANGE
NEW MEXICO
HEADQUARTERS
U. S. ARMY ELECTRONICS RESEARCH AND DEVELOPMENT ACTIVITY
WHITE SANDS MISSILE RANGE
NEW MEXICO
May 1963
1. Technical Report USA ERDA-23 has been prepared under the
supervision of the Instrumentation Department and is published for the
information and guidance of all concerned,
2. Suggestions or criticisms relative to the form, contents, pur¬
pose, or use of this publication should be referred to the Commanding
Officer, U. S. Army Electronics Research and Development Activity,
ATTN: SELWS-E, White Sands Missile Range, New Mexico.
FOR THE COMMANDER:
ju • n , miOiv
Major, AGC
Adjutant
I
U. S. ARMY ELECTRONICS RESEARCH AND DEVELOPMENT ACTIVITY
WHITE SANDS MISSILE RANGE
NEW MEXICO
WILLIAM G. SKINNER
COLONEL,, SIGNAL CORPS
COMMANDING
Approval. Technical Report USA ERDA-23 has been reviewed and approved
for publication:
PAUL kcStoOR
Capt, SigC
Director
Instrumentation Department
ROBERT C . BARTO
Chief
Telemetry Systems Division
Distribution. This report has been distributed in accordance with
SELWS-E List Nr. 1 and Special. Initial Printing 200 copies.
DDC Availability Notice. Qualified requesters may obtain copies of
this report from DDC.
I
ABSTRACT
Knowledge of the technical basis underlying the particular
choice of parameters, quantities , and configurations specified
in the Telemetry Standards could lead to the more effective use
of the document 0 During the preparation phase,, such technical
information is assembled to form the basis of the Standard-
Although there was no attempt to preserve or organize such in¬
formation during the recent preparation of the Standard for
PAM/FM Telemetry, some of this material is available and is
drawn upon to discuss interesting sections of the Standard,
I
CONTENTS
PAGE
ABSTRACT --.--.=.00.. ...... ----- lii
INTRODUCTION 1
PAM/FM STANDARDS - 2
Selection of Parameters 2
Sampling Rate Stability — 7
Frame and Pulse Structure - — 7
Synchronization - - - 7
Pre-Modulation Filter — 9
CONCLUSION - . 10
REFERENCES . - . II
v
t
I
INTRODUCTION
The Telemetry Working Group (TWG) of the Inter-Range Instrumentation
Group (IRIG) has recently completed a large scale revision of IRIG
Document 106=60, "Telemetry Standards/' This revision included the
addition of a new standard, PAM/FM Telemetry, which now appears as
Part IV of the document , Many of the people involved in this work
are convinced that improved communications between the elements of
the telemetering community, while standards are being prepared and
after they are published, will result in both better standards and
more willing acceptance of them. The standards must, of course, re¬
flect the needs and capabilities of the technology. The technical
people involved in the design, development, and use of telemetry
systems must be assured that the particular choice of parameters and
quantities is not capricious,
The Telemetry Working Group has established effective communications
within the technology during the preparation phase of standards. Tech¬
nical representatives from industrial, governmental, and professional
organizations are invited to participate in open meetings sponsored by
the working group in which each section of the proposed standard is
discussed in detail. After the meeting, a revised draft of the stand¬
ard is mailed to all attendees and to others who may be interested for
additional comment. The draft is also reviewed by professional and
industrial groups such as the Telemetry Standards Coordination Committee
(TSCC), the Aerospace Industries Association (AIA) , the Institute of
Electrical and Electronic Engineers (IEEE), etc,
Communications after the standard is published, however, can be very
much improved, Ev.-ryone within the technology needs to have access to the
technical information that led to the choice of each parameter and quan¬
titative limitation in the document. At the time standards are drafted,
this information, which becomes the technical foundation upon which the
document is based, is on hand in various degrees of organization. It
can and should, I believe, be preserved and made available to everyone
who has occasion to use the standard, A first step in this direction was
made in the original IRIG Document 106-60 by including some information
in an appendix and a glossary. Additional information of this type
could be placed in the appendices of future standards or contained in
an interpretive supplement.
1
During the preparation of the new PAM/FM Standard, no real effort was
made to preserve or organize for publication technical information of
the type discussed. Some of this material is, however, still available
and will be the subject of this paper.
PAM/FM STANDARDS
SELECTION OF PARAMETERS
In the preparation of Telemetry Standards, the parameters to be stand¬
ardized are selected to achieve the objectives of the program. These
objectives certainly include the assurance that the system will perform
reliably and efficiently and that the variety of airborne and ground
equipment be kept within reasonable bounds. In the case of the PAM/FM
Standard, the parameters selected for standardization are:
1. Receiver design i-f bandwidth, B.
2. Frequency deviation, peak, Fpp.
3. Sampling rate stability.
4. Frame structure,
■5; Pulse" duty cycle.
6. Synchronization.
7. Commutation.
8. Radiated spectrum,
9. Modulation.
At this point, it is necessary to distinguish between the new PAM/FM
Standard which appears as Part IV of IRIG Document 106-60 and the older
PAM/FM/FM Standard, PAM on a subcarrier, which appears in Section 2.4 of
the document. Part IV describes a newly standardized service that is
intended to supplement Section 2,4 by providing for PAM on an r-f carrier
with a capability for greatly increased pulse rates.
2
Receiver design i~f bandwidths are specified so that the missile test
ranges need only be prepared to accommodate the eight values ranging
from 12 „5 kc to 1.5 Me listed in Table IV of the Standard, The designer
is given maximum latitude in the choice of a sampling rate. He
chooses from a continuum of rates to meet his particular project require¬
ments. The chosen rate is then optimally related to one of the specified
receiver i-f bandwidths through the peak deviation, F^p, and permissible
total residual error. The relationship between the ratio of receiver
i-f bandwidth and total rms error, B/fs, is discussed at length by Drs,
Myron L, Nichols and L, L, Rauch and in the Aeronutronic Telemetry
Study Reports^o^, Figure 4 of the IRIG Document 106=60, revised, was
prepared by Aeronutronic as a result of the latter study and depicts this
relationship. The Figure is reproduced in this paper as Figure 1 for
convenience. Background information relating to the chart itself is
found in Section 6 of Reference 3,
To select the optimum bandwidth for a particular project, the designer
starts with the number of channels to be sampled and the frequency
response of the individual channels. An appropriate number of samples
per cycle of information is then chosen to bring aliasing error within
accuracy requirements5*6. The total sampling rate is now established.
The next step is to choose a B/fs ratio by reference to the chart in
Figure 4 of the Standard (Figure 1) which will hold crosstalk and
other error within a tolerable level. The chart is entered with the
total rms error that can be tolerated, and the factor B/fg is read directly.
The values read from the curve are minimum values required to limit total
residual (system) error to the indicated level, Use of higher B/fs
ratios effectively increases additive noise and raises the receiver thres¬
hold but decreases crosstalk. Since fg is fixed by the project require¬
ments, B may now be determined by applying the B/fs factor.
Let Mj, = B/fs;
then.
B = Mlfs,
The receiver design i-f bandwidth, B, is now specified. The peak-to-
peak deviation which, by Section 4,2,2 of the Standard may not exceed
0,75 B, now has an upper limit. The designer may now select an appro¬
priate video bandwidth, By, a parameter not covered in the Standard,
which meets his crosstalk requirements. Figure 6,2,4 of Reference 2
and Figures 11=6=1 through II-6-10 (in Reference 3) relate crosstalk
attenuation, rms error, and input signal-to-noise ratios to By/fs,
3
TOTAL RMS
ERROR * OF
FULL DATA
RANGE
DESIGN B|F
SAMPLING FREQUENCY
vs ERROR AT MINIMUM REQUIRED
RECEIVER POWER
FIGURE I.
Nominal values range from just under one to two or more depending upon
tolerable error, gatewidth, peak deviation, and so forth .
To proceed from the receiver design i-f bandwidth to the actual
receiver bandwidth, it is necessary to consider the frequency instability
of the system, including transmitter instability, Ts, receiver instability,
Rg, and doppler shift, Dg. The combined instability, Cs, may be calculated
as follows7:
Cs =
This roughly corresponds to the standard deviation of the signal about
its assigned frequency. Assuming operation at the lower end of the VHF
bandwidth with available equipment (transmitter instability of 0.01 per
cent and receiver instability of 0.005 per cent) and a vehicle radial
velocity of 5,000 mph,
cs =
= 25,200 cps,
including the inaccuracy of the basic crystal frequency. Since the
composite shift may occur in either a positive or negative direction,
the additional receiver bandwidth required to contain the signal is
2CS = 50.4 kc.
It can be argued that it is more realistic to consider Doppler shift as
an absolute value. Then
In the example cited and most practical situations, however, the effect
is small. It is worth noting that the shift may not always have the
negative sign of a receding vehicle.
A conservative design may even require that the instabilities be
combined as absolute quantities. Then in the case cited,
5
Tg = f0 1.0.01 per cent,
Rs = £0 +0.005 per cent, and
cs = fo ±0.015% +DS
= 2.25 x 108 x 1.5 x 1CT4 +DS
= ±53,750 ±3360 cps
= +37, l<kc
where fQ is the assigned carrier frequency. On this basis, the total
receiver bandwidth, B (ac tual ) requirement is approximately
factual) = B + 2Cs
if the vehicle is to be tracked both approaching and receding from the
ground station. In the example given above,
B (actual) = B + 74.2 kc .
The use of tracking filters or automatic frequency control (AFC) will
reduce the actual i-f bandwidth requirements to some extent. In any
case, the engineer must consider all of these factors in choosing an
appropriate i-f band shift factor ranging from 1.5 to 3.3 to apply to
the design i-f bandwidth to obtain the actual receiver bandwidth. A
sufficient number of bandwidths is specified in Table IV of the Stand¬
ard so that the calculated value must fall reasonably close to a stand¬
ard value. Within the restriction that the peak-to-peak deviation may
not exceed 0.75 B, transmitter deviation may be adjusted to aid in
tailoring the transmitted signal to one of the specified actual
receiver bs&dwi Jtbft., ,
This is essentially the process of moving from the channel requirements
and the frequency response of each channel to the selection of a
receiver i-f bandwidth which will contain the transmitted signal under
the assumed operating conditions. The transmitter and receiver insta¬
bilities used in the examples are those specified in Appendix I of
IRIG Document 106-60 for VHF operation.
The receiver bandwidths specified in Table IV of the Standard were
selected to include existing receiver bandwidths of 100 kc, 300 kc, and
500 kc for reasons of economy. Bandwidths above and below these values
were assigned at convenient intervals.
6
SAMPLING RATE STABILITY
Sampling rate stability, as specified, assumes the use of mechanical com¬
mutation for most applications at the lower pulse rates „ The stability
specified is, therefore, well within the state-of-the-art „ The stability
and pulse jitter tolerance statements refer to a consecutive number of
samples N "where N is the number of samples closest tc 1000 within an
integral number of frames." The maximum number of channels in a PAM
frame is specified as 130. Therefore, N is specified as
870 < N< 1130.
FRAME AND PULSE STRUCTURE
Members of the Telemetry Working Group are somewhat sensitive to questions
relating to the number of primary channels specified for PCM and extended
to PAM. Any discussion of this section inevitably leads to the observa¬
tion that electronic logic devices are composed of binary elements.
Hence, the number of primary channels should be specified as either 128
or 256. From a logical element point of view, the 130 figure is indefen¬
sible. However, the number represents a compromise between mechanical
and electronic commutators and a desire to keep the total number of
primary channels within reasonable limits. In the PCM case, the number
selected is compatible with the maximum number (2048) of bits per frame
allowed and an average word length of 15 bits. There is some advantage
in keeping all time multiplex systems compatible in this respect. Other¬
wise, the frame and pulse structure specified is straightforward.
SYNCHRONIZATION
The synchronization patterns permitted for PAM/FM include the conventional
scheme of three adjacent channels deviated to the maximum signal level
to identify the frame. In the 50 per cent duty cycle case, 20 to 25
per cent of the channel deviation is reserved for channel synchronization,
Channel synchronization is derived from the varying amplitudes normally
encountered from channel to channel in progressing through the frame in
the 100 per cent duty cycle systems. Frame identification cannot be
unique, however, in the latter configuration unless a coded pattern is
transmitted, since the data is permitted to occupy all levels within
the deviation range. Incidentally, Figure 5 C on Page 16 of the Stand¬
ard is in error and will be corrected at the next printing. The
Figure erroneously shows minimum data level occurring approximately
25 per cent above the lower deviation limit. This would, of course,
provide a unique synchronization pattern, but it is not correct. Figure
2 shows the correct waveform.
7
MAXIMUM SIGNAL
(POSITIVE or NEGATIVE) HALF SCALE
PAM PULSE TRAIN WAVEFORM , CONVENTIONAL
FRAME SYNCHRONIZATION 100 PERCENT DUTY
CYCLE
FIGURE 2
8
A unique pattern is possible if the PAM pulse rate is increased by a
factor of 2, 3, 4, etc. in the frame identification period. This tech¬
nique assures that transitions will occur at least one in each frame
and, in addition, provides a pulse pattern that cannot occur within
the data to uniquely identify the frame. The use of logical elements
to identify the coded pulses is unnecessary since they are easily
identified by the rate.
Section 4.5 of the Standard describes the synchronization patterns
permitted and limits the number of coded pulses which may occupy a
single PAM pulse period to seven. It further requires that the coded
pulses shall evenly divide the PAM pulse sample period. The maximum
number of coded pulses is derived from the last sentence of the section
which reads, "The minimum duration of the pulses comprising the coded
word is defined as 1/M times the data sampling period, where M is the
largest integer not in excess of the design i»f bandwidth divided by
the total sampling rate." In other words.
M(integer) max < —jT~
s
However, a more practical value for M would be 2, 3 or 4.
Permission to use coded frame identification patterns in the PAM
format has probably generated more comment than all other sections of
the Standard combined. So much comment indicates that the function of
this section was not made clear at the time the Standard was prepared.
There are advantages to the use of these patterns. By this simple
device, a unique synchronization pattern is available to identify the
frame in 100 per cent duty cycle systems at the expense of a relatively
few channel intervals. The equipment complication is slight. It is,
after all, the only way in which a unique pattern can be obtained
without restricting the deviation range of the data signal. It should
be extremely valuable in identifying the subcommutated frame.
PRE-MODULATION FILTER
The use of pre-modulation filtering is required by the standard to con¬
serve the r-f spectrum. Although no specific roll-off is stated for
the filters, the appendices contain a recommendation that the total
attenuation of the filter plus modulator and transmitter be 36 db per
octave beyond the design i-f bandwidth. The factors to be considered
in the selection of a pre-modulation filter are those which influenced
the choice of the video bandwidth. Other factors must also be
9
considered, including those of crosstalk and total system error. Opti¬
mum operation results when the overall frequency response of the trans¬
mitter modulation matches that of the receiver video stage. The response
of this complete circuit and that of the receiver i-f amplifier establish
the levels of crosstalk and, to a large degree, total system error of
the telemeter. A reasonable approach, then, to the selection of a
pre-modulation filter is to choose a receiver video bandwidth compatible
with crosstalk tolerance as previously described and then match the
modulator characteristics to it with a suitable pre-modulation filter.
CONCLUSION
The sections of the PAM Standard discussed in this paper are those which
generated the most comment throughout the industry during the prepara¬
tion phase and immediately following publication. It is hoped that
the additional information contained in this paper conveys some of the
consideration that went into the generation of the PAM/FM Standard.
10
REFERENCES
1. Nichols, M. H.t "Comparison of P£M and PCM," Research Report, Instru¬
mentation Engineering Program, University of Michigan, USAF Contract
No. AF 33 (616) -5796, Task #82048, Project No. 4107, 28 Feb 1961.
2. Nichols, M. H., and Rauch, L. L., "Radio Telemetry," Wiley (1956),
3. "Telemetry System Study, Final Report Volume II," Aeronutronic
Publication U-743, 18 Dec 1959.
4. "Telemetry System Study, Final Report Volume I," Aeronutronic
Publication U-743, 18 Dec 1959,
5. "Interpolation Errors," Advanced Telemetry Study Technical Report,
1 Part 1, 15 Feb 1961.
6. "Study and Experimental Investigation on Sampling Rate and Aliasing
in Time-Division Telemetry Systems," Aeronutronic Publication U-1387,
28 Sep 1961.
7. Bigelow, G. F,, "Status of Microwave Telemetry Implementation,"
IRE PGSET Record, Section 2.3, Oct 1962.
I
o o w
25 *k K> »H
< c o
f - JSO kk
W UH to
*J T3 V) C
c •a u
bO A h S
W 3 03 O
•f< o' B
v) v a>
jz H- c «
o rt -h 44
<u p, 4-1
*-> "3 ft>
m <?
4) O >H a>
X 4< H
*-» a> >h o
ooe
4k -H ft)
o o p, ft>
42 w 43
a), o *->
00 (0
•3 H c o
ft) rt o «-•
.— 1 -H -H
J 3 W T3
o <j rt rt
G -H H ft>
I J 4>
rt • m A -
B t)-H P 0
H H G -r
O rt rt 4J b
4-i -3 00 O ft
G G H +■
•H rt O G c
♦J OB
H(fl h-H
rt OO t
Oft) rt t
<H X 0) H 4
G *J > « ♦
x C a,
o 4k ft) ft) 4
V O VI M
*-> 4) a.
W H 0
45 -H p, £ £
o w c C
3 rt o ft) «■
V> J3 4J O
ft)
** ft) «-» H S
« j: ft £
rt ft) 43 »
43 6 H H £
P, K +J *
O « 00 -
G 4k C c
O O -H b
•H O C H
*J *-* 3 3
rt in u u
H ’a rt "
rt ft) » C 3
O <
V A 4) -H C
H B H +J
p, ft) ft) rt J
vi £ S (
a> in «j K 4
A rt o
*-» 43 4j -i
vi M C I
60>H 3 *H c
C O 'i
•H C A A I
H O W t> <
3 *H *H 3 4
Q 4J < Wt
♦j u w c
c -o « »
OO « k B
G rt 3
•H •'DO*
X W G O
— t ft) rt T3 „
H -H +J
ft) +) to ft)
T3 »H 43 '
G *-> X k
3 C P *
rt +■» 4k
W 3 ft) O
•H O' B
W ft) ft)
rt +J O > 4
O ft) 43 *H I
•H B «3 4J
*■) -Oft)
4-4 ft)
ft) O -H ft)
42 44 H
*-> ft) -H O
ooe
44 -H ft)
OOP,*)
43 W 43
* D*J*3-
o o rt rt
C -H H v .
« *■> 3 *h <
ft) * C
• H X O
1, H o«
J ft) *-» 3
) 43 ft)
1 « 0 C •
> ft) > tJ
J Oft -k (ft H
C ft) H rt
) -H H "O "0
c Z T)
O < C 4)
• *h a. rt A
4 *J
I rt 4 ft)
: B O -4 44
> 4*443 O
o rt
: 44 -T3 — « w
ft G H -H C
l >H rt rt O
> T3 > *H
: 43 c « *-»
> o rt u
4 3 *j W ft)
: w to »h w
< rt a
Q O UJ
§-HM ►-«
C vO P-
e- a o •-«
to o -4 to
♦» *o w c
c -o ft) -
60 rt h e i
c rt 3 •
•h « *o o <(
x w c o I
-4 ft) rt *3 4
£4 *H +j i
ft) +J tO © i
•3 -H A *
G *J X *->
3 C M 4
rt 4-* 44 I
w 3 «) o :
•H O' B -
W ft) ft)
rt «J «> > j
O ft) 43 -H I
•r-4 B ftj *-*
c rt a i
43 H C ft) I
O K-H44 1
ft) P, 4-4 4
*J -X3 ft) i
44 6) I
ft) a «rt a) i
43 4h H l
+J 4) -H O i
o O 6 I
4-4 *H ft) |
o o P, ft)
A W 43 '
ft)- O +-* -
* 3 *J 33 •
O O rt «
C -ri p 4)
W 3 — < C
ft) ft) Oft
• N X -< £
3 *H «J rt -rt
k G -H *J
rt 44 P </)>
0 60 O ft) ft)
3 )4 *J H
rt O G rt ft)
u O E +J
0 P .H G
o *j W *H
1) rt -rt
C 4) P 43 W
k > rt *-> W
HP, 3
k ft) ft) 4-4 O
0 W H O W
ft) P, -H
w h « -a
k P, *J E
/I COO
rt o 0 w «->
O +J o
a> •> C
a *-> H x o
CP, HP,
M E O «J 3
ft) 43 «
6 ♦» 4J B C •
H H ft) 2 *3
o rt oo rt H
W G ft) H rt
OkHrt'O
O G H G
M 3 S W rt
w rt o, -h )J
o rt ^ to
*u ? G s *o
-4 O < C ft)
Q 4) »rt P. « 43
:*wrtH vi
30 C H Ik G
3 -H « « O
0 -3 > *H
S 43 G rt *J
k O O O
k 3 *J W 3
< M W'H W
C£ —4
< rt Q
o o w
Z -H K) J-4
< C VO u,
H 43 cn *-4
W Ok to
Sf a\
W H w“
S rt 3
22 g-g
) o tS *3
JO • c c
*J .h rt
S w» C *j
3 *3 ft) -k to
* H B a
•ft 3 o o
» T3 O -H 43
r» e o c *-»
3 rt -a 45
4 *J O 44
J to O ft) o
♦ 43 4-»
J X *J W
- H 43 *H
ft *4 44 o W
3 ® O 3 rt
r§ ft, M'°
• <-4 W •> ft)
O ft) 3 ft) 45
■4 H n *-»
l> ft) rt
J ft) > 43 E
1) 43 -H P, C
3 V» +J O
ft O C 44
■» c ft) O
• *H 4-4 *H O
3, 44 44 «-»
•3 ft) «
k ft) H *3
3 -H ft) rt ft)
44 H P,-4
a *h o v jo
J o B H B
H ft) 0,3
0 P, ft) W
3 W 43 ft) vi
3 *J 43 rt
V) 4-»
*4 G O w
ft O H 60-H
■4 *H C
3 *J *3 -H G
3 rt « H O
k H ft) 3 -H
4 3 k Q ()
rt 44 H V)
60 O ft) 4)
H *-> H
O C rt ft)
° B 4J
H *k G
O *j W ,H
« -H
ft) H 43 W
6 1ft H W
P,. 3
ft) 4) 44 O
W H O w
ft) P, *k
H O *3
ft ♦; s
GOO
O ft) W *j
«-» O
ft) «• c
*J H X O
P, , HP.
a 0 «j 3
ft, 43 ft)
♦j *j a p *
*J ft) TJ
« 60 »k c} H
c ft) H rt
O «H H *3 *0
G H G
3 S W «
W *3 U, *H *J
« _ S V)
5 G S
O < C ft)
4) * H CU rt 45
H +J *J
o rt H ft)
43 H OklM
H H 4k 4> O
O w
A 4k *3 -4 t/>
60 C H -H C
3 *H rt rt O
O *3 > *rt
43 45 G « ♦»
♦J «3 « U
•k 3 4) VI O
< V)Wk w