Television system - evaluation of transmitting and receiving equipmen

Van Der Capellen, A. G.

English

NASA Technical Reports Server

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ICODEI 
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a 
PROGRESS RLPORT N O .  5 ON 
TV TRANSMITTER-CXCITERS AND POWER A M P L I F I E R S  
REPORT P E R I O D  1 NOVEMBER 1964 T O  1 DECEMBER 1964 
i 
P r e p a r e d  f o r  
GEORGE C .  MARSHALL SPACE F L I G H T  CENTER 
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
H u n t s v i l l e ,  A l a b a m a  
CONTRACT NO. N A S 8 - 1 1 6 0 9  
CONTROL NO. I C N  2-4-10-001985 
Prepared by 
A .  G .  V a n  d e r  C a p e l l e n  
OF 
RESDEL ENGINEERING CORPORATION 
Pasadena, C a l i f o r n i a  
GPO PRICE $ 
OTS PRICE(S) $ 
Microfiche (M F) 5378 
'I 
15 December 1964 
https://ntrs.nasa.gov/search.jsp?R=19650011733 2020-03-16T23:52:03+00:00Z
INTRODUCTION 
T h i s  is the f i f t h  i n  a series of monthly r e p o r t s  prepared f o r  the 
George C. Marshal l  Space F l i g h t  Center,  NASA, H u n t s v i l l e ,  Alabama, cove r ing  
t h e  per iod  1 November 1964 t o  1 December 1964, as s p e c i f i e d  i n  t h e  s u b j e c t  
c o n t r a c t .  
WORK AC C O W L  I SHE D 
1)  System t e s t  completed (P ro to type ) .  
2 )  Environmental  t es t  80% completed (Pro to type)  . 
3) Documentation 90% completed.  
4)  F a b r i c a t i o n  of t r a n s m i t t e r - e x c i t e r s  70% completed.  
5) ~ F a b r i c a t i o n  of power a m p l i f i e r s  (Model 91064) 80% completed.  
6) W r i t i n g  of i n s t r u c t i o n  manual completed.  
DISCUSSION 
A block diagram i s  inc luded  f o r  r e f e r e n c e .  
Subassembly t e s t i n g  i s  almost  completed on t h e  f i r s t  p roduct ion  u n i t .  
Second t e s t  of t h e  RF and X16 m u l t i p l i e r  s e c t i o n  has  been completed.  F i r s t  
t e s t  of t h e  AFC and Video s e c t i o n  has been completed.  T h i s  s e c t i o n  i s  now 
ready  f o r  c l e a n  up, i n s p e c t i o n  and then  p o t t i n g ,  a f t e r  which a second tes t  
f o l l o w s .  Subassembly t e s t i n g  on subsequent u n i t s  has  been done on power 
s u p p l i e s ,  c a v i t i e s ,  RF am/pl i f ier  s e c t i o n s  and AFC & Video s e c t i o n s .  
A formal q u a l i t y  acceptance  t e s t  procedure i s  ready  f o r  approval  and w i l l  
be submi t ted .  R e s u l t s  on t h e  s tudy  of s i n 2  p u l s e , t e s t i n g  a r e  d iscussed  m d e r  
problem areas. I -. 
PROBLEM AREAS 
The problem of proving  out  t h e  h igh  frequency v ideo  response  of t h e  
t r a n s m i t t e r  i s  a matter o f :  
1. Def in ing  which t echn ique  i s  t o  be used .  
2 .  C o r r e l a t i n g  the measurements w i t h  t h e  s p e c i f i c a t i o n .  
Three t echn iques  are known t h a t  w i l l  y i e l d  informat ion  about  h igh  frequency 
v i d e o  response .  
1. Measurement of h o r i z o n t a l  r e s o l v i n g  power which can be re la ted t o  
t h e  3 db v ideo  bandwidth. A camera and t e s t  p a t t e r n  are used f o r  
test  s i g n a l .  
2 2 .  Measurement of s i n  pu l se  deg rada t ion .  R e l a t i n g  t h i s  in format ion  t o  
bandwidth i s  a d i f f i c u l t  t a sk .  
i 
-1- 
A t  
x 
3 .  Direct meas rement of v ideo  response .  A m u l t i b u r s t  or a cont inuous  
sweep s i g n a l  is used i n  t h i s  case. c 3 
From the s t a n d p o i n t  t h a t  r ep roduc t ion  of an u n d i s t o r t e d  p i c t u r e  is t h e  
u l t i m a t e  c r i t e r i o n ,  measurements taken with camera and tes t  pattern would 
seem v a l i d .  However, t h i s  i s  a s u b j e c t i v e  c t e s t  and i t  does n o t  y i e l d  i n f o r -  
mat ion r e l a t a b l e  t o  t h e  s p e c i f i c a t i o n . ’ ,  (The s p e c i f i c a t i o n  c a l l s  f o r  a mod- 
u l a t i o n  index  of 6 a t  1 m c  and a modulation index of 1 a t  6 mc which i s  
e q u i v a l e n t  t o  a f l a t  r e sponse  up t o  6 mc.1 The 3 db bandwidth i s  no t  d e f i n e d ) .  
The only  measurement t h a t  y i e l d s  in fo rma t ion  d i r e c t l y  re la table  t o  t h e  
s p e c i f i c a t i o n  i s  t h e  d i r e c t  measurement of v ideo  r e sponse .  However t h i s  
method does not  i n d i c a t e  t h e  presence of overshoot  or r i n g i n g .  These are  
observed by employing t h e  s i n 2  p u l s e  method. 
The conc lus ion  then  would be t o  u se  both  two methods: ;  
1. , The s i n 2  p u l s e  t o  o b t a i n  informat ion  on overshoot  o r  ringing.,,‘ 
1 
2 .  , T h e  sweep (o r  m u l t i b u r s t )  s i g n a l  t o  o b t a i n  in fo rma t ion  on r e sponse  
i n  gene ra l  and bandwidth i n  p a r t i c u l a r .  
S i n c e  it was i n d i c a t e d  t o  u s  on t h i s  c o n t r a c t  t h a t  the s i n 2  p u l s e  methou 
was t h e  p r e f e r r e d  way of t e s t i n g  t h e  t r a n s m i t t e r ,  a n  a n a l y s i s  has  been made  t o  
r e l a t e  s i n 2  p u l s e  wid th  deg rada t ion  t o  bandwidth.  
The a n a l y s i s  showed t h a t  s i n 2  pu l se  wid th  measurements mainly y i e l d s  
q u a l i t a t i v e  in fo rma t ion  w i t h  r e g a r d s  t o  s y s t e m  bandwidth.  The measurement 
i n d i c a t e s  whether t h e  bandwidth i s  w i t h i n  c e r t a i n  l i m i t s ,  bu t  no g u a n t i t a t i v e  
in fo rma t ion  about  t h e  bandwidth i s  ob ta ined .  
On t h e  b a s i s  of measurements on two u n i t s ,  a l i m i t  h a s  been e s t a b l i s h e d  
Extreme d i f f i c u l t y  was encountered i n  k r o v i n g  ou t  t h e  test equipment,_/ 
which would a s s u r e  meet ing t h e  s p e c i f i c a t i o n s  of t h i s  c o n t r a c t .  
i n  p a r t i c u l a r  t h e  r e c e i v e r .  S i n c e  no s t anda rd  could r e a d i l y  be found t o  
independant ly  prove ou t  t h e  r e c e i v e r  bandwidth, a t echn ique  of comparing was 
used .  T h i s  proved t h a t  some degrada t ion  of t h e  s i n 2  p u l s e  was caused by t h e  
r e c e i v e r .  The f i r s t  measurements were t aken  w i t h  a down conver t e r  (1710 mc 
t o  100 mc).and a 100 mc d i s c r i m i n a t o r .  S ince  t h e  bandwidth of t h i s  system 
was under  susp ic ion ,  a new d i s c r i m i n a t o r  was c o n s t r u c t e d  w i t h  a c e n t e r  f r e -  
quency of 1710 mc i n  o r d e r  t o  o b t a i n  a l a r g e r  bandwidth.  Measurements w i t h  
t h e  t r a n s m i t t e r  and t h i s  d i s c r i m i n a t o r  showed an  improvement of approximately 
4 db a t  6 mc. 
Comparing t h e  s i n 2  p u l s e  deg rada t ion  when t h e  t r a n s m i t t e r  bandwidth was 
v a r i e d ,  a l i m i t  h a s  been determined.  T h i s  l i m i t  i s  . l o 5  microsecond f o r  an  
i n p u t  of .080 microsecond.  ( s e e  F igure  1 )  
-2- 
H a l f  amp1 1 t :I< 
n i  c r o 6 e c o n  ~1 
Half ampli tude wid th  = 
A 
50% 
k - . j y  
A .080 microsecond wid th  - . l O j  
5 0% 
i 
~ V ______I’ - -  - _ -  
INPUT 
FIGURE 1 
OUTPUT 
On t h e  b a s i s  of t h i s  l i m i t  a g r a t i c u l e  was made up t h a t  w i l l  b e  used 
T h i s  g r a t i c u l e  also d e f i n e s  t h e  i n  t h e  acceptance  t e s t .  
maximum a l l o w a b l e  r i n g i n g  (10% f i r s t  lobe, 5% second l o b e ;  
(see F i g u r e  2)  
see F i g u r e  3 ) .  
. l o 5  microsecond 
-*  c.L- 
I I 
O s c i l l o s c o p e  adjusted 
f o r  . l o 0  microseconci/cm 
h o r i z o n t a l  s ens  i t  i v  i t )  
- - _ _  - .  
.A Second lobe  
/ 
i 
Fi r s t  lobe  
FIGURE 3 
-3 -  
i J Q I C I F A T 5 D  EFFORT FOR :TEXT P E R I O D  
1) Finish environmental test on modified unit. 
2) Continue production transmitter exciter units. 
3) Continue production of power amplifiers. 
4 )  Continue documentation. 
5) Ship first transmitter-exciter and power amplifier. 
RESDEL ENGINEERING CORPORATION 
Approved By I * 
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Prepared By ‘ - I  .. : . . ;  c : .  1 -  , I  
A .  G. Van der Capellen 
M. F. Brown, Jr. 
Vice President 
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4 
1. 
EFFECT OF BAND-PASS FILTER ON AN FM SIGNAL 
Consider the following FM signal:  
1 
1 
v = s i n w t + @  s i n w t  
( c  m 
+ s i n  wmt 
If we drop the imaginary part:  
v ' e  j ( w c t  + B s i n  wmt) a e j w c t  e j e  sinwmt 
But by Guillemin, Mathematics of Circui t  Analysis p 509 eq 318, 
Taking the imaginary part: 
a0 
v = c J,(@) s i n  w + nw t 
,aD ( c  m ) 
(3) 
but because 
separat ing in to  odd and even parts: 
*- . 
* .  
= sin wct cos (2n+l)wmt + cos wct sin(2n+l)w t m 
J - sinwct cos(2n+l)wmt - cosw t sin (2n+l)omt C 
C 
[ 
= 2 cosw t sin(2n+l)wmt 
(2) = sin w + 2nw t + sin(w -2nw t 
( C  m 1 c m) 
= sin w t cos2nw t + cosw t sin2nw t 
C m C m 
+ sin w t cos2nw t - cosw t sin2nw t 
C m C m 
= 2 sin w t cos2nwmt 
C 
thus 
a0 
v = J~ (e) sinwct + 2~ J ~ ~ + ~  (e) coswct sin(2n+1)wmt 
n=O 
+ 2 c J~,(B) sincuct cos2nw t m n-1 
as an example let 8 = 1 
Jo (1) = .80 
251 (1) e .82 
2J2 (1) e .28 
2J3 (1) = .09 
From equation (1) we see that the instantaneous phase angle at 
wmt = n/2 will be the modulation index B .  We also note from eq. 16 that 
the phasor contributions due to the odd harmonics of the modulation will 
be perpendicular to the carrier, and the phasors due to the even harmonics 
will be parallel to the carrier. 
Jo (1) = .80 
2J1 (1) sinwmt = 2J1 (1) sinnI2 = .82 
2J2 (1) cos2wmt = 2J2 COBX = -.28 
etc. 
-2 - 
1 
.*I 
. 
The resu l tan t  phasor is  shown i n  Figure 1 as v/n/2, 4 which is the 
r e su l t an t  a t  w t 
l e s s  than four harmonics were summed in  the r e su l t an t  t ha t  the r e s u l t  would 
be j u s t  the vector sum of the n phasors. 
n/2 and the f i r s t  four harmonics. We can see t h a t  i f  m 
r 
0 
Figure 1 
For example, i f  only one harmonic were considered, the resu l tan t  
would be v / R / ~ ,  1 a s  shown i n  Figure 1. 
t o  wm = Aw 
quency w = 113 wm and the same amplitude then Bn 
same expansion is val id  so we have: 
This example might correspond 
6 mc. and a 6 mc. ideal f i l t e r .  
I f  we consider the same example with a d i f f e r e n t  modulating f r e -  
= 38, = 3 the n -
2"Wm 
-3 - 
. 
sinwt + 2J1 Bn sinw t coswt 2J2 Bb cos2wnt sinwt -k e tc .  , m e Jo 8, 
Af = 6 mc 
f = 2 m c  n 
= 3  'n 
a t  w t = x/2 m 
Jo ( 3 )  ", - e 2 5  
" 2J1 ( 3 )  s i n  wmt  E .68 , 
2J2 (3) cos 2w t - .96 m 
2J3 ( 3 )  s i n  3wmt - .64 
254 ( 3 )  cos 4w t .34 m 
2J5 (3) sin 5wm5 ", .14 
This i s  plot ted i n  Figure 2 and the resu l tan t  is shown a s  v/ls/2, 5 
which is read a s  the instaneous voltage a t  wmt = n/2 with 5 s ide  bands. 
The angle B 5 is the maximum phase angle and i s  equal t o  8 .  
I f  we now pass t h i s  s ignal  through a bandpass f i l t e r  which a d m i t s  
only the f i r s t  3 sidebands (the same f i l t e r  which admitted only the f i r s t  
sideband of wm = 6 mc), we see tha t  the resu l tan t  vector is  e/rr/2, 3 and 
phase angle i s  Q 3. We see a t  once t h a t  $3 > $5 or  the  modulation index j 
i s  apparently increased. 
We a l s o  not ice  t h a t  the angle w i l l  no longer be s inusoidal  i n  time 
but w i l l  be affected by the absence of the  higher sidebands. 
-4- 
e 
Figure 2 
From equation 16 we can ana ly t ica l ly  express the output of a bandpass 
f i l t e r  i n  terms of the number of harmonics passed, N. To do t h i s  we pro- 
ceed as follows. We 
v = v( t )  sinwit 
but by inspection of 
t r y  t o  put v(t)  i n t o  the following form, 
+ @ (t) 
the phasor diagrams w e  see tha t  
-5 - 
when a l l  s ide  bands a r e  passed. 
need only replace the upper l i m i t s  sunmation by 2n + 1 N and 2n 
If only N s ide  bands are passed, we 
N. 
As an example of t h i s  general case we may l e t  N 
(t) = Tan [ Jo($) ] 
1 so 
-1 2J1 (B) sinwmt 
We can draw some simple conclusions from t h i s .  
and Jo(B) = 1 so Q (t) = B sinWmt which is a standard r e s u l t .  
2) 
If B< < 1 then J1(B)=B/2 
No matter-what value B has /Q(t)/sn/2 
This can be seen by considering the band pass f i l t e r  a s  a nonlinear 
t r a n s f e r  function f o r  phase angles a s  shown i n  Figure 3. 
I 
8 out 
Figure 3 
The amount of harmonic d i s to r t ion  i n  the output is governed by the 
-6- 
r 
THE S I N E  SQUARED PULSE I N  FM 
A) To determine the spectrum of an FM c a r r i e r  of frequency f mod- 
u la ted  by a s ine squared pulse of half amplitude t i m e  t w e  f i r s t  consider 0' 
' modulation of the c a r r i e r  by a s ine squared wave such &at  i ts  frequency f 
is the  following: 
2 s  
f fo  + Afc s i n  
2t0 
but the instanious phase angle i s  
L d t  
.2to = Sfd t  = f o t  + S A f  s i n  2n C 
but s i n  2 (Y = [l-cos 2011 
so we may wr i t e  
( 5 )  
@ 
2ll 
rrt  Af t s i n  - + 2 
to 
c o  t - -  Af - =  2ll 2 71 
o r  e = Eo cos@ (t) = E cos 
0 0 
Equation (6) can be expanded in to  a Fourier s e r i e s  with the a id  of 
any standard reference such as Fink, Television Enpineering, p. 413,  eq. 
220 and the r e s u l t  is: 
e Af ")  + J1 (-2Af t ) 
c o  - =  Jo(-2Af t ) cos 2n c o  
Af  
t-cos 2; f + - - - 
0 ( 0  2c 2 t o  
L 
and using the fact , and f c  = f o  + 7 1 = - m 2to C 
Af 
l e t t i n g  m = -2Afcto, f 
t h a t  Jn (-m) = (-l)n Jn (m) we get: 
-. 
.J * 
e W 
0 ,  Jo(m) cos2rr f c t  + C Jn (m) 
EO n=l  
This s e r i e s  can be interpreted as a one sided voltage spectrum as 
f ollaws: 
I f  f =8mc , to f 62.5 ns. Then m = -2 Af t f -1 and f(m) = - = 8mc.  
2t0 
C c o  
Jo(-1) .8 
J1(-l) --.45 
J2(-1) .15 
These numbers a r e  plot ted i n  Figure 1. 
-.45 -.45 
Figure 1. Voltape Spectrum 
B) We can now make up the time wave form of the c a r r i e r  modulated by 
a pulse instead of a wave i n  the following way: 1. multiply the wave form 
0' 
of the  wave modulated c a r r i e r  by a pulse of height 1 and durat ion 0 t o  2 t  
and add t o  t h i s  the unmodulated c a r r i e r  multiplied by a zero pulse i n  the 
same in te rva l .  Since mult ipl icat ion of time wave form r e s u l t s  i n  convolu- 
t i o n  of frequency spectra,  then we can wr i t e  down the expression of the 
t o t a l  spectrum. 
Wave Form Spectrum 
Carrier Gc(f) = 6 (f-fo) 
Sin wave modulated 
OD 
Gw(f) = Jo(m) 6 
+ (-In) 6 (fbf C + nfm)] 
2 
s in2nt - f 
Posi t ive Pulse 0 e-2jnt  f 
Phase Factor 
-2 - 
sin2rrt (f-fc) 
0 
Therefore, GTe2jntof = J o ( m )  [. 0 nto(f-fc) 
To draw conclusions from the above equation we proceed as follows. 
The G+ spectrum i s  the s i n  Q’/Q curve with i t s  f i r s t  zeros a t +  8 m c  and 
i t s  shape i s  imposed on each of the l i nes  of the s ine  square wave modu- 
la ted c a r r i e r .  The c a r r i e r  i tself  is present with t h i s  shape a l s o  on it. 
With a modulation index of 1 or  less  only the f i r s t  pa i r  of s ide  bands is  
important so the composite spectrum is as shown i n  Figure 2. 
A 
-12 -8 f o  +4 +8 +20 to = 6211s. 
Firmre 2 
C) I f  we wish t o  consider a pulse t r a i n  with time T between pulses, 
we know tha t  the envelope of the spectrum would remain unchanged and t h a t  
the spectrum would be composed of d i sc re t e  l i n e s  separated by frequency 
1 f a -  T ’  
-3 - 
-1 
Analysis of the Effects  of a Band Pass F i l t e r  on a Sine Squared c 
Pulse of H a l f  Amplitude Duration 7. 
A) Frequency Spectrum of the Pulse - As the f i r s t  s t e p  i n  the ana lys i s  
we s h a l l  f ind the frequency spectrum of the pulse by evaluating its b i -  
l a te ra l  Fourier transform. 
pick t = 0 a t  the center  of the pulse. 
The transform w i l l  be e a s i e r  t o  evaluate  i f  w e  
-7 
v ( t )  = 5 [ l + c o s q  
. J  
W 
V(w) = l v(t)e'jwt d 
-W 
F i m r e  1 
/ t / < T  
7 
e v(t)e-jWtd- 
-7 
7 7 
= f coswt v ( t )  d t - j  l v ( t )  sinwtdt 
t t -7 
even odd => = 0 
7 
= % s( l+cos F) coswt d t  
-7 
7 7 
J17 = ' f  1 coswt d t  + f s cos 7 coswt d t  
7 -7 
7 7 7 
0 0 0 
= s coswt d t %  Jcos (tu + 4) t d t %  s cos ( w - A / T ) t  d t  
sin(w-X/T)t 7 / s i n  w h r / T ) t  T + f  w + 1 1 / 7  0 = -  T + f w o  0 
s inw7 + sin(co.rfrr) + s i n ( w ~ - ~ l  
h/ 7 W-R/7 
v(w) = -
W 
We can now v i sua l i ze  these terms. 
.- . . 
c 
1 
7 I .  
Figure 2 
7 
To in te rpre t  the spectrum a s  shown i n  Figure 2, i t  would be handy 
t o  i n s e r t  some numbers. 
I f ,  T 62.5ns then the 6 db point, 2af = w= K/T  or  f = %lt = 8 mc. The 
frequency beyond which the spectrum is e s sen t i a l ly  zero if f l / ~  16 mc.  
B) Effect of a Low Pass F i l t e r  on the Pulse - As the second s t e p  i n  
the analysis  we pass the spectrum of the pulse through an idea l  f i l t e r  
whose cutoff i s  the 6 db point of the pulse spectrum. 
For example: H(w) = l , / w / S  a/7 
H(w) = O,/w/>  r[/7 
So the  spectrum of the  output pulse w i l l  be V'(w) = H(w) V (w) 
v ' ( W )  0, /W/>Ir /T 
Taking the inverse.Fourier  transform we have: 
a/ 7 
v ( t )  = l / a  J V(w) coswt dw 
0 
--. 
0 
-2 - 
- - ~- 
.+ 
Y 
a . 
4 taking the terms one a t  a t i m e .  
I f  w e  introduce the var iab le  x = w + A/T  dx = dw and use the 
X X 
dx = cos b Si(ax) + s i n  b C i  (ax) / sinax+b i d e n t i t y  0 
0 
(7-t) d c i  (t+i)x 6 +cosrtt si (  ) s inlrt 7 cos S i  - 7 7 
C i  ((7-t)x) / 
0 
+ 
expanding as before and l e t t i n g  x w- d7. 
Adding (l), (2), and (3), we see tha t  the terms with cosine in t eg ra l s  
cancel and we have 
v ( t )  = 1/2n (1 + cos?} (S i (  L-.;ll t + T  R -si ( F)) 
A p lo t  of t h i s  function is shown i n  Figure 3. 
We see tha t  the pulse is about 18% higher than the input pulse and the 
half  amplitude duration of i t  is  a l i t t l e  less than 7 .  
the output pulse are about 18% of the’ input .  
The f i r s t  lobes of 
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Tv transmitter-exciters and power amplifiers progress report, 1 nov. - 1 dec. 1964

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