Telemetry bands are being reassigned to UHF at 1500 and 2200 MHz. Conversion primarily requires changes in equipment used in RF link, while many of same subcarrier oscillators, mixer amplifiers, and frequency discriminators can be used

Salter, W. E.

Wallace, G. R.

English

NASA Technical Reports Server

May 1973	 .	 B73-10170 
NASA TECH BRIEF 
Marshall Space Flight Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
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Pre-emphasis Determination for an S-Band

Constant Bandwidth FM/FM Station 
Airborne	 Ground 
' , 
Data Input 
#1	 f CS=C O #1 
•	 I 
Constant Bandwidth	 i 
SCO's 
8 kHz Spacing 
I	 I I	 I 
Data Input sco #11 
#11
	 fc = 96 kHz
	
Video	 Discriminator 
Output (#1)11
Mixer	 RF Assy
Discriminator 
Amplifier 
TOIL 
= 2278 MHz 	 Receiver	
. (p6) R  
Position Of	 Variable 
Flight Recorder	 Attenuator	 V'' (If Used)	 ' Disc  
r'	 (#7) 
Telemetry users in the U.S. are limited to three - fre-
quency bands: 216 to 260 MHz, 1435 to 1535 MHz, 
and 2200 to 2300 MHz. At the present time, however, 
telemetry bands are being reassigned to UHF at 1500 
and 2200 MHz. This change has raised a question con-
cerning conversion of existing constant-bandwidth (CBW) 
FM/FM systems operating in the VHF band to the UHF 
band at 2200 MHz (S-band). 
The conversion, however, is not as big a problem as 
it may appear at first glance. Primarily, changes are 
required in the equipment used in the RF link, while 
many of the same subcarrier oscillators (SCO's), mixer 
amplifiers, and frequency discriminators can be used. 
In a recent study, pre-emphasis schedules were deter-
mined for 11 constant-bandwidth FM subcarriers modu-
lating an S-band transmitter at three receiver signal-to-
noise ratios (i.e., 9, 15, and 25 dB). It is anticipated 
that the use of one of the pre-emphasis curves with a 
telemetry system will ensure that approximately equal 
output signal-to-noise ratios for all channels in a de-
creasing S/N ratio situation can be obtained while 
operating at one of the three preselected S/N ratios.
Heterodyne Discriminator 
Translator	 ,
	
411) 
The CBW system used in the experiment is illustrated 
(see figure) with an alternate approach, represented by 
crosshatched blocks, to such system testing. 
The pre-emphasis schedule for the system was ob-
tained by operating the receiver at the IF carrier-to-
noise ratio of 9 dB, while adjusting the individual un-
modulated SCO outputs to produce identical subcarrier-
to-noise ratios at the receiver video output. Measuring 
the subcarrier-to-noise ratio at the video output differs 
from the established practice of making the measure-
ment at the output of the bandpass input filters of the 
frequency discriminators. This is more desirable since 
the results obtained are independent of any particular 
bank of ground discriminators. This technique estab-
lishes only the relative levels of the individual SCO's 
while the absolute level depends upon the bandwidth 
limitations placed on the total RF spectrum. The gain 
control on the mixer amplifier can be used to adjust 
the total multiplex level to achieve the desired spectrum 
bandwidth. This is permissible since small variations in 
the total multiplex level do not alter the relative re-
lationships of the individual subcarrier-to-noise ratios. 
S/
(continued overleaf) 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately owned rights.
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The measured pre-emphasis data are compared with the 
simplified analytical solution. If it is determined that 
inadequate performance is obtained because of the 
9-dB IF S/N ratio; other pre-emphasis curves can be 
obtained for higher S/N ratios by repeating the pro-
cedure. 
Notes: 
1. Information concerning this innovation may be of 
interest to the designers and manufacturers of line-
of-sight data transmission systems and associated 
equipment.
2. The following documentation may be obtained from: 
National Technical Information Service 
Springfield, Virginia 22151 
Single document price $3.25 
(or microfiche $0.95) 
Reference: NASA TMX-64648 (N72-25182) 
Pre-emphasis Determination for an S-Band Con-
stant Bandwidth FM/FM Station 
Source: G. R. Wallace and
W. E. Salter of
Sperry Rand Corp. 
under contract to
Marshall Space Flight Center
(MFS-22 135)
S 
B73-10170	 Category 02 S


Pre-emphasis determination for an S-band constant bandwidth FM/FM station

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