Prior to the ASTP joint flight it was observed during various tests on the USA's VHF/FM system, that the 121.75 MHz receiver unsquelched when exposed to certain RF power levels at a frequency of 142.417 MHz. Tests were conducted in an effort to arrive at a solution. Several recommendations were made but the most feasible was to insert a selective band pass filter in the transmit/receiver line of the VHF/FM transceiver. The tests were performed on the filter to determine the frequency response and rejection capabilities at 142.417 MHz

Davis, R. J.

English

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NASA_ CR-
I	 121.75 MHz BAND PASS FILTER
9
Job Order 17-060
(NASA-CR-144553) THE 121.75 MHz BARD PASS
	 X176-11349
FILTER (Lockbeed Electronics Co.) 14 p
HC $3.50	 CSCL 09C
onclas
G3/33 02603
Prepared By
Lockheed Electronics Company, Inc.
Aerospace Systems Division
Houston, Texas
Contract NAS 9-12200
For
SPACECRAFT SYSTEMS TEST OFFICE
TRACKING AND COMMUNICATIONS DEVELOPMENT DIVISION
NadonW Aenonau" and Spode A--I--- - -*- ! d —
LYNDON B. JOHNSON SPACE CENTER
September 1975
LEC-6995
Shuttle
JSC-09971
121.75 MHz BAND PASS FILTER
Job Order 17-060
PREPARED BY
-IDavis, Project Engineer
Lockheed Electronics Company, Inc.
APPROVED BY
^ LEC
45:F ;ZR49-0-^--
oe se, Supervisor
Spacecraft Systems Test
Section
NASA
- 1 00^XL-
William  Long 'He
Spacecraft Systems Test
Office
ynrw -S. Creamer,Jr., anager
acking and Communications
stems Department
Prepared By
Lockheed Electronics Company, Inc.
For
Spacecraft Systems Test Office
Tracking and Communications Development Division
NATIONAL AERONAUTICS AND SPACE ADMINISTRAT&ON
LYNDON B. JOHNSON SPACE CENTER
HOUSTON, TEXAS
September 1975
ii
iii
PREFACE
-v
This report - describes the results of tests performed on a
121.75 MHz -band pass fitter. It is the filter recommended
in LEC document 4457 as a solution for the rejection of an
interfering signal at 142.417 MHz.
E •
a.
ACKNOWLEDGEMENTS
This document was prepared in response to Action Document
7060-21 = 60, submitted by the Spacecraft Systems Test Office
(SSTO) of the Tracking and Communications Development Division.
William C. Long, Office Head, was the Technical Monitor for
this task. Robert J. Davis, of the Spacecraft Systems Test
Section, Lockheed Electronics Company, Inc., prepared this
document.
iv
CONTENTS
Section	 Page
1. SUMMARY	 . . . . . . . . .	 1-1
2. 121.75 IrHiz BANDPASS FILTER TEST REPORT. . . . . . . . . 2-1
3. CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . 3-1
v
1. SUMMARY
Prior to the ASTP joint flight it had been observed during
various tests on the USA's VHF/FM system, that the 121.75 MHz
receiver unsquelched when exposed to certain rf power levels at
a frequency of 142.417 MHz. Consequently, tests were conducted
per LBC Document 4457 in an effort to arrive at a solution.
Several recommendations were made but the most feasible was to
insert a selective band pass filter in the transmit/receive line
of the VHF/FM transceiver. The tests shown in Section 2 were
performed on the filter to determine the frequency response and
rejection capabilities at 142.417 MHz.
1-1
2. 121.75 MHz BANDPASS FILTBR TEST REPORT
The test results are shown on the following pages of this section.
Ran band pass characteristics of the filter per set up on page
2-2 with resulting data plot on page 2-4.
Also conducted a test with the filter connected in the planned
flight position as shown on page 2-8. The resulting plot of
unsquelched levels vs frequency shows the rejection capability
at 142.417 MHz.
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3. CONCLUSIONS
The frequency response of the filter shows it to have a 3 dB
bandwidth of 11.35 MHz or i S.67S MHz about a center frequency
of 121.75 MHz. It also shows the interfering frequency, 142.417
MHz, to be well out of the band pass region.
Unsquelch tests were als- r--•.xducted and the rejection capabilities
were more than adequate, es,.e-._ally at the interfering frequency
of 142.417 MHz.
3-1


The 121.75 MHz band pass filter

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