MIL-STD-291C
5. DETAILED REQUIREMENTS
5.1 TACAN surface transponder signal. The standard signal, to be radiated and received by the transponder of the TACAN system, shall be vertically polarized and the radiated signal shall have the following characteristics:
5.1.1 Radio frequency (r.f.). The transmitted frequency shall be maintained within plus or minus 0.002 percent of that specified.
5.1.2 R.F. pulse spectrum. The peak effective radiated power contained in each of the two
0.5 MHz bands centered on frequencies plus or minus 0.8 MHz above and below the nominal channel frequency shall not exceed 100 milliwatts (mw), and the peak effective radiated power contained in each of the two 0.5 MHz bands centered on frequencies plus or minus 2.0 MHz above and below the nominal channel frequency shall not exceed 2.0 mw. Each lobe of the spectrum shall be less than the adjacent lobe nearer the nominal channel frequency.
5.1.3 Continuous wave (cw) output. Cw output between pulse pairs shall not exceed 5 microwatts (µw) with the beacon in normal operational mode. The peak signal amplitude for a period of 1 µsec between pulses of a pair on X channels and 19 µsec between pulses of a pair and pulses of the main reference group on Y channels shall be at least 20 decibel (db) below the peak pulse amplitude. During the Y channel auxiliary reference burst group, the energy shall be at least 20 db below the peak pulse amplitude for at least 4 µsec between pulses of the group.
5.2 Pulse shape. The pulse envelope as detected by a linear detector shall have a rounded shape falling within the following limits:
5.2.1 Pulse top. The instantaneous amplitude of the pulse shall not, at any instant between the point of the leading edge which is 95 percent of the maximum voltage amplitude and the point of the trailing edge which is 95 percent of the maximum amplitude, fall below a line which is 95 percent of the maximum voltage amplitude of the pulse and is parallel to the base line.
5.2.2 Pulse rise time. The time required for the leading edge of the pulse to rise from 10 to
90 percent of its maximum voltage amplitude shall be 2.0 ± 0.25 µsec.
5.2.3 Pulse fall time. The time required for the trailing edge of the pulse to fall from 90 percent to 10 percent of its maximum voltage amplitude shall be 2.5 ± 0.5 µsec.
5.2.4 Pulse duration. The pulse duration which is measured between the points on the leading and trailing edges of the pulse which are 50 percent of the maximum voltage amplitude of the pulse shall be 3.5 ± 0.5 µsec.
5.3 Pulse droop. Prior to amplitude modulation by the antenna of the composite r.f. pulse train, the percentage modulation of the pulse train at 15 or 135 Hertz (Hz) shall not exceed 0.08 percent (see 3.5 and 3.6). This shall be measured with the transponder operating normally and shall include the effects of droop and recovery time of the main and auxiliary reference groups.
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