§ 87.151   Special requirements for differential GPS receivers.

   (a) The receiver shall achieve a message failure rate less than or
   equal to one failed message per 1000 full-length (222 bytes)
   application data messages, while operating over a range from −87 dBm to
   −1 dBm, provided that the variation in the average received signal
   power between successive bursts in a given time slot shall not exceed
   40 dB. Failed messages include those lost by the VHF data receiver
   system or which do not pass the cyclic redundancy check (CRC) after
   application of the forward error correction (FEC).

   (b) The aircraft receiving antenna can be horizontally or vertically
   polarized. Due to the difference in the signal strength of horizontally
   and vertically polarized components of the broadcast signal, the total
   aircraft implementation loss is limited to 15 dB for horizontally
   polarized receiving antennas and 11 dB for vertically polarized
   receiving antennas.

   (c) Desensitization. The receiver shall meet the requirements specified
   in paragraph (a) of this section in the presence of VHF-FM broadcast
   signals in accord with following tables.

   (1) Maximum levels of undesired signals.
   Frequency^1 Maximum level of undesired signal at the receiver input
   (dBm)
   50 kHz up to 88 MHz −13
   88 MHz-107.900 MHz [see paragraph (c)(2)]
   108.000 MHz-117.975 MHz excluded
   118MHz −44
   118.025 MHz −41
   118.050 MHz up to 1660.5 MHz −13

   ^1The relationship is linear between single adjacent points designated
   by the above frequencies.

   (2) Desensitization frequency and power requirements for the
   frequencies 108.025 MHz to 111.975 MHz.
   Frequency^1 Maximum level of undesired signal at the receiver input
   (dBm)
   88 MHz ≤f ≤102 MHz 15
   104 MHz 10
   106 MHz 5
   107.9 MHz −10

   ^1The relationship is linear between single adjacent points designated
   by the above frequencies.

   (3) Desensitization frequency and power requirements for the
   frequencies 112.00 MHz to 117.975 MHz.
   Frequency^1 Maximum level of undesired signal at the receiver input
   (dBm)
   88 MHz ≤f ≤104 MHz 15
   106 MHz 10
   107 MHz 5
   107.9 MHz 0

   ^1The relationship is linear between single adjacent points designated
   by the above frequencies.

   (d) Intermodulation immunity. The receiver shall meet the requirements
   specified in paragraph (a) of this section in the presence of
   interference from two-signal, third order intermodulation products of
   two VHF-FM broadcast signals having levels in accordance with the
   following:

   (1) 2N1 + N2 + 72 ≤0 for VHF-FM sound broadcasting signals in the range
   107.7-108 MHz; and

   (2) 2N1 + N2 + 3 (24 −20log delta f/0.4) ≤0 for VHF-FM sound
   broadcasting signals below 107.7 MHz, where the frequencies of the two
   VHF-FM sound broadcasting signals produce, within the receiver, a two
   signal, third-order intermodulation product on the desired VDB
   frequency.

   (3) In the formulas in paragraphs (d)(1) and (d)(2) of this section, N1
   and N2 are the levels (dBm) of the two VHF FM sound broadcasting
   signals at the VHF data broadcast (VDB) receiver input. Neither level
   shall exceed the desensitization criteria set forth in paragraph (c) of
   this section. Delta f = 108.1 − f1, where f1 is the frequency of N1,
   the VHF FM sound broadcasting signal closer to 108.1 MHz.

   [ 69 FR 32881 , June 14, 2004]

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Subpart E—Frequencies

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