§ 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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