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Motorola Self-Quieting Frequencies for GM300, MaxTrac, Radius, etc. Compiled by Robert Meister WA1MIK

Background Information:

Most radios contain oscillators in the synthesizer and/or receiver circuit. These can generate signals on specific frequencies and of sufficient strength to be heard by the receiver. These unintended signals are often called "birdies." Some Motorola sales literature mentions them as "self-quieting frequencies" because the signal is of sufficient strength to be heard by the receiver, and it quiets all the background noise.

Not all radio models have these frequencies documented, but it is obvious that any radio that shares the same frequency-generating components can exhibit this problem. This phenomenon can even happen with multiple receivers mounted close to each other. Some radios offer alternate oscillator or IF frequencies, intended to be used in those situations where a self-quieting frequency must be utilized.

GM300, Radius, MaxTrac, and MaraTrac mobile radios all share similar circuitry and are susceptible to these self-quieting signals, even though they're only documented for the GM300. Depending on how the radios were manufactured, some of these frequencies may still be usable on some radios. They should not just be avoided; they should be considered "not available" for public safety radios.

Known Signal Sources:

Most of these are harmonics of the 14.4 MHz reference oscillator on the RF board. The GM350 and GM950 radios are European models and apparently they utilize a 16.8 MHz reference oscillator.

The receiver's second local oscillator crystal can also be the source of signals that can be found at multiples of 10.245 MHz (VHF-LO), 44.645 MHz (VHF-HI, UHF, 800 MHz), or 38.695 MHz (900 MHz).

Another potential signal source is the 7.776 MHz microprocessor crystal on the logic board. And of course any or all of these crystal frequencies or their harmonics can mix in ways that I can't even begin to comprehend.

Model-specific Self-Quieting Frequencies:

Self-quieting frequencies that should be avoided on the M130 radios:
VHF: 147.330, 158.400, 161.070 and 172.800 MHz.
UHF: 446.400, 446.450, 454.200, 454.220 and 457.445 MHz.

Self-quieting frequencies that are not available on the M208/M216 radios:
LB: 30.735, 40.980 and 43.200 MHz.

Self-quieting frequencies that are not available on the GM300 radios:
VHF: 144.000, 147.330, 158.400, 161.070 and 172.800 MHz.
UHF: 403.080, 403.200, 405.900, 417.600, 426.945, 429.955 and 432.000 MHz.
UHF: 446.400, 446.450, 454.200, 454.220, 457.445, 460.400 and 460.800 MHz.

Self-quieting frequencies that should be avoided on the GM350 radios:
MB: 67.200, 83.780 and 84.000 MHz.
VHF: 151.200 and 168.000 MHz.
UHF 300 MHz: 312.515 and 313.425 MHz.
UHF: 403.200, 420.000, 436.800 and 453.600 MHz.

Self-quieting frequencies that should be avoided on the GM950 radios:
MB: 67.200, 83.780 and 84.000 MHz.
VHF: 151.200 and 168.000 MHz.
UHF: 403.200, 420.000, 436.800 and 453.600 MHz.

Specific Crystal/Oscillator Harmonic Frequency Lists:

The following lists are specific to the GM300, MaxTrac, Radius, and MaraTrac mobiles.

Harmonics of the 14.4 MHz reference oscillator on the RF board:
28.800, 43.200, 57.600, 72.000, 86.400, 100.800, 115.200, 129.600, 144.000, 158.400, 172.800, 187.200, 201.600, 216.000, 230.400, 244.800, 259.200, 273.600, 288.000, 302.400, 316.800, 331.200, 345.600, 360.000, 374.400, 388.800, 403.200, 417.600, 432.000, 446.400, 460.800, 475.200, 489.600, 504.000, 518.400, 532.800, 547.200, 561.600, 576.000, 590.400, 604.800, 619.200, 633.600, 648.000, 662.400, 676.800, 691.200, 705.600, 720.000, 734.400, 748.800, 763.200, 777.600, 792.000, 806.400, 820.800, 835.200, 849.600, 864.000, 878.400, 892.800, 907.200, 921.600, 936.000, 950.400 MHz.

Harmonics of the 10.245 MHz second local oscillator on VHF-LO radios:
20.490, 30.735, 40.980, 51.225, 61.470, 71.715, 81.960, 92.205, 102.450, 112.695, 122.940, 133.185, 143.430, 153.675, 163.920, 174.165, 184.410, 194.655, 204.900, 215.145, 225.390, 235.635, 245.880, 256.125, 266.370, 276.615, 286.860, 297.105, 307.350, 317.595, 327.840, 338.085, 348.330, 358.575, 368.820, 379.065, 389.310, 399.555, 409.800, 420.045, 430.290, 440.535, 450.780, 461.025, 471.270, 481.515, 491.760, 502.005, 512.250, 522.495, 532.740, 542.985, 553.230, 563.475, 573.720, 583.965, 594.210, 604.455, 614.700, 624.945, 635.190, 645.435, 655.680, 665.925, 676.170, 686.415, 696.660, 706.905, 717.150, 727.395, 737.640, 747.885, 758.130, 768.375, 778.620, 788.865, 799.110, 809.355, 819.600, 829.845, 840.090, 850.335, 860.580, 870.825, 881.070, 891.315, 901.560, 911.805, 922.050, 932.295, 942.540, 952.785 MHz.

Harmonics of the 44.645 MHz second local oscillator on VHF-HI, UHF, and 800 MHz radios:
44.645, 89.290, 133.935, 178.580, 223.225, 267.870, 312.515, 357.160, 401.805, 446.450, 491.095, 535.740, 580.385, 625.030, 669.675, 714.320, 758.965, 803.610, 848.255, 892.900, 937.545, 982.190 MHz.

Harmonics of the 38.695 MHz second local oscillator on 900 MHz radios:
77.390, 116.085, 154.780, 193.475, 232.170, 270.865, 309.560, 348.255, 386.950, 425.645, 464.340, 503.035, 541.730, 580.425, 619.120, 657.815, 696.510, 735.205, 773.900, 812.595, 851.290, 889.985, 928.680, 967.375 MHz.

Harmonics of the 7.776 MHz microprocessor crystal on all radios:
15.552, 23.328, 31.104, 38.880, 46.656, 54.432, 62.208, 69.984, 77.760, 85.536, 93.312, 101.088, 108.864, 116.640, 124.416, 132.192, 139.968, 147.744, 155.520, 163.296, 171.072, 178.848, 186.624, 194.400, 202.176, 209.952, 217.728, 225.504, 233.280, 241.056, 248.832, 256.608, 264.384, 272.160, 279.936, 287.712, 295.488, 303.264, 311.040, 318.816, 326.592, 334.368, 342.144, 349.920, 357.696, 365.472, 373.248, 381.024, 388.800, 396.576, 404.352, 412.128, 419.904, 427.680, 435.456, 443.232, 451.008, 458.784, 466.560, 474.336, 482.112, 489.888, 497.664, 505.440, 513.216, 520.992, 528.768, 536.544, 544.320, 552.096, 559.872, 567.648, 575.424, 583.200, 590.976, 598.752, 606.528, 614.304, 622.080, 629.856, 637.632, 645.408, 653.184, 660.960, 668.736, 676.512, 684.288, 692.064, 699.840, 707.616, 715.392, 723.168, 730.944, 738.720, 746.496, 754.272, 762.048, 769.824, 777.600, 785.376, 793.152, 800.928, 808.704, 816.480, 824.256, 832.032, 839.808, 847.584, 855.360, 863.136, 870.912, 878.688, 886.464, 894.240, 902.016, 909.792, 917.568, 925.344, 933.120, 940.896, 948.672, 956.448 MHz.

Acknowledgements and Credits:

Some of this information came from Motorola radio sales/catalog pages. The lists of harmonics of the various oscillators and crystals were generated by a custom computer program.

Contact Information:

The author can be contacted at: his-callsign [ at ] comcast [ dot ] net.

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This page originally posted on Sunday 27-Feb-2011.

This web page, this web site, the information presented in and on its pages and in these modifications and conversions is © Copyrighted 1995 and (date of last update) by Kevin Custer W3KKC and multiple originating authors. All Rights Reserved, including that of paper and web publication elsewhere.