Com Dev Wireless Group GLOBALCELL-IID Manual Descriptions

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Norwood,

Here are the answers to the 4 questions that you requested. If you need
anything more please give me a call.

-Brett

Brett Moser, Senior System Architect [e-mail]
Phone: [phone] Fax: [phone] http://www.comdev.cc/
COM DEV Wireless Group - Digital and Software Systems
863 Pacific Street, San Luis Obispo, CA 93401

1) Description of the oscillator circuit and how the temperature effect is
stabilized

The oscillator circuit is referenced to an oven controlled crystal oscillator.
The oven controlled crystal oscillator has a 0.5ppm frequency stability over
the temperature range of -30 degrees C to 60 degrees C.

2) Description of the audio limiting circuit

The audio limiting circuit is implemented in a Digital Signal Processor.
The signal input into the audio limiting circuit has a range of [-1,1). The
refrence level used through the system is a 1kHz tone with an amplitude of
+/- 2^(-6.5) produces a FM modulated carrier with 2.9kHz peak frequency
deviation. The audio limiting circuit thus limits the peak signal amplitude
to +/- 0.04578.

3) Description of the audio low pass filter

The audio low pass filter is implemented in a Digital Signal Processor. The
filter is a 25 tap interpolate-by-5 FIR filter with a cut-off frequency of
3kHz.

4) Desciption of the RF spurious filter

The RF spurious filtering is performed by two components: the high power
cavity tune combiners, and the transmit bandpass filter. The high power
cavity tune combiners provide 20-30dB attenuation 300kHz outside the channel.
The transmit bandpass filter attenuates spurious emmisions outside the transmit
cellular band of 870MHz - 894MHz.