ETTC'2003 - SEE

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Abstract:
Research on digital PCM/FM telemetry receiver
Chen dahai Xie nan Pu renbi
Institute of Electronic Engineering of China Academy of Engineering Physics
P.O.BOX 919-517, Mianyang, Sichuan, P.R.China
E-mail: chendahai@hotmail.com
In this paper, a scheme of digital PCM/FM telemetry receiver is introduced and a Matlab
simulation model is established to perform design and simulation. The digital receiver directly
samples the IF PCM/FM signal and the demodulations will be implemented with digital methods.
Computer simulation results reflects the presented scheme works well.
Key words: Digital PCM/FM receiver, IF directly sample, DDC, FM demodulation, PCM
demodulation
1 Preface
PCM/FM is a widely used telemetry system, a typical s-band PCM/FM telemetry system is
shown in fig.1. In the transmitter, binary NRZ (non return zero) coded data are first pre-filtered to
limit its bandwidth and then frequency modulate the carrier and transmit. In the receiver, the
signal received by the antenna is filtered and amplified by two mixing stages and down converted
to a low intermediate frequency and demodulated with a frequency discriminator, the output of the
discriminator feed to a code synchronizer to regenerate the original PCM data and clock.
PCM
data
antenna
LNA
Prefilter
f
p
Ist
local
osc
FM transmitter
∆f
1st IF
amplifier
antenna
Channal
2nd
local
osc
BP
filter
f
IF
receiver
AGC
2nd IF
amplifier
FM discri
-minator
Fig.1 Block diagram of a typical s-band PCM/FM telemetry system
Code
syncro
-nizer
data
&clk
However, Several parameters are key for the PCM/FM system, the bandwidth of the pre-filter,
maximum modulate frequency deviation, and IF bandwidth, they are evaluated with Eq.1~3.
Where fpre, fIF, Δf, Rb represents respectively the bandwidth of pre-filter, IF bandwidth and
maximum modulate frequency deviation and symbol rate.
1