Multitone RPR 563, Инструкция по изменению

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RPR 563
TM1195 Issue 1 Page 3 - 6
Data Filter
18. The data signal passes through low-pass filter Transistor TR24 which is controlled by
the Battery Economy Circuit (BEC). The data signal is then fed to IC1 pin 15 where it
is squared up and output at pin 16. This open collector output is then fed via TR26 to
the Decoder Board. Data polarity can be changed by fitting R350 or R351; the default
polarity is with R350 fitted.
Noise Squelch
19. Demodulated audio is applied to the de-emphasis network R365, C154 before
application to high-pass filters TR53 and TR41. TR41 emitter output is then applied to
amplifier chain TR40, TR39, TR38, TR42 and TR43. Temperature stability is provided
by TR42. The signal at TR43 collector is passed via C166 where it is DC-shifted by D3
and then rectified by TR37, TR28, before application to Schmitt Trigger TR45, TR46,
TR36, TR47.
20. Transistor TR46 base is sitting at approximately half-rail voltage. When there is no
carrier present (i.e. high noise level) TR45 base will be high, switching TR36 on. The
base of TR47 will be low, switching TR47 on, thus holding TR45 base high.
21. When carrier is present (i.e. no noise) TR45 base will be lower than TR46 base, pulling
TR36 base low. TR36 will switch on, pulling TR47 base high, switching TR47 off, thus
holding TR45 low.
22. The output of the Schmitt Trigger is at the collector of TR36. When TR36 is switched
on (no carrier present), TR48 is switched on via R419, thus charging C85, switching
TR49 on, and TR50 off. When TR36 is switched off (carrier present), TR48 is switched
off, causing C85 to discharge. The discharge time is approximately 100ms and is
determined by C85 and R420. Transistor TR49 is switched off once C85 has
discharged, thus switching TR50 on.
23. The collector of TR50 collector (/TONE.Rx) is connected to the Decoder Board via
PL301 pin 2.
Sub-Audio Tone Generator
24. The oscillator for the PLL (IC2) runs at the tone output frequency and is set by RV3.
Tone output from IC2 is at pin 5. Filtering is provided by two low-pass filter stages
TR51 and TR52. Output is applied to SK301 pin 9 for test purposes, and via potential
divider R65/R64 to the modulator driver IC5.