DATONG R.F. CLIPPER MODEL RFC (Blue Box)
30-jul-2014 A fault in the schematic corrected.
Vintage and working!
DATONG R.F. CLIPPER Model RFC
About 30 years ago Datong Electronicss Limited produced model RFC (RF) clipper in a light blue aluminium box or a fully assembled PCB as model RFC/M. Later manufacturer has stopped production for radio amateurs and has focused on products for military purposes. Therefore, one can not find complete information about the device.
INFORMATION COLLECTED FROM INTERNET
All information I could find on the Internet has been collected and compiled in this article as a reference for fellow hams. Occasionally the clipper is offered on eBay or at a flea market. Maybe it's worth for you to see if the principle is suited for a homemade RF clipper project.
I have merged fractionated schematics on the Internet into one diagram. At first glance it seems a complicated circuit, but on closer inspection it turns out to be a simple design.
The microphone signal is amplified by IC1 and more or less limited to 450-2600 Hz (-3dB). IC2 and IC3 ensure that the amplified signal is rotated by 90 º in phase for the next phase modulator IC4.
IC6 is a 240 KHz oscillator. IC7 is divide that signals by 4 and rotated by 90 º in phase, so that a 60 kHz signal is available for the phase modulator. Further the signal goes to pin 10 of IC5, where it is filtered and amplified. At pin 12 of IC5 arises an SSB signal with suppressed carrier, where L1 is tuned to 3000 Hz ± 50 Hz. The next stage is a limiter with two diodes. IC5 then amplifies and filters between pins 3 and 5. L2 is tuned to 1700 Hz ± 50 Hz. The clipped signal from IC5 (pin 1,5) goes to the product detector part of IC6. The latter is feed by a 60 kHz signal from IC4 resulting in a original low frequency but compressed signal for emitter of TR1.
INDUCTORS L1, L2, L3
A homebrewer asked me more details about the inductors. All three (TOKO?) inductors on my PCB are marked with 1980. On the Internet https://sites.google.com/site/datongarchive/rfc I found the right information, see below.