Bulletin: SM4900 Vendor: Yaesu Subject: FT-736 Operating At 9600 Baud FT736 & 9600 Baud Operation --------------------------- by James Miller G3RUH 1992 Mar 02 These notes tell you where to get FM RX audio direct from the discriminator, and where to modulate the FM TX varactor directly. These modifications are non-destructive and take no more than a few minutes. The signals bypass the "DATA SOCKET" for high grade FM operations. The RX mod is suitable for: * UOSAT 9600 baud downlink and terrestrial links * 1200 baud AFSK/FM Standard Packet - BUT IT'S UNSQUELCHED. The TX mod is suitable for: * FO-20/PACSAT uplink (1200 bps Manchester FM) * UOSAT 9600 baud uplink direct FSK and terrestrial links * 1200 baud AFSK/FM Standard Packet. ---****--- FT736 - FM Direct from Discriminator ------------------------------------- Detected FM direct from the receiver discriminator is available from the RX UNIT at the junction of R91 and C83. These components are shown in the top right-hand corner of the schematic. Proceed thus: 1. Disconnect FT736 from the mains electricity. (Safety). 2. Remove top cover only. 3. RX Unit is the vertical module on the left. 4. Locate R91 which is about 25mm from the top, 50mm from the radio rear. the resistor is "on-end", and near a couple of glass diodes. 5. Scrape any paint off R91's free end and wet with solder. 6. Your RXaudio lead should be a fine screened cable; connect the inner to R91, and the outer braid to a ground point (e.g. can of TO09) 7. Route the cable out though any convenient aperture in the case. 8. Remove C82. It's by the end of CD01, the 455D block. 9. The discriminator sensitivity (FM Normal) as about 6 kHz/volt. Important note on 9600 Baud Use ------------------------------- FT736 receivers are fitted with an LFH12-S IF filter for FM. (CF01 at the top front of the RX Unit). This is a "12 kHz" bandwidth filter which is only just OK for 9600 bps FSK operation. It is recommended you change this to 15 kHz or better still for UOSAT use, 20 kHz bandwidth which will allow more tolerance for doppler shift, and give a better "eye". Suitable filters are: LFH-15S / CFW455E, and LFH-20S / CFW455D. You may prefer to replace the FM-N filter instead. For Full-Duplex satellite use ONLY, increase modem C25 to 1uF. ---****---