Like a PSK stations for S5 packet, 70cm WBFM stations are also S53MV project. Originally they are two one sided PCB-s. Frequency is determined with CB XTAL-s. S51RM and me made one two sided PCB with PLL (MB1504) and VCO. Microcontroller sends frequency data to PLL chip according to DIPswitch position. RTX operating from 430-440 MHz in 50kHz steps. Here in S5 we are using these stations with Manchester modem and for speeds from 19k2 bps to 76k8 bps. You can download S5-PLL70.DOC (ZIP on WORD document) and PLL70 schematic diagram (ZIP on three PostScript files - you can print it with GhostScript program). Documentation is in Slovene language, but you can find it useful because it contains a part list.

LOCKING OF TX VCO and SPLATTERING

This few lines are for users of this station.....

In Croatia (9A) they noticed, that such a construction of WBFM (S53MV and RM) causes huge splattering up to 30MHz below operating frequency for about first 5-10ms of transmission. Cause is TX VCO. After discussion with S52D and S56A we finally eliminate this problem with one 100k (R28) resistor and one schottky BAT47 (or similar) diode (D9). Now TX VCO is locked after 0.5 -2ms and no more splattering is observed. R28 is soldered to collector of T3 (BC238) and D9 is soldered to other end of R28 and to TP1 (cathode at TP1). The point is, to supply voltage of a locked PLL to varicap diode at the beginning of transmission. So now we can use TX delays 3ms instead 15-30ms before and that is huge reduction of unnecessary QRM :-) . New PCB-s will have this solution already implemented.