==== 1 understand the synthesiser ==== CMOS logic chips of the day 1980 worked up to 5MHz reliably and were cheap. TTL could do 50MHz but were power hungry. Do a PLL around 2.5MHz spanning 1.25MHz, multiply it up by 8 and cover 10MHz. A useful range. Choose an IF frequency so our Low freq PLL can be on near the same frequency, both Rx and Tx. Thus reducing the complexity. 2.5 MHz x 8 = 20MHz. 20MHz x 2 = 40MHz, anything near, yes 45.0MHz. So a 45.0MHz first IF it is. We need two high frequency oscillators, Rx and Tx. Low Band Tx output freq = (Xtal x 2) - (PLL x 8) Rx input freq = (Xtal x 2) + (PLL x 8) - 45.0MHz How do we achieve this? Another PLL with two oscillators, RX and Tx. Rx Oscillator on (Rx freq + 45.0MHz) mixes with (xtal x 2) then Low Pass filtered, we get about 23MHz. Divide by 8 with a TTL chip and PLL to the Low freq PLL with its reference of eg. 12.5KHz / 8. Tx Oscillator on (Tx freq) mixes with (xtal x 2) then Low Pass filtered, we again get about 23MHz. Divide by 8 with a TTL chip and PLL to the Low freq PLL. ========== The Channel Switches =========== One or two rotary switches, 12 position with A/B or two 10 position. Inverse logic, with diodes, eproms not directly compatable. ie. the two switch model cannot select CH10, 11, 12 of the one switch model eprom. Units switch eprom address bits 0-3. Tens switch eprom bits 4-7. Inverse logic ========== UHF =========== Just use Xtal x8 in the calcs below. Also Rx LO on the low side. Tx = Xtal x8 + low PLL x8 From a UHF unit 51.5625 x 8 = 412.5 + (45 /2) => 434.00 Tx One crystal 51.5625 x 8 = 412.5 - 18.5 + 45 => 439.00 Rx 21.5 MHz / 12.5KHz => 1720 PLL Divide by N 0x6b8 hex 18.5 MHz / 12.5KHz => 1480 " 0x5c8 hex Another UHF 48.8025 => 408.xxx and 418.xxx , 2nd VCO ~18MHz. ========== 6m conversion, generating the eprom ========== 37.9 MHz Xtal on the RF board, replacing 53.760MHz. (changing coils and caps etc..) The formula Tx ( (Xtal x 2) - TxFreq ) / 8 = Low freq PLL, convert to HEX. Add the mode bits to the top nibble: 07 becomes 17. I generated the HEX file with "hexedit" on Linux. Typed in by hand. 37900 Xtal 52500 => tx 1864 or 0x748 Rx 75800 - 45000 = 30800 -52525 = 21725 / 12.5 => 1738 = 0x6ca Rx 75800 - 45000 = 30800 -53500 = 22700 / 12.5 => 1816 = 0x718 Rx 75800 - 45000 = 30800 -53975 = 23175 / 12.5 => 1854 = 0x73e 000000 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff * 0000d0 ff ff ff ff ff ff ff ff ff ff ff ff 3e 3c 3a 38 0000e0 ff ff ff ff ff ff ff ff 36 34 32 30 2e 2c 2a 28 0000f0 ff ff ff ff ff ff ff ff 26 24 22 20 1e 1c ca 18 <- Ch1 LSBits Rx 000100 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff * 0001d0 ff ff ff ff ff ff ff ff ff ff ff ff 17 17 17 17 0001e0 ff ff ff ff ff ff ff ff 17 17 17 17 17 17 17 17 0001f0 ff ff ff ff ff ff ff ff 17 17 17 17 17 17 16 17 <- Ch1 MSBits Rx 000200 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff * 0002d0 ff ff ff ff ff ff ff ff ff ff ff ff 22 24 26 28 0002e0 ff ff ff ff ff ff ff ff 2a 2c 2e 30 32 34 36 38 0002f0 ff ff ff ff ff ff ff ff 3a 3c 3e 40 42 44 46 48 <- Ch1 Tx 000300 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff * 0003d0 ff ff ff ff ff ff ff ff ff ff ff ff 17 17 17 17 0003e0 ff ff ff ff ff ff ff ff 17 17 17 17 17 17 17 17 0003f0 ff ff ff ff ff ff ff ff 17 17 17 17 17 17 17 17 <- Ch1 Tx * 000400 - 0007ff not used. ========= EPROM Notes ========== The type "2716" is the first 5V only eprom. The earlier 2708 (1k bytes) needs the +12V and -5V as well. The NMOS type eproms are needed here as pullup resistors are used on the outputs for a "high" greater than 5V for the CMOS synth chip. CMOS eproms do not work unfortunately. Beware, there were some 3rail 2716's.