speeddemon wrote:what would you use for a pll to replace old pll lc7120 chip
An MC145170 will replace almost any CB type PLL and is still available new, so that would be the logical choice there.
BUT: There are two buts.
1) Because of the high speed of the device (it can directly divide up to about 150 MHz!) the PCB layout is critical. You won't have too much success building the PLL circuit on perfboard, it will need a properly made (commercially fabricated) double sided board with a ground plane layer and good supply bypassing. See the recent thread with the Hornet SSB radio for an example of the correct board.
2) Before you even think about converting the PLL section, get the rest of the radio working 101% first, including the new micro.
If you have RF issues such as warbling or distortion when doing the PLL conversion, you will be able to be sure the cause is in the new PLL that way. Otherwise you'll never know if the cause of the problem was that or a dying 40 year old capacitor / other component / hackup by previous owner.
And have you ever done your atmega 16 pll02a ssb circuit mod with a 3digit 7segment common cathode display?
No, it was kept to two digits deliberately for two reasons. The first was to keep the stock appearance of the radio, but the main reason was to keep noise as low as possible.
There are enough pins on a Mega16 to provide "static" drive to the 14 LED segments - this means that the display voltages only change when the digit being shown changes. This is the same method used by mechanical channel switches like those found on the older style radios such as Cybernets.
More than two digits require the display to be "multiplexed". This shows the digits only one at a time, but fast enough so the human eye can't detect it. The display looks continuous, but it's actually changing 250 to 400 times a second. These current changes induce noise into the circuit which can be heard as a buzzing or hissing sound. Go any faster than that and the digits go dim and start to get ghosting on the unlit segments.
There are ways around it, such as using octal latch chips between the micro and LED drivers / resistors. That will let you multiplex at over 20,000 times a second, above the human hearing range and therefore silent. The downsides are the additional parts (two ICs per digit) and the additional wiring / PCB real estate required.
What are the three digits you want to show? A single LED could be driven static from one of the spare outputs and be used to indicate "zeros" or "fives", i.e. off for 27.595 and on for 27.590 MHz. The two stock digit display could then be set to show the channel number, or the KHz on Rx + MHz on Tx. For 27.595 in "frequency" mode it could show "27" on transmit and "59" on receive.
is there any changes in your code to make that type of display work?
Easy, once you know how you are going to wire the display to the micro...