new cobra 25/channel mods?

[no12nv]

i have a new 25 nw/ltd... done receive and 40 watt mad... both work graet... i am looking for a pll mod to give me the <alpha channels> 27.145/195 specifically... but this radio is using a cobra branded pll ic which i have never seen or cannot find info on... can anyone help or point me in the right direction please..

[The Defpom]

The PLL is a ROM type, they cannot be expanded. The PLL is the same as a TC9106 except that the inputs are inverted.

I have successfully done a band swap to one of these, to convert it to NZ channels, but it is not something that most people would be able to do, I designed a board years ago to replace the PLL, which is the only way to modify the channels, and before you ask, I will not sell the boards, I only have them for my own use, which is infrequent.

[no12nv]

thanks scott.. even if i inject a new mixing osc? will it just lock it out if i do? its not a biggie.. i was just wanting to get more out of this lil box of dreams... thanks again

[The Defpom]

The PLL generates different internal N codes for its frequency divider between TX and RX, so the board to replace the PLL must do the same.

Lou Franklin designed a mixer circuit which switches the radio from low side to high side injection (or vice versa), and allowed a conversion my by mixing in a another crystal frequency, but I do not think he sells them anymore. (Lou is actually a silent member of the forum, but he does not come around often), and they only work on certain circuit types, I am not sure off the top of my head if it will work on yours.

[no12nv]

no biggie... .. did he not author the "screw drivers guide" ? i have that old book around here somewere.. havent see it or used it in years but ... lol i should look for it anyway for shits n giggles

[no12nv]

does the pll still mix with a 10.240 what if i just changed that ?

[The Defpom]

Yes, he has authored a few books, and service manuals.

For more info about the mixer, if he still has it on his site, go to :http://www.cbcintl.com

[lbcomms]

Mixer mods won't do you any good with that PLL - it does not use mixing on the PLL, instead it divides the VCO frequency directly to synthesise the frequencies. If there's nothing to mix, you can't change the ingredients

You can't change the 10.240 crystal either, as the 455Khz shift (used to switch between TX and RX modes) is derived from this crystal (10.240 Mhz divided by 2048 them multiplied by 91 = 0.455 Mhz, in other words 455Khz). If you change this crystal, the radio will not be able to receive!

There are only 2 ways to do it.

If you only want one or 2 channels, then 16.xxx Mhz crystals can be switched in. You'll need TWO custom made crystals for each channel.

Other way is to replace the existing PLL with a Digiswitch chip, this will give you 3 to 6 megs complete coverage, but it will cost you more than what the radio is worth. The DS chips cost just under $100 to buy, plus another $40 to $80 to program and fit to the radio. They are worthwhile for a good quality SSB radio, but uneconomic for a cheapie AM set.

Hope this helps,
Sue