Low channel mod for UPD-2816

[Harley3315]

The directions state kit setup for uppers and lowers. But no mention on how.

Yeah I hope you figure it out. What about an s kit for like cobra 25 and uniden 68 66 type that was just a low kit if I remember right any chance of getting some of those??

The directions state kit setup for uppers and lowers. But no mention on how.

 

[dss56]

Yeah I hope you figure it out. What about an s kit for like cobra 25 and uniden 68 66 type that was just a low kit if I remember right any chance of getting some of those??

I have all those kits Expo 100 A-S-I -L-C-D. Im looking for the N kit to see if low channel can be done. I also have the Galaxy N kit.

 

[Harley3315]

I have all those kits Expo 100 A-S-I -L-C-D. Im looking for the N kit to see if low channel can be done. I also have the Galaxy N kit.

For sure the n kit would be nice for the pc 122 122xl and all of the trc variants to be able to both up and down. As I recall you could only do the chip swap to a 2816 to go up other wise but it wasn't on center slot you had to use the clarifier to center up. And I was unaware you had the skit for the smaller cobras.

 

[dss56]

For sure the n kit would be nice for the pc 122 122xl and all of the trc variants to be able to both up and down. As I recall you could only do the chip swap to a 2816 to go up other wise but it wasn't on center slot you had to use the clarifier to center up. And I was unaware you had the skit for the smaller cobras.

I have installed the Galaxy N kit in a cobra 29ltd Am 27.425 to 28.045 and in a TRC465 ssb and get the same channels ch 42 up to 104

 

[dss56]

The only "non-crystal" mod I've ever heard of won't move you down 45 channels, it moves you down 45-and-a-half channels. This trick involves taking the transmit/receive pin (#9) on the 2816 loose, and "inverting" the signal that feeds into it. Takes a DPDT switch, a NPN transistor like a PN2222 and three resistors.

What this does is to change the PLL chip to "receive" frequency when you key the mike and to "transmit" frequency while receiving. So they say. Kinda like the old days, when a CB had two crystals for each channel, one for transmit and one for the receiver, each for one channel. Some of those radios, like the Johnson Messenger would go below channel 1 by putting the transmit crystal in the receiver socket, and the receiver crystal in the transmit socket. Seems to me the KKK made this trick famous, to keep their communications "private".

Never have tried the "invert pin 9" trick. The additional stuff you have to do to shift the radio one half of a channel, and get it on frequency looks like a pain. By the time you do all that, the 'crystal' kit looks attractive in comparison.

The reason you can't just use switches on the input pins to the chip is that the 2816 has in internal "ROM", or Read-Only Memory. The actual binary code that sets the channel frequency is INSIDE that part of the chip where you can't change it. All the switch wires do is to select which "legal" binary code gets fed into the actual PLL circuit. Changing the wires from the channel switch only gets you a different legal channel.

The "crystal" kit used for some SSB radios won't cut the mustard with this radio. A kit for the 2816 must contain the whole oscillator circuit, along with the crystal, one for each added band. The output from a "A", "A+", or "N" kit overrides the mixing signal that normally sets the PLL to a legal-only channel frequency. A crystal alone can't do this.

This chip was meant to be 'channel proof', but turned out only to be 'channel-resistant'. Newer PLL chip types are even tougher to convert. Cheaper AM-only CB radios truly are "channel-proof", unless you spend twice the radio's sale price to convert it. By the time you spend that much, you can afford a radio that comes with more than three sets of 40 channels. Mods that cost twice what the radio did just aren't very popular.


73

Nomadradio I know its an old post do you or anyone have this inverting pin 9 on the 2816pll in the cobra 29ltd radios. Looking to mess around nothing better to do.

I took pin 9 low and radio is transmitting 40 below but not receiving the 40 below. Was wondering if inverting pin 9 will do the trick to have the receive work with the transmit low channels.

I do have the expo A kits for this chip just wanted to try this mod.

thanks

 

[nomadradio]

Has to be inverted while receiving and transmitting, both. Just remember the radio is a half-channel off frequency on the 'new' channels.

73

 

[dss56]

Has to be inverted while receiving and transmitting, both. Just remember the radio is a half-channel off frequency on the 'new' channels.

73

nomadradio.
do you have any info on how to do this mod?

thanks