Sam's photofact Help

[Plumber-G]

I downloaded my first Sam's Photofacts yesterday and need some help. To clarify my skill level I am really a Plumber who works with Pipes and ..... I know there is a way to determine if the circuit is working by measuring voltages at different points, I assume that is what the black boxes with numbers are about??? How do we do that?? also there is the Truth Chart I get what it is about but how do i do it??

Is there a how to use sams manual or am I really as dense as I feel<GRIN>

Thanks
Plumber-G

 

[nomadradio]

The black boxes with the white numbers serve to identify points in the circuit.

It made life easier for the artist drafting the diagram, and lets you continue a wire across pages, from one diagram to the next.

Truth charts?

Okay, no jokes about "fib charts".

What kind of radio is this? A truth chart only matters for a radio with a PLL.

It took Sams a while to catch on to the whole "truth chart" thing with PLL radios. The very-earliest Sams coverage of PLL radios wouldn't have one. Radios from 1978 or 79 and after usually have it.

73

 

[Plumber-G]

The SBE Trinidad III has a PLL
I think what I am asking is how do I use this information??

I don't expect you to give a class just point me in the right direction.... of course if you want too I am all ears

Thanks

 

[nomadradio]

Uh oh.

A 40-channel Trinidad III, eh?

Model number should be "SBE-45CB".

No info free online that I can find.

It's listed as being in Sams CB series volume 204.

The truth chart shows the combination of logic zeros and ones that feeds into the input pins of the PLL chip for each channel. The PLL chip will have a minimum of six input pins, and some of them have as many as 9 or 10.

As a rule "0" means zero volts, or ground. And "1" means the PLL chip's supply voltage, usually 5 or 8 Volts depending on who made the radio.

This combination of six, seven or even 8 binary bits is set by the contacts in the channel selector.

This pattern of ones and zeroes becomes the binary number the channel selector feeds into the PLL chip's input pins for each channel.

73

 

[Plumber-G]

WOW that's pretty cool,
With your explanation the light went ON about how a PLL works. The Trinidad III used a PLL Board and later CB used a single PLL chip to synthesize the channels?? Is that correct?

I appreciate all the Help
Thanks
Plumber-G

 

[nomadradio]

Now I gotta go down in the basement to find volume 204. Don't remember the layout of that radio off the top of my head.

More than one way to build a PLL. First ones required a half-dozen chips. Later, by 1978-79 you would see this shrunk down to two chips, and then by 1980, every 40-channel CB had a one-chip PLL.

Sounds like you would enjoy Lou Franklin's book "The Screwdriver Expert's Guide".

http://cbcintl.com/

Download the sample PDF link on that page and see what you think.

73