Author Topic: Understanding how CB radio works  (Read 11335 times)

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Understanding how CB radio works
« Reply #15 on: January 19, 2011, 12:30:58 PM »
In the following pic you can see the path of the receiver through the "front end" of the radio. Also shown in dark green is the local and fundamental frequency paths to the mixers.


Buddy kc4umo

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Understanding how CB radio works
« Reply #16 on: January 19, 2011, 12:31:25 PM »

Your welcome,I have a ques.does the tx run thru the center pin of coax or the shield?
I kno its a stupid one but on the diagram it looks like the rx is coming thru the center conductor ???


Good question,
The receive and transmit go through the center conductor. The receive is picked off through block labeled L.P.F

Here is another attachement that shows the receive, trans mit paths, along with the frequency and audio paths.

I will complete the other half of the schematic shortly



Buddy kc4umo

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Re: Understanding how CB radio works
« Reply #17 on: June 16, 2012, 10:51:01 AM »
RF Sampling

Buddy kc4umo

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Re: Understanding how CB radio works
« Reply #18 on: June 26, 2012, 04:36:09 PM »
RF Sampler with DEMOD out
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Offline 577-Jersey

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Re: Understanding how CB radio works
« Reply #19 on: August 21, 2013, 04:53:04 PM »
Pretty cool,,love the blocks!

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Re: Understanding how CB radio works
« Reply #20 on: August 26, 2013, 07:18:26 AM »
Thanks bro. Will get back to this one day lol.
Buddy kc4umo

Offline kopcicle

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Re: Understanding how CB radio works
« Reply #21 on: April 12, 2016, 03:44:24 AM »
Maybe I remember this ...
the 10.240mhz is divided two different ways
by 1024 to get the 10khz channel spacing and by 2 to get 5.12mhz that is then tripled for 15.360
So ...
.91+ 15.360 + 10.695 = 26.965mhz
The difference between 10.695 and 10.240 is 455khz which "kinda" explains the receive .
nifty little bit of engineering save for the Tc9106 rom locked pos .
This is for the classic Uniden 25/29 LTD mix
I spent just short of 20 seconds in a recent 29 before turning it into a door stop ....

~kop

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Re: Understanding how CB radio works
« Reply #22 on: April 12, 2016, 05:19:02 AM »
Sounds like you are on it just fine.
Door stop eh? Not to hard  of a radio to work on.  just don't work on them as much as I used to.
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Offline kopcicle

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Re: Understanding how CB radio works
« Reply #23 on: April 23, 2016, 02:12:52 PM »
was meaning to say that the recent "soundtracker" scheme was a disaster ...

I have another for you .

                            am                   lsb                 usb
n                         113                   113               113
3xF0 (MHZ)      33.8575          33.8525         33.8578
Nx10khz (MHZ)  1.13                 1.13               1.13 
Fl (MHZ)           34.9875           34.9825         34.9875
Fif (MHZ)            7.8025             7.7975           7.8025
Ft (MHZ)           27.185             27.185           27.185   

What if ...

F0 (MHZ)         11.285833333  11.284166667  11.285933333               
Nx10khz (MHZ)  1.13                 1.13                  1.13 
Fl (MHZ)           12.415833333  12.414166667 34.9875
Fif (MHZ)            7.8025             7.7975              7.8025
Ft (MHZ)           4.613333333    4.616666667    4.613333333

(if -1.13 MHZ)   3.483333333    3.486666667    3.483333333

@ 3.48mhz  with at least a decade of count (1.13 MHZ)left going down this would allow 80m coverage :-)
Admittedly the 10khz channel spacing is a kludge and the receive audio isn't the best but the lot of the UPD858 SSB chassis are known to be stable frequency wise and have terrific transmit audio .

Yes it would require a complete re-tune of the if and rf but the transformers are still available in the form factor necessary .
I may be full of static but the thought passed and I  had to share ...

~kop