cb into a unicom?

Status
Not open for further replies.
Joined
Aug 29, 2007
Messages
59
What happens if you take an old CB radio remove the crystals and replace them with airport frequencies and the antenna was trimmed to the proper length could the radio now function as a unicom. I though about this for two reasons cb's is in AM mode and so is air band and air band and cb are also symplex.
 

OCO

Member
Premium Subscriber
Joined
Jul 17, 2011
Messages
923
Location
Central Michigan
What happens if you take an old CB radio remove the crystals and replace them with airport frequencies and the antenna was trimmed to the proper length could the radio now function as a unicom.
No, it won't work - there's the issue of about 90-110 Mhz difference in operating frequencies of the two bands - the components involved in the radios are of such different values that you'd never be able to retune it to function at all, let alone the legalities involved in the type acceptances required for aircraft radios.
 

OCO

Member
Premium Subscriber
Joined
Jul 17, 2011
Messages
923
Location
Central Michigan
We knew what the intended question was - no different than a lot of 'em........

('tis the season to be charitable .....)
 

zz0468

QRT
Joined
Feb 6, 2007
Messages
6,029
What happens if you take an old CB radio remove the crystals and replace them with airport frequencies and the antenna was trimmed to the proper length...
The radio would cease functioning. That's it.

...could the radio now function as a unicom. I though about this for two reasons cb's is in AM mode and so is air band and air band and cb are also symplex.
There's a lot more to determining what frequency a radio will operate on besides the local oscillator. First, the LO has to be capable of operating at the desired range, and merely changing the crystal won't necessarily do that. There are different types of crystals, for one thing. Then any multiplier stages, and amplifier stages, both TX and RX must be able to operate on the desired frequency.

The components in a CB may not even be able to operate at aircraft frequencies, even if you changed component values to allow the resonant circuits to tune. Transistors have an upper frequency limit, and the aircraft band may be well above the upper limit of some of the active devices. And on and on and on...
 

OCO

Member
Premium Subscriber
Joined
Jul 17, 2011
Messages
923
Location
Central Michigan
ZZ:
And I get accused all the time of telling people how to build a clock when they ask me the time........:D (kidding) (great answer)
 

ecps92

Member
Joined
Jul 8, 2002
Messages
10,570
Location
Taxachusetts
It becomes a very large paperweight or a nice door-stop. ;)

What happens if you take an old CB radio remove the crystals and replace them with airport frequencies and the antenna was trimmed to the proper length could the radio now function as a unicom. I though about this for two reasons cb's is in AM mode and so is air band and air band and cb are also symplex.
 

K9WG

Member
Joined
Nov 12, 2010
Messages
1,364
Location
Greenfield, Indiana USA
IF you could re-crystal it.
IF you could change the tuned circuits
IF you could drive the transistors

I bet it would have some really bad spurs and harmonics..... ;)
 
Joined
Aug 29, 2007
Messages
59
What happens if you take an old CB radio remove the crystals and replace them with airport frequencies and the antenna was trimmed to the proper length could the radio now function as a unicom. I though about this for two reasons cb's is in AM mode and so is air band and air band and cb are also symplex.
Since there is an issue with that can they be re crystal to a lower frequency and be used? something like Marine HF or Aviation frequencies?
 

pjtnascar

Member
Joined
May 18, 2011
Messages
366
Location
Sussex County, NJ
Why would you want to destroy a CB radio? Experimenting is cool, but you're not really supposed to play around with the insides of a CB. Be very careful with the stuff you play with. You may generate a signal on a frequency that you weren't even trying for, and cause interference on a local governement or public safety band. Not worth the risk. More likely though, you'll just destroy a CB radio for no reason.
 

zz0468

QRT
Joined
Feb 6, 2007
Messages
6,029
Since there is an issue with that can they be re crystal to a lower frequency and be used? something like Marine HF or Aviation frequencies?
It depends. Most radios can be moved SOME outside their design frequency range. CB radios have been moved up to the 10 meter band, as an example. that's probably about as good as it gets. Note that the move is a few MHz at most. You could probably move it down about the same amount. Figure you could probably make it go from about 25-30 MHz without anything other than realignment and maybe some minor component changes.

The legalities are that you can move it to the ham band and transmit. You can move it anywhere else you can make it go, and receive only.

I'm not sure why you would want to bother. Most CB radio performance is atrocious anyway, and moving it too far is likely to only make it worse.
 

K9WG

Member
Joined
Nov 12, 2010
Messages
1,364
Location
Greenfield, Indiana USA
Don't do this at home.

CB radios have been moved up to the 10 meter band, as an example
I tried that back in the 1980s with an old RS CB. Was able to swap out the crystals and re-align the receiver and transmitter. The power went down to about 3 watts and the modulation sounded like a cow in a blender.
 

ecps92

Member
Joined
Jul 8, 2002
Messages
10,570
Location
Taxachusetts
And reversing the Crystals in the older CB Radios on Ch. ?? [Anyone remember] got you onto the Civil Air Patrols 26.62 Mhz AM Frequency. :confused:

I tried that back in the 1980s with an old RS CB. Was able to swap out the crystals and re-align the receiver and transmitter. The power went down to about 3 watts and the modulation sounded like a cow in a blender.
 

KE4NYV

Member
Joined
Apr 18, 2003
Messages
1,002
Location
Williamsburg, VA.
I had to read that a bit closer. I thought the thread was titled "CB into a UNICORN". Man, that installation would be a bitc*!
 

mancow

Member
Database Admin
Joined
Feb 19, 2003
Messages
5,936
Location
N.E. Kansas
At least he's thinking. That's the kind of speculation that leads to study which in turn leads to experimentation and then understanding. I can't count the wild and stupid projects I got myself into in the time leading up to the point that I finally had a fairly decent overall understanding of how things work.
 

K9WG

Member
Joined
Nov 12, 2010
Messages
1,364
Location
Greenfield, Indiana USA
At least he's thinking. That's the kind of speculation that leads to study which in turn leads to experimentation and then understanding. I can't count the wild and stupid projects I got myself into in the time leading up to the point that I finally had a fairly decent overall understanding of how things work.
BTDT (Been There Done That) :D
 
Status
Not open for further replies.
Top