CK5
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Anybody here on the boards tune cb's?
- Thread starter cybrfire
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- Mar 3, 2000
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What are you looking to do ? If you want anything done a great place to check out is sparkyscb shack. They have great prices and do killer work.
I have heard of people taking an off the shelf CB to somebody that can "tune" them and make them better. Not sure what is done or how its done. Just sort of an optimizing the radio.
I dont know how to do it but in the trucker world the CB tune shop at the I80 walcott truck stop by davenport here in Iowa is the best in the country. Look em up and call to see what they need from you. then send the stuff to me, I'll run it over there(45 min from me) and send it back to you when its done.
If you pop the cover off the back of your radio there's a bunch of stuff on a PCB. Many components are adjustable resistors, capacitors, coils, and resonators.
What "tuning" will do is ensure (within the accuracy of the test equipment used) that your unit is broadcasting on the correct center frequency, and that the input/output impedance of the radio is as close to 50 ohms as possible.
"Peaking" on the other hand, focuses on tuning the PA (power amplifier) and AM (or SSB) circuitry to maximize power output to legal levels. While the FCC may permit up to 4 Watts AM, your particular radio may come from the factory with an output of say, 3.7 Watts.
When you're dealing with a maximum power of 4 Watts, each bit of loss is substantial. The above example is 0.34 dB below maximum permitted power. When you compound that with cheap connectors and coax (about 1.2 dB of loss), and an inefficient antenna (let's say 1.7 SWR, and 0dBi)... you're looking at an effective radiated power of ~65% of that maximum 4 Watts.
Even with higher powered radios, these same issues are real problems that must be dealt with. Any effort that is spent ensuring your radio is properly aligned, and transmitting most efficiently is good.
Additionally, if you want to ensure you're getting the best out of your radio, invest in some GOOD COAX and through-hole antenna mount. For 27 MHz, some low-loss RG-8x is about perfect <0.7 dB per 100' or so.
Additionally, using quality connectors and terminations will minimize insertion loss and leakage. Silver SO-239 and PL-259 connectors are about the best you can get Amphenol and Times Microwave make great connectors.
Coax length is a bunch of hogwash. To minimize losses, make your coax as short as possible. Avoid coiling your coax. Avoid sharp bends (as that will push the center conductor close to the outer shield, altering the impedance and possibly creating a diode-like junction in the dielectric). Secure the coax to minimize vibrations (which will prevent breaks in the center conductor and damage to the outer braid).
Your antenna needs a good ground plane to operate effectively. A fibeglass roof is not a ground plane. A bumper is not a ground plane. A metal roof is an OK ground plane. The side of your vehicle is better than a bumper, but still not ideal. I run my 10 meter antenna (28 MHz) on the bedrail of my pickup, and on the trunklid of the Mustang (neither are ideal locations, but a 90"+ antenna only fits in a few spots).
