Peak and tune, matching

[roadranger]

Is it absolutly necessary to peak and tune a CB right out of the box? I have a Cobra 29 ltd, and I am using it with an unkown linear amp. With the amp off, the ant. tunes to 2:1 or a little higher. When I switch it on, the ant. tunes nearly 1:1. The ant. is a Francis double wrapped fiberglass, valued as low as $10.00 at some Love's Stopping Centers. It handles 200 w. Then, is it absolutly necessary to "match" the CB to the Amp? Let's get the jokes out of the way, and then get down to buisness. Who wants the first crack, Warren?

 

[prcguy]

Antenna match is not affected by an amplifier unless you have so much power its heating the antenna and causing something to change. Are you measuring the match at the radio end? If so, with the amp on you are measuring the input match of the amplifier, not the antenna.
prcguy

 

[TheJerk]

Your amplifier is not built really well is the reason the SWR changes. Take the amplifier out of the mix, and tune the antenna directly (using a stand-alone meter, not the radio's SWR meter), then the antenna will be tuned. Most SWR meters cannot be used with an amp on (they are not capable of reading with higher than stock power).

And to answer your question, a peak and tune is completely different than matching to an amplifier. A peak and tune does exactly that, it peaks and tunes the radio (or in other words it maxes out the wattage, correct or not). Matching to an amplifier involves turning a radios output down in most cases as they can easily overdrive most amplifiers and burn them up. That second statement depends largely on the amplifier itself...

That Francis will not take 200 watt for very long, FYI.

 

[Astro25]

Well, you do want the radio "matched" to the amplifier (at the very least in terms of appropriate dead key power to the amp.).

If you're going to run the Cobra barefoot without an amp, then yes you'll notice a small improvement with a tune up. Stock they dead key about 3-4watts, maybe swing to 10. Tuned up and you'll get a 4-5watt dead key, and a swing to about 20 watts (sometimes more on older production units, or with 1969 finals and a 2314 driver). This is typically achieved by clipping the audio limiting circuit, although there's cleaner ways to go about doing that depending on radio.

 

[roadranger]

No problems...

Antenna match is not affected by an amplifier unless you have so much power its heating the antenna and causing something to change. Are you measuring the match at the radio end? If so, with the amp on you are measuring the input match of the amplifier, not the antenna.
prcguy

There is not heat. Nothing gets hot. The only reports I get are "scratchy" and "fuzzy", the I just turn down the mike gain a little, and all is fine. I have had it reported as " the best radio I've heard yet."

 

[roadranger]

Hey, Jerk...

I have placed two different swr meters at the ant. after the amp (six feet of coax between the amp and meter). RS didn't measure up so great, but the Sears seemed to measure the swr at 2:1 either way. It seems that when you turn off the amp, it attenuates the signal out. switch it on again, and the swr is near 1.25:1 on the Cobra's swr meter. Not complaining, it all seem to work fine. My question is, why should I pay some retired hammie $75-100 to peak, tune and match at the next truck stop?

 

[Murstech]

Its probably better if you dont do anything to the radio. The amplifier is far beyond what a peaked and tuned radio can do anyway. And you dont want to risk overdriving the amp or someone messing with your AMC circuits.
About the only mod you may ever want to do is the "controlled carrier" mod to reduce your unmodulated carrier level. But I have done that mod before and below a 3 watt carrier I started to lose AMC control so make sure if you ever have that mod done that you make the technition show you the AMC is controlling the modulation.

 

[TheJerk]

Its probably better if you dont do anything to the radio. The amplifier is far beyond what a peaked and tuned radio can do anyway. And you dont want to risk overdriving the amp or someone messing with your AMC circuits.

And depending on his amp, he could be over driving it now...I could overdrive my 5-pill with a out-of-the-box Cobra29.

 

[TheJerk]

I have placed two different swr meters at the ant. after the amp (six feet of coax between the amp and meter). RS didn't measure up so great, but the Sears seemed to measure the swr at 2:1 either way. It seems that when you turn off the amp, it attenuates the signal out. switch it on again, and the swr is near 1.25:1 on the Cobra's swr meter. Not complaining, it all seem to work fine. My question is, why should I pay some retired hammie $75-100 to peak, tune and match at the next truck stop?

Like I said...remove the amp from the circuit and set the SWR...SWR does not change (with power) once its set. You are most likely seeing "reflected" power as an increase in SWR.

As stated, depending on the transistor configuration of your amp; the power from a stock radio could burn the amp up.

Good Luck

 

[roadranger]

okay...

Like I said...remove the amp from the circuit and set the SWR...SWR does not change (with power) once its set. You are most likely seeing "reflected" power as an increase in SWR.

As stated, depending on the transistor configuration of your amp; the power from a stock radio could burn the amp up.

Good Luck

...I get it. I'll have it looked at.