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Cobra 29 variable power.

Discussion in 'CB Radio Modifications' started by Ocean cruiser, Jun 12, 2021.

  1. Ocean cruiser

    Ocean cruiser Active Member

    May 20, 2019
    Likes Received:
    Hey guys, I have a cobra 29 ltd classic that has variable power. All the way down it goes to 1 watt. All the way up it shows 6 watts. When I drop the dead key to 1 1/2 or 2 watts and I modulate, it only swings to 3 rms. Peak it does 20. How can I get it to swing the whole 6 watts? What would be causing it to do that? Thanks for the help


  2. nomadradio

    nomadradio Analog Retentive

    Apr 3, 2005
    Likes Received:
    Cheap variable mod. The better ones will still swing forward with the carrier level reduced.

    What kind of wattmeter are you using? They should all read the same on a carrier alone. But what a wattmeter will read with modulation can vary all over the place.

  3. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

    Apr 23, 2018
    Likes Received:
    Is the Limiter still intact?

    Variable Power - the mod itself, does it only control the amount of power ALL of the power Signal (audio) and BIAS (DC power)

    On a Cobra 29 - you have 12 volts DC Power available to use, with audio - you still have that 12 volts - but audio is ADDED. (12 volts reference here is "battery power supply level)

    So with a "variable" mod - there are two things to remember.

    Controlling the power - means you adjust all the power - or you can control the CARRIER and let the Audio thru unhindered to modulate that carrier level. There's a difference between Variable power and Variable Swing mods.

    The reason I ask about "limiter" is - when you install a variable mod, the power you control is already past the limiter and is unable to offer any other sort of way to "restore" audio already clipped and limited back at the Audio amp mic amp states where it works,- it's already done

    Think of this like; having a limiter in a radio and using a variable mod (not a variable swing mod) - is much like - you driving a car - with the brakes on - using it to control your speed unable, never ever letting off the throttle to even allow the car to slow down. You "slow it down" by applying the brakes that much more. The engine can't offset the throttle - it's set - so all you do is modulate the Brakes - producing the heat in the brakes all while using a poorly performing car.
    • When you have simple variable mod, that effect is what it is like, the signals already amplified, you're choking down what is there.
    • You can make the argument for restrictor plate too, but i those matters the throttle is adjusted but you still have brakes - Restrictor plate would more akin to Limiter and Variable - only not always at full throttle.
    A Variable Swing mod is the opposite, you use the engine to control speed more - from decelerate engine braking and acceleration using throttle to go and get anywhere Keeping the Limiter in is like having the brakes available so you can slow down (lessen the input signal) but you still have the engine ready to accelerate

    When you have a variable swing mod, the CARRIER (DC side of this) is controlled more than the Audio power present. So more audio can be applied to a lower-power-level (lesser) Carrier signal - creating an envelope that the others see on their meters as having a lot of swing.
    #3 Handy Andy, Jun 13, 2021
    Last edited: Jun 13, 2021

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