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  1. #1
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    RF connected/destroyed Load detector?

    Hello, I have RF PA which supplies the load that can be disconnected or destroyed and therefore the processor in the amplifier must recognize this in order to turn the amplifier off or not to turn it on.

    My solution is relative simple. Load have DC resistance under 2 Ohm and therefore have small DC current from V1 over R2, L3 into Load, If load is connected on OK is on C1 logical 0 if Load is disconnected or destroyed is DC current over L3 near 0 and on C1 is logical 1.
    My solution works reliably, but it's 9/10 parts.
    Does anyone think of a simpler solution, solution with significantly less components ?

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  2. #2
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    Re: RF connected/destroyed Load detector?

    But if the load is disconnected the PA will also be burned due to reflected waves from Open Circuit.. Take this account into..( I presume the PA has a capability to rive 50Vpp signal level..If the load is disconnected, this amplitude will reflect to back and and amplitude will rise to roughly 100 Vpp and your protection circuit may lag and bumm )
    Instead, the amplifier must be connected another proper load to avoid it dysfunctional.You should use a switch to terminate the PA by observing signal amplitude and I cannot suggest a cheaper circuit here..
    But if you don't mind the cost , use RF detector and take my suggestions into account..



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  3. #3
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    Re: RF connected/destroyed Load detector?

    You're right, but
    - PA is designed to cope with full reflected power for some time
    - in terms of reflected power there is a SWR meter in the device that turns off the PA if the SWR exceeds 5
    Yet, or that's why I need a simple load dector
    If deveii is turn On MCU
    -must make sure the load is connected before turning on the PA
    -at least theoretically I can't rule out that the load damages, that the SWR does not know and the load detector could

    I am quite satisfied with the detector described above, but now the device has three optional outputs switchable relays and that means either three detectors or one and always know the status of only the currently connected output,
    That's why I ask a much simpler way to detect the load.



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    Re: RF connected/destroyed Load detector?

    If the circuit purpose is to detect load DC resistance, it looks appropriate.

    It's surely possible to slightly reduce the circuit effort. But it doesn't make much sense if we suggests a modified circuit. It's your design, you know the constraints, you have to assemble and verify it. You either have the knowledge to redesign it under the given requirements or not. It doesn't look bad as is.



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    Re: RF connected/destroyed Load detector?

    So you should check the Load is connected well then you will turn on the PA, is that right ?? If it's so, I would use a switch to check the Load is well connected then this switch will rely the Load to the PA.
    It's a consistent method but little bit expensive because you have to drive the Load with a signal in order to get the status of the Load ( for instance it can observe common SWR meter ) if the Load is OK, then switch is controlled by uC.



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