Re: [Amps] High SWR,

[Roger <sub1@rogerhalstead.com>]

Roger Parsons wrote:
> I know this has been said before, but just because your SWR meter says there 
> is x Watts of power coming back down the line, it doesn't mean that it is 
> being dissipated in your transmitter.
The power really is on the line, but as you say, it's not dissipated in 
the finals.
The easiest way to explain, or rather the simplest analogy is to think 
of a lossless coax and a resistive mismatch.  Put 100 watts into it and 
have 50% reflected back from the antenna. At the transmitter That 
reflected power is "re" reflected  so now you have 150 watts forward on 
the coax with 50 reverse.  At the antenna we have 25 watts reflected the 
next time around and end up with 75 watts reflected and 175 watts 
forward. and so it goes. In this case taking it to the logical 
conclusion you end up with 200 watts forward out of a 100 watt 
transmitter and 100 watts reflected. (and that's with only 50% reflected)
>  All it means is that the transmitter sees a load other than 50 Ohms (or 
> whatever) - and it may or may not be able to match it. If you have a really 
> bad mismatch you can (apparently) have the situation that your 100W 
> transmitter is (say) transmitting 1kW and getting 900W back. Obviously that 
> can't really happen - the reason that it seems to is that the SWR meter is 
> measuring Volt-Amperes (reactive power) rather than Watts (real power) 
In the case of a resistive mismatch it is real power, but things in real 
life are seldom that simple.
In either case it doesn't matter as long as it's within the range of the 
pi-net in the amp.

73

Roger (K8RI)
> - that is that the current and voltage are not in phase - except in the 
> special case of a 1:1 SWR.
>
> 73 Roger
> VE3ZI
>
>
>
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