On 7/7/2015 6:17 AM, Ian Jackson wrote:
In message , Jerry Stuckle
writes

So why don't manufacturers design transmitters with 1 ohm output
impedance, Rick?

They probably would - if they could (at least for some applications).
That would then enable you to step up the TX output voltage (using a
transformer), so that you could drive more power into a higher (eg 50
ohm) load.


Oh, it's completely possible. It's just a matching network, anyway -
one which has to be in place anyway, because the output of a tube amp is
relatively high impedance, and the output of a transistor amp is
relatively low impedance. In fact, a 144W transistor amp running on 12V
wouldn't even need a matching network. It's output would have 1 ohm
impedance.

But of course, the overall output impedance would then become
correspondingly higher. You would also be drawing correspondingly more
current from the original 1 ohm source, and if you used too high a
step-up, you would risk exceeding the permitted internal power
dissipation (and other performance parameters).


And why would the output impedance change just because the load
impedance changes? They are two separate things.

But according to you, no step-up is required - you can drive any
(comparatively) high impedance source most efficiently from a low impedance.

So yes, you are getting more power output when you match* the source
impedance to the load - but it doesn't necessarily mean you always can
(or should) go the whole hog.
*Or, at least, partially match.


So, which is it? First you say the output impedance of the transmitter
should be very low for maximum power to the antenna. Now you say it
should be matched. Then you say it shouldn't be matched.

Which is it?

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