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Re: [Amps] Transceiver Output Impedance

To: "'Robert Carroll'" <>, <>
Subject: Re: [Amps] Transceiver Output Impedance
From: "Saandy Eban" <>
Date: Sun, 9 Mar 2008 11:01:03 +0200
List-post: <">>
.....this is definitely not so!
The load impedance of the final transistors is defined by Ohm's law so that
for a defined high power the load they expect to see can be a few ohms only.
Here is where the output transformer comes into play: it transforms the low
LOAD impedance the transistors expect to see to 50 Ohms at the amplifier's
Think of the fact that immediately after the amplifier you have filters
designed for 50 Ohms.
You cannot expect good results from them if the do not operate in a 50 Ohms
Soooo, this thesis cannot be correct, simply because of physical reasons.
73 and all the best:
Alex    4Z5KS

-----Original Message-----
From: [] On
Behalf Of Robert Carroll
Sent: Sunday, March 09, 2008 2:10 AM
Subject: [Amps] Transceiver Output Impedance

I have been told that modern solid state HF transceivers have been designed
to deliver rated power into a stated load resistance-almost always around 50
ohms-but that their effective internal impedance looking into the output
port while it is active and delivering rated power is nowhere near 50 ohms
but rather closer to a few ohms if you can define such an impedance at all.
Is this more or less accurate?  I ask in connection with the 87A input match
problems Rit Nesbitt mentioned a few days back on this reflector.



Bob W2WG

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