Re: Just how good (or not) is error correction on DAB

In message <XIo0i.11678$d9.6001@xxxxxxxxxxxxxxxxxxxx>
Richard Evans <R.P.Evans.NoSpam@xxxxxxxxxxxx> wrote:

Boltar wrote:
mention this, since running high-power transmitters with the load
disconnected used to be a good way of destroying them, until

How come? If you run an audio amp with the speakers disconnected it
does it no harm at all since no current flows in the output stage. Why
are transmitters different?

B2003

An audio amp used a different type of circuit than an RF amp.

To be honest I never completely understood why an RF amp can be damaged
if an aerial is not connected. I have some idea, but I'm not sure of all
the details.

The difference is that the RF output is matched to a transmission line
of a defined impedance, which should be terminated by a load of the
same impedance in order to achieve optimum delivery of power. With a
microwave oven this is all somewhat inexact, but the transmission line
is a short length of waveguide duct and the load is the water in your
sponge cake mixture. If no load is present, power will be reflected
back into the waveguide, overheating the magnetron. Luckily domestic
magnetrons seem to be fairly tolerant of this kind of abuse, but if
you try it with lower-frequency transmitters which don't have
protection, you may zap your expensive RF power transistors and even
burn out the coaxial cable.

--
Richard L.
.

Relevant Pages

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