In article ,
Bruce W.1 wrote:

That's the part that's difficult to measure. Some of my good HT
antennas that came with the radio, when tested alone on a good ground
plane, have lousy SWR. Yet these radios are fully capable of being
connected to an external antenna.

A perfect quarter wave is 36 ohms. Yet HT's are happy driving an
external 50 ohm antenna.

Well, for one thing, the transmitter "sees" the total load - the
quarterwave's radiation resistance, the radiation resistance of
whatever is servicing as the ground plane / counterpoise / other half
of the dipole, and the losses of both. The role of GP/counterpoise is
usually taken by a combination of the HT's metal body, and the user's
skin (capacitively coupled to the HT body). The radiation resistance
and losses of the HT body and user's skin are difficult to predict,
and no doubt vary all over the place depending on the situation, sweat
levels, phase of moon, etc., but I imagine they're high enough to
boost the total feedpoint impedance up well above 36 ohms.

For another things, HT finals _have_ to be reasonably tolerant of poor
matches, or the failure rate would be astronomical - there's just too
much variation in antenna feedpoint impedance to allow such devices to
be designed with finicky, sensitive finals. I would guess that modern
HTs all use internally-ballasted multiple-emitter RF transistors which
are very conservatively rated (e.g. voltage breakdown ratings of
several times higher than the power supply voltage, plenty of excess
current-dissipation margin due to the ballasting) and may include
automatic high-SWR power foldback circuitry as well.

--
Dave Platt AE6EO
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