On Mar 15, 9:11*am, billcalley wrote:
Hi All,

* *I always hear that antennas have to be matched to their radio, but
in receivers (such as FM and shortwave radios) I see mostly long
random length antennas used, and these antennas -- be they a
telescoping whip or a long wire out a window -- are used over some
really wide bandwidths. *How is this possible if an impedance match
must always be maintained for radios? *And since there cannot be a
good match over such wide bandwidths with any (typical) wire antenna,
what is the downside to using these completely unmatched long antennas
for receivers? *(Poor gain patterns with lots of nulls? *Lower
sensitivity due to bad noise figure or gain match for any LNA or
frontend amp? Degraded overall antenna gain)?

Thanks; I'm very confused on this subject!

-Bill

What has not been mentioned much is that AM band broadcast receivers
and FM band receivers are designed to to tune over a fairly wide band
of frequencies; so very difficult to build antenna that will mtach at
all those different 'wavelengths'.

For example; the broadcast band (North America) is roughly 550
kilohertz (that's 545 metres wavelength) to about 1.7 megahertz (about
176 metres). That's 3:1 ratio!

On FM, 88 to 108 megahertz (3.4 to 2.8 metres) the ratio is less but
still cnsiderable at 1.2:1 So again very difficult to design and build
an 'all frequencies' antenna.

For stations designed to receive only one frequncy the antennae can be
constructed for that only; hence the matching can be as optimum as
possible.