On Sat, 15 Mar 2008 04:11:21 -0700 (PDT), 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

In a short answer to your question, NO!

The finals won't burn out as there are none and you won't be feeding
radiation into your room.

However, as you probably noticed from the FM radio with the extendable
antenna, you sometimes get a better signal when you extend the antenna
nd move it to the right location.

A good (and matched) antenna may allow you to receive signals you
could not have received with a random length antenna.

Most radios that I have seen usually have a matching network built in
to match the antenna that comes with the radio. In most cases they
aren't that elaborate, just a small coil and a trimmer capacitor.

My father learned that as great as his 50 foot long copper wire worked
for listening to his favorite short wave broadcasts, the signals
improved immensely when I installed an fan-dipole for his three
favorite bands. Did he 'need' that antenna? no, he could hear his
stations without it, but the signal strength was improved and he was
able to pick up more stations.

Dad also ordered an antenna tuner kit, assembled it and attached it
to his 50 foot wire. He found a great improvement in signal strength
using the tuner, almost equal to the multi-band dipole I installed.

Signal to noise ratio are not synonymous with gain. One can have a
lower-gain antenna with high s/n that outperforms a higher-gain
antenna with low s/n. When it gets critical, the s/n can be the
determining factor as to whether you receive intelligent communication
or not.

You are probably digging for technical, theoretical information more
than practical, but just in case...

If you look in stereo magazines, you seldom see radio ads bragging
about how much better they receive than the competition. If you look
in Ham magazines, that's a very important feature. Most consumers are
looking for stereos that play music well and they listen to local
stations. Most ham operators want to pull that weak signal out of the
noise to make the contact.

Just some thoughts.

Hope this is helpful to someone.
Buck
N4PGW

--
73 for now
Buck, N4PGW

www.lumpuckeroo.com

"Small - broadband - efficient: pick any two."