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

Bill;

I haven't looked at the back of a radio in a long time, but those that I
have looked at usually had a trimmer capacitor that helped tune the
antenna to the radio input. This is the impedance match you are looking at.

Dave WD9BDZ

On Mar 15, 3:11*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

Well, I 'm not an expert, but it seems that with a transmitting
antenna, the idea is to transfer as much power as possible to increase
efficiency, and so the antenna needs to be closely matched to the
output of the transmitter for best results. But the receiving antenna
is a different problem, since no power from the antenna is needed to
drive the receiver, and so who cares about the match? The idea with
the receiving antenna is to get the most voltage and highest S/N ratio
with no load. The input to the receiver should be buffered with a high
impedance FET amplifier, or some such, so the receiver draws almost no
power from the antenna. This leaves you free to design the antenna and
input tuning circuit for the highest Q and lowest noise figure without
worrying about impedance match.

Just my opinion.

-Bill

On 3ÔÂ15ÈÕ, ÏÂÎç7ʱ11·Ö, 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



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On 3ÔÂ15ÈÕ, ÏÂÎç7ʱ11·Ö, 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



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manufacturers... but lack the time to contact suppliers, negotiate
contracts, arrange shipping or monitor product quality? Don't worry -
Let seriouswholesale deal with all that for you.

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Audio, and Computer Accessories now by visiting the online wholesale
catalog at seriouswholesale. com You'll have peace of mind thanks to
the seriouswholesale Quality Control, 12-month Warranty on all
products, and easy secure payment by credit card through Paypal.

Selling on eBay or your own online store? Send products direct from
our warehouse to your customers using our unique drop-shipping
service. You can profit by selling hundreds of different products,
without holding any of your own inventory! Any questions you have will
be answered by the seriouswholesale English-speaking customer support
team... Their aim is to make your China electronics importing business
easier to run than ever before.

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On 3ÔÂ15ÈÕ, ÏÂÎç7ʱ11·Ö, 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


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manufacturers... but lack the time to contact suppliers, negotiate
contracts, arrange shipping or monitor product quality? Don't worry -
Let seriouswholesale deal with all that for you.

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Audio, and Computer Accessories now by visiting the online wholesale
catalog at seriouswholesale. com You'll have peace of mind thanks to
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products, and easy secure payment by credit card through Paypal.

Selling on eBay or your own online store? Send products direct from
our warehouse to your customers using our unique drop-shipping
service. You can profit by selling hundreds of different products,
without holding any of your own inventory! Any questions you have will
be answered by the seriouswholesale English-speaking customer support
team... Their aim is to make your China electronics importing business
easier to run than ever before.

Welcome to http://www.seriouswholesale.com.

seriouswholesale - Buy from the source, profit without the hassle.

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Not sure about the higher frequencies but in the HF band we absolutely need
an antenna coupler that matches the impedance to the selected frequency. If
a coupler fails we can barely throw a signal a few miles whereas when the
coupler does it's job we can bounce a signal off of the ionosphere at night
for a few thousand miles.

Claude
Montreal

"billcalley" wrote in message
...
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

Not sure about the higher frequencies but in the HF band we absolutely need
an antenna coupler that matches the impedance to the selected frequency. If
a coupler fails we can barely throw a signal a few miles whereas when the
coupler does it's job we can bounce a signal off of the ionosphere at night
for a few thousand miles.

That's certainly true at the transmitting end. A good impedance match
is needed in order to enable the transmitter to deliver power
effectively into the antenna, from whence it can be radiated.

It's rather less true at the receiving end, at least in the lower-
frequency HF bands. In these bands, the ability to receive a usable
signal is often dominated by the amount of natural and man-made noise
in the band, and not by the receiver's own self-generated noise. Even
with a serious impedance mismatch between the antenna and the
receiver, enough signal reaches the receiver front-end to overcome the
receiver's own internal noise.

If you happen to live in an area which is blessed by a very low
background-noise level (e.g. out in the country, away from power
lines) and you're DXing in the HF bands, then a good impedance-matched
antenna will let your receiver take best advantage of the low noise
level.

If you're SWLing in a city, surrounded by power lines and electric
motors and neon lights and computers, the background noise level is
going to be much higher, and the weak distant stations will be drowned
out by the noise anyhow... and an inefficiently-matched antenna such
as a whip or longwire will give you enough signal to hear the stations
which are _not_ drowned out by the noise.

As an example - if your receiver has decent sensitivity, and a low
internal noise level, you may find that you can hear a signal with
decent audio quality all the way down to S0 or below (if there's no
noise obscuring it). You then find that with an impedance-matched
antenna the band's background noise is S6 or so. Assuming that you
can make use of a signal which is somewhat below the broadband noise
level, let's say that you decide you can copy stations whose own
individual signals are S5 or better, and that lower-level signals are
blanketed by the noise.

At this point, you realize that you can use an antenna which is 5
S-points (nominally, 30 dB) less efficient, and still receive the same
set of stations. With a less efficient antenna, the stations' signals
will be weaker... but so will the external band noise, by the same
ratio, and thus the signal-to-noise ratio of each station will remain
unchanged.

As an example, my ARES/RACES group has a multiband HF setup in our
city's police and fire admin building, which is downtown near the main
commercial-and-restaurant street and the light-rail system. We have a
trap-dipole antenna strung up above the building's roof. On the
80-meter band, the broadband noise level across the whole band is
rarely less than S9! We could probably receive the same set of
stations using an antenna consisting of two coat-hangers and some damp
string!

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

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."

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.

In article
,
terryS wrote:

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!

HOWEVER, if you will look at the Antenna Design for a AM Broadcast
Receiver, using a Ferrite Loop Antenna, you WILL notice that the
Loop IS Tuned to the specific part of the band that the receiver is
being tuned to, by Linked Ganged Variable Capacitors, in the Receivers
Frontend. These designs have been around for MANY years, (1940's anyway)
and are a very mature technology.