Michael Black wrote:
"Larry Gauthier \" ) writes:

If you find yourself with two radios that are similarly-equipped in
terms of antennas, but one gets your favorite stations while the
other does not, then the one that does not is either broken or has
designed-in lousy sensitivity.

Actually, it might be the reverse, depending on what exactly is
happening.

I have a all in one stereo I got at a garage sale. It had lousy
reception of a non-local station that is always receivable here on
other radios, even lousy ones. I naturally thought the antenna was
the problem. But I did something and realized I likely was
attenuating the signal, and the issue wasn't "not enough antenna" but
too much. I took off the whip antenna, and that thing gets perfect
reception on that non-local station, whereas before it
was noisy.

Clearly, the stereo was being overloaded by local signals, which
impacted
on it's ability to receive the strong but comparatively weaker
non-local station. Removing the antenna attenuated the local
station(s) enough that the stereo didn't overload, but the non-local
station was still strong
enough to be received fine.

Most consumer broadcast receivers are too sensitive if anything,
because
they don't handle strong signals that well, yet the strong signals
overloading them make them useless for receiving distant signals. A
less sensitive receiver wouldn't be as good for distant reception, but
the local signals wouldn't mask those distant signals with overload.

I don't know if this is the case here, but it is worth looking into
since it's the last thing people generally expect. I notice when I
got a Grundig portable sw receiver at a rummage sale in September, the
manual specifically states to keep the whip antenna shorter when on
the FM broadcast band (the antenna being longer for the shortwave
bands), and having been prompted by the manual and experience, I do
notice that not so great reception on the FM band is improved when
I shorten the whip antenna.

Michael VE2BVW

Michael...you were absolutely correct (100%) about shortening the whip for
FM broadcasts. I shortened the whip to its fully collapsed position and it
worked, and the station I wanted came in at an acceptable level. Great
info. So now my logical question is why are the FM whip antennas even
extendible if they play better fully collapsed. I guess it depends on a
bunch of variables such as power of the transmitter and location of where
the signal is being transmitted from. I know from past experience that
extending the antenna can help sometimes.

But shortening it worked - what is the quick logic if you don't mind. I
know that everything is frequency and wavelength and they are inversely
proportional. I would have never thought that shortening the antenna would
have solved the problem - I even thought I tried that before, but I must not
have stayed with it long enough. Thanks again to you and everyone else for
all your help :-) .

Pete

Pete wrote:
"So now my logical question is why are the FM whip antennas even
extendible if they play better fully collapsed?"

Length is adjustable to tune the antenna to resonance so that excess
reactance does not block too much signal from the receiver. Resonance
depends on the station you want to receive.

Wavelength = 300 / MHz

At 100 MHz, wavelength = 3 meters

If the best antenna length were 1/4 wavelength, length would be about
0.75 meter = 75cm/2.54cm/in.= 29.53in. which may be shortened by 5% for
"end effects" which calculates to about 28 inches for a 100 MHz station.
Higher frequency stations may require shorter lengths and lower
frequency stations may require longer lengths. We don`t know the design
of the radio and what inherent reactance may reside inside. So, we
really don`t know how long the adjustable antenna needs to be.
It is far better to experiment with the length of the antenna to get the
best results.

Some radios use the same antenna for several bands of a multiband tadio.
So adjust the antenna if necessary for best results.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
Pete wrote:
"So now my logical question is why are the FM whip antennas even
extendible if they play better fully collapsed?"

Length is adjustable to tune the antenna to resonance so that excess
reactance does not block too much signal from the receiver. Resonance
depends on the station you want to receive.

Wavelength = 300 / MHz

At 100 MHz, wavelength = 3 meters

If the best antenna length were 1/4 wavelength, length would be about
0.75 meter = 75cm/2.54cm/in.= 29.53in. which may be shortened by 5%
for "end effects" which calculates to about 28 inches for a 100 MHz
station. Higher frequency stations may require shorter lengths and
lower frequency stations may require longer lengths. We don`t know
the design of the radio and what inherent reactance may reside
inside. So, we really don`t know how long the adjustable antenna
needs to be.
It is far better to experiment with the length of the antenna to get
the best results.

Some radios use the same antenna for several bands of a multiband
tadio. So adjust the antenna if necessary for best results.

Best regards, Richard Harrison, KB5WZI

Thank you Richard. I understand what you said. This was a lower to mid
frequency station (97.5 MHz), and it required a shorter length, but other
stations right next to it came in fine at a longer extension. This is weird
stuff, and its obviously dependent on the radio guts and what is going on
with that one station as far as location and power, etc. It is refreshing
to be in a newsgroup where people are helpful, and not condescending and
vulgar like so many others if you know what I mean. Thanks again to you
all.

Pete

Michael Black wrote:
I have a all in one stereo I got at a garage sale. It had lousy reception
of
a non-local station that is always receivable here on other radios, even
lousy
ones. I naturally thought the antenna was the problem. But I did
something
and realized I likely was attenuating the signal, and the issue wasn't
"not enough antenna" but too much. I took off the whip antenna, and that
thing gets perfect reception on that non-local station, whereas before it
was noisy.

Clearly, the stereo was being overloaded by local signals, which impacted
on it's ability to receive the strong but comparatively weaker non-local
station. Removing the antenna attenuated the local station(s) enough that
the stereo didn't overload, but the non-local station was still strong
enough to be received fine.

Most consumer broadcast receivers are too sensitive if anything, because
they don't handle strong signals that well, yet the strong signals
overloading them make them useless for receiving distant signals. A
less sensitive receiver wouldn't be as good for distant reception, but
the local signals wouldn't mask those distant signals with overload.

In my days installing/maintaining FM receivers for background music (67 KHz
SCA subcarrier), I ran into that a few times. In one installation, I
installed our standard 3 element yagi on the roof and aimed it toward our
transmitter. I had line-of-sight to our transmitter some 30 miles away
(48.2 Km for our Canadian friend) but had horrible reception.
Our station was on 98.9 MHz (35KW), and at the top of the hill from my
receiving location (90° azimuth) , were 3 TV (Ch 4, 5 & 7) and 2 FM stations
(98.1 MHz & 100.7 MHz). I surmised the combined 716KW of those stations was
overloading the receiver. A dipole made from some lamp cord wire, stapled
to the ceiling of the room and fed into 75 ohm coax worked perfectly.
Sometimes simplest is bestest! :-)

Bryan WA7PRC

On Tue, 3 Apr 2007 19:07:47 -0400, "Pete" wrote:

Hi everyone,

I am new here, so please excuse my ignorance about antennas, or if I am in
the wrong ng. I could not find any help getting the answer to my question
by googling.

I have a cheap boom box radio that I recently bought at Walmart and it plays
great music, and cd's, and cassettes. Unfortunately it will not play my
favorite FM oldies station (97.5 MHz) either in my workshop, or my house (it
plays several other stations fine). My other boom box will play the station
(and its 20 years old), and they are both of relatively equal value (the
older one is a brand name - Panasonic). If anything, I would think the new
one should have 20 year newer technology in it, and it should play at least
as good - dunno.

They both have a telescopic whip antenna (I hope that is the right
terminology), and the new one will not play the station I want by either
rotating the antenna, or moving the radio to different positions. I have
tried everything. The only way it will play the station I want, is to put
my hand on the antenna (or even around the antenna - ie I don't even have to
touch it - interesting - I guess my body makes a real good antenna - I have
always wondered about this phenomena). I tried touching it with other
metallic devices (eg, wire, coat hanger etc), and it has no effect. The
only way it will play the station is by getting near the antenna with my
hand.

I see no way of mounting an FM antenna to the receiver (ie the antenna is
factory mounted to the back of the radio.

I have a couple of questions if you will allow me :

- Is there anything I can do to the existing telescopic whip antenna (such
as wrap it in aluminum foil or something else weird like that) that will
enable the radio to pick up the station I want. And also, please explain
why it plays the station I want when I put my hand on or around the antenna.

- I thought AM and FM antennas were different technologies (so to speak - eg
amplitude modulation versus frequency modulation). How come portable AM/FM
radios only have a single telescopic whip antenna (please excuse me if that
is the wrong terminology). Is the whip for FM, and the AM is inside the
radio, or it uses the cord (just a guess).

Any comments would be greatly appreciated. Thanks...Pete


You could look around for a GE SuperRadio III -- it runs about $40-50
nowadays, and has a separate FM antenna terminal you can hook up a
decent antenna to. This radio also has two speakers, a woofer and
tweeter, and sounds pretty nice, tho' it is mono.

bob
k5qwg

Pete wrote:

....

Pete:

I use a cheap (purchased at a flea market) TV-VHF-UHF-FM amplified
antenna--can be line powered or operated from batteries.

Funky, I know, but it does what I need.

JS