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

Thanks a lot for the great info Michael...I love technical stuff, and I find
your comments very interesting. You guys have been very helpful. Thanks
again to all of you...Pete

Richard Clark wrote:
On Tue, 3 Apr 2007 23:06:19 -0400, "Pete" wrote:

Thank you Richard...that is the kind of comment I was looking for (I
took Neil's with a grain of salt-there is absolutely nothing wrong
with the radio). I was trying to be polite in my post, but I am way
smarter than that.

Hi Pete,

No, it is still advice to consider. Your new radio does have the
performance of a lemon in comparison to your old set.

Hi Richard...Make sure to read Michael Black's interesting info in this
thread. I definitely believe the radio (cheap as it may be) is doing
exactly what it is designed to do. I do not believe it is a lemon, and
there is no doubt in my mind the older Panasonic has better circuitry in it
(it is a better set and has a graphic equalizer also - the newer one doesn't
even have bass/treble controls but it sounds good), but they are roughly
comparable.

Actually, the old one probably costs quite a bit more (on a relative basis)
considering how cheap you can buy this stuff these days compared to the
price twenty years ago. Just for your info, I have an old Electrovoice
stereo receiver downstairs (with dials/knobs) and it still works fine after
36 years.

Also FYI, I have a new Sherwood stereo receiver upstairs (with the fm
antenna that came with it installed), and it also picks up the station I am
talking about weaker than the other stations, but I was able to tweak the
antenna and it comes in acceptable. It is interesting that the old
Panasonic boombox has no trouble. Sorry if I am going off on a tangent. I
have more comments below :-) ....Pete



I will try wrapping the wire around the antenna tomorrow and let you
know what happens (is it okay to use phone wire which has several
individually insulated wires in it). BTW could you please tell me
why the reception comes in when I put my hand around the antenna (ie
what is my body doing to the signal), and also answer my second
question about one antenna for both AM and FM. Thanks again...Pete

Yes, it is a mystery still....

Your body is a conductor, admittedly a very poor one, but the power
levels we are talking about, and the currents involved don't ask very
much. The wavelengths involved for FM are about your height. If we
shift to AM, you would have to be the Jolly Green Giant (hence hand
waving usually doesn't do much good). That you don't even have to
touch the antenna is also an indication in the small power necessary,
it is more about your height and proximity.

Multi wire, such as you have, will make little difference. However,
this is not to say that things won't remain marginal. You do have the
experience with another radio that works in the identical environment,
so that suggests some hope. There are "magic" lengths of wire, but
you can escape that discussion by crafting various different lengths
by bending, trimming, but still keeping things high (all of this is
predicated on putting the antenna into the sight of the transmitter).

The same antenna is NOT for both bands. The AM antenna is undoubtedly
the old stand by we call the loopstick. This is a long rod of ferrite
material with a coil or wrapping of wire - you've probably seen these
before. A car antenna certainly does double duty, but this is not
generally found in portable radios. This is because the car radio
sits inside a metal cage that demands an external sky hook.

73's
Richard Clark, KB7QHC

Thanks again Richard for all the good info. I kind of knew about the
loopstick stuff but just wanted to make sure. You guys have been
great...Pete

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