"Phil Allison" wrote
...

"Richard Clark"

Now, as to your experience of receiving signals on the wrong
frequency, that is a classic situation of image rejection being poor
due to the lack of a tuned front-end (something that dissappeared with
the dinosaurs). If I were to guess on the basis of 40 year old
experience fixing these suckers, your off-frequency signals are
probably shifted by twice the IF frequency of your receiver. The
classical FM IF frequency of 10.7 MHz might apply, but time has
marched on and designers may select their own. This old standard
would argue that you shouldn't experience images except where they
would be out-of-band (the 88-107 band with this IF would force that).


** Hearing the same FM station at more than one spot is still possible
even with a 10.7 MHz IF frequency - if the signal is very strong. The
reason is harmonics of the incoming carrier generated in the RF stage
interacting with harmonics of the local oscillator in the mixer.

It sound like the "Luxemburg Effect". The signal was from the dipole
antenna.
Are now the FM stations which use the dipoles?

Eg:

A 100MHz FM carrier generates a harmonic at 200MHz in the receiver.

When the local oscillator is adjusted to 94.65 MHz, its second harmonic is
189.3 MHz.

The difference frequency is then 10.7 MHz - so goes through to the FM
detector.

In this situation, the FM deviation is doubled so the recovered audio will
be distorted on loud passages.
S*

amdx wrote:
"Richard Clark" wrote in message
...
On Fri, 19 Mar 2010 15:22:42 -0500, "amdx" wrote:

So I installed the antenna on the outside of the boat and the radio
inside,
now one station I listen to is weak, but if I unplug the antenna and let
the
center pin touch ground of the connector on the radio it comes in great.
Just curious why it is working this way.
Hi Mike,

You moved the antenna.

Most loss of signal as you describe comes from not being a weak
signal, but the mixture of signals that combine negatively at some
spot due to multiple reflections. When you replaced the line cord as
antenna for this better implementation, you also found that "sour (not
sweet) spot." This can occur for any frequency with the equal
likelihood of reflections combining negatively. Move your antenna a
quarter wave and see what happens.

Your description of your having an aluminum boat almost guarantees a
multitude of RF-bright reflections. At short wavelengths, this also
guarantees many, many regions that will exhibit destructive (as well
as constructive) combinations of those reflections.

Put your antenna as far away from the superstructure or hull as
possible. This will reduce the reflection path differences.

BTW, the mod did cure the computer hash.
Mike
FM has what is called a "full quieting" effect. It would suggest that
your first signal levels were just barely above the level of full
quiet (and perhaps not even that good).

73's
Richard Clark, KB7QHC
Richard, after I read your letter I did a little better checking and found
my signal is not weak it is to strong, I'm getting interference from other
frequencies.
Also I get stations on the wrong frequency.
I went out and collapsed the antenna to minimum about 1/3 of what it was
and
my problem station is perfect and the other station I listen to is still
good. The local
NPR station isn't good though. But I can download the podcast of Science
Friday :-)
Thanks, Mike


The usual, lousy FM tuner. They don't make'em like they used to. It's
the same with television sets, one large signal and they fall off the
rocker.

If you have a radio with a signal strength meter you could notch out a
strong station. But that only works it it's just one and far away from
the NPR frequency. The only other options are to get a better radio, a
directional antenna, or just live with it and use the podcast.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

"Joerg" wrote in message
...
amdx wrote:
"Richard Clark" wrote in message
...
On Fri, 19 Mar 2010 15:22:42 -0500, "amdx" wrote:

So I installed the antenna on the outside of the boat and the radio
inside,
now one station I listen to is weak, but if I unplug the antenna and
let the
center pin touch ground of the connector on the radio it comes in
great.
Just curious why it is working this way.
Hi Mike,

You moved the antenna.

Most loss of signal as you describe comes from not being a weak
signal, but the mixture of signals that combine negatively at some
spot due to multiple reflections. When you replaced the line cord as
antenna for this better implementation, you also found that "sour (not
sweet) spot." This can occur for any frequency with the equal
likelihood of reflections combining negatively. Move your antenna a
quarter wave and see what happens.

Your description of your having an aluminum boat almost guarantees a
multitude of RF-bright reflections. At short wavelengths, this also
guarantees many, many regions that will exhibit destructive (as well
as constructive) combinations of those reflections.

Put your antenna as far away from the superstructure or hull as
possible. This will reduce the reflection path differences.

BTW, the mod did cure the computer hash.
Mike
FM has what is called a "full quieting" effect. It would suggest that
your first signal levels were just barely above the level of full
quiet (and perhaps not even that good).

73's
Richard Clark, KB7QHC
Richard, after I read your letter I did a little better checking and
found
my signal is not weak it is to strong, I'm getting interference from
other frequencies.
Also I get stations on the wrong frequency.
I went out and collapsed the antenna to minimum about 1/3 of what it
was and
my problem station is perfect and the other station I listen to is still
good. The local
NPR station isn't good though. But I can download the podcast of Science
Friday :-)
Thanks, Mike

The usual, lousy FM tuner. They don't make'em like they used to. It's the
same with television sets, one large signal and they fall off the rocker.

If you have a radio with a signal strength meter you could notch out a
strong station. But that only works it it's just one and far away from the
NPR frequency. The only other options are to get a better radio, a
directional antenna, or just live with it and use the podcast.

--
Regards, Joerg
This morning I got on the boat and the signal that was improved to good by
shortening the antenna is now bad. 94.5 has interference from 101.1.
Oh well!
Mike

amdx wrote:
"Joerg" wrote in message
...
amdx wrote:
"Richard Clark" wrote in message
...
On Fri, 19 Mar 2010 15:22:42 -0500, "amdx" wrote:

So I installed the antenna on the outside of the boat and the radio
inside,
now one station I listen to is weak, but if I unplug the antenna and
let the
center pin touch ground of the connector on the radio it comes in
great.
Just curious why it is working this way.
Hi Mike,

You moved the antenna.

Most loss of signal as you describe comes from not being a weak
signal, but the mixture of signals that combine negatively at some
spot due to multiple reflections. When you replaced the line cord as
antenna for this better implementation, you also found that "sour (not
sweet) spot." This can occur for any frequency with the equal
likelihood of reflections combining negatively. Move your antenna a
quarter wave and see what happens.

Your description of your having an aluminum boat almost guarantees a
multitude of RF-bright reflections. At short wavelengths, this also
guarantees many, many regions that will exhibit destructive (as well
as constructive) combinations of those reflections.

Put your antenna as far away from the superstructure or hull as
possible. This will reduce the reflection path differences.

BTW, the mod did cure the computer hash.
Mike
FM has what is called a "full quieting" effect. It would suggest that
your first signal levels were just barely above the level of full
quiet (and perhaps not even that good).

73's
Richard Clark, KB7QHC
Richard, after I read your letter I did a little better checking and
found
my signal is not weak it is to strong, I'm getting interference from
other frequencies.
Also I get stations on the wrong frequency.
I went out and collapsed the antenna to minimum about 1/3 of what it
was and
my problem station is perfect and the other station I listen to is still
good. The local
NPR station isn't good though. But I can download the podcast of Science
Friday :-)
Thanks, Mike
The usual, lousy FM tuner. They don't make'em like they used to. It's the
same with television sets, one large signal and they fall off the rocker.

If you have a radio with a signal strength meter you could notch out a
strong station. But that only works it it's just one and far away from the
NPR frequency. The only other options are to get a better radio, a
directional antenna, or just live with it and use the podcast.

--
Regards, Joerg
This morning I got on the boat and the signal that was improved to good by
shortening the antenna is now bad. 94.5 has interference from 101.1.
Oh well!


You really need a better quality radio and with radios and a lot of
other stuff older = better :-)

I mean, considering what the boat must have cost ...

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

In article ,
"amdx" wrote:

I have an FM radio inside an aluminum boat. The radio worked ok with the
AC cord as the antenna but I got interference when I used my laptop.
I found the circuit that ran from the power transformer to the antenna input
on the
FM IC. I installed a connector that is used on car radios and wired the
center pin
to the foil that went to the FM IC (capacitor on pcb isolated) and the
shield side to
dc ground near the IC. I then plugged in a telescoping car antenna and it
worked
great on the bench .
So I installed the antenna on the outside of the boat and the radio inside,
now one station I listen to is weak, but if I unplug the antenna and let the
center pin touch ground of the connector on the radio it comes in great.
Just curious why it is working this way.
BTW, the mod did cure the computer hash.
Mike

It's probably a severe impedance mismatch between your new antenna and
the old pickup coil. You might need to create a little step-up
transformer between the board and jack. I looked at a few FM chip specs
and they leave it up to the designer to figure out the right input
transformer. You'll probably need trial and error to figure it out.
--
I won't see Google Groups replies because I must filter them as spam