Here in UK , like probably elsewhere in the world, FM stations need to be
seperated 200Khz to avoid mutual inteference. A good RX ought with good IF
filtering ought to be able to seperate two 200 Khz spaced FM signals I
think.
But of course stations are only 100Khz apart so it nigh on impossible to
seperate stations under these conditions as far as I know.

Well, if filtering won't sort out the problem, can you seperate the stations
any other way? Can you make a circuit that responds only to the wanted
station when it is just fractionally stronger than the unwanted station?
That's the only thing I can think of, apart from antenna solutions. Do we
have technology these days to do what we thought was impossible in this
case?

Richard:

Stations can be separated with a directional antenna.

Roger K6XQ

Richard:

Stations can be separated with a directional antenna.

Roger K6XQ

"Richard" wrote in message
...

Can you make a circuit that responds only to the wanted
station when it is just fractionally stronger than the unwanted station?

That's called "capture ratio". Better receivers have lower numbers -
smaller difference required to suppress unwanted station. They have numbers
like a VERY few dB.

To get this you need very flat IF within the passband - no ripples in
response.

A wideband limiter and wide and very linear discriminator.

The National "Criterion" series of tuners from 50 years ago were among the
first to attempt this. IIRC, there were HH Scott tuners like this as well.

All bets are off if you're trying to recover stereo.

73 de bob w3otc

"Richard" wrote in message
...

Can you make a circuit that responds only to the wanted
station when it is just fractionally stronger than the unwanted station?

That's called "capture ratio". Better receivers have lower numbers -
smaller difference required to suppress unwanted station. They have numbers
like a VERY few dB.

To get this you need very flat IF within the passband - no ripples in
response.

A wideband limiter and wide and very linear discriminator.

The National "Criterion" series of tuners from 50 years ago were among the
first to attempt this. IIRC, there were HH Scott tuners like this as well.

All bets are off if you're trying to recover stereo.

73 de bob w3otc

I believe that you are asking about narrowing the I.F. bandwidth. If you use
narrow filters, this is quite possible. Since FM stereo stations occupy a
150kHz bandwidth, you would be clipping the sidebands, resulting in lost
information. If you are only receiving in mono, this wouldn't be an issue.

Pete

"R J Carpenter" wrote in message
...

"Richard" wrote in message
...

Can you make a circuit that responds only to the wanted
station when it is just fractionally stronger than the unwanted station?

That's called "capture ratio". Better receivers have lower numbers -
smaller difference required to suppress unwanted station. They have
numbers
like a VERY few dB.

To get this you need very flat IF within the passband - no ripples in
response.

A wideband limiter and wide and very linear discriminator.

The National "Criterion" series of tuners from 50 years ago were among the
first to attempt this. IIRC, there were HH Scott tuners like this as
well.

All bets are off if you're trying to recover stereo.

73 de bob w3otc

I believe that you are asking about narrowing the I.F. bandwidth. If you use
narrow filters, this is quite possible. Since FM stereo stations occupy a
150kHz bandwidth, you would be clipping the sidebands, resulting in lost
information. If you are only receiving in mono, this wouldn't be an issue.

Pete

"R J Carpenter" wrote in message
...

"Richard" wrote in message
...

Can you make a circuit that responds only to the wanted
station when it is just fractionally stronger than the unwanted station?

That's called "capture ratio". Better receivers have lower numbers -
smaller difference required to suppress unwanted station. They have
numbers
like a VERY few dB.

To get this you need very flat IF within the passband - no ripples in
response.

A wideband limiter and wide and very linear discriminator.

The National "Criterion" series of tuners from 50 years ago were among the
first to attempt this. IIRC, there were HH Scott tuners like this as
well.

All bets are off if you're trying to recover stereo.

73 de bob w3otc

I believe he is talking about adjacent channel signals which are much
stronger than the desired and trying to see if there is a way to "fix" that.
Capture does not apply for this situation. Capture is a co-channel effect
and is better the wider the whole system is, not just the IF.

--
Steve N, K,9;d, c. i My email has no u's.


"R J Carpenter" wrote in message
...

"Richard" wrote in message
...

Can you make a circuit that responds only to the wanted
station when it is just fractionally stronger than the unwanted station?

That's called "capture ratio". Better receivers have lower numbers -
smaller difference required to suppress unwanted station. They have
numbers
like a VERY few dB.

To get this you need very flat IF within the passband - no ripples in
response.

A wideband limiter and wide and very linear discriminator.

The National "Criterion" series of tuners from 50 years ago were among the
first to attempt this. IIRC, there were HH Scott tuners like this as
well.

All bets are off if you're trying to recover stereo.

73 de bob w3otc

I believe he is talking about adjacent channel signals which are much
stronger than the desired and trying to see if there is a way to "fix" that.
Capture does not apply for this situation. Capture is a co-channel effect
and is better the wider the whole system is, not just the IF.

--
Steve N, K,9;d, c. i My email has no u's.


"R J Carpenter" wrote in message
...

"Richard" wrote in message
...

Can you make a circuit that responds only to the wanted
station when it is just fractionally stronger than the unwanted station?

That's called "capture ratio". Better receivers have lower numbers -
smaller difference required to suppress unwanted station. They have
numbers
like a VERY few dB.

To get this you need very flat IF within the passband - no ripples in
response.

A wideband limiter and wide and very linear discriminator.

The National "Criterion" series of tuners from 50 years ago were among the
first to attempt this. IIRC, there were HH Scott tuners like this as
well.

All bets are off if you're trying to recover stereo.

73 de bob w3otc

Steve Nosko wrote:
I believe he is talking about adjacent channel signals which are much
stronger than the desired and trying to see if there is a way to "fix"
that. Capture does not apply for this situation. Capture is a co-channel
effect and is better the wider the whole system is, not just the IF.

Capture effect:

http://en.wikipedia.org/wiki/Capture_effect

It's an intersting phenomena, and potentially useful. If I could phase null
(at the antenna) the local stronger signal then it would dissappear as
inteference if it was a few db below the wanted signal.

Only problem is, is that if you cannot get the inteferring signal below the
wanted one, it's works very bad for you, because you cannot listen to an
inteferred with signal. Which is better than nothing I guess in some cases.

Pity that somehow you cannot design circuitry which recognises a 100Khz
difference between the wanted FM station and the unwanted FM station and
proceed to demodulate the wanted one only. If it were possible, it would
have been done by now. Maybe you could do it digitally,I dunno.