Hi, guys,

ISTR.......
(through the mists of time) that the excessive bandwidth of an AM
transmission signal can interfere with the reception of a NBFM signal,
though the converse is not true. Can anyone confirm this (or else
flatly deny it/affirm it)?

Thanks,

p.
--

The BBC: Licensed at public expense to spread lies.

I don't think you can make a flat statement either way with the information
supplied. The only thing that's for sure is NBFM has a constant power
envelope whereas AM has a highly variable envelope. And why do you say AM
has excessive bandwidth?. NBFM only can only approaches the bandwidth
efficiency of AM when the FM modulation index gets very small.
When FM gets narrow enough (expressed by modulation index, not deviation),
it's interference rejection is no better than AM.

Joe
W3JDR

...
Hi, guys,

ISTR.......
(through the mists of time) that the excessive bandwidth of an AM
transmission signal can interfere with the reception of a NBFM signal,
though the converse is not true. Can anyone confirm this (or else
flatly deny it/affirm it)?

Thanks,

p.
--

The BBC: Licensed at public expense to spread lies.

I don't think you can make a flat statement either way with the information
supplied. The only thing that's for sure is NBFM has a constant power
envelope whereas AM has a highly variable envelope. And why do you say AM
has excessive bandwidth?. NBFM only can only approaches the bandwidth
efficiency of AM when the FM modulation index gets very small.
When FM gets narrow enough (expressed by modulation index, not deviation),
it's interference rejection is no better than AM.

Joe
W3JDR

...
Hi, guys,

ISTR.......
(through the mists of time) that the excessive bandwidth of an AM
transmission signal can interfere with the reception of a NBFM signal,
though the converse is not true. Can anyone confirm this (or else
flatly deny it/affirm it)?

Thanks,

p.
--

The BBC: Licensed at public expense to spread lies.

In article , Paul Burridge
writes:

ISTR.......
(through the mists of time) that the excessive bandwidth of an AM
transmission signal can interfere with the reception of a NBFM signal,
though the converse is not true. Can anyone confirm this (or else
flatly deny it/affirm it)?

Paul, you need to be a bit more specific on the above.

First, if the AM carrier is not close to the FM center frequency, then
the only energy from the AM signal is from the sideband content of
the AM.

Second, if the AM sideband energy is below the FM carrier level,
the FM receiver limiter is going to do its suppression thing and
(in the receiver) lower the AM sideband level. The amount of AM
suppression depends on the relative no-modulation signal levels of
the two.

Alternate second: If the AM signal, any part, is stronger than the
FM signal's level, then the AM signal is going to "take over" and
that limiter will suppress the FM signal.

If the FM signal's swing happens to intrude on the passband of the
AM receiver - and its level is high enough - then some distorted
modulation from the FM signal will come through. The higher the
relative FM signal is to the AM level, the worse the interference from
distorted FM content. Conversely, if the AM signal is stronger than
the FM, then the distorted interference from the FM signal is less.

Very basic RFI stuff. You can confirm this yourself with a receiver
capable of demodulating AM and FM (make it narrowband if you
want, doesn't matter much here) and reasonably-calibrated AM
and FM signal sources. The interference of one against the other
will be due almost entirely to relative signal levels and the carrier
(no modulation) frequency differences versus the receiver selectivity
bandwidth.

About the only thing different between FM and NBFM in the receiver
is the final selectivity bandwidth. There will be some sort of limiting
in there even with simple detector types.

Len Anderson
retired (from regular hours) electronic engineer person

In article , Paul Burridge
writes:

ISTR.......
(through the mists of time) that the excessive bandwidth of an AM
transmission signal can interfere with the reception of a NBFM signal,
though the converse is not true. Can anyone confirm this (or else
flatly deny it/affirm it)?

Paul, you need to be a bit more specific on the above.

First, if the AM carrier is not close to the FM center frequency, then
the only energy from the AM signal is from the sideband content of
the AM.

Second, if the AM sideband energy is below the FM carrier level,
the FM receiver limiter is going to do its suppression thing and
(in the receiver) lower the AM sideband level. The amount of AM
suppression depends on the relative no-modulation signal levels of
the two.

Alternate second: If the AM signal, any part, is stronger than the
FM signal's level, then the AM signal is going to "take over" and
that limiter will suppress the FM signal.

If the FM signal's swing happens to intrude on the passband of the
AM receiver - and its level is high enough - then some distorted
modulation from the FM signal will come through. The higher the
relative FM signal is to the AM level, the worse the interference from
distorted FM content. Conversely, if the AM signal is stronger than
the FM, then the distorted interference from the FM signal is less.

Very basic RFI stuff. You can confirm this yourself with a receiver
capable of demodulating AM and FM (make it narrowband if you
want, doesn't matter much here) and reasonably-calibrated AM
and FM signal sources. The interference of one against the other
will be due almost entirely to relative signal levels and the carrier
(no modulation) frequency differences versus the receiver selectivity
bandwidth.

About the only thing different between FM and NBFM in the receiver
is the final selectivity bandwidth. There will be some sort of limiting
in there even with simple detector types.

Len Anderson
retired (from regular hours) electronic engineer person

On 17 Feb 2004 04:56:57 GMT, (Avery Fineman)
wrote:

In article , Paul Burridge
writes:

ISTR.......
(through the mists of time) that the excessive bandwidth of an AM
transmission signal can interfere with the reception of a NBFM signal,
though the converse is not true. Can anyone confirm this (or else
flatly deny it/affirm it)?

Paul, you need to be a bit more specific on the above.

Thanks, guys. I think you covered what I wanted to know...

Now I have another question on the same subject. Imagine if you will,
a NBFM recieiver, set to listen on one particular channel. Now
consider 3 seperate sweep transmitters located say 100yds away. Each
sweeps slowly across the band which encompasses the RX's receive
channel.
Sweep transmitter 1 puts out only an unmodulated carrier wave. STX 2
puts out an FM signal of the same power level; STX 3 puts out an AM
signal of the same power. Assume the extent of modulation is likewise
identical - or as identical as it can be given different classes. Now,
which of the three TXs is going to 'take over' the RX channel for the
longest time? IOW, which of the TX signals appears broadest to the FM
RX?

Thanks,

p.
--

The BBC: Licensed at public expense to spread lies.

On 17 Feb 2004 04:56:57 GMT, (Avery Fineman)
wrote:

In article , Paul Burridge
writes:

ISTR.......
(through the mists of time) that the excessive bandwidth of an AM
transmission signal can interfere with the reception of a NBFM signal,
though the converse is not true. Can anyone confirm this (or else
flatly deny it/affirm it)?

Paul, you need to be a bit more specific on the above.

Thanks, guys. I think you covered what I wanted to know...

Now I have another question on the same subject. Imagine if you will,
a NBFM recieiver, set to listen on one particular channel. Now
consider 3 seperate sweep transmitters located say 100yds away. Each
sweeps slowly across the band which encompasses the RX's receive
channel.
Sweep transmitter 1 puts out only an unmodulated carrier wave. STX 2
puts out an FM signal of the same power level; STX 3 puts out an AM
signal of the same power. Assume the extent of modulation is likewise
identical - or as identical as it can be given different classes. Now,
which of the three TXs is going to 'take over' the RX channel for the
longest time? IOW, which of the TX signals appears broadest to the FM
RX?

Thanks,

p.
--

The BBC: Licensed at public expense to spread lies.

There are a lot of variables here, but ...
"the same power. ...modulation is likewise identical" is rather un-defined
since you have an AM & an FM sweeper.

If the bandwidth for the two modulated "sweepers" is about the same (i.e. AM
& NBFM), I think they will produce near the same level of interference. The
AM might be a little less since the side bands are only 25% the carrier
power and the FM sidebands can be a higher percentage (I'm not too sure with
NBFM, since NBFM side bands aren't much different from AM sidebands), but
this depends upon the modulation amount at any given time. As the side
bands get into the channel they start to cause trouble.
The carrier only sweeper will be a little better since it has no sidebands
to get into the IF before the carrier does, so it'll have to get closer to
center channel before causing trouble.

How-zat?

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



"Paul Burridge" wrote in message
...
On 17 Feb 2004 04:56:57 GMT, (Avery Fineman)
wrote:

In article , Paul Burridge
writes:

ISTR.......
(through the mists of time) that the excessive bandwidth of an AM
transmission signal can interfere with the reception of a NBFM signal,
though the converse is not true. Can anyone confirm this (or else
flatly deny it/affirm it)?

Paul, you need to be a bit more specific on the above.

Thanks, guys. I think you covered what I wanted to know...

Now I have another question on the same subject. Imagine if you will,
a NBFM recieiver, set to listen on one particular channel. Now
consider 3 seperate sweep transmitters located say 100yds away. Each
sweeps slowly across the band which encompasses the RX's receive
channel.
Sweep transmitter 1 puts out only an unmodulated carrier wave. STX 2
puts out an FM signal of the same power level; STX 3 puts out an AM
signal of the same power. Assume the extent of modulation is likewise
identical - or as identical as it can be given different classes. Now,
which of the three TXs is going to 'take over' the RX channel for the
longest time? IOW, which of the TX signals appears broadest to the FM
RX?

Thanks,

p.
--

The BBC: Licensed at public expense to spread lies.

There are a lot of variables here, but ...
"the same power. ...modulation is likewise identical" is rather un-defined
since you have an AM & an FM sweeper.

If the bandwidth for the two modulated "sweepers" is about the same (i.e. AM
& NBFM), I think they will produce near the same level of interference. The
AM might be a little less since the side bands are only 25% the carrier
power and the FM sidebands can be a higher percentage (I'm not too sure with
NBFM, since NBFM side bands aren't much different from AM sidebands), but
this depends upon the modulation amount at any given time. As the side
bands get into the channel they start to cause trouble.
The carrier only sweeper will be a little better since it has no sidebands
to get into the IF before the carrier does, so it'll have to get closer to
center channel before causing trouble.

How-zat?

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



"Paul Burridge" wrote in message
...
On 17 Feb 2004 04:56:57 GMT, (Avery Fineman)
wrote:

In article , Paul Burridge
writes:

ISTR.......
(through the mists of time) that the excessive bandwidth of an AM
transmission signal can interfere with the reception of a NBFM signal,
though the converse is not true. Can anyone confirm this (or else
flatly deny it/affirm it)?

Paul, you need to be a bit more specific on the above.

Thanks, guys. I think you covered what I wanted to know...

Now I have another question on the same subject. Imagine if you will,
a NBFM recieiver, set to listen on one particular channel. Now
consider 3 seperate sweep transmitters located say 100yds away. Each
sweeps slowly across the band which encompasses the RX's receive
channel.
Sweep transmitter 1 puts out only an unmodulated carrier wave. STX 2
puts out an FM signal of the same power level; STX 3 puts out an AM
signal of the same power. Assume the extent of modulation is likewise
identical - or as identical as it can be given different classes. Now,
which of the three TXs is going to 'take over' the RX channel for the
longest time? IOW, which of the TX signals appears broadest to the FM
RX?

Thanks,

p.
--

The BBC: Licensed at public expense to spread lies.

Paul,
You still need to be more specific:
What is the modulating frequency and deviation of the FM signal? Is it the
modulation frequency a single tone or noise-like?. What is the IF bandwidth
of the FM receiver? What is the sweep rate of the interfering signal? We'll
assume the AM signal is modulated with the same frequency at 100%
modulation.

In general, the CW signal would be least intrusive for a given sweep rate
because it's energy is only in the IF of the receiver for a period of time
equal to RXbw/sweeprate. If this time is small compared to the inverse of
the post detection (audio) bandwidth, it might be inaudible. If the
modulation is noise-like and the FM modulation index is high, the
interference will be worse and longer in duration. If the FM modulation
frequency is high, the modulation index is low, and the sweep rate is low,
it could sound like 3 seperate signals sweeping through the passband (AM
would be similar to this last case).

Joe
W3JDR


"Paul Burridge" wrote in message
...
On 17 Feb 2004 04:56:57 GMT, (Avery Fineman)
wrote:

In article , Paul Burridge
writes:

ISTR.......
(through the mists of time) that the excessive bandwidth of an AM
transmission signal can interfere with the reception of a NBFM signal,
though the converse is not true. Can anyone confirm this (or else
flatly deny it/affirm it)?

Paul, you need to be a bit more specific on the above.

Thanks, guys. I think you covered what I wanted to know...

Now I have another question on the same subject. Imagine if you will,
a NBFM recieiver, set to listen on one particular channel. Now
consider 3 seperate sweep transmitters located say 100yds away. Each
sweeps slowly across the band which encompasses the RX's receive
channel.
Sweep transmitter 1 puts out only an unmodulated carrier wave. STX 2
puts out an FM signal of the same power level; STX 3 puts out an AM
signal of the same power. Assume the extent of modulation is likewise
identical - or as identical as it can be given different classes. Now,
which of the three TXs is going to 'take over' the RX channel for the
longest time? IOW, which of the TX signals appears broadest to the FM
RX?

Thanks,

p.
--

The BBC: Licensed at public expense to spread lies.