Actually, the typical FM rcvr can handle up to +/-7kHz deviation unless it
has had new filters added for narrowbanding, etc.....this is due to the
filters not having a sharp cut off at the 5 khz point....My GE MSTR II rcvrs
can accept up to 7 kHz dev signals on strong signals..on weak signals, the
wider deviation starts to confuse the squelch ckt and thus the rcvr starts
to squelch..but the rcvr is designed for 5 kHz deviation...and this is
normal of FM filters...

FM broadcast stations are +/- 75 kHz...not 150 kHz! The max b/w of a FM
broadcast signal is 200 kHz.....(which is normal channel spacing also)
including the subcarriers..
and Modulation Index is Dev/highest freq of modulation....but MI IS not the
limiting factor in a rcvr...It is overall deviation and bandwidth (B/W is
equal to 2x (dev PLUS Mod freq). You can have a 3 kHz dev with 1 kHz tone
and the MI is 3....increase to 5 khz dev with a 1 kHz tone and the MI DROPS
to 1.6...thus MI is NOT the issue....the overall BW in the above examples
would be 8kHz and 12 kHz respectively.

Yes, FM vs PM if done right is not noticeable on the air...unless the PM has
not been corrected or the FM does not have preemphasis...
PM is easier to implement on xtal radios and is much more stable in older
designs....FM is better in PLL radios..also FM allows Digital modes (DCS,
etc) where as PM cannot handle it (DC offsets dont work with PM).

Chris
WB5ITT

"Jim - NN7K" wrote in message
om...
Other things enter into the equasion: includeing how WIDE the signal
is-- Most repeaters have recieve filters that accept modulation to:
+- 4.9 KHZ (and that ONLY if you are relatively close to the input
frequency) over +- 800 HZ can accentuate clipping of your signal-
if you exceed +- 5 KHz, you will lose some audio, due to "clipping", and
it gets worse , if you are off frequency ! "tis a case of TOO MUCH
audio being WORSE than too little! Essentially, Phase modulation
is the same as Frequency modulation, and there should be little diff.
between the 2, as far as the recievers are concerned. The "Modulation
Index" is the limiting factor- Keep in mind that a Commercial FM station
(150 KHz +- deviation) , has also , many subcarriers in the signal, that
you don't hear (like background music for stores, sterio piolets, stock
market data, ect) ALL in their carrier- you can detect those with
filters at the appropriate freq, and BANDWIDTH. and, there are outfits
that sell adapters for fm recievers to decode them (but you wont hear
the normal broadcast, thru them!) Television stations do similar things
with their audio, and video! These are called SUB CARRIERS. In sum
total, IF your modulation index exceeds the bandwidth of your reciever
,the audio will be limited (or eleminated)! But that doesn't mean that
your audio isn't there, only that the reciever refuses to accept your
overmodulation-- dont try to speak LOUDER, try whispering, and see if
you get a response! Jim NN7K




Falky foo wrote:
Didn't do detailed analysis.. just realized that the VX-6 was hitting
repeaters better than the VX-150, even when using the same antenna.
Wondered if that difference was because of the different modulation
types.

Now- what did I say ?? Syntax? what does +/- 75 Khz add up to?? 200
Khz?? NO , it adds up to a 150 KHz channel bandwidth ( +/- 75 KHz),
with 200 KHZ Channels!! But, I digress: on WEAK signals, clipping
of signals, at least in the Motorolas that I am used to, will start
(clipping, chopping, DISTORTING, the signal, once you exceed +/- 5
KHz)! The point I try to make is, unlike human experience, TOO MUCH
can be far worse than too little, when comes to LOUDENESS into a
microphone (at least on FM)! Its kind of like the worlds cheapest
hearing aid-- a button that states "YELL, I'M DEAF" ! It may work in the
real world, but, when applied to radio, t'aint necessarily so! And, in
trying to keep from technological overkill, try to keep it in SIMPLE
terms, as MOST folks here don't have Engineering Degrees! The point
is, that the modulation type (Phase, or Frequency) isn't necessarilly
what is causing the difference, at a given power level on radios, but
the deviation component (at a given power level) can have drastic
implications on a (Repeated, or Directly) recieved signal, Vs. a
carrier,or very narrowly modulated signal ! Jim NN7K (Retired U.P.,
and S.P. Radioman, and Communications Dept Electronic Technician)



CWB wrote:
Actually, the typical FM rcvr can handle up to +/-7kHz deviation unless it
has had new filters added for narrowbanding, etc.....this is due to the
filters not having a sharp cut off at the 5 khz point....My GE MSTR II rcvrs
can accept up to 7 kHz dev signals on strong signals..on weak signals, the
wider deviation starts to confuse the squelch ckt and thus the rcvr starts
to squelch..but the rcvr is designed for 5 kHz deviation...and this is
normal of FM filters...

FM broadcast stations are +/- 75 kHz...not 150 kHz! The max b/w of a FM
broadcast signal is 200 kHz.....(which is normal channel spacing also)
including the subcarriers..
and Modulation Index is Dev/highest freq of modulation....but MI IS not the
limiting factor in a rcvr...It is overall deviation and bandwidth (B/W is
equal to 2x (dev PLUS Mod freq). You can have a 3 kHz dev with 1 kHz tone
and the MI is 3....increase to 5 khz dev with a 1 kHz tone and the MI DROPS
to 1.6...thus MI is NOT the issue....the overall BW in the above examples
would be 8kHz and 12 kHz respectively.

Yes, FM vs PM if done right is not noticeable on the air...unless the PM has
not been corrected or the FM does not have preemphasis...
PM is easier to implement on xtal radios and is much more stable in older
designs....FM is better in PLL radios..also FM allows Digital modes (DCS,
etc) where as PM cannot handle it (DC offsets dont work with PM).

Chris
WB5ITT

"Jim - NN7K" wrote in message
om...

Other things enter into the equasion: includeing how WIDE the signal
is-- Most repeaters have recieve filters that accept modulation to:
+- 4.9 KHZ (and that ONLY if you are relatively close to the input
frequency) over +- 800 HZ can accentuate clipping of your signal-
if you exceed +- 5 KHz, you will lose some audio, due to "clipping", and
it gets worse , if you are off frequency ! "tis a case of TOO MUCH
audio being WORSE than too little! Essentially, Phase modulation
is the same as Frequency modulation, and there should be little diff.
between the 2, as far as the recievers are concerned. The "Modulation
Index" is the limiting factor- Keep in mind that a Commercial FM station
(150 KHz +- deviation) , has also , many subcarriers in the signal, that
you don't hear (like background music for stores, sterio piolets, stock
market data, ect) ALL in their carrier- you can detect those with
filters at the appropriate freq, and BANDWIDTH. and, there are outfits
that sell adapters for fm recievers to decode them (but you wont hear
the normal broadcast, thru them!) Television stations do similar things
with their audio, and video! These are called SUB CARRIERS. In sum
total, IF your modulation index exceeds the bandwidth of your reciever
,the audio will be limited (or eleminated)! But that doesn't mean that
your audio isn't there, only that the reciever refuses to accept your
overmodulation-- dont try to speak LOUDER, try whispering, and see if
you get a response! Jim NN7K




Falky foo wrote:

Didn't do detailed analysis.. just realized that the VX-6 was hitting
repeaters better than the VX-150, even when using the same antenna.
Wondered if that difference was because of the different modulation
types.