Green Xenon wrote:
"So I ask what would be the disadvantage of using AM instead of FM for
this?"

Short answer is: losing insensitivity to carrier level when recovering
the modulation.

Advantage of AM is reduced bandwidth and simpler demodulation.

Advantage of FM is that once a certain minimum carrier level is applied
to the detector.
the demodulated signal is independent of the carrier level. A balanced
detector allows non-linear RF amplification, insensitivity to amplitude
variations, and no response to noise which is amplitude (AM) in nature.

Disadvantage of FM is that it requires about twice the bandwidth of FM.

Best regards, Richard Harrison, KB5WZI

I miswrote. FM requires about twice the bandwidth of AM.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
I miswrote. FM requires about twice the bandwidth of AM.

Quoting my 1957 ARRL Handbook: "Narrow-band f.m. or p.m.,
the only type that is authorized for use on the lower
frequencies where the phone bands are crowded, is defined
as f.m. or p.m. that does not occupy a wider channel than
an a.m. signal having the same audio modulating frequencies.
Narrow-band operation requires using a relatively small
modulation index." It goes on to say a modulation index
of 0.6 is about optimum for those conditions.

Is NBFM still allowed?
--
73, Cecil http://www.w5dxp.com

In article ,
Cecil Moore wrote:

Quoting my 1957 ARRL Handbook: "Narrow-band f.m. or p.m.,
the only type that is authorized for use on the lower
frequencies where the phone bands are crowded, is defined
as f.m. or p.m. that does not occupy a wider channel than
an a.m. signal having the same audio modulating frequencies.
Narrow-band operation requires using a relatively small
modulation index." It goes on to say a modulation index
of 0.6 is about optimum for those conditions.

Is NBFM still allowed?

I read through the current Part 97 regs a few months ago, and
concluded that it is. See 97.305 (Authorized Emission Types), and
97.307 (f) (1).

The current standard allows a modulation index of up to 1, at the
highest modulating frequency. This applies to all angle-modulation
modes (PM and FM).

The rules aren't specifically worded as "f.m. or p.m. that does not
occupy a wider channel than an a.m. signal having the same audio
modulating frequencies" these days - the restrictions are in terms of
the modulation index, and the general requirement that one not use
"more bandwidth than necessary for the information rate and emission
type being transmitted, in accordance with good amateur practice."

I don't recall having run across any narrowband FM on the HF bands...
I think there are still a few 10-meter repeaters operating around the
country somewhere, but FM HF simplex seems to be either completely
dead, or used just by occasional experimenters.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

I don't recall having run across any narrowband FM on the HF bands...
I think there are still a few 10-meter repeaters operating around the
country somewhere, but FM HF simplex seems to be either completely
dead, or used just by occasional experimenters.
====================================
When the 10m band opens , here in Europe FM is quite common between
29.5 and 29.7 MHz . It is sometimes even possible to open the Boston
Mass. repeater on 29.600 MHz.

Frank GM0CSZ / KN6WH

Cecil wrote:
"Is NBFM still allowed?"

Interesting question but I was responding to the question in the thread
tille.

FM usually occupies about twice the bandwidth of AM. Spread spectrum
ordinarily occupies more bandwidth.

Spread spectrum was patented by Nikola Tesla in 1903. FCC now codifies
rules for spread spectrum in Wi-Fi, Bluetooth, cordless phones, etc.

Terman says about twice the bandwidth is required for FM as compared
with AM on pages 589 and page 590 of his 1955 opus.

The signal for spread spectrum is a form of FM but usually the signal is
transmitted on a bandwidth considerably larger than the frequency
content of the original information says Wikipedia.

Best regards, Richard Harrison, KB5WZI

Frank, GM0CZ / KN6WH wrote:
"It is sometimes even possible to open the Boston, Mass. repeater on
29.600 MHz."

FM is almost essential to repeater operation due to the inherent
automatic gain control of the FM mode. Once the weak signal point called
the "FM improvement threshold" is exceeded, further carrier strength
increases have no effect on the recovered modulation. The pip squeak is
as loud as the power house. Remodulate that on the repeater output.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
Cecil wrote:
"Is NBFM still allowed?"

Interesting question but I was responding to the question in the thread
tille.

FM usually occupies about twice the bandwidth of AM. Spread spectrum
ordinarily occupies more bandwidth.

Spread spectrum was patented by Nikola Tesla in 1903. FCC now codifies
rules for spread spectrum in Wi-Fi, Bluetooth, cordless phones, etc.

Terman says about twice the bandwidth is required for FM as compared
with AM on pages 589 and page 590 of his 1955 opus.

The signal for spread spectrum is a form of FM but usually the signal is
transmitted on a bandwidth considerably larger than the frequency
content of the original information says Wikipedia.

Best regards, Richard Harrison, KB5WZI

The invention of spread spectrum is generally credited to George
Antheil and Hedy Lamarr (yes, the actress) and their patent of 1942.


--
Jim Pennino

Remove .spam.sux to reply.

Jim Pennino wrote:
"The invention of spread spectrum is generally credited to George
Antheil and Hedy Lamarr (yes the actress) and their patent of 1942."

Yes, I believe Lamarr and her husband encoded several tones in sequence
using a player-piano roll. The system was used in WW-2. Poor old Tesla
only invented the a.c. power system, wireless power transmission, and
demonstrated his remote control of a boat using spread spectrum to avoid
interference more than 40 years before Hedy Lamarr`s patent. T.A. Edison
did his best to deny Tesla credit for anything. That`s commerce.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
FM usually occupies about twice the bandwidth of AM.

Thanks for adding "usually" to your original statement.
I was just pointing out that if the FM peak deviation
is equal to the maximum modulation frequency, then the
FM signal occupies the same bandwidth as AM. The S/N
ratio advantage usually enjoyed by FM over AM occurs
when the FM peak deviation is *greater than* the maximum
modulation frequency. FM seems to have been the original
"spread spectrum" mode. :-)
--
73, Cecil http://www.w5dxp.com