I think we're on two different wavelengths here. What
I am talking about is practical application, not
theoretical mumbo-jumbo.
OK, yes, I'm talking about the theoretical limitations. Your earlier post
said that even theoretical PM falls apart at low frequencies, and that's
where I
--- Jeff DePolo WN3A [EMAIL PROTECTED] wrote:
I guess this begs the question - at that point,
where you're doing
preemphasis and modulation via math versus analog
circuitry and synthesizing
the modulated carrier, do you call it PM or
preemphasized FM? I would argue
the latter since you
Hi Joe,
At some point in DSP, audio processing, synthesis, etc-all thrown into a bag and each manipulated withnumbers or programming, we sort of lose base with whatwe are doing. We could create AM, FM, PM, SSB, PSK,FSK, what have you.
And as amateurs and technical people, it'd be good if we
--- [EMAIL PROTECTED] wrote:
Hi Joe,
This is an interesting article:
http://www.repeater-builder.com/rbtip/fmtheorydiscussion.html
He suggests that de-emph came first to get around
the
rising noise of an FM receiver. In any case, I think
most people agree that it was done for noise
I guess I'm not following your logic. If you could get
a PM exciter to produce a .01 Hz tone at 5 KHz
deviation, the amount of audio required at 1 Hz would
be 40 dB below that. The amount of audio required to
modulate 5Khz deviation at 1KHz tone would be 60 dB
below the 1 Hz level, or 100
[EMAIL PROTECTED] wrote:
Actually, if we could get everyone to adjust
their repeater deviation to 4 kHz, a lot of adjacent channel problems would
be
reduced to acceptable levels. Just a thought..
Thank you, Paul, K3VIX (a 26-year Motorola veteran designer).
73,
Bob
Especially
--- Jeff DePolo [EMAIL PROTECTED] wrote:
Real modulator voltages have to start somewhere as
a
reference. If we take .1 volt P to P to deviate a
PM
exciter to 5KHz of deviation at a 1KHz audio tone,
then it will take 1 volt P to P to drive the same
modulator to 5KHz deviation at 100 Hz
--- [EMAIL PROTECTED] wrote:
Hi Joe,
I'd like to look at the above statement for just a
minute. Since we're all in agreement that PM has a
6db
per octave inherent pre-emp (that would be 20 dB
per
decade), let's look at the numbers in something
other
than a theoretical light- ie; real
Again, I think you're off base with your supposition.
You want us to believe that PM is why we Pre-emp FM.
That's simply not the case. This is not supported by
anything I have ever seen or read, only by you.
Not that I really care but look at this as to why PM was used for the FM
Well, if nothing else, that page shows that even back then, people used
FM and PM interchangeably. In the beginning of the article, it touts
their frequency modulated (FM) system, but later it states success of
the system was due to choosing phase modulation.
Bob (S-Com Bob), would it be a fair
Hi Joe,
You want us to believe that PM is why we Pre-emp FM.
Yup. It's a PM world, and you must make your FM equipment work in that world.
That's simply not the case. This is not supported byanything I have ever seen or read, only by you.
These areconclusions we drewfrom old documents from
Hi Joe,
Bob (S-Com Bob), would it be a fair statement to say that traditionally,transmitters have generally been PM (either true PM or emphasized FM),but receivers have been FM all along? I base this on your last post.
Yes, absolutely!
To further state the case, assume that there are two
[EMAIL PROTECTED] wrote:
To further state the case, assume that there are two
parallel universes.
Que Star Trek theme music... ;-
In one universe, all hams use phase modulators and phase demodulators.
The terms 'preemphasis' and 'deemphasis' are unheard of. The whole
system has flat
--- [EMAIL PROTECTED] wrote:
Hi Joe,
You want us to believe that PM is why we Pre-emp FM.
Yup. It's a PM world, and you must make your FM
equipment work in that world.
That's simply not the case. This is not supported by
anything I have ever seen or read, only by you.
These are
It was just over a year ago that there was a long thread about FM and
PM. Someone posted a link to a short magazine article (Ham Radio, it
seems it was, but not sure) that shed light on the fact that PM was
the first popular method of modulation for land mobile use. I've
searched the
Hi Joe,
In one universe, all hams use phase modulators and phase demodulators. The terms 'preemphasis' and 'deemphasis' are unheard of. The whole system has flat response. Since their phase demodulators track their phase modulators, the hams communicate via voice and data over their PM
Hi Laryn,
It was just over a year ago that there was a long thread about FM and PM. Someone posted a link to a short magazine article (Ham Radio, it seems it was, but not sure) that shed light on the fact that PM was the first popular method of modulation for land mobile use. I've searched
Hi Joe,
This is an interesting article:http://www.repeater-builder.com/rbtip/fmtheorydiscussion.htmlHe suggests that de-emph came first to get around therising noise of an FM receiver. In any case, I thinkmost people agree that it was done for noise controlpurposes, which it does do well. If
--- [EMAIL PROTECTED] wrote:
Hi Joe,
Fact: PM does not reproduce DC well. Actually, it
doesn't reproduce DC
at all (beyond a spike) because in DC there is no
change in the phase of
the signal. The closer you get to DC, the worse PM
will perform. FM, on
the other hand, has no such
Real modulator voltages have to start somewhere as a
reference. If we take .1 volt P to P to deviate a PM
exciter to 5KHz of deviation at a 1KHz audio tone,
then it will take 1 volt P to P to drive the same
modulator to 5KHz deviation at 100 Hz of audio. I
think everyone will agree with this
Hi Joe,
I'd like to look at the above statement for just aminute. Since we're all in agreement that PM has a 6dbper octave inherent "pre-emp" (that would be 20 dB perdecade), let's look at the numbers in something otherthan a "theoretical" light- ie; real numbers.Real modulator voltages have
[EMAIL PROTECTED] wrote:
Hi Joe,
Hi Bob.
Fact: PM does not reproduce DC well. Actually, it doesn't
reproduce DC
at all (beyond a spike) because in DC there is no change in
the phase of
the signal. The closer you get to DC, the worse PM will
perform. FM, on
Hi Joe,
As a blanket statement, the above is not true. I can generate a beautiful 10 Hz or 1 Hz or 0.01 Hz phase modulated output at any deviation you want using one of the newer function generators.OK. I'll accept that. However, let me add that if you consider theaverage stock exciter, is
[EMAIL PROTECTED] wrote:
The board being discussed on this list with the high-order filter and
the limiter, assuming it's designed right, would be an excellent
addition to the repeater builder's arsenal. Replace the 'blob' and get
around the soft limiting and the other problems. We talked
Hi Joe,
By 'different repeaters', you mean with different cutoffs, right? Or doyou mean specifically designed for the circuitry it will be driving?
I'm thinking that different discriminators put out different levels, and their impedance is pretty high so you don't want to load them, things
Or a 80D or 140D ...
Neil
wd8chl wrote:
Hi Skipp,
And we've seen some sloppy engineering in the
design of the audio and limiter circuits.
What you're saying here Bob... is that you've
owned at least one Icom IC-230 at some time in
the past.
:-)
Wow-there's one
Coy Hilton wrote:
First I would like to read each of your personal definitions of FM and PM, then your dissertations on exactly why one is better than the other, Complete.
I apologize, this is long.
Definitions:
FM: Modulation of a carrier that its instantaneous frequency differs
First I would like to read each of your personal definitions of FM
and PM, then your dissertations on exactly why one is better than
the other, Complete.
If I remember, The FCC requires 6 DB/octive preemphasis/ deemphasis
from 300 to 3000 hz. on PM or FM and that is pretty much the human
I don't believe any definitions of PM and FM matter. PM is a Phase
Modulator, and FM is a Frequency Modulator. What is important is what
each does to the signal, or requires to maintain the 'status quo', or
integrity, of the signal.
If you're going to limit your range to 300-3000 Hz, there is
--- In Repeater-Builder@yahoogroups.com, mch [EMAIL PROTECTED] wrote:
Yes, I think the vast majority on this list know quite a bit more of the
differences, but that's another issue, as John Q. Ham is not subscribed
to this list. (John Q. Ham doesn't BUILD repeaters)
Joe M.
I dunno-I've
True, but were they members of this list? ;- (my original selection)
There are now over 2000 members. I suspect the number of repeater
trustees is still far greater - especially globally.
Joe M.
wd8chl wrote:
--- In Repeater-Builder@yahoogroups.com, mch [EMAIL PROTECTED] wrote:
Yes, I
Hi Coy,
First I would like to read each of your personal definitions of FM and PM, then your dissertations on exactly why one is better than the other, Complete.
FM and PM are bothreferred to as "angle modulation" because the the radio wave's "angular velocity" (frequency or phase)is being
Hi Skipp,
And we've seen some sloppy engineering in the
design of the audio and limiter circuits.
What you're saying here Bob... is that you've
owned at least one Icom IC-230 at some time in
the past.
:-)
Wow-there's one I haven't heard in a long time-I had one of those
[paste]
[EMAIL PROTECTED]
I will readily admit that available PM exciters
can have all sorts of shortcomings. They distort
when you ask for a lot of deviation at very low
frequencies like CTCSS. There are inherent
nonlinearities in the varactor tank circuit
that create a little
Hi Skipp,
And we've seen some sloppy engineering in the design of the audio and limiter circuits.What you're saying here Bob... is that you've owned at least one Icom IC-230 at some time in the past. :-)
While the mobiles probably suffer from the same kind of engineering shortcuts, I was
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