From rec.radio.amateur.homebrew 774
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From: rkarlqu@scd.hp.com (Richard Karlquist)
Newsgroups: rec.radio.amateur.homebrew
Subject: Re: single sideband
Message-ID: <2c4lhr$6pi@hpscit.sc.hp.com>
Date: 14 Nov 93 07:08:43 GMT
References: <1993Nov13.164257.15906@cs.rit.edu>
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In article <1993Nov13.164257.15906@cs.rit.edu>,
Albert T Davis <atd@cs.rit.edu> wrote:
>
>I have been out of this for a while....
>
>Is the filter method still the most common for SSB generation?
>Why?
>
>It seems to me that the phasing method is far superior
with today's technology.
>
>al.
The phasing method of SSB is principally a ham radio technique.
Other services that have to meet FCC requirements reliably never, to
my knowledge, attempted to use phasing SSB. Basically, the problem
you run into is that it is difficult to get enough carrier suppression
without hitting the mixer so hard that you get too much audio distortion
and splatter. The ham rigs had adjustments to get the mixer perfectly
balanced (at least at one temperature) to get around this, but that
would be undesirable commercially. On the other hand, with active
audio phase shift networks and divide by 4 RF drive, you can actually
get pretty decent unwanted sideband suppression, except for amplitude
balance, which is still a crapshoot. Also, ham rigs could get by with
more distortion and splatter that the FCC normally allows. For example,
may popular ham linears won't meet FCC commercial regs that say 11th
order intermod has to be down 60 dB. or thereabouts. (It's been 15
years since I designed HP marine radios so don't hold me to the
exact number). Commercial rigs use asymmetrical
SSB filters that have very steep slopes on one side to filter out the
residual carrier. The demise of the separate transmitter and receiver
pretty much eliminated any remaining reason for using the phasing system
since you are going to have a crystal filter for receive anyway, so
you might as well use it. Regarding the legendary audio quality of
phasing rigs (I don't know how much truth there was to that), you can
get excellent audio quality with a filter rig by using a really good
filter. The 5 MHz. ones used for the old FDM analog telephone trunks
are excellent. You can still buy them from a company called Lumda.
Of course, with everyone running a speech compressor these days, I
don't think high fidelity is a priority except with the Ancient
Modulation gang.
Rick Karlquist N6R
rkarlqu@scd.hp.com
From rec.radio.amateur.homebrew 783
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From: wmeahan@ef0424.efhd.ford.com (Bill Meahan)
Newsgroups: rec.radio.amateur.homebrew
Subject: Re: single sideband
Message-ID: <wmeahan.13.2CE94C50@ef0424.efhd.ford.com>
Date: 16 Nov 93 21:55:28 GMT
References: <1993Nov13.164257.15906@cs.rit.edu> <2c4lhr$6pi@hpscit.sc.hp.com> <1993Nov15.164550.18931@cs.rit.edu>
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In article <1993Nov15.164550.18931@cs.rit.edu> atd@cs.rit.edu (Albert T Davis) writes:
>From: atd@cs.rit.edu (Albert T Davis)
>Subject: Re: single sideband
>Date: Mon, 15 Nov 1993 16:45:50 GMT
>Richard Karlquist writes:
>>The phasing method of SSB is principally a ham radio technique.
>This is why they abandoned the phasing method back in the days of tubes.
>It was all true then. It was difficult to get even 20 db or so of
>carrier and alt sideband suppression.
True for systems that attempted to generate the SSB signal at the operating
frequency, but not necessarily true otherwise. The Gonset GSB-100 that was my
first voice transmitter generated the SSB signal via phasing at 9.00 MHz (easy
enough to get good suppression at a single, FIXED frequency) and used a single
crystal notch filter to further reduce any remaining carrier. Operation on
the various bands then required mixing with an appropriate frequency just like
the filter rigs.
As I recall, I always got comments on how good my voice quality was while
still getting adequate suppression.
73 de WA8TZG
--
Bill Meahan |EFHD Information Systems Staff
Computer Applications Engineer |Ford Motor Company
wmeahan@ef0424.efhd.ford.com |I don't speak for Ford, just me
"Managing a software project is like herding cats"
From rec.radio.amateur.homebrew 787
Path: ucbvax!agate!howland.reston.ans.net!usenet.ins.cwru.edu!lerc.nasa.gov!purdue!yuma!galen
From: galen@picea.CFNR.ColoState.EDU (Galen Watts)
Newsgroups: rec.radio.amateur.homebrew
Subject: Re: single sideband, phasing and T2/R2
Message-ID: <Nov15.155239.54713@yuma.ACNS.ColoState.EDU>
Date: 15 Nov 93 15:52:39 GMT
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In article <1993Nov14.020154.9354@ke4zv.atl.ga.us> gary@ke4zv.UUCP (Gary Coffman) writes:
>In article <1993Nov13.164257.15906@cs.rit.edu> atd@cs.rit.edu (Albert T Davis) writes:
>>I have been out of this for a while....
>>Is the filter method still the most common for SSB generation?
>>It seems to me that the phasing method is far superior with today's technology
>>al.
>It remains difficult to achieve a precise 90 degree phase shift over
>3 octaves of audio frequencies. DSP offers the potential to solve that
>problem though.
>Gary Coffman KE4ZV | Life's a journey, | gatech!wa4mei!ke4zv!gary
>Destructive Testing Systems | not a destination. | uunet!rsiatl!ke4zv!gary
>534 Shannon Way | Live it. | emory!kd4nc!ke4zv!gary
>Lawrenceville, GA 30244 | |
In the April, 93 issue of QST is the 'Multimode Phasing Exciter' alias the
T2 board. Uses 1% componenets in the phase shift network. I have the board
(along with the companion R2) but I haven't built it, as I can't decide if
I should put it on 440 SSB or 1750m CW/SSB. You must also have a 90 deg.
phase shift for the RF, which I can get for 440 from Mini-Circuits.
Anybody built these boards and willing to talk?
Galen, KF0YJ
From rec.radio.amateur.homebrew 791
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From: rkarlqu@scd.hp.com (Richard Karlquist)
Newsgroups: rec.radio.amateur.homebrew
Subject: Re: single sideband
Message-ID: <2c8ohb$abo@hpscit.sc.hp.com>
Date: 15 Nov 93 20:24:11 GMT
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In article <1993Nov15.164550.18931@cs.rit.edu>,
Albert T Davis <atd@cs.rit.edu> wrote:
>
>This is why they abandoned the phasing method back in the days of tubes.
>It was all true then. It was difficult to get even 20 db or so of
>carrier and alt sideband suppression. Even discrete transistor circuits
>are probably not good enough here. How much carrier suppression is
>required? It seems to me that today's IC's should be able to do it.
Regarding IC's as balanced modulators: "today's" IC's (i.e. MPY600)
are not necessarily any better than 1970's IC's (i.e. MC1496) in terms
of balance. They just run at higher frequencies. Probably the best
that can be hoped for is internally trimmed IC's. This is better than
a 1496 w/o external trimming, but not as good as an externally tweaked
1496. The other problem with Gilbert cell IC's is that to get good
IMD, you have to operate them at very low levels. This exascerbates
the carrier suppression problem because the signal is small compared
to the carrier. Since Gilbert cells have high noise levels, dynamic
range is a big problem.
>If not, generate it at a low IF and use a simple notch.
Because even for a 20 kHz. IF, "a simple notch" is quite difficult to
implement. That's a whole separate discussion.
>
>> ........ On the other hand, with active
>>audio phase shift networks and divide by 4 RF drive, you can actually
>>get pretty decent unwanted sideband suppression, except for amplitude
>>balance, which is still a crapshoot. ....
>
>Why is amplitude balance a crapshoot? With op-amp circuits it should be
>easy, for the audio. You might have a valid argument on the RF side.
>Can you explain?
Like you said, you can make the audio network about as good as you
want fairly easily by using .1% resistors and 1% capacitors along
with 50 MHz. opamps in a state variable configuration. That would
probably be good for 60 dB. opposite sideband rejection (if it were
the only factor). You can get the LO phase difference as close
as you want to 90 degrees by using a sufficiently fast flip flop.
You can get the RF in-phase splitter just about perfect by using 1%
51 ohm resistors. The crapshoot part is that you don't have perfectly
matched mixers, either in amplitude or phase. I suppose you could
put in sockets and try a bunch of them. Remember that as a rule of
thumb, all errors must be less than 1% to get 40 dB. rejection.
>
>> ...... Also, ham rigs could get by with
>>more distortion and splatter that the FCC normally allows. For example,
>>may popular ham linears won't meet FCC commercial regs that say 11th
>>order intermod has to be down 60 dB. or thereabouts. (It's been 15
>>years since I designed HP marine radios so don't hold me to the
>>exact number).
>
>Isn't the problem mostly in the linear amp? If this is the case I don't
>see how the method of generating SSB should change that. 15 years ago,
>the technology was not good enough. I agree.
Well, now that you mention it, the 11th order stuff was mainly
crossover distortion in the power amp. However, the MC1496 mixers
gave us a lot of trouble with 3rd order IMD, which is also spec'ed, but
not at 60 dB. Most ham linears don't meet commercial 3rd order IMD.
>
>Actually, I was thinking of using the phasing method for receive too,
>thereby eliminating the need for the expensive crystal filter. Convert
>early. Use a simple LC filter, similar to that used in the first IF
>of a dual conversion receiver, then do most of the amplification and
>filtering at audio. It is probably necessary to amplify the I and Q
>channels separately because the phase shift is likely to be noisy.
>It is easier to design a good audio amplifier than a good RF amplifier.
Of course the problem with this method is you will be limited to
40 dB. or so selectivity for the opposite sideband (which is really
the adjacent "channel" so to speak.) That is pretty lousy receiver
performance.
>
>I have designed and build audio filters with slopes that put any RF
>filters I have ever seen to shame. Doing the filtering at audio
>makes it easy to have truly variable bandwidth, notch filters (pre
>and post mixing) and other signal processing. It seems to me that
>this benefit would be too great to pass up.
OK, now I see where you're coming from!
What you really want to do is: instead of the phasing method of SSB,
use the Weaver method of SSB (also called the "third" method, or the
zero IF method). In this method, you build a direct conversion
receiver with the IF centered at zero Hz. (DC). A conventional
direct conversion receiver has the "carrier" frequency at DC but the
IF is centered at 1.5 kHz. (for a 3 kHz. BW). As with the phasing
method, you use dual mixers in quadrature. You then need an additional
pair of mixers driven at 1.5 kHz. to combine the audio from the I and
Q IF's. Now what happens is that the audio selectivity equals the
RF selectivity so there is no limit to the skirt selectivity you
can get. Imperfections in the mixer balance, phase and amplitude
errors do not cause reception of out of band signals. Instead,
they result in aliasing of high frequencies to low frequencies
and vice versa. But that just causes a little audio distortion
(40 dB. = 1 %). LO leak thru results in a 1.5 kHz. tone in the
audio. That *is* fairly easy to notch out. Go ahead, build this
system and write it up for Communications Quarterly. I'll be
interested to see how well you can do.
Rick Karlquist N6RK
rkarlqu@scd.hp.com
From rec.radio.amateur.homebrew 792
Path: ucbvax!agate!howland.reston.ans.net!vixen.cso.uiuc.edu!sdd.hp.com!col.hp.com!srgenprp!alanb
From: alanb@sr.hp.com (Alan Bloom)
Newsgroups: rec.radio.amateur.homebrew
Subject: Re: single sideband
Message-ID: <CGnovG.LC5@srgenprp.sr.hp.com>
Date: 17 Nov 93 21:54:51 GMT
References: <1993Nov13.164257.15906@cs.rit.edu>
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Albert T Davis (atd@cs.rit.edu) wrote:
: I have been out of this for a while....
: Is the filter method still the most common for SSB generation?
: Why?
: It seems to me that the phasing method is far superior with today's technology.
The phasing method works fine for transmitting, but does not have good enough
unwanted-sideband rejection for receiving. Since mosts radios these days
are transceivers, and you need the crystal filter anyway for receiving,
you might as well use it for transmiting as well.
AL N1AL
From rec.radio.amateur.homebrew 809
Path: ucbvax!hplabs!sdd.hp.com!col.hp.com!bobw
From: bobw@col.hp.com (Bob Witte)
Newsgroups: rec.radio.amateur.homebrew
Subject: Re: AM+FM=SSB?
Message-ID: <2d84v3$2eu@hp-col.col.hp.com>
Date: 27 Nov 93 18:06:27 GMT
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Mike Butts (mbutts@netcom.com) wrote:
: In the ARRL's "Solid State Design for the Radio
: Amateur", by Hayward and DeMaw, on p. 184 of
: the 1986 edition, after a nice summary of
: filter and phasing principles, plus a mention
: of Weaver, they say:
: "Also, it may be shown mathematically that
: a carrier which is amplitude modulated
: properly and frequency modulated
: simultaneously will yield a single-
: sideband output."
: I haven't succeeded in figuring this out.
: Can someone show this mathematically or otherwise?
: Has it ever been done in a real system?
Short hand-waving explanation follows...
Amplitude modulation has sidebands symmetrical about the carrier
(i.e. upper sideband is mirror image of lower sideband)
NARROWBAND FM has the same sidebands as AM but with one sideband
out of phase with the other.
Combining (subtracting?) an AM and narrowband FM with the same
modulating signal can cancel out one of the sidebands. I think
subtracting may be in order here to get rid of the carrier and
leave only the desired single-sideband.
The matching requirements throughout the system are significant.
That is, any mismatch between the modulating schemes will result
in a partial appearance of the unwanted sideband.
Bob Witte / HP PMO (Colo Springs) / bobw@col.hp.com / KB0CY / (719) 590-3230
From rec.radio.amateur.homebrew 818
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From: alanb@sr.hp.com (Alan Bloom)
Newsgroups: rec.radio.amateur.homebrew
Subject: Re: AM+FM=SSB?
Message-ID: <CHAAup.Asv@srgenprp.sr.hp.com>
Date: 30 Nov 93 02:56:48 GMT
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Mike Butts (mbutts@netcom.com) wrote:
: In the ARRL's "Solid State Design for the Radio
: Amateur", by Hayward and DeMaw, on p. 184 of
: the 1986 edition, after a nice summary of
: filter and phasing principles, plus a mention
: of Weaver, they say:
: "Also, it may be shown mathematically that
: a carrier which is amplitude modulated
: properly and frequency modulated
: simultaneously will yield a single-
: sideband output."
: I haven't succeeded in figuring this out.
: Can someone show this mathematically or otherwise?
Assume the SSB signal is made up of a bunch of sine waves of different
frequencies within the bandwidth of the SSB signal. You can combine
any two of the sine waves to get a signal in the form of a modulated
sine wave, with a different phase and frequency. For example, trig
identities give:
sin(wt) + sin((w+delta)t) = 2 * cos((delta/2)t) * sin((w+delta/2)t)
^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^
modulation RF sine wave
If the two sine waves have different frequencies or phases, the
expression looks a litle different, but you still get a modulated
sine wave.
If you combine two modulated sine waves, you get a third modulated sine
wave, again at a different frequency and with more complex modulation.
And so on with all the rest of the frequency components of the SSB signal.
The result is that any SSB signal can be represented as a single sine wave
with a varying frequency and amplitude.
In other words, the SSB signal can be broken up into two components:
an amplitude modulation and a frequency/phase moculation. It is possible
to separate the two and modulate them separately. The technique is to
hard-limit the SSB signal, which leaves you with the FM component only.
You than amplify this signal, using non-linear class-C amplifiers for
efficiency, up to the output amplifier stage. The AM component is
recovered from the original SSB signal with a diode envelope detector.
It is amplified and used to AM-modulate the final amplifier. The result
is the original SSB signal.
Note that both the FM modulation and the AM modulation have DC components,
so the modulators must be DC-coupled throughout.
: Has it ever been done in a real system?
I understand it has been done. The complexity is not really worth the
increase in efficiency, expecially when you add the expense of a high-level
DC-coupled AM modulator.
AL N1AL
From rec.radio.amateur.homebrew 825
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From: mbutts@netcom.com (Mike Butts)
Newsgroups: rec.radio.amateur.homebrew
Subject: AM+FM=SSB?
Message-ID: <mbuttsCH5s3w.6w@netcom.com>
Date: 27 Nov 93 16:21:32 GMT
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In the ARRL's "Solid State Design for the Radio
Amateur", by Hayward and DeMaw, on p. 184 of
the 1986 edition, after a nice summary of
filter and phasing principles, plus a mention
of Weaver, they say:
"Also, it may be shown mathematically that
a carrier which is amplitude modulated
properly and frequency modulated
simultaneously will yield a single-
sideband output."
I haven't succeeded in figuring this out.
Can someone show this mathematically or otherwise?
Has it ever been done in a real system?
By the way, Appendix 1 of this fine book has a
one-page treatment of phasing SSB math.
73 de KC7IT
Mike Butts, Portland, Oregon mbutts@netcom.com
From rec.radio.amateur.homebrew 828
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From: k23690@lehtori.cc.tut.fi (Kein{nen Paul)
Newsgroups: rec.radio.amateur.homebrew
Subject: Re: AM+FM=SSB?
Message-ID: <2d8qbi$oc7@cc.tut.fi>
Date: 28 Nov 93 00:11:30 GMT
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Mike Butts (mbutts@netcom.com) wrote:
> In the ARRL's "Solid State Design for the Radio
> Amateur", by Hayward and DeMaw, on p. 184 of
> the 1986 edition, after a nice summary of
> filter and phasing principles, plus a mention
> of Weaver, they say:
> "Also, it may be shown mathematically that
> a carrier which is amplitude modulated
> properly and frequency modulated
> simultaneously will yield a single-
> sideband output."
> I haven't succeeded in figuring this out.
> Can someone show this mathematically or otherwise?
> Has it ever been done in a real system?
The only practical implementation I know of was used in OSCAR 7 B-mode
linear transponder. (A linear transponder passband is just a SSB signal
a few hundred kHz wide).
The amplitude information is separated at the transmitter input and
the phase information is hard limited and amplified in class-C stages.
The amplitude information controls a PWM power supply feeding the output
transistor (running in class-C) and thus also AM-modulating the signal.
The resulting signal is SSB. The total efficiency (unregulated DC to
RF) is very high, which is extremely important in satellites.
This system was developed by Karl Meinzer DJ4ZC.
I checked The Satellite Experimenters Handbook and in the list of
references there are a few related articles.
K. Meinzer,
Lineare Nahchrichtensatellitentransponder Durch Nichtlinear Signalzerlegung
(Liner Communications Satellite Transponder Using Non-linear Signal
Splitting), Doctoral Dissertation, Marburg University, Germany, 1974.
K. Meinzer,
A Frequency Multiplication Technique for VHF and UHF SSB.
QST , Oct 1970, pp 32-35.
A more developed system will be used in some transmitters in the Phase-3D
satellite, which will be launced in 1995/1996. The block diagram for the
10 GHz transmitter looks really complicated with separate feedback control
loops for phase and amplitude. A class-C UHF/SHF output stage moduleted
by varying the supply voltage, is not a particulary good AM modulator
and thus the feedback loop in the amplitude channel is required to
predistort the applied voltage.
Paul OH3LWR
--------------------------------------------------------------------
Phone : +358-31-213 3657
X.400 : G=Paul S=Keinanen O=Elisa-Tampere A=ELISA C=FI
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Telex : 58-100 1825 (ATTN: Keinanen Paul)
Mail : Hameenpuisto 42 A 26
FIN-33200 TAMPERE
FINLAND
From rec.radio.amateur.homebrew 832
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From: atd@cs.rit.edu (Albert T Davis)
Newsgroups: rec.radio.amateur.homebrew
Subject: Re: AM+FM=SSB?
Message-ID: <1993Nov28.173001.11912@cs.rit.edu>
Date: 28 Nov 93 17:30:01 GMT
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AM + FM = SSB with carrier works in the limit if the modulation
index is low enough that only the first sideband of the FM is
significant. Remember that FM has an infinite number of sidebands.
From rec.radio.amateur.homebrew 833
Path: ucbvax!agate!howland.reston.ans.net!vixen.cso.uiuc.edu!sdd.hp.com!col.hp.com!bobw
From: bobw@col.hp.com (Bob Witte)
Newsgroups: rec.radio.amateur.homebrew
Subject: Re: AM+FM=SSB?
Message-ID: <2d84v3$2eu@hp-col.col.hp.com>
Date: 27 Nov 93 18:06:27 GMT
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Mike Butts (mbutts@netcom.com) wrote:
: In the ARRL's "Solid State Design for the Radio
: Amateur", by Hayward and DeMaw, on p. 184 of
: the 1986 edition, after a nice summary of
: filter and phasing principles, plus a mention
: of Weaver, they say:
: "Also, it may be shown mathematically that
: a carrier which is amplitude modulated
: properly and frequency modulated
: simultaneously will yield a single-
: sideband output."
: I haven't succeeded in figuring this out.
: Can someone show this mathematically or otherwise?
: Has it ever been done in a real system?
Short hand-waving explanation follows...
Amplitude modulation has sidebands symmetrical about the carrier
(i.e. upper sideband is mirror image of lower sideband)
NARROWBAND FM has the same sidebands as AM but with one sideband
out of phase with the other.
Combining (subtracting?) an AM and narrowband FM with the same
modulating signal can cancel out one of the sidebands. I think
subtracting may be in order here to get rid of the carrier and
leave only the desired single-sideband.
The matching requirements throughout the system are significant.
That is, any mismatch between the modulating schemes will result
in a partial appearance of the unwanted sideband.
Bob Witte / HP PMO (Colo Springs) / bobw@col.hp.com / KB0CY / (719) 590-3230
From rec.radio.amateur.homebrew 834
Path: ucbvax!agate!howland.reston.ans.net!usc!sdd.hp.com!col.hp.com!bobw
From: bobw@col.hp.com (Bob Witte)
Newsgroups: rec.radio.amateur.homebrew
Subject: Re: AM+FM=SSB?
Message-ID: <2d85ct$2eu@hp-col.col.hp.com>
Date: 27 Nov 93 18:13:49 GMT
References: <mbuttsCH5s3w.6w@netcom.com> <2d84v3$2eu@hp-col.col.hp.com>
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I wrote:
< AM + FM = SSB discussion >
: Short hand-waving explanation follows...
: Amplitude modulation has sidebands symmetrical about the carrier
: (i.e. upper sideband is mirror image of lower sideband)
: NARROWBAND FM has the same sidebands as AM but with one sideband
: out of phase with the other.
: Combining (subtracting?) an AM and narrowband FM with the same
: modulating signal can cancel out one of the sidebands. I think
: subtracting may be in order here to get rid of the carrier and
: leave only the desired single-sideband.
: The matching requirements throughout the system are significant.
: That is, any mismatch between the modulating schemes will result
: in a partial appearance of the unwanted sideband.
I just remembered, I once worked out the math to this, but for
the case where the carrier does not get cancelled out.
See Chapter 6.10 of "Spectrum and Network Measurements" by R.A Witte,
Prentice Hall, 1991.
Bob Witte / HP PMO (Colo Springs) / bobw@col.hp.com / KB0CY / (719) 590-3230