BPSK

[glen herrmannsfeldt]

There is discussion in another newsgroup in whether
Manchester coding is, or is not, a form of BPSK.

I usually consider it as synchronous phase modulation
(the wikipedia page seems to use the work coherent where
I would use synchronous).

I thought I would ask here, as there doesn't seem to
be much else to ask here.

-- glen

[Rich Seifert]

Yes, it is precisely BPSK. The "zero" symbol (half-period high, half-period low) is a 180-degree phase shift of the "one" symbol (half-period low, half-period high).

Sorry for the long latency on response, I don't check this group (or any of the old Usenet groups) very often. Usenet has passed into history, for the most part.

--
Rich Seifert Networks and Communications Consulting
21885 Bear Creek Way
(408) 395-5700 Los Gatos, CA 95033
(408) 228-0803 FAX

Send replies to: usenet at richseifert dot com

[glen herrmannsfeldt]

Rich Seifert <use...@richseifert.com> wrote:

(snip, I wrote)

>> There is discussion in another newsgroup in whether
>> Manchester coding is, or is not, a form of BPSK.

>> I usually consider it as synchronous phase modulation
>> (the wikipedia page seems to use the work coherent where
>> I would use synchronous).

> Yes, it is precisely BPSK. The "zero" symbol (half-period
> high, half-period low) is a 180-degree phase shift of the
> "one" symbol (half-period low, half-period high).

It seems that signal processing people disagree, though I
am not sure why.

> Sorry for the long latency on response, I don't check
> this group (or any of the old Usenet groups) very often.
> Usenet has passed into history, for the most part.

Sorry for the slow reply. It seems that the server that I posted
from doesn't get incoming posts. I switched servers temporarily,
and notice that there was a reply.

Thanks,

-- glen

[Albert Manfredi]

Except that Manchester is not modulating an RF carrier. My view is that the two are related, but Manchester is baseband and BPSK is modulation of a carrier.

[Albert Manfredi]

On Friday, October 26, 2012 3:57:45 PM UTC-4, Albert Manfredi wrote:
> Except that Manchester is not modulating an RF carrier. My view is that the two are related, but Manchester is baseband and BPSK is modulation of a carrier.

Actually, there's even more of a difference.

In BPSK, a 1 or a 0 is determined by a single phase shift from the carrier frequency. The modulation is either in phase with the carrier or it is 180 (or theoretically any other) phase different from the carrier, and each of those states represents one bit.

In Manchester, instead, you need both the "0 phase" and the "180 phase" states (in quotes because I'm relating phase to high and low) to represent a single bit of information.

[glen herrmannsfeldt]

Albert Manfredi <bert...@hotmail.com> wrote:
> On Friday, October 26, 2012 3:57:45 PM UTC-4, Albert Manfredi wrote:
>> Except that Manchester is not modulating an RF carrier.
>> My view is that the two are related, but Manchester is
>> baseband and BPSK is modulation of a carrier.

Are you distinguishing it by frequency? Consider that RF goes down to
60kHz (used to be 20kHz but I think that one shut down).

> Actually, there's even more of a difference.

> In BPSK, a 1 or a 0 is determined by a single phase shift
> from the carrier frequency. The modulation is either in
> phase with the carrier or it is 180 (or theoretically
> any other) phase different from the carrier, and each of
> those states represents one bit.

In general, there can be any frequency relationship
between the carrier and modulating frequency.

In the synchronous case, there is a definite relation
between the two, usually that the carrier is an integer
multiple of the modulation rate, or possibly a simple
fraction.

> In Manchester, instead, you need both the "0 phase" and
> the "180 phase" states (in quotes because I'm relating
> phase to high and low) to represent a single bit of information.

Manchester is the special case where the modulation (bit rate)
is at the same frequency as the carrier, and (if the
carrier is considered as sine) either 0 or 180 degree
phase shift.

That is, you have a whole cycle of either sin(wt) or
sin(wt+pi). It is baseband in the sense that the
sidebands can be considered as going down to 0Hz.

-- glen

[Moe Trin]

On Fri, 26 Oct 2012, in the Usenet newsgroup comp.dcom.lans.ethernet, in article
<k6f06t$et7$1...@dont-email.me>, glen herrmannsfeldt wrote:

>Are you distinguishing it by frequency? Consider that RF goes down to
>60kHz (used to be 20kHz but I think that one shut down).

Huh? I suppose you are referring to the frequency standard stations
WWVL (was on 20 KHz), WWVB (on 60 KHz) from Fort Collins, Colorado
(USA) and GBR and/or MSF (was Rugby, England, now moved to Anthorn,
England), but these are not the only very low frequency stations still
in regular use. GQD (Anthorn, England) is operating on 19.6 KHz, and
there are several US Navy transmitters (NAA in Cutler, Maine, NLK in
Jim Creek, Washington among others) in the range 17 to 23 KHz.

Not withstanding the above, the International Telecommunications Union
defines radio services down to 9 KHz (the band 9 to 14 KHz is for
radio navigation services, such as the now retired "Omega" system - see
<http://en.wikipedia.org/wiki/Omega_(navigation_system)> for details -
the band 14-19.95 KHz is "Maritime", 19.95-20.05 KHz is "Standard
Frequency and Time Signals", 20-70 KHz is "Maritime" and so on) and the
fact that few stations use those bands in no way changes the definition
of "radio frequencies".

If you look back in the archives of "comp.protocols.time.ntp", you'd
find Prof. Mills (RFC5906 and others) ranting about the interference
(4th harmonic) from analog television _receivers_ making WWVB unusable
in Deleware. Don't know if that's still the major problem it was.

Old guy