From: "an_old_friend" on Mon 8 Aug 2005 13:56


wrote:
From: John Smith on Sun 7 Aug 2005 23:27

You may not have seen the ham magazines of the 50s when
single channel SSB voice was beginning to take off. There
was great antipathy towards PHASING methods of modulation-
demodulation of SSB. Hams weren't told about PHASE, didn't
have the tools to see phase, few could afford 'scopes that
had passbands beyond 5 MHz. It was EASIER to build filter
SSB mod-demod even though it CO$T a lot more for those crystal
filters. Less thinking involved. AM voice spectra was
easier to understand and "brute-force" filtering to eliminate
an unwanted sideband almost intuitive. Despite some good
attempts at showing PHASING methods in the 50's magazines,
readers and editors alike didn't like it. Even after Mike
Gingell (UK ham, now living in USA) did his Polyphase Network
PhD paper on a low-cost, easy-component-tolerance quadrature
phase circuit, the U.S. periodicals didn't care for it. The
RSGB did and showed How and showed what UK and Yurp hams
were doing with it in the pages of Radio Communication. That
was 30 years ago...but European hams are having fun with that
Gingell polyphase network in homebrew SSB building.

Sorry to butt in, but a bit confused here from the only famialr with
AM voice sidebands ad the talk of phasing sidebands are you refering to
a compatable system (that is can the brute force filtered SSb uint talk
to the phasing unit or are you discuing to different and Incompatable
systems (obviosuly if they were incompatable inerta is decent reason to
keep one over the other, after it has kept morse in place a LOT longer)

Both SSB modulate-demodulate systems are compatible. Each
produces a SINGLE AM sideband. In the Phasing system one
needs two balanced mixers and a 0 degree and 90 degree
relative phase shift (commonly called 'quadrature') of BOTH
the audio AND the RF carrier. The two balanced mixer outputs
are then algebraically summed for the result.

The reason it works has to do with the relative RF phases of
the conventional AM sideband products. The upper sideband
components are differnt from the lower sideband components
even though the sideband magnitudes (and frequencies) are the
same. I could show how mathematically but this medium doesn't
show equations well and John Carson's formula is rather long.

The trick is to get a wideband audio phase shift network
that retains the quadrature (90 degree) difference all across
the desired audio bandwidth. The RF carrier can do that but
the percentage bandwidth is small so the RF quadrature is
relatively easy to do in hardware. The audio network is not
easy to do. It is the SELECTION of audio phase and carrier
phase into the mixers that determines whether or not an upper
or lower sideband is desired. The amount of rejection of the
unwanted sideband depends on the tolerance of holding the
relative phase shifts as close as possible to 90 degrees.

The "suppressed carrier" part of SSB is by virtue of the
mixers balancing out the RF carrier in their output.

The Gingell Polyphase Network takes 0 and 180 degree audio
in and produces four audio outputs, each in quadrature with
their adjacent output. The tolerance of exact quadrature is
so good one can use ordinary 5% tolerance resistors and
capacitors (relatively inexpensive) without matching them
in pairs/quads. Much better than half-century old tube
technique passive networks which required 1% or better R
and C and always had a finite relative phase error.

I migt as well learn something, and I am not afraid to admit the limits
of my knowledge that is of course the first step in increasing it

Absolutely. [few extras in here admit to gaps in knowledge
since they are Morsemen who don't need theory]

There's considerable data on phasing SSB generation-demodulation
in older textbooks and some on the Internet. A search on
"Phasing SSB" will turn up some interesting homebrewed-designed
phasing generators and a few complete transceivers.

My former boss and still my friend, Jim Hall, KD6JG, pointed me
to a very interesting circuit in the RSGB magazine Radio
Communication back in the early 70s. Jim did some early work
on "third method of SSB" that is referenced in the "Collins
SSB book" (familiar name) by Pappenfus, Bruene, and Schoenike
then with Collins Radio. I snitched a bit of mainframe time
and did a circuit analysis of it that got mentioned in Pat
Hawker's column in Radio Communication a few months after
Peter Martinez' circuit/experiments were featured. [the same
G3PLX that would go on to innovate PSK31 much later]

For others who were in early radar work, particularly avionics
weapons systems, "phasing systems" are the key ingredient to
"monopulse radars" that can determine elevation and azimuth
from a radar antenna boresight line without physical movement
of the antenna. Those started showing up in the 1950s. The
"phase shift networks" at microwaves (X and K bands) are quite
a bit diffeent than R-C ones at audio! :-)

yee haw