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[TenTec] Enhanced SSB

To: <tentec@contesting.com>
Subject: [TenTec] Enhanced SSB
From: w4njf@midflorida.com (Bill Fulling)
Date: Sat Apr 19 08:09:51 2003
Hello Doctor!
Great thread on what SSB is supposed to be.
"Hi-Fi" SSB is a oxymoron.I read somewhere that SSB was developed in the
early '30s by Phillips Electric of Holland at the request of the Dutch
gov't(and Shell Oil) to provide reliable voice comm between Holland and
Batavia,NEI (now Jakarta,Indonesia).Do you know what system they used back
73 de Bill W4NJF

Bill Fulling
----- Original Message -----
From: "Dr. Gerald N. Johnson, electrical engineer" <geraldj@isunet.net>
To: <tentec@contesting.com>
Sent: Friday, April 18, 2003 12:12 PM
Subject: Re: [TenTec] Enhanced SSB

> SSB achieves its superior communications performance compared to double
> sideband AM by saving the carrier power and concentrating the
> transmitter  power into just one sideband AND by allowing half the
> receiver bandwidth so for threshold level signals, the received noise
> power is half thus improving the received signal to noise ratio.
> Reduction of equipment weight and power supply capacity are incidental
> side effects. By the reduction in transmission and receiver bandwidth,
> SSB allows at least a doubling of the number of QSOs per MHz.
> Generating SSB by phasing network was MORE bandwidth limited by
> circuitry than SSB by filtering. True there's a LF roll off from the
> slope of the filter getting LF opposite side band (and some enhanced
> carrier) suppression, but the audio phase shift networks of the past
> were always compromises. Adding a 100 Hz to the low end required taking
> 1 KHz from the top end in those RC networks. I did an analysis of all
> the known phase shift networks back about 1971 or '72 while exercising
> main frame network analysis programs. That is once I found such a
> network analysis program that was portable enough to run on the ISU main
> frame. I found that most had an average phase difference closer to 80
> degrees than 90 degrees. The commercial B&W was the best of the pack.
> This effectively prevented switching sidebands by the simple inversion
> of the audio, one simply couldn't achieve good sideband suppression on
> more than one position of the sideband selection switch without
> shuffling the RF phase shift to match the error in the audio phase
> shift. That phase shift error problem is why we use LSB on 80 and USB on
> 20. The first ham SSB was with phasing and was on 20 meters, 9 MHz IF
> and 5 MHz VFO (command set). 9 - 5 gave 75 meters but the opposite
> sideband. Three times the VFO - 9 gave LSB for 40 meters.
> The modern phase shift network is ten times more complex than that used
> in the 50s and 60s and is still bandwidth limited. Modern analog phasing
> equipment still very carefully limits the audio bandwidth and the
> harmonic distortion of the audio amplifiers (transmitter AND receiver)
> to minimize bandwidth. Distortion products from the transmitter audio
> amplifier will show up on BOTH sidebands coming out of the phasing
> exciter, whether DSP or analog.
> Spectrum studies for audio communications dating back nearly to
> Alexander Graham Bell have shown that the LF components of male voices
> contribute little to communications but a great deal to power
> dissipation in the communications circuit, so its considered practical
> to roll off rapidly below 300 Hz. Hurts naturalness a bit but not
> articulation. The same thing is true for high frequency components much
> above 2400 Hz. Silabent energy does extend further, but adds virtually
> nothing to understanding of the voice communications. Hence the
> classical filter rigs, the Collins KWS1/75A4 and S-line use 2.1 KHz
> filter bandwidth and set the carrier 300 Hz from the passband corner. As
> do Ma Bell's frequency multiplexed wire and microwave voice circuits
> since the 30s when frequency multiplex was developed. Collins supplied
> LF mechanical filters by the TON for such frequency multiplexed wire
> line and microwave service. The emphasis for elimination of low
> frequency energy was to save circuit power without loss of
> understanding. Remember that in the early days of long distance, there
> weren't any rural electric cooperatives hand to supply DC power to the
> necessary amplifiers, they had to be supplied through the phone wire and
> efficiency was very necessary to work at all.
> Use of SSB has a conflict with hearing quality, that comes from tuning
> accuracy. It takes more care to tune SSB for quality hearing than AM or
> FM. New hams seem to have great difficulty tuning for quality, often
> tuning for bare intelligibility and accepting a 200 Hz or more error. In
> commercial circuits that has been attacked by leaving in a little
> carrier or for VHF by transmitting a pilot tone out about 3 KHz (with a
> strong LP filter to take out the pilot tone). Operator skill can help
> the quality immensely by tuning so that the transmitted harmonics of the
> lower frequency components of the voice come out of the speaker at the
> harmonic frequency.
> Back in the December 1956 SSB issue of the Proceedings of the IRE (the
> classic reference work at engineering level about SSB and
> communications, recommended reading), John B. Costas pushed DSB
> suppressed carrier because it gave most of the transmitted energy
> savings, and could be received with the SSB receiver (though those
> running SSB that noticed I had both sidebands on 40 meters back about
> 1958 did tend to stop talking to me), and better could be received with
> a receiver whose LO was phase locked to the two double sideband
> components to be exactly in phase with the original suppressed carrier.
> Hence tuning was very easy, the receiver was more complex, but the
> transmitter was simplified and the received quality was always high (at
> least in the Costas receiver).
> I find that I often want a narrower SSB filter than the 2.4 of my
> Corsair II, fortunately with the passband tuning, that is easily
> achieved with a tweak of a knob. Then to clean up harmonic artifacts
> created in the radio I have a switchable cutoff frequency passive low
> pass filter in the speaker circuit. Typically that LP filter is set for
> about 2.1 KHz.
> As for spectral efficiency, I have found by decades of experiment, that
> opposite sidebands can overlap further than same sidebands for the same
> effective interference to communications. E.g. I can run USB on 75
> meters with my carrier about 3 to 3.5 KHz from a LSB signal and still
> communicate while running that close both on LSB the interference is
> much more severe. I think that has to do with the energy density of the
> male voice above 1.2 KHz being small. And in my receiver, interference
> in that range is less annoying than if its from the low audio portion of
> the male voice spectrum. E.g. overlap of SSB spectra is less annoying if
> its from the opposite sideband than from the same side band for the same
> amount of overlap.
> There is a rule in part 97 about using the minimum spectrum required for
> the communications, right next to the one about using the minimum
> POWER...
> So as I see it, "HIFI" SSB is contrary to good communications principles
> and to the letter of the FCC rules covering amateur radio. Other than
> catering to an ego that demands greater bandwidth and "fidelity" is
> accomplishing nothing but to waste spectrum. Perhaps some future digital
> mode (I have one in the works) will allow fitting 10 or 20
> communications within the same spectrum as normal bandwidth SSB and
> perhaps 40 independent communications within the spectrum wasted in a
> single "HIFI" SSB signal.
> 73, Jerry, K0CQ
> --
> Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
> Reproduction by permission only.
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