One sideband louder than two?

[w1vtp]

Moreover, by running only 2/3 of a complete AM signal you deprive us of the option of tuning to the side that has the least amount of interference.

Exactly!  I never listen to both sidebands with my Flex.  But if someone checks in and I'm listening to the other sidebend I won't hear him.  Additionally, if there is a carrier on one side, I will not be able to do exactly what VJB says in this quote

Use both sidebands, PLEASE!

[KF1Z]

Nice 5 year old thread.

[WA3VJB]

Nice 5 year old thread.

Well then I shall renew the request -- Please keep your AM signal intact. Do not neuter a sideband.

[w1vtp]

5 year old thread - nontheless it's a topic banging around from time to time.  My EICO 753 does that with the AM mode.  There is no reason why a SSB with carrier left intact shouldn't sound OK especially if a 6 KC filter method is used. Just might be a nice thing if the carrier osc. could be moved from one side of the filter to the other - to accomodate the above mentioned commentary about slopbuckets and carriers.

The phasing method wouldn't work due to phase shift problems over the modulating AF frequency spectrum.   


Al

[w3jn]

Has anyone acheived real am broadcast style audio out of a collins 8010 exciter.

You'd be better served by starting a new topic rather than necroing this old one.  You'll probably generate more interest.

I don't know the answer to your question, but I suspect not.  You can always bypass the sideband filter.

[KM1H]

Ive received excellent reports from a TS-950SD with the audio switches set for 3300Hz and have switched sidebands when needed to either get away from or annoy a slopbucket. With help from the LK-500 with the external PAC-5 transformer and the fan on high it seems to get thru just fine with just a little help from the rigs compressor.

There is also a mod that allows it to transmit thru the 6KHz AM filter but I havent done that as its a bit complicated to still use the 2.7 filter on SSB.

Hopefully the overhauled 100V will be on line soon and I can test AM on LSB, USB, and DSB.

Carl

[K5UJ]

The WBCQ setup is interesting.   The solid state 50 KW rigs like the DX50 are supposed to be around 90% efficient. 

I think at one time Ten Tec made a fake AM rig, the Paragon maybe, back in the 1980s.  I occasionally hear carrier+one sideband on the air, most recently from a KWS-1.  Sounded like crap.

[k4kyv]

                                 WHY ONE SIDEBAND PLUS CARRIER IS NOT THE SAME THING AS AM

One sideband + carrier is not AM, in the sense of the mode that is the reason for the existence of this bulletin board.  One sideband + carrier is just what it says.  Slopbucket with poor carrier suppression. It is AM ony in the strictest sense that SSB is merely a special form of AM. The specific form of AM portended by this BB is full carrier double sideband amplitude modulation. We just call it "AM" for short.

Due to inherent fundamental mechanics of the modulation and demodulation process, one sideband + carrier cannot be received on an envelope type detector such as the diode detector without severe distortion, unless the modulation percentage is kept very low - something on the order of 30% maximum.

The only reason SSB + carrier even vaguely resembles AM when copied with an envelope detector, is that the peak-to-average ratio of the human voice waveform is extremely high. While voice peaks drive the detector into unintelligible gibberish, the average modulation level remains at a low percentage of modulation, so that the signal may come through reasonably intelligibly, but it still sounds like crap and the voice peaks are distorted. That is the same reason why an analogue VU meter dwells in the 20-30% region most of the time while it spikes up into the red zone on louder voice peaks.

We can make another analogy by considering the detection process in a receiver.  In the early days of SSB, most amateur receivers didn't have a product detector, so the majority of hams received SSB with a diode detector and BFO, in exactly the same manner as they had copied CW ever since CW had replaced spark. But to clarify the SSB signal, not only did the receiver have to be tuned exactly on frequency, the rf gain had to be turned way back with the audio gain set at or close to maximum. The BFO provided the reinserted carrier, and the output from the i.f. amplifier provided the modulation.  If the rf gain was set to maximum as with normal AM reception, the i.f. output to the detector was too great, the diode detector was overloaded, and all that came out of the speaker was unintelligible distortion. In other words, the percentage of modulation was too high.  By cutting back the rf gain control, the carrier (BFO) remained  the same, but the percentage of modulation (from the receiver's final i.f. stage) was reduced to a point where the signal could be detected with little or no audible distortion. The diode detector still demodulated the signal in the exact same way that it demodulates a full carrier AM signal. In this case, the "carrier" is the BFO and the modulation is provided by the received SSB signal.  But since there is only one sideband, the modulation percentage must be kept low by retarding the rf gain setting on the receiver to eliminate the severe distortion.

This distortion that occurs when SSB + carrier is received with an envelope detector is called "quadrature distortion" and can be fully demonstrated vectorially. This is fairly well explained in Single Sideband for the Radio Amateur, the popular ARRL publication that first appeared in the 1950s.



                         THE PROPER TRANSMISSION AND RECEPTION OF ONE SIDEBAND PLUS CARRIER

As explained above, one sideband plus carrier cannot be properly received with a normal envelope type AM detector.  But it can be satisfactorily received by treating it as a regular SSB signal, or distortion free, by using a properly locked synchronous detector, which is nothing more than a product detector with an additional phase-locked loop circuit to lock the BFO exactly in synch with the received AM carrier. Unlike the envelope detector, the product detector can handle the full output from the receiver's i.f. amplifier, so the rf gain does not have to be reduced for distortion-free reception.  With a synch detector, SSB + carrier can be made to sound exactly like regular DSB AM.  In fact, using my Sherwood synch detector, I have had another station switch between AM and SSB + carrier, and could not tell any difference in the sound. When the synch detector is used for reception, the transmitted carrier serves only as a pilot carrier to give the BFO something to lock onto, and does not actually demodulate the sideband directly.

But, if SSB + carrier is transmitted with the intention of receiving the signal with a synchronous detector, it is very wasteful of power to transmit a full carrier.  Only enough carrier is needed to provide a reliable lock with the PLL (phase-locked loop). With a good synchronous detector, the carrier can be reduced to at least the vicinity 20 dB below the p.e.p. of the sideband, and still get a reliable lock. By using a pilot carrier reduced to this level in combination with the synch detector, the annoying frequency error that usually occurs with amateur SSB and gives it the "Donald Duck" sound, is eliminated, but the reduced level of transmitted carrier would not waste an excessive amount of power nor cause the linear amplifier to overheat or run at low average efficiency.  Years ago, before the advent of satellites, AT&T's transatlantic and ship-to-shore radiotelephone circuits could be monitored on an ordinary short wave receiver, as they transmitted SSB with a pilot carrier.  

This is where the ESSB guys are missing the boat; if they transmitted a low-level pilot carrier and used synch detectors for reception, their signals could be made to sound very close if not identical to regular full carrier double sideband AM, while maintaining nearly the same power efficiency as ordinary fully-suppressed carrier SSB.

[Opcom]

Moreover, by running only 2/3 of a complete AM signal you deprive us of the option of tuning to the side that has the least amount of interference.

So it would make sense when one side is being obliterated and you know it -- deliberate SSB QRM right on the net frequency, for example. Then I might as well send a carrier + the other sideband, full bore, right?  

My homebrew rig can't do this but my old CE 100V + linear can.

Jon

yes and that works well provided the intended listeners can move their bandwidth to cut out the QRM or narrow it to receive only your transmitted carrier+SB.  And thank you Don, you are 100% right and that was a very interesting illustration of why it sounds distorted.

[w3jn]

SSB+carrier can't be received with a Costas loop sync detector either, which depends upon the phase relationships of both sidebands to maintain phase lock.   The Costas loop doesn't require a carrier at all, just both sidebands.  However I'm not aware of any Costas sync detectors in any HF receivers with the possible exception of the Sony ICF-2010 which as I recall uses a AM stereo demodulator chip for its sync detector.  A Costas detector could be implemented in a SDR also but again I'm not sure if this has been done in the popular SDR hammy software.

[kg8lb]

Nice 5 year old thread.

Well then I shall renew the request -- Please keep your AM signal intact. Do not neuter a sideband.

  X2 !

[KM1H]

Then why do so many report many riceboxes on AM as having an excellent sounding signal on a BA receiver? Ive no complaints either listening to them on a BA or a ricebox in AM mode.

The specific form of AM portended by this BB is full carrier double sideband amplitude modulation. We just call it "AM" for short.

OK, all you guys with controlled carrier modulation get the hell off the forum, His Lordship has spoken

[k4kyv]

Then why do so many report many riceboxes on AM as having an excellent sounding signal on a BA receiver? Ive no complaints either listening to them on a BA or a ricebox in AM mode.

All the modern riceboxes that I know of to-day run both sidebands in AM mode.  Many of those rigs can be made to sound just as good as plate modulated AM, and one could be fooled into believing they were running a converted broadcast transmitter. Some of the early US-made rigs like the KWS-1 and the Drake TR-7, and some first primitive transceivers had an "AM" mode that ran SSB+carrier.

OK, all you guys with controlled carrier modulation get the hell off the forum, His Lordship has spoken

 "Controlled carrier modulation" is still full carrier double sideband AM, whose carrier varies in amplitude at a syllabic rate in step with the voice. Controlled carrier was first introduced in the 1930s, using normal high level plate modulation. One way this was accomplished was using a special saturable reactor to control the primary voltage to the plate transformer in the final amplifier power supply to follow the variations of the modulator plate current.  Another method was to wire the class B modulator, class C final and power supply in series, so that with no modulation the modulator just drew static plate current, and thus limited the DC input to the final.  On modulation peaks, the modulator drew full current, which also passed through the rf final in the series circuit, bringing up the DC input to the final up to full value.

Rigs  like the Drake TR- and T4- series, Heath DX-40 and DX-60 and Knightkit T-60 and T-150 used controlled carrier screen modulation, all full carrier double sideband AM just the same.

[KX5JT]

I always try to control my carrier.  Whether it's changing with the amount of modulation or not, I sure like to set it to where I like it.

[WD5JKO]

OK, all you guys with controlled carrier modulation get the hell off the forum, His Lordship has spoken

Wow. Having trouble believing my eyes. Have tolerance your hinus.The AM'ers as a group are better combined as apposed to be broken into fractured and bickering groups.

Jim
WD5JKO

[KM1H]

Relax Jim, that was just some Yankee sarcasm   Ive no idea where that long post of Dons originated as it looks as if it was copied from somewhere.

However I still maintain that the various phasing rigs of old that allowed switching to DSB, LSB, and USB AM sounded good. I cant remember trying AM on a NCX-3 or NCX-5 when I had them as loaners. At home from the late 50's I went from various CE 10A to 20A, Phasemaster, HT-37, and then a long term 100V to C Line, to TS-930/940/950SD.

There are a couple of CC rigs here that get used with the Alpha 76PA and I flog a T-150A at the summer cottage.

Carl

[WU2D]

It's a wash.  Unless the receiver is filtering out one sideband only, the receiver will see a 3dB decrease in recovered audio.

You could build a detector which can utilize both sidebands, for instance synchronous double-sideband product detection either with hardware or in software definition. Since the upper and lower sidebands are mirror images above and below zero ( the carrier frequency), they can be combined in phase (not in quadrature as with SSB demod in the Phasing or Weaver method) to reinforce the signal.


http://www.arrl.org/files/file/Technology/tis/info/pdf/9709qex003.pdf

Mike WU2D

[Rob K2CU]

Some interesting reading on this thread. In 1964 I put together a 6146 class C transmitter with a homebrew modulator using a pair of 807s. Our simple Lafayette HE-30s were AM mode radios with CW/SSB capability done by dumping a BFO into the diode detector. You had to turn off the AVC because the BFO drove the AVC so that the S meter read around 30 over nine. Of course, with the AVC off, the RF input would over drive the later IF stages into full limiting/distortion. You had to turn down the RF Gain so that the RF/Mixer/IF stages had a chance of keeping the input linear. The Af gain was turned way up to hear the signal out of the detector.

Perhaps SSB plus Carrier should be thought of as an alternative to DSB AM when conditions warrant it.  Many people have made mention of tuning in one of the two sidebands when interference on the other calls for it. The bandwidth is often either shifted or cut in half under these conditions. So, under certain conditions, SSB AM might make sense to fight through the crud. IF you really need to get through, just switch over to SSB and run full bore anyway. So, what's the point. IF you are looking for maximum detected audio and want to rely on the carrier for detection, The carrier at 375W and peak SSB signal at 375 W will get you at 1500W PEP. You will get the same recovered audio with DSB AM if you detect both sidebands since they are each at half the voltage level of the SSB AM peak sideband voltage. The difference is that you use half the bandwidth. So, if you throw away one of the DSB AM sidebands, you are losing 6 dB of recovered audio.

The deal is the detection process. The diode detector has a logarithmic transfer function. Many mathematical functions can be represented by a series summation of other simpler functions, much like a square wave can be represented by a weighted sum of odd harmonics. For the log function, the principle term in the sum is a square term. hence the term "Square law detector."  A problem with this detector for DSB AM is that the square term not only multiplies the carrier times each sideband to down convert to baseband, it also multiplies the sidebands by  each other to produce second harmonic distortion. Other, higher order terms produce some additional distortion, but most products are at RF frequencies, and the coefficients of these terms drop off in value quickly. 

IF distortion reduction is your thing, and you want self detecting of DSB AM, then something like the precision detector cleans it up by not being a square law detector. It operates more like a self driven synchro detector. The diode type detector works fairly well with SSB AM. You probably have done it many times without realizing it. Every time you tune off to the side of a DSB AM signal, to get away from an interfering SSB station, you are eliminating one of the sidebands and detecting SSB AM with your own simple diode detector. Any distortion you hear from the desired signal detection process would be the higher order terms coming into play and/or level issues between the carrier down on the slope of the passband filter or other issues. IF you have an SDR setup, try it with the SDR receiver set to AM, tune in a DSB AM signal normally, and then pull in one side of the filter to the carrier. Either way, you have made the DSB AM signal into an SSB AM signal.

My disappointment in this whole thing is that the precision detector, perfect of DSB AM, is not good for SSB AM. An SSB AM signal, say a 1 KHz tone signal plus a carrier, would look just like a two tone SSB signal. and a precision detector (rectifier) would have a harmonically distorted waveform. It almost works since most of the harmonics of voice signals of 1.5KHz and up fall above the receiver audio stage upper cut off frequency.

Bottom line, consider SSB AM as just another tool to fight interference, especially if you push it to full bore on both the carrier and sideband. When the conditions are clear, run full DSB AM and enjoy the copy!

[k4kyv]

Bottom line, consider SSB AM as just another tool to fight interference, especially if you push it to full bore on both the carrier and sideband. When the conditions are clear, run full DSB AM and enjoy the copy!

But if you are going to run SSB, what's the point of running all that carrier?  Just have the other op turn on his BFO, or better still, if he has the capability, switch to synchronous detection. Use just enough carrier to give the synch detector something to lock onto, or to use as a reference for zero-beating the frequency.  With a diode detector and BFO turned off, any SSB + carrier modulation to a depth greater than about 30% is wasted anyway, since the quadrature distortion renders it unusable.

A diode detector is not a square law detector, because the logarithmic characteristic occurs only at very low levels, right at the threshold of response.  Usually, the i.f. amplifier delivers more than enough signal to the diode detector to make it function approximately as a linear detector.

The square law detector is interesting.  The early AM broadcast sets from the 20s and early 30s used triodes wired as grid leak detectors, because even though this detector had a square-law characteristic, it offered much greater sensitivity than would a simple diode detector.  Unfortunately, this square-law characteristic resulted in considerable audio distortion. Most of those old radios had a crackly sound even from strong local stations.  Since most people had never even heard a radio play before, this distortion was accepted by the public as something normal for the medium.  But it so happens that the square-law characteristic gives the audio output a distorted waveform that is the exact opposite of the distorted waveform that results from envelope detection of SSB + carrier.  Theoretically, a true square-law detector at the receiver would give perfect reproduction from a SSB + carrier signal modulated up to 100%, but the DSB AM signal would appear distorted!

I'm not sure if anyone has ever run any experiments with this, but it would be an interesting investigation. Maybe dig out some of the square-law detector circuits from the early days of radio, or use modern solid state technology, and build a true square-law detector.  I suspect the threshold of detection would have to be adjusted to closely match the level of the received signal, in order to get the two distortions to exactly cancel. It would be interesting to see how a SSB+carrier signal received with a square-law detector would perform in the presence of noise and interference, compared to DSB AM received with a linear envelope detector, considering of course, the total sideband power transmitted in each case.

PS: The reason you can tune to one side of a DSB AM signal, using envelope detection and no BFO but narrowing up the receiver to receive only one sideband, and not have severe distortion, is that removing the other sideband lowers the modulation percentage of the signal received through the narrow filter enough to stay below the threshold of severe distortion.

[KF1Z]

Yes, run both sidebands so those who want to only hear half the signal can.

Sounds kinda funny, dumping on people who run "SSB + carrier", because you want the ability to choose one sideband + carrier to listen to...

[k4kyv]

Yes, run both sidebands so those who want to only hear half the signal can.

Sounds kinda funny, dumping on people who run "SSB + carrier", because you want the ability to choose one sideband + carrier to listen to...

Actually, I have to admit there is some merit to that.  With DSB (with or without carrier) the listener can choose which sideband to receive, depending on the QRM that pops up while the station is making a transmission.  Somewhat a form of diversity reception, particularly useful during long "old buzzard" transmissions. SSB + carrier would be useless in that case, since there is no way the transmitting station could be aware of which sideband is suffering from the most interference, not being able to monitor the frequency while transmitting. If that one sideband gets obliterated by interference, you are up the creek without a paddle.

The Sherwood synchronous detector has on "offset tuning" mode that allows the listener to shift to one sideband, by moving the receiver to one side of the passband without losing BFO lock.  This allows it to work just like it would with envelope detection, but the product detector receives the signal more effectively without the distortion.

[flintstone mop]

I don't know if this was answered on AME. It was a mode selectable on a Motorola ALE type radio. Very user un-friendly. It was not designed to be a HAM radio. It's specific purpose was for the HF emergency systems in use throughout the USA.
The AME was Amplitude Modulation Equivalent. A compatible sideband transmission.

http://en.wikipedia.org/wiki/Compatible_sideband_transmission

The transmitters at WBCQ that use the reduced carrier and are modulating  USB. The audio is exceptional for SSB, but is more susceptible to selective fading distortion than a full carrier. The selective fading effect is eliminated with the use of a sync detector. On my R390A the audio is lower.


This is what Allan / Timtron use at WBCQ on  5.110, 9.330, etc.................7.415 is full carrier 50kw....I can't believe they get that power from single phase 220 and three other transmitters running 12kw ea with the reduced carrier. And I think he has a commercial AM (5KW) older plate modulated TX on the same pole.