View Full Version : lower sideband on 40 and 80
It's kind of odd that upper sideband is used on the majority of the bands, but lower is used on 40 and 80. Also, the "upper sideband" is always used on CW, even on 40 and 80...
If it weren't for the use of lower sideband on 40 and 80, we probably could eliminate that mode entirely ! So does anybody know how this convention came about ?
09-24-2003, 11:02 AM
It had to do with the harmonic realationship and the mixing of the base signal the sum and the difference are oposite side bands......
09-24-2003, 03:09 PM
Back in the late 1940s and well into the 1950s it was soon discovered that a single exciter could be made to cover both 75 meters and 20 meters. Since there were all sorts of BC-457 and BC-458 ARC-5 transmitters around that were considered "useless" for amateur radio work (they didn't cover 80 meters or 40 meters) but had very stable (at least for the times) VFO circuitry, many basic exciters were made to operate on 9 MHz. By mixing with the output of the 5 MHz VFO signal from the ARC-5 transmitters the frequencies of either 75 meters or 20 meters could be realized. But, since getting to 75 meters involved the subtraction of the VFO frequency and since getting to 20 meters involved the addition of the VFO frequency, the sidebands were reversed.
Thus, using lower sideband on 75 meters and upper sideband on 20 meters became the norm. Of course today virtually all of the transmitters and transceivers can operate using either sideband on any amateur radio frequency covered by the unit. However, the "convention" of using lower sideband on 160, 75, and 40 meters with the "convention" of using upper sideband on 20 meters and higher frequencies has become the basic "norm" of amateur radio operation.
Central Electronics, a major manufacturer of early SSB transmitters (CE-10 series and CE-20 series), had a conversion kit for the ARC-5 transmitters that had a new, calibrated for 75 through 10 meter, dial, etc. for use with their transmitters.
09-24-2003, 03:23 PM
I moved this from the Talk and Opinions forum to the Questions and Answers forum since it is more appropriate in the Q&A forum.
One of the QRZ.com moderators
09-24-2003, 05:49 PM
Just some comments ...
As I recall, the CE20A was selectable sideband. For perhaps a year that was my only transmitter (no amplifier, either!) with what was then called the Lakeshore Phasemaster VFO, a stabilized BC457 (or whatever it was.) It had internal modifications from the surplus unit, including, of course, the removal of the finals, and the addition of an internal AC power supply and regulator. Worked extremely well.
I think the early Galaxy III transceiver was LSB only on 40 and 75 and USB only on 20. Whether that was necessary, or simply expedient and conventional I have no idea. A few other rigs, such as the Eico 753, and I believe the National NCX-3, were also non-selectable sideband, but I suspect most of that was economics. Early Swans, like the 350, were non-selectable, but a kit could be added to the Swans to offer opposite sideband operation.
Probably by the mid sixties most sideband rigs except the very bottom line ones (like the Heath singlebanders) were selectable. Basically the cost of an additional crystal and switch component was all that was required.
And so technically the need for LSB on 40 and 75 and 160 disappeared. It has become a de facto 'law' though, and I have seen people complain about the use of opposite sideband. Used unwisely, it can cause needless interference, but with the practice of "listen, listen, listen," it really isn't a problem.
Note that most (I believe all) untampered-with SSB CB sets offer selectable sideband and there can indeed be both a LSB and a USB contact on the same channel at the same time, provided the opposing units are not really close. However, the channel spacing avoids the interference that can be caused by opposite sideband operation on ham bands.
Our 60 meter channels would be ideal for LSB/USB channelized operation, thereby doubling them to 10 channels instead of five, using the same principles as in CB. The catch is the NTIA does not permit LSB operation by the government agencies, at least on voice (LSB and ISB operation is permitted on AFSK, data, and other modes) and would be unable to monitor and see who was operating, and who was interfering!
I'm not going to pretend to be an expert on this ( because I'm not ) but I believe one of the other major differences between the way sideband was generated in those early days, vs. nowdays had to do with "filtered" vs. "Phased" sideband generation.
Now it is easy to put an oscillator on one side or the other of the filter's passband, but back then, there were a lot of discrete components involved to generate that sideband signal!
I used a Central Electronics 100V phase-generated sideband transmitter for a fairly long time , and it was one of the most satisfying rigs I have ever had the pleasure to use! That, in conjunction with a Collins 75A-4 was my first phone station after upgrading from Novice to Advanced. I had to give it back to the owner when I moved from Illinois to Maryland, and have always regreted that !
There were about 50 knobs on that rig ( I exaggerate ) that all had to be adjusted properly in order to balance out the carrier and get the sideband phase "just right". Most of the adjustments were behind two flip down cover plates, or inside the rig somewhere. The rig even had a built in oscilloscope to show you your signal as it was being transmitted in real time! I dare say that there is nothing like that in most of the boxes that are being used by hams today!
I loved the question, it brought back many pleasant memories!
73 from Jim AG3Y
</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">Our 60 meter channels would be ideal for LSB/USB channelized operation, thereby doubling them to 10 channels instead of five, using the same principles as in CB. [/QUOTE]<span id='postcolor'>
Not so. The CB channels are AM channels that can be used with SSB. That is the channels are wide enough to hold two (upper and lower) sidebands. The 60-meter amateur channels are only 2.8 khz wide. That is enough to hold only one sideband (and you had better have your rig's audio adjusted correctly).
If you tried using the published "carrier" frequencies and LSB your emissions would NOT be within the amateur allocation. If you offset the carrier frequency upward to get your emissions inside the amateur channel, you would just be creating unintelligible QRM for those using USB in the channel.
Just a friendly reminder, the current regulations only allow for one sideband to be used, as well! Be very careful, we don't want to lose what precious little we have gained by improper operation!
73 from Jim AG3Y
09-24-2003, 06:45 PM
</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">Our 60 meter channels would be ideal for LSB/USB channelized operation, thereby doubling them to 10 channels instead of five, using the same principles as in CB. The catch is the NTIA does not permit LSB operation by the government agencies, at least on voice (LSB and ISB operation is permitted on AFSK, data, and other modes) and would be unable to monitor and see who was operating, and who was interfering! [/QUOTE]<span id='postcolor'>
Ed, Those are 3kHz channels. On a typical ham radio tranciever if you switched to LSB from USB with the same indicated frequency you would be transmitting on the next lower channel. There is more of an issue than if Uncle Sam can hear what's going on.
09-24-2003, 06:59 PM
This is the #"No Bull" #answer:
I am not going to get too technical, #but techinal enough:
The earliest SSB transmitters used what is called phase derived SSB. #The phasing network was tricky to tune, #and expensive. #It would have required two of them to cover both sidebands. #Since output of the phasing network was around 8 MHz, #the mixed products above 8 MHz were upper sideband, #and the products below were lower sideband. #It wasn't until later when someone devised the crystal lattice network that upper or lower on the same frequency became practical.
09-24-2003, 08:27 PM
Actually, filter derrived SSB as well as phasing type SSB was in use even in the 1930s. However, it wasn't until after World War II that not only did SSB "take off", but also the thousands of surplus crystals became available to construct filter networks that were cheap and did a good job.
9 MHz was the usual SSB generator frequency because when mixed with the 5 MHz output of an ARC-5 (or other VFO) it produced a two band transmitter that had VFO coverage.
Most phasing rigs of the 1950s and into the 1960s actually use inband generation. A notible exception is the Hallicrafters HT-37 which used a fixed SSB generation module and then heterodyned the signal to get the proper frequency. Basically, the HT-37 was the same as the HT-32 except that the SSB generation in the HT-32 was by the filter method and, at the time, was more expensive to construct.
Adapters like the Heath SB-10 actually null the frequency and attenuate the unwanted sideband at the frequency of operation. Of course, the SB-10 is a phasing rig. One thing about phasing rigs when compared with a filter rig is that their audio, in general, is more "pleasing" to the ear. But, phasing rigs are a real "pain" since you have to adjust most of them whenever you change frequencies.
Of course those, like the HT-37 that kept the SSB generation at a fixed frequency were not apt to have this problem when changing frequencies since this was done by the heterodyne method. But, until the tubes warmed up, and the remainder of the circuitry came up to temperature, you had to constantly "tweek" the SSB generator for best carrier null.
As for switchable sidebands: Even the Heath "mono-banders" started having selectable sideband after a couple of years. However, the VFO wasn't compensated so that when you went to the sideband other than the "normal" for the band, your frequency was shifted about 3 KHz. Of course this was the "A" versions of the mono-banders. The Central Electronics rigs did have the ability to change sidebands. However, the National NCX-3 used the old 9 MHz SSB generator and the 5 MHz VFO trick to get 75 and 20 meters. 40 meters was accomplished by a 2nd oscillator (crystal controlled) that mixed with the VFO to allow the mixing product to come out to 7 MHz. Since it was a bare minimum SSB transceiver, you had only one sideband (no provision was made to get to the other sideband).
Although rigs that could transmit both sidebands were available in the late 1940s and well into the 1950s, the "convention" of lower sideband on 160, 75, and 40 meters and upper sideband on 20 meters and higher frequencies had already been established. Today it is most certainly possible to use either sideband on any amateur frequency. But, most amateurs adhere to tradition and keep the sidebands per the convention.
Many rigs today still use the VFO frequency in the 5.0 to 5.5 MHz range. This is why a number of them have problems getting onto the new 60 meter band. The VFO frequency is too near the desired operating frequency!
09-24-2003, 08:51 PM
I guess that they had too many surplus MC-300 and MC-400 filters: LOL
For those that aren't knowing what I am talking about, these were very popular SSB super group modems used by Ma Bell, and others. They used a 5.2 MHz LO and lattice filter.
09-28-2003, 01:54 AM
""""Just a friendly reminder, the current regulations only allow for one sideband to be used, as well! Be very careful, we don't want to lose what precious little we have gained by improper operation!""""
09-28-2003, 04:18 AM
He was referring to the "new" 60 meter band where upper sideband is the ONLY mode that is allowed. Also, you are not allowed more effective radiated power than 50 watts into a dipole. Also, your bandwidth cannot exceed 2.8 KHz maximum.
09-28-2003, 04:38 AM
I believe he's referring exclusively to the channelized 60M band. There's very little breathing room there and if you plan to operate in that spectrum you better have your ducks in a row.