I recently became aware that there are companies selling Double Side Band radios for use on digital HF frequencies (FT8 specifically) on 40m, 30m, and 20m. In this post we’re going to take a look at what these rigs are, what they were originally designed for, and then you can decide whether these should be used for digital communications on HF.
Disclaimer: I don’t own a digital DSB rig. This post is intended to discuss the realities of such a design so that somebody looking to purchase a starter radio is completely informed of what they are getting into.
What is DSB?
Double Side Band describes an AM radio transmission which has had its carrier suppressed (aka filtered out). That means that only the sidebands are amplified, which in turn means that the transmission is 1/3 more efficient, because 1/3 of the useless signal isn’t transmitted. SSB (Single Side Band) goes a step further and filters out the redundant half of the transmission yet again, and so 2/3 of the original waveform is cut out, leaving a Single Side Band. This is what we’re accustomed to when communicating in most HF modes. Double Side Band foregoes the added filtering and still puts out everything but the carrier.
Why DSB digital?
Among the vendors who are selling kits for DSB Digital transceivers, at least one of them references Peter Parker’s (VK3YE, not Spiderman) Beach40 design as a design inspiration, But let’s look at what Peter actually says that the Beach40 was for. This is taken from his website and is for reference only. I hope you don’t mind, Peter!
It’s a project for the tinkerer… if you’re not quite ready to assemble an SSB transceiver, give this simpler DSB rig a shot.
Peter Parker VK3YE on the Beach40 transceiver project
You’ll notice that it’s not intended for anything more than a project for a homebrewer– somebody who intends to build radios from scratch- to get on the air with without having the complexity of a SSB transceiver, and ostensibly to eventually graduate from. So, why are vendors putting out DSB digital transceivers that are solely intended for digital communications?
These digital DSB rigs are apparently intended to lower the cost and complexity of a transceiver by omitting the sideband filter and the alignment that goes along with it, and just transmitting both sidebands regardless of whether this is needed.
Is DSB good for Digital modes?
I’m not going to come out and tell you whether you should think DSB digital is bad or not. Instead lets look at some facts about DSB, and then you can determine this for yourself.
Extra Data Transmission
A SSB transmission is 3khz wide, but a DSB transmission is twice that at 6khz. When an audio signal is transmitted at say 1500hz, its opposite is transmitted at -1500hz. Thus you have two signals being sent but only one is needed.
Take for example 7074khz and 7078khz. These are the FT8 and JS8Call frequencies commonly in use. If you’re transmitting a signal on 7078khz, at 1500hz, then you’re outputting TWO signals: One at 7079.5khz, and one at 7076.5khz. Only the Upper Side Band can be decoded, because the Lower Side Band at 7076.5khz is technically “reversed” and cannot be decoded. So, if you were using one of these rigs for JS8Call, the FT8 crowd might not appreciate it very much. But there’s a catch.
You can’t use these rigs for JS8Call, because they are crystal controlled. They are not frequency agile. They can only be used for FT8. This is of course unless you go to the trouble of finding other crystals and figure out a way to switch them out.
How does power output look? They tout about 3W of DSB output on 40m, but that’s DSB output. That’s 1.5W per side band. And since only one sideband is useful, effective wattage is half that listed.
There is one other thing to consider: The receiver lacks filtering as well. That means that you’re effectively doubling the receiver bandwidth, which reduces sensitivity by at least 3db.
Counting the Cost
Lastly, there is cost. These digital DSB rigs are selling for about $40. That’s definitely cheap, but is it a value? For $59 and a little bit of hackery you can have a BITX40 that is frequency agile and can be used on any digital mode or with voice, is Single Side Band and puts out 5-7W.
Now that the BITX40 is gone, the perceived value does go up a bit. It is an inexpensive entry into ham radio, and as an owner of QRP Guys pointed out below, it’s good for experimenting and learning with.
What do you think? To digital DSB rigs belong on the air? Let us know your thoughts in the comments below.
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I’m building this one Ryan:
https://qrpguys.com/digital-transceiver
Author
Hey Terry, please report back your results. I’d love to hear your impression of it!
Actually you can use it for JS8CALL, if the frequency is not currently in use. No one owns a spot on the dial. Most hams can find and change out a crystal, especial one they put on the board themselves. I have watched the BITX groups for a while and the BITX40 kit has a lot of issues and a lot of fixes. It’s a hobby people, let’s stop getting excited and thinking ever new thing that comes alone is going to be the end of the hobby. I am sure the cw people cursed the am crowd when they showed up.
I have purchased two of these boards. I planning on testing them side by each into dummy loads at first. Then it looks like probably 7.110 for JS8CALL.
Author
You’re right, it’s possible to use JS8Call, but not on the default frequencies. Also the BITX40 has far fewer issues than the uBITX and is cheaper too. It’s a great radio. I’d love to hear how your experiments turn out.
Probably illegal in the USA in the CW and narrow bandwidth data bands. It would have to be used in the voice bands. It’s putting out a 6khz wide AM suppressed Carrier. AM is not legal in the Narrow data bands.
Author
The general consensus is that the legalities aren’t an issue, but this post is rather focused on the technical aspects: Low power output, poor sensitivity, etc.
We put out the kit as a low cost way to try ft8. It’s not intended to be a full featured rig that you will use all the time, but as a platform for experiments and tinkering, just as Peter said. It is entirely legal to operate dsb digital in the cw band, just like it is legal to operate ssb digital there. There will be far less interference from a 1 Watt DSB signal running FT8, than there will be from a 100 Watt SSB station running FT8. If you want to experiment and try the mode of FT8, and have a choice of 3 bands, the Qrpguys kit is a bargain.
Disclaimer. I am a co-owner of Qrpguys.
Doug KI6DS
Author
Hi Doug,
I applaud you for commenting here. I want to be clear: There’s two sides to this story, and both sides have merit. It’s obviously caused a lot of controversy. As a learning tool, I agree that it has quite a bit of value. You also make a great point about 100W FT8 signals. They splatter so badly!
Hi Doug, I have seen the kit in person as you showed it to me! The production quality is excellent, regardless of the debate over the mode. My comments on this now, as previously, are not intended to refer to yours or any particular kit, they are purely technical in nature relating to DSB and digital modes DSB generally.
Regarding your comment “There will be far less interference from a 1 Watt DSB signal running FT8, than there will be from a 100 Watt SSB station running FT8.”… I think this is wrong. 1W is 20dB down on 100W. I have never heard of an SSB transmitter whose unwanted sideband is at only -20dBc. Typical would be -60dBc or better. In that case, 1,000,000W of SSB would be required to produce 1W in the unwanted sideband. “Splatter” also cannot be an issue since the usual IMD3 performance of linear power amplifiers is around -30dB; even this requires the presence of two tones, but FT8 is only a single tone so any transmitter non-linearity has nothing else to intermodulate against.
73 Hans G0UPL
Hans, I am referring to the amount of bandwidth taken up by the 100 Watt signal. There is a ham close to me who totally overloads my receiver when he transmits at 100 watts. He never hears me, but he certainly affects my reception. I don’t see the need for anyone ever to use 100 Watts for FT8, yet I know guys who use a Kilowatt. My point is that I just don’t see DSB causing a problem at 1 Watt. We did the transceiver as an experimental project, for hams to be able to try FT8 without a huge expenditure. We chose DSB because it was cheap, easy and LEGAL to do. Most of the complainers don’t seem to realize that it is 100% legal to transmit DSB FT8 according to FCC rules and regulations in effect today. That may change, and if it does, we would abide by those changes. It is a fun project, it works, and you will make contacts with it.
Author
Yeah I think the main point is that the folks who plug in a rigxpert to their radio and just start operating are not doing any favors with their highly overdriven audio splattering all over the place. It’s possible to run 100w properly, but most don’t.
Hi Doug,
I have no doubt about legality and am not commenting on your transceiver in particular. Just making technical discussion on DSB and other misunderstandings.
Watts don’t take up bandwidth. The mode being transmitted is what takes up bandwidth. An unmodulated carrier has zero bandwidth regardless of the power being transmitted. In this regard FT8 (done properly on SSB) is fairly innocent as it occupies only 50Hz which is relatively narrow. I’d estimate around 90% of QSO partners I encounter on CW are using around 100W and CW is also quite narrow.
Improperly done SSB, if the volume sent into the SSB transceiver’s input is too high, will cause clipping and the audio harmonics will tend to inter modulate with each other. This is an improperly setup transmitter – and is nothing to do with the power level nor the mode.
Properly adjusted equipment having suitable performance should be able to operate in reasonably close proximity to each other, such as on the same site at field day.
I have no doubt your 100W nearby ham is much more likely to cause you trouble, than your 1W causes him. Assuming you are both using FT8 on the same band, you are both within the same SSB channel so splatter has nothing to do with this. Two possible causes exist for the interference he causes you: his transmitter and your receiver. Your receiver is the place to start, both because you have most easy access and control over it, and because it is the most likely cause of the problems. Your close-in within band dynamic range is the crucial performance characteristic here. If the receiver you are using is your SA602 then you can totally expect to have problems: the SA602 has well known limitations on dynamic range and IP3, and your filtering ahead of it is also very limited. Poor phase noise performance of oscillators is also a possible culprit, in this regard in sure since your SA602 transceiver is crystal-controlled it probably has good phase noise performance. The nearby ham’s transmitter phase noise can also be a problem if it isn’t at a good low level.
Even if everything is excellent… I suspect operating near a 100W transmitter spaced only some hundreds of Hz away from you is always going to be challenging. The same would apply to CW or any other mode. But at least in CW, SSB etc you could move many kHz away from each other. Then this is a limitation of FT8 generally perhaps. The fact everyone is close to each other, makes it difficult for nearby stations to coexist on the same band. Every mode has advantages and disadvantages and I guess this is one if the DISadvantages of FT8.
Vy 73 de Hans G0UPL
You wrote: “That means that only the sidebands are amplified, which in turn means that the transmission is 1/3 more efficient, because 1/3 of the useless signal isn’t transmitted.”
It is actually better than that. In regular AM with a modulation index of 1 (100% modulation), the carrier has 66.67% of the power, and the sidebands have 16.67% each. With lower modulation indices the power in the carrier goes up at the expense of the sidebands.
Jeff aa6xa
This is a hobby and as I have said before again and again “It is cheaper than a psychiatrist and less trouble than a mistress”. This wonderful hobby has been my “out” for over 60 years and saw me though all the problems and issues of life. I have built most of the QRP Guys kits (thank you Doug!).
I was in a slump and wanted to build something new and connect it to my shack lap top for digital, something I have never done before. It was inexpensive, it worked, and has become a center point in our radio club as another member had just built the D4D DSB xcvr and was experimenting with that. We (I and other club members) are having fun, not clobbering the bands with useless kilowatt chatter, not interfering with anyone, and learning new things.
My DSB rig will no doubt go on a shelf and I will change over to a Signal Link (I picked up at a swap years ago but was afraid to try) and another better xcvr soon now that I know more about FT8 and the digital modes. My self confidence about digital and my own abilities are restored or at least improved. I think Doug and The QRP Guys achieved their goal all for $40.00.
This IS a HOBBY (look up the definition of a hobby) and it achieved its goal at least in my life. Thanks for all the comments (I read them before writing this). I have learned something, spent little, came away with a smile, and go on, hopefully to encourage others in our club to do the same. Are we having fun yet? I am!
Dave K8WPE since 1960
But is it legal?
A pure audio tone into an SSB signal is a CW signal, A1 when I was a kid. A pure AFSK signal into an ssb transmitter results in an FSK signal, F1. You can’t tell the difference from a CW transmitter, or a transmitter where the oscillator is shifted between discreet frequencies.
DSB until now has meant analog. AM with carrier is allowed, so is DSBsc, as well.as SSB, and probably variants like two sidebands with reduced carrier or SSB with full or reduced carrier.
The premise seems to be that since DSB is legal, this is legal.
But this isn’t a DSB signal. It’s FSK with a duplicate signal the other side of zero beat. I’m not sure how that classifies. (If your CW transmitter put out two signals, it’s not legal. If you don’t feed a pure audio signal into an SSB transmitter, yiu don’t get CW or FSK, it becomes something else, probably not legal.)
Aside from that, a problem with DSB is the need to have the reinserted carrier exactly between the sidebands. Otherwise that 1KHz audio signal translates to 990 and 110 KHz at audio, where they clash. Which is why DSB has generally been seen as a “poor man’s SSB”, and expecting reception on a good SSB receiiver, which turns the DSB signal into SSB internally. Or a synchronous detector that gets information from both sidebands to know where to reinsert the carrier.
DSB used to mean high level modulation, convert an AM transmitter so the balanced output stage acts as a balanced modulator. Nowadays, it almost always is an NE602, followed by amplification.
Two high level balanced modulators and a quadrature RF source, and you get SSB. A computer provides the quadrature audio signal. Since a computer is needed for this anyway, a tiny bit more circuitry gives you a proper digital signal, and SSB to boot.
This isn’t 1971 where people studied for the US novice license and built a one tube transmitter to get on the air. People come into the hobby in a radically different form, so isn’t it more likely the technically minded have the background to go more complicated than “simple”? Yet we still try to sell “simple” with all the limitations.
Dsb is good on the phone bands. Yes this is a hobby,but a hobby that blends into professional careers and activities. Gov set this “hobby ” up for a pool of trained operators due to war time conditions,etc. Not exactly totally “hobby”. Now it is totally hobby except for skywarn, ARES,MARS,Its our duty as a licensed amateur radio operator ,no matter what your license class, to practice good operating ethics and technical ability to repair and or build such equipment without money being exchanged for our services, and to advance the technical aspects of radio technology as a whole.dONT FORGET,WHAT YOU SEND OUT CAN INTERFERE WITH OTHER SERVICES USING BAD OPERATING PRACTICES.
DSB can be a good mode in the PHONE bands. it has no use in narrowbanded digital modes.1 watt? ive worked many countries with 1/2 watt.when you have alot of operators on ft8 running dsb there is going to be interference to others.Period.With all the new technology on the market like arduino,rasberry pi,etc, Why build a rig that WILL interfere with another ham. Its our duty to make sure we use the least power, and the least bandwidth to make a contact. We as a community in general need to push for the cleaner signal also.Some kits are full of junk on the output.IF YOU ALL THINK ITS OK TO INTERFERE OR WALK OVER ANOTHER HAMS TRANSMISSION, GO TO CB.IF YOU ACTUALLY TAKE PRIDE IN BEING A PROUD MEMBER OF AN ELITE GROUP OF PEOPLE WHO HAD TO STUDY AND LEARN ELECTRONICS,OPERATING LAWS AND PRINCIPLES AND REALLY TAKE TO HEART WHAT THE RULES AND REGULATIONS MEAN, THEN WELCOME FELLOW HAM. YOU WILLHAVE A SIGNAL THAT WILLBE CLEAN OF HARMONICS AND SPURS THAT ARE DOWN BY SO MANY DB. YOU WILLBE MINDFULL OF OTHERS FIRST BEFORE TRANSMITTING. YOU WILL LISTEN AND THEN LISTEN AGAIN BEFORE YOU KEY YOUR MIKE OR CW KEY OR IN THIS CASE THE FT8 SIGNAL THRU YOUR TRANSCEIVER AND COMPUTER. YOU ALL WILL BE MINDFULL OF USING THE LEAST POWER ,AND THE MODE WITH THE LEAST BANDWIDTH. PERIOD.
dsb ,DONT CARE WHO IS BUILDING THE RIG, DOESNT BELONG IN THE NARROW BANDED DIGITAL SECTIONS. juST BAD PRACTICE AND SHOWS ALOT OF OTHER HAMS DONT CARE EITHER.
JUST MY OWN OPINION AND NOT OF STAFF AND MANAGEMENT OF THIS WEBSITE.
73
David
AC9XH
A1D is literally in the definition of data in Part 97. A digital mode using an audio frequency tone with A1D will have two sidebands and a carrier — three detectable signals, and perfectly legal.
If you make a DSB transmitter, you can send a data mode on it, or you can do phone. There are rules about where phone and data are allowed, but none that say AFSK over some other modulation somehow makes it not that modulating anymore.
Hmm, amidst all the yelling in your post, I think you may have forgotten the importance of homebrew and its place in the hobby. A DSB transmitter is an easy first step, that makes for a great proving ground for first principles before moving on to more difficult designs. To say no one should ever make one is to disregard its place in the pantheon of introductory projects going back decades.
Your same argument could be used to say no one should ever make an AM transmitter because it will knowingly step on someone’s SSB signal, being twice as wide.
I do totally agree that use of a DSB transmitter for FT8 or JS8 may be unkind on the bands. But there are many places where one can carve out some space for a digimode qso that won’t clobber people in some mode du jour watering hole.
Author
Thanks for the comments, Josh! Much appreciated. Yep, DSB is totally legal, no doubt about it. The post was meant to provoke thought about the subject- and it has! but please do check other posts on this site as well as the YT channel, homebrew is definitely our speed 🙂
This is old news and was discussed to death when the first DSB rig kit came out for FT8 and other digital modes two years ago. As better rigs come out these will be in the junque box. My two different kit rigs have sat on my bench for a year now and I can’t even give them away, at least to local club members. The digital modes use has exploded far beyond any ones expectations and kept a lot of old and new hams entertained during Covid. Hans at QRP Labs has come out with a better mouse trap and I expect more will follow.
I know my opinion doesn’t count. This is a hobby and a lot of folks are having fun even if the frequencies are tight.
Let’s Ham On my friends. This is a funner hobby with all the new stuff coming out. Like the SSB vs AM discussions I heard back in the 1950s and even 1960s this too will pass. Digital was fun for me for about six months and now I am on to other things that continue being fun. Some of it I can’t even spell, like Arudoeennow and some of the chips we need aren’t even available right now for building stuff….. but we will find a way around it. That’s the fun of this hobby. Nuff Sed.
I have been licensed for 61 years and hope the Good Lord gives me a few more years because it takes longer at my age to have the same fun I had as a kid. I am now tutoring an 82 year old dentist in the hobby and he is asking questions I have to study to even give him a decent answer. Fun? You betcha!
Dave K8WPE
[…] we looked at a digital DSB transceiver kit for FT8 that’s been making the rounds, and talked about the pros and cons of such a design. […]