Thanks Peter,. I'd wondered why resolving DSB with a DSB receiver was problematic but your diagrams made the reasons obvious. The inverted audio is a neat workaround. While the Si5351-based rigs with microcontrollers are great, the simplicity of a DSB rig has lots of appeal.

Peter: You have long been one of the leading gurus on DSB. I remember absorbing all the info I could from your website when I was getting started in DSB back in 2001. It's great that you found the article about DSB with inverted audio. It would be very cool to build a transmitter with the inverted audio, then confirm that it could be received with a direct conversion receiver without distortion. The incompatibility of DSB TXs and DC RXs seems like a very cruel trick of nature. There are only a few people in the world who think about this, and most of them are in the comments section of this KZfaq video! An elite group indeed. Back in 2015 your review of a DSB rig got me thinking about this incompatibility: soldersmoke.blogspot.com/2015/07/peter-parker-reviews-dsb-kit-and.html It is easy to see how a slight frequency difference between TX VFO and RX VFO would cause a lot of distortion, but similar distortion would be caused by a phase difference between the two VFOs. AM SW Broadcast receivers try to minimize the effects of fading by using an internal oscillator to replace the wavering carrier -- but they have to have it exactly on frequency and locked in phase with the distant station's carrier. I have a little Sony portable that has this "synchronous detection" circuitry. It is a complicated task and I don't think you could do it with the highly suppressed carriers of our rigs. Inverted sidebands to the rescue! Thanks for the great video and all the tribal knowledge. 73 Bill N2CQR

Hello VK3YE nice trix to simplifie circuits, very nice to read your videos always good luck from SM6AAL in Sweden!

Interesting video Peter.

Damn, that's a neat trick! I'll have to test this and see how easy it would be to push this into a simple DSB rig with synthetized LO as a feature. The inversion LO could be derived from the MCU controlling the synth. Ofc at that point the desire to do the inversion completely on TX in the MCU digitally intensifies. Seen some attiny based inversion voice scramblers out there.

Peter, you have an eye for some very interesting and unusual material. So if commercial crystal filters and the predominantly US and Japanese amateur radio markets had not taken off around this time, audio-inverted DSB might have been widely used for a period. Thanks for sharing.

In practice it requires less components to build a simple RC phasing audio network with reasonable, though not perfect 90 degree I and Q modulation to a simple diode balanced modulator, than to invert the audio, (And still end up eith 2 side bands). Even with a simple 4 component 90 degree audio phase shift network with about 90 per cent unwanted sideband rejection, you only waste about 10 per cent of transmit power, not half. Less than 1db lost. Especially if you also roll off the lows below about 300 Hz. Even a 20 db sideband rejection (easy to do) only 1 per cent of your precious QRP power is wasted. In practice 30 to 40db is the average suppression. (Think BW 2Q4/350 network. Only 4 capacitors and 4 each 1 % resistors.)

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SSB is better than DSB because you put all the power in just 1 side band. At equal power, you double the output in just SSB. In double sideband you are duplicating the information.Using the same bandwidth of the two sidebands you can create a single sideband with twice the width at the same power. Creating a high fidelity transmission at the same power of lo-fi DSB There is no point to better the DSB. DSB is also banned in several countries. You simple use an SDR connected to your receiver and tune as you like. In the Widht you like. With all the DSP filters you like. Or just use an smartphone.