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 Post subject: Untested SSB SDR Idea. Any feedback or suggestions please
PostPosted: Jul Sun 11, 2021 9:30 am 
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Joined: Mar Thu 01, 2018 1:30 am
Posts: 820
Untested idea. Is it gonna work? Any feedback on design improvement or insight, why it would work or wouldn't work? Any modifications? I'm trying to design some ultra simple SDR transceivers with no SMD chips.


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 Post subject: Re: Untested SSB SDR Idea. Any feedback or suggestions pleas
PostPosted: Jul Sun 11, 2021 4:58 pm 
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Joined: Jun Tue 10, 2008 6:06 pm
Posts: 689
Location: San Antonio, TX
Isn't this still the "Antique Radio Forum"? WAY over my 80 years of experience! :roll:


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 Post subject: Re: Untested SSB SDR Idea. Any feedback or suggestions pleas
PostPosted: Jul Sun 11, 2021 6:30 pm 
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Joined: Mar Thu 01, 2018 1:30 am
Posts: 820
rxradio wrote:
Isn't this still the "Antique Radio Forum"? WAY over my 80 years of experience! :roll:


This forum is rare one as many users here are very knowledgeable about everything RF, from novices to retired engineers having 30+ years of experience. In the past I've received guidance and answers to my questions. There is no other forum like this one!

I'm trying to cut down parts. This is supposed to be the heart of a SDR based SSB transceiver. Three transformers are doing the mixing! When you mix 0 and 90 degrees phases of RF and AF you get a single sideband signal. It's called the phasing method or direct conversion method. The software does the rest and is able to suppress the unwanted sideband by 60dB or more, no crystal filter or building a large complicated circuit is required!


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 Post subject: Re: Untested SSB SDR Idea. Any feedback or suggestions pleas
PostPosted: Jul Sun 11, 2021 7:37 pm 
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Joined: Jun Sun 15, 2014 5:37 pm
Posts: 1496
Location: Montreal, Quebec
The phasing method was used to generate SSB in 1948, and used as "signal slicers" to improve receivers around the same time.
I
That's 70 years ago, doesn't that make it antique?

An SDR is the same thing, except the audio phase shifting is done in digital.

But this won't work, no non-linear element to cause the mixing.


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 Post subject: Re: Untested SSB SDR Idea. Any feedback or suggestions pleas
PostPosted: Jul Sun 11, 2021 11:12 pm 
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Joined: Mar Thu 01, 2018 1:30 am
Posts: 820
SDR generates SSB with phase shift. This circuit is not exactly a mixer but two switches built around 2n7000 mosfet alternately muting the I & Q audio to ground in accordance with 0 and 90 degrees of LO drive. I've a hunch this might work but it's tricky and it will need many more tweaks.


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 Post subject: Re: Untested SSB SDR Idea. Any feedback or suggestions pleas
PostPosted: Jul Sun 11, 2021 11:48 pm 
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Joined: Mar Thu 01, 2018 1:30 am
Posts: 820
This is a proper design. How is it? I designed it last night with specific care to balance. The transmission line transformer at the output combines the two RF signals and also provide good balance.


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