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Saturday, May 4, 2019

SDR vs. HDR - Is the Superhet Dead?


Pete N6QW had this very interesting video about Software Defined Radio on his blog.  Thanks to G3WGV for putting this presentation together. 

It is very interesting, but -- for me -- it is also troubling.   I think something important is being missed in this discussion. You have to listen carefully, but if you do the thing being missed becomes apparent. 

Like many others, G3WGV asserts that very soon, 100 percent of commercial radios will be SDR.  Traditional superhet radios will be a thing of the past. 

OK, but I will make a parallel assertion:  Looking ahead, I think 100 percent of TRULY homebrewed rigs will be HDR.  

Of course, this really just comes down to how you define "homebrew."  I'm a traditionalist here.  I think of homebrewing as actually building -- from discrete components -- all the stages that send or receive radio signals.  By my definition, I don't think you can really "homebrew" an SDR radio.  Taking an ADC chip and connecting it to a computer running SDR software is not -- by my definition -- homebrew.  Even if you wrote the software yourself, writing code is not the same as wiring up all the stages that go into a superhet-style transceiver.    

There were a few lines in G3WGV's talk that seemed to confirm this difference:  The SDR radio is defined as a "server." Commercial manufacturers like SDR because they can use the same components that go into cell phones (exactly -- and people will soon have the same relationship with these "radios" that we have with their cell phones). 

I kind of grimaced when G3WGV described the two sets of users of SDR technology: the "early adopters" who are "technology enthusiasts",  and the "pragmatists" who don't care what's in the box -- they just want to talk on it.  I think "pragmatist" is a nice way of saying "appliance operator." Even the "early adopters" are pretty far from the world of traditional homebrew.  And for me that gets to the point that is being missed in all this -- this shift away from hardware is also a shift away from homebrew.   

But hey, this is a hobby.  To each is own!  Have it your way.  For myself, I plan to continue with the hardcore, radical fundamentalist, hardware-defined, discrete component, fully analog homebrew radio.  This morning I am attempting to stabilize a cap and coil VFO.  And I'm liking it.  As the world shifts to SDR, I look forward to the appearance on e-Bay of massive quantities of old forsaken HDR rigs.  We will buy them for pennies on the dollar and use the parts for new HDR Superhet rigs.  

Viva  E. Howard Armstrong!   Viva!   






12 comments:

  1. The analog vs digital debate is as old as both have existed. But I think you’re looking at it from a singular point of view based on what you enjoy doing. I’m a designer of electronic musical instrument (both analog and digital) and a ham. I love analog circuits but in almost every way digital technology is more powerful and flexible. I’ve been working more and more with DSP coding and find it a lot more creative and expressive than anything I could do with discrete parts. For non-programmers I can see this might seem daunting, but the great thing about code is that the results are predictable and repeatable and the performance is not affected by real world limitations of components. For instance the dynamic range of a typical floating point number is far greater than any circuit that could ever be made.

    I would say keep making superhet radios... they are certainly elegant and beautiful. But don’t look at DSP as the enemy... it’s really an incredible technology they had tons of potential for ham radio. It’s still creative and hackerish but it’s just a different kind of hacking than building analog gear.

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  2. superhet is great and all but so was analog tv. I know I like the new 1080p video on TV so I know I won't be going back to an analog tv with a set top converter box just so I can stay with the old technology. And SDR while not 'old school', lets us experiment with new modes very easily. I know, I did drink the cool-aid and bought a flex 6700. Let me see you open 7 different receivers on a kenwood, icom, yaesu at the same time. Or let someone else use your radio at the same time you do....It is futile to resist Bill, in the end, you will be assimilated .....mz lowell indiana

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  3. When some people say they enjoy travelling they mean they enjoy visiting different places; the journey is just a means to an end. For others it’s the actual journey they enjoy, perhaps more than arriving at the destination. Ham radio is a hobby, something that is about enjoyment, fulfilment and personal development - for some that’s about operating - that’s their destination and they want to get there as quickly and efficiently as they can. But for some of us it’s in the journey to a working radio that we find our fulfilment. Just like the person who gets a kick from walking a journey that the majority might do by air, I get a kick from working out how I can get this particular handful of components to communicate with someone perhaps on the other side of the world. I enjoy thinking about it, I enjoy sketching out ideas, I enjoy trying them out on LTSpice and, of course, I enjoy making magic smoke as I try them out for real. For me, the fun is not in the arrival - in just operating the appliance (to be honest that can be an anti-climax) - it’s very much in the journey. SDR might present us with cutting-edge technology to do communication - and, yes, they’ll be some who get the same sort of thrill from working on the code - but for those of us for whom trudging barefoot through the radio landscape is our excitement, the superhet is not dead, neither is TRF or direct conversion. I’m happy to let some travel in the fastest and easiest way money can buy, as long as there’s room for me to trudge along with my handful of discrete components. In the end, it’s not a case of my way is better than yours, or this way is out-moded - it’s more a case of whatever floats your boat is ok!

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  4. All the cool and interesting parts that will advance the homebrew art are SMD and as such homebrewers are going to have to embrace ecad and board manufacture to continue to move homebrew forward.

    There will always be some who will want to make a superhet with whatever popcorn parts are available, I have been collecting popcorn for quite some time for that very reason, but if i really want to take my basic designs and make them better, I am going to have to embrace new technology. Relays or diode steering, sure you can do that, but they have rf switches that do the job better and with less loss, but they are SMD.

    FPGA are becoming cheap, wont be long before someone in the ham world implements a complete IF stackup in one, microcontrollers are cheap and ubiquitous, 24bit adc dac are cheap for under $20 in parts you can do what Hans is doing in the QSX

    I wont go as far as saying the superhet is dead, but the simple rigs being made in 5 years time will probably not include a Xtal filter and will have some form of digital IF whether that is direct conversion to baseband or something else.

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  5. The bottom line is that SDR performs better, is an asset in combating local RFI and visually engaging. The discrete vs chip debate isn't healthy IMO. Solder Smoke should be embracing all aspects of home construction, no cleaving a rift between them.

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    1. I do not think Bill is trying to be divisive, its more or less just friendly banter among fellow builders and constructors.

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  6. Very interesting and this talk needs to be 'processed'. However, here are some points that have me curious:
    1. How do we achieve front-end filtering, harmonic suppression etc. on an SDR? We will still need banks of filters anyway. SDR doesn't solve this problem. In fact, undersampling only aggrevates this.
    2. As of now, the news of Superhet's death has been exaggerated. The best sounding radios are still superhets or direct conversion.
    3. The return of analog in the music world points us to a fallacy: Analog has infinite resolution, the digital is limited
    4. The trouble with digital stuff is that it works wonderfully, until it falls off the cliff, then nothing works. The failure is dramatic. If you overload an ADC, you are cooked. If you corrupt the SD card, your radio is a dud.
    4. Just like motor cars didn't kill the cycle, analog radios will continue. We are still pushing the envelope on crystal radios!
    Now, let me get back to laying out my raspberry pi based SDR, you think I have all day?

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  7. Let's not forget that this is the Soldersmoke Blog!
    I'm in it for the journey too - not the destination. At work I develop 'SDRs' for consumer cable and satellite receivers (Yes - ADCs with multi-GHz sampling rates in consumer products!). At home it's discrete - for the fun of it - and for the solder smoke!

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  8. Interesting thread and ideas.

    I've just bought a fully analogue radio (K2). The rationale behind this versus buying a commercial SDR or semi-DSP rig is that there is still an opportunity to fully understand the hardware and be able to maintain it in the future and learn something up front. When you have a full SDR rig, the majority of the functionality is 100% opaque and difficult to peer inside, modify, extend and even understand. I am a software dev by day and did a lot of embedded stuff in the past so this is familiar to me and it's not a life I want to live either. It's fraught with frustration and pain the moment you crack open even the best of vendors' toolchains.

    Also we're still not there. Taking the FT450D as an example, the IF in that is all digital once downconverted into I/Q signals. It's a remarkable rig for the money but it sounds like crap. I figured this was just a maturity issue, but nope I played with an IC7300 and it sounds the same. Awful. Ringy filters and everything sounds like gargling in a muddy bin the moment you want some selectivity. I'm sure our algorithms will mature and some of this will be resolved in the future but we haven't got anywhere near the output quality of a decent crystal filter yet.

    And lets not forget the amount of power the average SDR drags. Just the receive current on a FT450D is 1.1 amps. Same with the IC7300 (0.9-1.25A).

    I think the best use of computation here is still for control purposes at the moment. That means driving that VFO, band switching, keyer etc. Make the complicated things simple, not the simple things complicated.

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    1. Great points. I feel better about my extremism now. 73 Bill

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  9. The Odd Couple show comes to mind. Bill pontificating against SDR, and Pete embracing it.

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  10. In 1964, you could open 1ST and see a one tube transmitter, but you could also read about cutting edge parametric ampliflers. People had their Benton Harbour lunch boxes, but up there was mostly building and experimenting.

    73 had lots of construction articles, simple and complicated. CQ still ran theory and construction articles. A few year later, Ham Radio started up, more esoteruc, but not too far.

    Along the way, things changed. Technical was dropped, 2m fm became the entry point. Magazines died, and magazines dumbed down. QST shuffled technical articles off to QEX, so they were mostly invisible to most.

    That' s where your black box comes from. I can remember vague early articles about sdr, just text, no details. But they no.longer run next to articles about improving your VFO drift. I think the 1986 ARRL HANDBOOK has a chapter on DDS, but it's isolated. I think the 2001 HANDBOOK has a chapter on sdr. Both are mostly black box construction, isolated from the rest.

    For a long time, QEX subscriptions required a 1ST subscription first, making it costly. If I'm reading the ARRL site prooerly, that's no longer the case, so QEX is no longer more expensive than many magazines. So now is the time to subscribe, I'm.going to, so the black box is no longer so obscure.

    Michael

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