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Author Topic: In the age of "virtual technical parity" Do Specs matter anymore?  (Read 5584 times)
M0HCN
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Posts: 473




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« Reply #15 on: March 11, 2013, 10:56:39 AM »

At HF, it's more a case of 'as good as they need to be', rather than 'as can be'.
Indeed.
Quote

It will need either Polar Loop or Cartesian feedback - the latter is probably the easiest if an amplifier is to be added later, but needs some very good mixers in the feedback chain.
Cartesian is nearly trivial if you are doing DUC/DDC in the exciter, a phase offset added to the NCO in one path will correct the phase shift, otherwise switching mixers are impressive at the sorts of drive required to get a reasonable noise floor. I started off with an analogue design but had nightmares dealing with DC offsets so have now gone to a ADC/FPGA/DAC based approach, it has its moments, but overall I am happier with it.
 
In the case of a DUC/DDC design it helps to have a good shaped dither generator that can put the noise up above the LPF cutoff (And switched attenuators in both paths help as well), lots of gate array area, but helpful.

Polar loop is IMHO a bit of a nightmare for any modulation mode that crosses zero amplitude, like say SSB.....

73, Dan.
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G3RZP
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« Reply #16 on: March 12, 2013, 12:40:37 AM »

>Cartesian is nearly trivial if you are doing DUC/DDC in the exciter, a phase offset added to the NCO in one path will correct the phase shift, otherwise switching mixers are impressive at the sorts of drive required to get a reasonable noise floor.<

The guy I know who did one for professional applications didn't find them to be that good: to get the IMD and noise floor simultaneously was his problem. That was a few years back, admittedly, and he was at VHF, so switching times affect the IMD.

With careful design, you could do a pretty good job on an HF amateur rig.

Vlad Petrovic at Bath University originally did Polar Loop for SSB, back some 30 plus years ago, in the days when Joe McGeehan was the Professor. Provided you have enough gain, there's enough carrier leak to stop it unlocking.
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K0JEG
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« Reply #17 on: March 12, 2013, 03:33:03 AM »

The other question is, will the population support a company that takes a chance on a radical new design? The IF DSP was a no-brainer, but I remember a lot of complaining about audio DSP being inferior to other filtering techniques. But we had to get audio DSP to prove the concept and get some R&D started on how to improve it, which led to IF DSP.

SDRs are generally in the same boat. Look over in the QRP forum to see a very long debate over the merits of the KX-3 vs the FT-817. The KX-3 is a very popular radio, and a great leap forward in shrinking technology, but there doesn't seem to be enough of an improvement for a consensus. Why is the Flex radio still a niche product if it is so much better? It can't all be the way the company is run.

I think many people look at Moore's law and try to apply it to everything. While it does lead to innovation in just about all technological areas, physics and economics will grind innovation to a halt once you get past the silicon chip level. Why don't we have direct-sampling SDRs? The technology exists and has for some time now. Well, because the chips and real-time processing power are still at a price point that is too high for most amateurs.
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G3RZP
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« Reply #18 on: March 12, 2013, 03:23:53 PM »

Many years ago (almost 50!), as a young development engineer, I was told 'There are no prizes for vastly exceeding the specification'. It proved to be partially true in that case, as specs written for one technology didnt apply to another.....But it's a good start to a philosophy.
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K0JEG
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« Reply #19 on: March 13, 2013, 03:14:05 PM »

Many years ago (almost 50!), as a young development engineer, I was told 'There are no prizes for vastly exceeding the specification'. It proved to be partially true in that case, as specs written for one technology didnt apply to another.....But it's a good start to a philosophy.

You must not have worked for a audiophile-level amplifier company!  Cheesy
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G3RZP
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« Reply #20 on: March 14, 2013, 08:56:03 AM »

No, definitely pure radio - and HF at that!
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M0HCN
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« Reply #21 on: March 14, 2013, 12:08:01 PM »

'There are no prizes for vastly exceeding the specification'.
Agreed, but with the proviso that that applies in a design for production context. Sometimes, when doing r&d for your own use it can be fun (and educational) to see just how far you can push an idea.

73, Dan.
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TANAKASAN
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« Reply #22 on: March 14, 2013, 02:26:28 PM »

"Sometimes, when doing r&d for your own use it can be fun (and educational) to see just how far you can push an idea."

Oh yeah! Now why can't the majority of the amateur population think like that? As soon as I read that comment I was reminded of the 'Huff and Puff' oscillator stabilization system which started off as quite a complex piece of electronics and ended up as two or three chips.

“Everything should be made as simple as possible, but no simpler.”

Albert Einstein



Tanakasan
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K2GWK
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« Reply #23 on: March 19, 2013, 02:57:45 PM »

[I thought to myself,"Thanks to you politicians."

Don't forget to thank the business community (in particular the big box retailers) and consumers (who shop at big box retailers) while you are at it.

But I sympathize, it's difficult to consistently buy U.S. made goods, no matter how much one tries.

The problem is that most people can not afford made in the USA. It simply costs too much to make it here for many different reasons.
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