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Author Topic: Sherwood Engineering Receiver Test Data  (Read 2263 times)

N0GV

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Re: Sherwood Engineering Receiver Test Data
« Reply #105 on: April 07, 2021, 06:18:17 PM »

To K6BRN - Hi Brian, great to see that you have been working on the SDR stuff so long and hard. Most folks don't realize just how small a community the RF world really is.

My only ask here is -- can we manage to bump up the Air Spy HF+ to a slice size of 10 MHz and bit depth of 20 bits while keeping the price under $500? That is a tight design and price point. Sure, we might not have the 110dB of 2 kHz DR but 90 dB would be adequate at that point and we would be able to monitor about 1/2 the HF band at a single shot.....

Sorry I can't help with the SDR side of things, I've spent my professional life in the LNA/Freq Agile/superduper small signal realm where NF< 0.25 dB has real utility.....  But I am absolutely fascinated by the possibilities of the SDR radios......

Currently sort of contemplating my navel about a Quantum receiver using magnetic flux quanta....

Anyhow, the discussion here I view as useful, whenever two folks with a common interest argue about how to get to a common goal it has been my experience that good things come of it!

All the Best,

Grover
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K6BRN

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Re: Sherwood Engineering Receiver Test Data
« Reply #106 on: April 07, 2021, 08:29:13 PM »

Hi Grover (NG0V):

Quote
My only ask here is -- can we manage to bump up the Air Spy HF+ to a slice size of 10 MHz and bit depth of 20 bits while keeping the price under $500?

No.  Not today.  And not with all complex DSP done in a desktop/laptop with samples transferred via USB.  Way too slow.  Complex preprocessing will need to be done in an FPGA.  So - a different and more expensive architecture is needed compared to current USB dongles.

The Icom IC-7300 is probably pretty close to what you are asking for, though.  The ADC does not have 20 ENOB and the digital IF output is narrowband - but it's a fun and cost effective transceiver anyway, that works well under most conditions - plus it has a great user interface.

(No, I don't own one - but I have used one)

Quote
I've spent my professional life in the LNA/Freq Agile/superduper small signal realm where NF< 0.25 dB has real utility.....  But I am absolutely fascinated by the possibilities of the SDR radios......

Interesting - because the two (low NF and DSP) are tightly linked in LPI systems of many types.

Quote
Currently sort of contemplating my navel about a Quantum receiver using magnetic flux quanta...

If you enjoy studying quantum phenomena, check out the latest published work in secure photonics systems.  Fascinating field.  Might be worth a look.

Best Regards,

Brian - K6BRN
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W6RZ

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Re: Sherwood Engineering Receiver Test Data
« Reply #107 on: April 07, 2021, 10:00:25 PM »

There are higher end USB 3.0 SDR's that can do wide bandwidth. Here's a video of an Ettus B210 showing all the smart meter traffic in the entire 33 cm band (902 to 928 MHz).

http://www.w6rz.net/902-928MHz.mp4

It's a little expensive at $1472

https://www.ettus.com/all-products/ub210-kit/

Here it is transmitting a 30 MHz wide DVB-S2 signal.

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K6BRN

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Re: Sherwood Engineering Receiver Test Data
« Reply #108 on: April 08, 2021, 09:50:46 AM »

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There are higher end USB 3.0 SDR's that can do wide bandwidth.

Perhaps.  But not in the sub-$500 range and not without significant pre-processing in the receiver and TX chain outside of PC.  The DVB waveform has many, many ready-made mixed signal/DSP ASICs "off the self" for embedment into OEM products.  So I'm not sure what the point is.

And in that sense, it's just another version of the Flex-6600,  IC-7300, IC-9700, etc., except thay are not DVB chipset based and are optimized for HF/VHF, etc.  But they are "SDRs" as well, with USB ports.  And go for quite a bit more than $500, too.

With the right FPGAs/ASICs/ADCs/DACs, GHz of bandwidth are not only possible, but commonplace.

Brian - K6BRN




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W6RZ

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Re: Sherwood Engineering Receiver Test Data
« Reply #109 on: April 08, 2021, 10:40:34 AM »

There are sub $500 options.

https://www.nuand.com/bladerf-1/

https://www.nuand.com/bladerf-2-0-micro/

I only mentioned the Ettus product because that's what I have here. They're a division of a larger company (National Instruments), so there's a premium because of that.
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W6RZ

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Re: Sherwood Engineering Receiver Test Data
« Reply #110 on: April 08, 2021, 11:17:50 AM »

An x86 processor is a formidable DSP. With all the vector instructions that have been added over the years, it can do amazing things.

For example, you can have a 20 MHz LTE base station running with the devices I listed and a PC. Of course, you can't do that in a ham band and work with a regular phone.

But I'm hoping that software for a TDD eNodeB version will come along. That would allow phones with LTE band 42 to work in the 3400 MHz ham band. Imagine being able to attract kids to ham radio where their first radio is their IPhone.
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N6YWU

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Re: Sherwood Engineering Receiver Test Data
« Reply #111 on: April 08, 2021, 11:29:45 AM »

My only ask here is -- can we manage to bump up the Air Spy HF+ to a slice size of 10 MHz and bit depth of 20 bits while keeping the price under $500? That is a tight design and price point.

A LimeSDR Mini can stream a bandwidth of over 10 MHz (using USB 3.0), full duplex (e.g. including Tx), and cost under $200.  My M1 Mac can easily run FFTs on a 10 Msample/s stream in real-time.  Probably one of the newer iPads could as well.

The LimeSDR Mini ADC bit-depth is only 12-bits though, and it's not very sensitive on HF, in my preliminary testing.  (I purchased one for use as a signal generator).  Probably needs an external LNA.

But that means it's possible once the cost of ADCs with higher bit-depth comes down.
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N6YWU

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Re: Sherwood Engineering Receiver Test Data
« Reply #112 on: April 08, 2021, 11:45:17 AM »

Is that the discovery you are talking about or the older radio?

I'm talking about the Airspy HF+ Discovery.

Quite a bit of marketing jargon around this radio, too, such as "...polyphase harmonic rejection structure..."  That would be a digital (probably FIR) filter similar to those found in every receiver with digital processing.  "No filter, no work!"

It's not the filter, it's the mixer.  A polyphase mixer is like a Tayloe IQ/quadrature (e.g. 2 phase) mixer, except with more than 2 phases (thus the "poly") to reduce harmonic pass-thru.  But a Tayloe switch style mixer does usually include some filtering embedded after the analog switch matrix.
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K6BRN

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Re: Sherwood Engineering Receiver Test Data
« Reply #113 on: April 08, 2021, 07:17:09 PM »

So you're saying that the FIR filter after the mixer is the "polyphase harmonic rejection structure..."  which is a filter.  In this case, a cleanup filter. Ohooo Kaay...

I'm still wondering why this is considered remarkable.

Brian - K6BRN
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N6YWU

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Re: Sherwood Engineering Receiver Test Data
« Reply #114 on: April 08, 2021, 07:37:29 PM »

So you're saying that the FIR filter after the mixer is the "polyphase harmonic rejection structure..."  which is a filter.  In this case, a cleanup filter. Ohooo Kaay...

I'm still wondering why this is considered remarkable.

Not the "cleanup" filters after the mixer, but the mixer itself does not pass thru certain harmonics (or they are strongly attenuated) by the multi-phase mixer (unlike 1 or 2 phase switched mixers, which pass all odd harmonics), before the analog filtering and sampling to digital.  (Any DSP filtering comes much later in software.)

It's slightly remarkable because it seems to be rare in low-cost implementations, which mostly only use two-phase IQ switched mixers.  (My guess is that the generic idea might date back to the days of mechanical rotating commutator mixers back in the day of spark gap stuff.)
« Last Edit: April 08, 2021, 07:40:12 PM by N6YWU »
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