SDRplay announces the RSPdx

Talk about other SDR products like the FunCube, HackRF, BladeRF etc.
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jon
Posts: 12
Joined: Sat Feb 14, 2015 5:14 pm

SDRplay announces the RSPdx

Post by jon » Sat Nov 02, 2019 9:28 am

SDRplay have announced the RSPdx:

The RSPdx is a replacement for the highly successful RSP2 and RSP2pro SDR receivers, which have been extensively redesigned to provide enhanced performance with additional and improved pre-selection filters, improved intermodulation performance, the addition of a user selectable DAB notch filter and more software selectable attenuation steps . The RSPdx , when used in conjunction with SDRplay’s own SDRuno software, introduces a special HDR (High Dynamic Range) mode for reception within selected bands below 2MHz. HDR mode delivers improved intermodulation performance and fewer spurious responses for those challenging bands.

The RSP2 and RSP2pro design is over 3 years old now, and so the RSPdx has taken advantage of a lot of the learning from our work on the newer RSP1A and RSPduo designs as well as ongoing feedback from customers.
The datasheet for the RSPdx can be found here: https://www.sdrplay.com/resources/RSPdxDatasheet.pdf

These three videos give more information as follows:
This introductory Video shows the features and demonstrated the RSPdx in action over a wide range of frequencies: https://youtu.be/lyaLm5cGJU0
This unboxing video talks some more about what you can expect to see and some of the key benefits: https://youtu.be/ibGAkpfpM7E
Over on the Hamguides YouTube channel, Mike, KD2KOG introduces the RSPdx and looks forward to receiving feedback on ideas on where you’d like more video guides: https://youtu.be/ypb3YvhZf6E

In the coming weeks, links to more demos and articles relating the RSPdx will be added to our apps and support catalogue: https://www.sdrplay.com/apps-catalogue/

The pricing for the RSPdx will be similar to the RSP2pro (approximately $199 USD or £159 GBP excluding taxes) and the current schedule is for units to be available from around 22nd November – either direct from this website (click on purchase) or from our authorised channel partners and resellers: https://www.sdrplay.com/distributors/

aurgathor
Posts: 87
Joined: Wed Apr 25, 2018 8:14 am

Re: SDRplay announces the RSPdx

Post by aurgathor » Wed Nov 13, 2019 1:50 am

Why did you switch away from the Hi-Z input?

radiolistener
Posts: 58
Joined: Thu Jan 25, 2018 10:48 pm

Re: SDRplay announces the RSPdx

Post by radiolistener » Thu Nov 14, 2019 9:19 am

aurgathor wrote:
Wed Nov 13, 2019 1:50 am
Hi-Z input?
"Hi-Z" is a marketing thing which is usually used for bad design RF frontend.
The same thing with "14 bit" taken with decimation and which works worse than 8 bit ADC from RTLSDR.

The only good thing of these RSP is 8 MHz bandwidth. All other things are just marketing.
If you want better reception quality, I recommend to use RTLSDRv3.

Just look at their datasheet: "good / best / good"
Did you ever seen such "good" and "best" specifications in real component datasheets? :D

Just imagine, you're opening some LDO datasheet and see that bullshit:
Output voltage min: good
Output voltage max: best
:lol:

Another example, just imagine, you're opening datasheet for ADS6143 and see that:
26-BITS* ADC
* for 1 Hz bandwidth
and after some time you're found that datasheet is changed and now it declares:
31-BITS* ADC
* for 0.001 Hz bandwidth
If you don't understand what is wrong with this, I can explain - both claims are true, the difference is bandwidth used for bits estimation. But as you can see, there is no mention that ADS6141 is 31-bits ADC.

aurgathor
Posts: 87
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Re: SDRplay announces the RSPdx

Post by aurgathor » Fri Nov 15, 2019 6:58 am

> "Hi-Z" is a marketing thing which is usually used for bad design RF frontend.

Why? If I understand it correctly, a Hi-Z input makes it easy to connect a long piece of wire and use that as an LW/MW antenna.

With a coax, one has to use a balun, or accept a significant mismatch between simple LW/MW antennas and the input.

As far as I concern, a Hi-Z input is not necessarily better or worse, it's simply different. I don't know the impedance of the Hi-Z input on the RSP2, but *really* old TVs didn't come with a coax input. The input was either 240 or 300 ohm.

> The same thing with "14 bit" taken with decimation and which works worse than 8 bit ADC from RTLSDR.

LOL. Do you have an axe to grind or what? :roll:
That has nothing to do with my question. I'm not sure what they use, if it's the MSi2500 than I think that chip has a 12 bit ADC. But even if the ENOB of that ADC is only 11.1 or so, I'm still having a really hard time to believe that it would be worse than the RTL2832U's 8 bit.

radiolistener
Posts: 58
Joined: Thu Jan 25, 2018 10:48 pm

Re: SDRplay announces the RSPdx

Post by radiolistener » Fri Nov 15, 2019 9:17 am

aurgathor wrote:
Fri Nov 15, 2019 6:58 am
> "Hi-Z" is a marketing thing which is usually used for bad design RF frontend.

Why? If I understand it correctly, a Hi-Z input makes it easy to connect a long piece of wire and use that as an LW/MW antenna.
There are two reasons:
1) high impedance leads to high thermal noise
2) impedance matching problems

Hi-Z is good for low quality equipment with very bad untuned antennas (such as random piece of wire or something like that) which is often used by unqualified user. But if you want to get best performance and low noise, then Hi-Z is a piece of shit.

For common users with no RF-knowledge Hi-Z is really better, because it don't needs tuning and they don't bother about noise floor and sensitivity.

If you want to get best noise floor and sensitivity, you're needs to use hi-end equipment and good tuned antenna. It needs good impedance matching and low loss components and very good RF knowledge. This is too complicated for common users.
aurgathor wrote:
Fri Nov 15, 2019 6:58 am
With a coax, one has to use a balun, or accept a significant mismatch between simple LW/MW antennas and the input.
there is physical limitations, which leads to noises and loss when you trying to match very different impedance.

And don't forgot about thermal noise. Higher impedance means higher thermal noise. This is very critical for hi-end equipment., because it reduces sensitivity and dynamic range.
aurgathor wrote:
Fri Nov 15, 2019 6:58 am
> The same thing with "14 bit" taken with decimation and which works worse than 8 bit ADC from RTLSDR.

LOL. Do you have an axe to grind or what? :roll:
That has nothing to do with my question. I'm not sure what they use, if it's the MSi2500 than I think that chip has a 12 bit ADC. But even if the ENOB of that ADC is only 11.1 or so, I'm still having a really hard time to believe that it would be worse than the RTL2832U's 8 bit.
I'm pretty familiar with SDR, signal processing, and I have different SDR receivers with different ADC. I compared SDRPlay performance with DDC receivers with fair 12-bit ADC and with fair 14-bit ADC. And I can say that SDRPlay looks like piece of shit on the background of real 12-bit ADC receiver performance.

I also compared SDRPlay with RTLSDRv3 and I didn't find any advantage of SDRPlay. SDRPlay has worse IMD and worse sensitivity in comparison with RTLSDRv3.

SDRPlay can work with a little stronger signals than RTLSDR, so it looks like it uses a little better than 7-bit ADC inside. But it cannot beat RTLSDR in IMD performance and both SDRPlay and RTLSDR have almost the same dynamic range.

In addition SDRPlay has worse NCO noise and spurs and terrible gain control than RTLSDR. Also there is needs to mention, that SDRPlay has a lot of frequency gaps and dead frequencies.

In average RTLSDR and SDRPlay have almost the same performance. RTLSDR has a little better IMD and better sensitivity and SDRPlay has a little better overload level and more wide bandwidth.

But I prefer RTLSDR for listening, because it has better sensitivity, better IMD and less NCO spurs and noises.

For example, here is comparison between SDRPlay and RTLSDR on short wave, both connected to the same antenna and working simultaneously. Do you see any advantage of SDRPlay against RTLSDR? I don't. ;)

The only good thing of SDRPlay is preselector filters and LNA on the input. But it cannot fix bad dynamic range and IMD performance and you can get the same result (or even better) with RTLSDR by using external filters and LNA.
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hotpaw2
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Re: SDRplay announces the RSPdx

Post by hotpaw2 » Sat Nov 16, 2019 5:44 pm

Someone wrote: "I also compared SDRPlay with RTLSDRv3 and I didn't find any advantage of SDRPlay. "

Was that comparison done for HF? And, if so, was the RTLSDRv3 in Direct Sampling mode or using an up-converter.

In my experience, the Direct Sampling mode of my RTLSDRv3 unit seemed quite deaf on MF and LF, especially compared to an Airspy HF+, Discovery, or even RSP2, same antenna. Perhaps I need to try again using an LNA in front of the RTLSDRv3?

radiolistener
Posts: 58
Joined: Thu Jan 25, 2018 10:48 pm

Re: SDRplay announces the RSPdx

Post by radiolistener » Sat Nov 16, 2019 7:34 pm

hotpaw2 wrote:
Sat Nov 16, 2019 5:44 pm
Was that comparison done for HF?
yes, this is done on HF. You can see screenshot above.
On VHF, SDRPlay has significantly worse sensitivity than RTLSDRv3.
hotpaw2 wrote:
Sat Nov 16, 2019 5:44 pm
And, if so, was the RTLSDRv3 in Direct Sampling mode or using an up-converter.
I tested RTLSDRv3 in Direct Sampling mode. With no filters and no LNA, just as is.

From 100 kHz to 14.4 MHz RTLSDRv3 works perfectly just out of the box. From 14.4 to 30 MHz RTLSDRv3 has more images than SDRPlay, because it working in the second Nyquist zone for this frequency range and don't have filter on the input. But it still usable.

I recommend to disable RTLAGC and automatic gain when using RTLSDR, it's better to control gain manually, in such way you can get the best quality.

snn47
Posts: 192
Joined: Tue Dec 27, 2016 11:00 pm

Re: SDRplay announces the RSPdx

Post by snn47 » Wed Dec 04, 2019 6:57 am

In this discussion receiver performance and the point where an antenna and/or cable are connected to the receiver need to be seen seperately.

PS: These comments are no tintended to discourage anyone, but I am trying to point out that at such low frequencies, you can only try to find the best compromise. Due to the much larger dimensions of the wavelength, when compared to a few 10m at shortwave, you cannot built a halfwave dipole or 1/4 wave groundplane (Eifeltower would be good for about 200 kHz) .

Antenna impedance is just one factor to consider.
We have (a)symetrical antenna, cable and receiver inputs, of varying (complexe) impedance to consider which varies with frequency.
Are antenna/cable/input all symmetrical/asymmetrical.
What polarization do the signals have, what is the antenna height or ground conductivity to name a few.

What is the antenna efficiency. Any type of unshielded conductor a resistor, a nail or a noodle cooked in salt water to any (a)symmetrical antenna input of any impedance will provide reception, the question is only how well does it perform?. A 10-20 m cooper wire from a discarded transformer, directly connected to 50 Ohm input LP of an IE-500 up-converter connected to a 2m TRx will receive DCF-77 @77.5 kHz wavelength ~3870m in Europe.

Why? If I understand it correctly, a Hi-Z input makes it easy to connect a long piece of wire and use that as an LW/MW antenna.
Long wire implies that the wire is long in relation to the wavelength, for LW with ~3000 m wavelength @0.1 MHz and MW ~300m wavelength @1 MHz, which provides challenging mechanical problems for LW/MW. Is your wire (very) short or really long in relation to the wavelength)?

Antennas which are short in relation to the wavelength, have a very low complexe impedance, e.g. capacitive top loaded roads, of much less than 1 Ohm and require retuning/matching when frequencies are changed. Almost all antennas are not capable of providing a large bandwidth, I consider factors of 8 to 10 to be exceptionally broad antenna.
With a coax, one has to use a balun, or accept a significant mismatch between simple LW/MW antennas and the input.


You don’t need a balun, unless you have a symmetrical antenna, which is 1500 m @0.1 m (MW) and 150 m @1 MHz (LW) for a ½ wave dipole. A long wire is not a symmetrical antenna. Due to the large variation in wavelength you will have large mismatch.

As far as I concern, a Hi-Z input is not necessarily better or worse, it's simply different. I don't know the impedance of the Hi-Z input on the RSP2, but *really* old TVs didn't come with a coax input. The input was either 240 or 300 ohm.


Really old TV had symmetrical inputs only, because symmetrical parallel wires of ~240 Ohm were used to connect the (indoor rabbit ears) dipoles/Yagi antenna to the TV. Coax cable were to expensive for a mass product like TV and BC at the time.
Only much later unsymmetrical coax inputs of 60 or 75 Ohm added/used for antenna. Since most people had still their symmetrical parallel wires they needed a Balun to connect them to their TV when id only had a asymmetrical coax antenna connector.
Last edited by snn47 on Thu Dec 05, 2019 4:56 am, edited 1 time in total.

snn47
Posts: 192
Joined: Tue Dec 27, 2016 11:00 pm

Re: SDRplay announces the RSPdx

Post by snn47 » Wed Dec 04, 2019 7:21 am

@radiolistener
For example, here is comparison between SDRPlay and RTLSDR on short wave, both connected to the same antenna and working simultaneously. Do you see any advantage of SDRPlay against RTLSDR? I don't. ;)
It is diffuicult comparing pictures, but looking at the sidebands and the two signals above and below the highlighted signal I see a difference in amplitude, which could be difference in compression, unless your signals were below the point when compression will start.

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