New RSP1A owner disappointed with spurious responses

[DBMandrake]

Hi All,

A bit of advice and feedback needed, especially from owners of rtl-sdr.com blog v3, Airspy Mini and SDRPlay RSP1A devices.

I've dabbled for a couple of years with an rtl-sdr.com blog v3 adaptor with great success and more recently decided that I wanted a bit more bandwidth and something with more dynamic range that is better able to cope with in strong in band interfering signals.. (blocking performance etc)

In the £100 price range I'm willing to pay the two contenders seemed to be the SDRPlay RSP1A and the Airspy Mini, with 14 and 12 bit ADC's respectively. I did all the research I could, read all the reviews I could find, checked software compatibility etc, and weighed up the numerous pros and cons of both devices and finally settled on the RSP1A.

Unfortunately after using it for a couple of days I feel like I've made the wrong decision and I'm actually pretty disappointed in its performance, even compared to my rtl-sdr v3! So much so that I'm very likely going to send it back in the next few days while I still can. (Distance selling laws etc)

The biggest issues I have with it are all with the Zero IF modes - the massive DC spike, (on the order of 25dB in software like SDR Console) which can't be corrected on much of the software I'd like to use and and numerous internal spurries (birdies) that the device seems to generate and pick up in its IF (post tuner) stages. Pictures tell a thousand words so I've captured some videos demonstrating what I'm seeing and uploaded them to Youtube, so I hope people can take a few minutes of their time to watch these to get a better idea of the issues I'm seeing and maybe try to reproduce it with the same settings. In these examples I'm using SDR++ and SDR Console but I see similar problems in other software as well. In all these videos there is no antenna connected, so I'm only examining internal spurries.

In this first video I'm using SDR++ as it gives more detailed control over the tuner settings than SDR Console, sample rate is set to 8Mhz, IF filter to 6Mhz LNA and IF gain are set fairly low but not right down. As well as the DC spike there are two unstable, mirrored spurries which wander around like drunks, later in the video I adjust the IF gain which causes the frequency of these spurries to change and move all over the place.

While turning the IF gain up high hides/swamps these particular spurries, the device as a whole performs poorly with the IF gain turned up high, in fact in both SDR++ and SDR Console I find I have to keep the IF gain towards the bottom end for best signal performance, in which case the spurries are clearly evident when tuning to a quiet frequency range.

In the second video I'm using SDR Console and seeing the same issue at a different frequency, I step through some different LNA and IF gain settings to show how it affects the spurries, I then switch to my RTL-SDR v3 adaptor also with no antenna connected and step through different gain settings to show how clean the noise floor is even up to relatively high gain levels - there is an uncorrected IQ imbalance causing a small spike (IQ correction in SDR Console doesn't seem to work for me for RTL-SDR, seems like a bug as it works in other programs on the same adaptor) but there are no spurries like the RSP1A. Near the end I switch to 2Mhz Low IF mode and most of the problems go away.

In the third video I demonstrate the massive main clock spur harmonic around 120Mhz and sidebands surrounding it, which are both really quite bad and right in the middle of the aircraft band. (The centre spur is 50dB above the noise floor!) There is an image of this spur at 120.8Mhz as well which is about 30dB above the noise floor.

I then switch the LNA and IF gain to various values and while I can suppress the sidebands of the clock harmonic the 120 and 120.8Mhz spurs are still very strong. I then switch to my rtl-sdr v3 adaptor and there is a small spur at 120Mhz (also a main clock harmonic I believe) but it is only 20dB above the noise and there nothing at 120.8Mhz, no sidebands or other crap showing up on the RSP1A. So apart from that one clock spur the nearby aircraft band's noise floor is clean.

The amount of crap in this region in Zero IF mode on the RSP1A is pretty bad IMHO. Near the end of this video I switch to 2Mhz Low IF mode and while it cleans up the rest of the spectrum dramatically including the DC spike, it doesn't get rid of the clock harmonic or it's sidebands at 120Mhz, which are right on top of a commonly used aircraft frequency and still 50dB above the noise floor.

In my final video I am set to 2.7Mhz first in 6Mhz then 3Mhz Zero IF mode to show that the spurries are present at low frequencies as well. In 2Mhz low IF mode things are cleaned up considerably but at the expense of losing most of the available bandwidth of the device. So am I doing something wrong or is this device just not very good ? After the anticipation of waiting for it to arrive I'm pretty gutted really.

I don't seem to be the only person experiencing these problems as I was able to find the following discussions when I looked hard enough:

This one refers to "wobbling spurs" which drift in frequency and the owner went as far as using cold spray to identify which chips may have been generating it. My own theory on the wobbling spurs / spurries is that there may be a free running DC/DC converter in the device which is leaking some of its switching frequency into the IF stages - when you first "start" the device in SDR Console for example the spurs race quickly down in frequency then start wobbling, and the fact that their frequencies change dramatically when you adjust the gain of the LNA and IF amplifiers suggests to me that a change in the current drawn by these amplifiers is affecting the free running frequency of the DC/DC converter that is leaking into the receiver path.

Another thread here shows screenshots very similar to mine, however SDRPlay support have tried to fob this off by saying that the noise humps are a result of sigma delta encoding without enough noise on the input, however in my opinion that doesn't explain why they wobble around in frequency so much and the frequency is affected so much by the gain settings, which shouldn't have any effect. (But would have an effect on the power drawn by the chip potentially affecting the source of the spurious signal)

Does it perform better than my rtl-sdr v3 in some ways ? Yes it does. Its large signal performance, eg weak signal reception with a nearby strong signal is considerably better, as you would hope from the 14 bit ADC vs 8 bit. This is particularly notable on one FM Broadcast station which is always distorted sounding with a sharp notch visible in the middle no matter what bit rate or filter settings I use on the rtl-sdr v3 - on the RSP1A this FM station looks normal on the spectrum graph and sounds nice and clear pretty much regardless of gain or bandwidth settings. In fact broadcast FM reception is great and definitely better quality than the rtl-sdr v3.

Is it more sensitive for ADS-B ? Yes, but only very marginally. I left both running together with identical dipoles spaced about a metre apart, using dump1090 for the RTL-SDR and SDRPLay_dump1090 for the RSP1A, both feeding into Flight Radar so I could easily see the count of how many packets each received and the RSP1A was receiving about 5-10% more packets, although the range it was receiving them from wasn't significantly different, and sometimes the rtl-sdr v3 was receiving planes from further away. So it was slightly better here on average but the rtl-sdr v3 held its own very well and neither had a decisive advantage.

Is it better on HF than the Direct Sampling mode of the rtl-sdr v3 ? Well, sort of. It certainly has a lot more gain on HF since the rtl-sdr v3 devices direct sampling mode feeds directly into the ADC without the benefit of of an adjustable LNA, so the RSP1A had more gain and a way to adjust it. And if you're willing to sacrifice most of your bandwidth and use a low sample rate in low IF mode adjacent channel selection is better.

However in the Zero IF mode it was pretty much useless because there were so many internally generated spurries that it was hard to know what was real and what wasn't without disconnecting the antenna to check all the time. While the rtl-sdr v3 had lower gain, the SNR was still surprisingly good and was able to receive everything the RSP1A could, and it was largely free of spurries apart from the mirroring of spectrum around 14Mhz which is a limitation of how the direct sampling mode works. (28.8Mhz sample rate without a 14Mhz low pass filter)

To get good performance from the RSP1A on the HF bands I found it has to be used in Low IF mode restricting bandwidth to 2Mhz or less, so similar to what I can already achieve with the RTL-SDR and the benefit of a birds eye view of a large spectrum width simply doesn't materialise when Zero IF mode introduces so many spurries and a large DC spike.

Having the switchable MW/FM/DAB filters is nice in theory but I never once found a situation where they helped - I obviously don't live close enough to any large transmitters (the nearest is 15 miles away I think) to need the notch filters, so the 11 preselection filters are already sufficient for out of band signals, it's in band interference between strong and weak signals I'm more concerned about.

So I'm pretty gutted to be honest, as the improvement over the rtl-sdr v3 wasn't as big as I hoped and in many ways it is considerably worse - it's implementation of a Zero IF architecture seems to be flawed, and there is something in there using a free running oscillator which is inadequately filtered and/or shielded, plus the very large spur from the main clock finding its way into the signal chain.

It's such a surprise to find the low signal performance of the £30 rtl-sdr.com v3 to be so competitive with a device three times its price, and for its noise floor to be so clean and largely free of the crap that I'm seeing on the RSP1A. Apart from a slight IQ imbalance in some software like SDR Console and a minor clock spur the rtl device is very clean and it remains an absolute bargain in the price range.

So what next ? I'd like feedback/suggestions but I think I'm going to have to send it back in a few days and give an Airspy Mini a try to see if it fares any better. I don't really need HF as I'm not big into HF and I have some useful HF performance for casual listening from the rtl-sdr v3 anyway. (And it performs surprisingly well now I've directly compared it against a device that is specifically designed to cover that range)

I guess what I really want is something similar to an rtl-sdr but with wider bandwidth, a better ADC with better instantaneous dynamic range, and the Airspy Mini with 12 bit ADC is quite possibly that, and possibly what I should have chosen to begin with. Plus it supports SDR# which I think is still my favourite SDR software for casual tuning around - something that I can't use (apart from very old versions or hacks) with the RSP1A. (I haven't even mentioned SDRUno, which IMHO is god awful)

Are there any Airspy mini owners who can report on their performance in similar scenarios to the ones I presented in my Youtube videos (minus the HF testing) and can comment on how clean the noise floor is on these and how resistant they are to adjacent channel interference when used in the full 6Mhz mode ? Or who can do a direct comparison with the rtl-sdr blog v3 device I am using as my benchmark ?

High gain and 11 preselection filters means nothing to me if the noise floor even with no antenna is connected is not clean and I can't tell what's real and what's fake - I'd rather have a device with a little lower gain that is clean and free of spurious signals.

Thanks for your time everyone.

 

[iMONITOR]

That surprises me.

 

[ultrajv]

its possible that these are coming from your PC or USB. Different clock speeds on SDRs produce different spurii. You should not be using high gain, on SDR. less is better. The spurii might be a result of too much gain. You should know that gain is best near the antenna, not the SDR. I have several lime sdr minis and they have a large DC spike, it dosnt bother me as I tune round it. I think you need to try it on another PC or use a better USB cable, perhaps try ferrites on the USB cable. Also, realise that gain should be adjusted to give best signal and least noise. If you keep turning it up, you will cause overload and that will cause trouble such as images, spurri, excess noise.

Microsoft Word - Gain and AGC in Uno .docx (sdrplay.com)

 

[DBMandrake]

That surprises me.

Really ? Which bit ?

But yes, it surprised me too, and not in a good way.

I thought I'd made a good choice after doing my research, I wanted to like it, but it was one of those times where the more you use something and become familiar with it the more you get a sinking feeling that it's not what you hoped it would be and start to find some hidden shortcomings that seem to get missed or glossed over in reviews or discussions.

It gave me renewed respect for the rtl-sdr.com v3 dongle I've been using which I'd always considered a very cheap entry level device (which in reality it is) which still manages to punch above its weight on the analogue side, particularly in the area of having a very clean noise floor mostly free of spurs, (at least in normal down conversion mode using the tuner) and with no wobbly birdies...

And to give a bit more background although I'm relatively new to the world of SDR's and the concept of direct conversion Zero IF receivers, I was many years ago a radio ham, back in the days when everything was analogue, (apart from RTTY/AMTOR/Packet) there was no such thing as an SDR a ham could afford, and did my share of antenna building and testing, building pole mounted VHF/UHF preamps, radio repairs, kit building etc, so while I'm pretty rusty I do have a decent grasp of how down conversion receivers work, how IF frequencies affect selectivity, how IF imaging occurs, blocking/desensitisation of weak signals by nearby strong signals and how it relates to instantaneous headroom etc...

So I know what the limitations with the basic RTL dongle's are, largely due to the 8 bit sampling and insufficient instantaneous headroom and hence the desire for an upgrade to something a bit more capable in the sampling and bandwidth area.

But there just seems to be some problems with the analogue design in this unit. I had a quick look inside and there is no shielding at all apart from some metallic spray on the inside of the case, so if there is a tiny SMPS to provide a negative rail or >5 volt rail (which seems likely) then there is no shielding between that and the rest of the circuitry.

And while 11 preselection filters and 3 notch filters seems like a good idea on paper that's an awful lot of components (the filters take up nearly half the board layout using dozens of SMD components) and an awful lot of active switches to to switch between all these different modes. There's also enough trace lengths through all these components that the input filter circuit traces probably act like an internal antenna which probably explains why the clock harmonic is being received so strongly as well, probably just through RF propagation from the signal bouncing around inside the case.

The same electrical design in proper compartmentalised shielded can arrangement as used on professional equipment would probably be OK, however I wonder if the built in tracking filter in the tuner of the R820T2 family is not just a simpler and better approach partly because it eliminates the large number of external filter components, traces and analogue switches in the RSP1A approach.

While my RTL dongle can be overloaded by strong in-band signals due to lack of dynamic range I've never noticed problems with strong out of band signals upsetting it, so depending on the bandwidth of the tracking filter and how well it tracks the input frequency it may be a better approach than a large number of fixed bandwidth filters, and I understand that the Airspy Mini uses the same frontend tracking tuner as the RTL dongles ?

One thing I haven't been able to find out, is does the Miracs tuner in the RSP1A also have a built in tracking filter or is it entirely dependant on the bank of 11 fixed bandwidth externally switched input preselection filters ?

 

[ultrajv]

I noticed you avoided my post but in your case, youre problems are user error. It will take you time to get used to the world of SDRs, youre analogue knowledge is fooling you and isnt impressive (its just wrong in this case). Youre obsessed with finding faults and blaming them on poor design but you cant see the biggest of all is you. Im still a ham by the way

 

[DBMandrake]

its possible that these are coming from your PC or USB. Different clock speeds on SDRs produce different spurii.
You should not be using high gain, on SDR. less is better. The spurii might be a result of too much gain. You should know that gain is best near the antenna, not the SDR.

You probably didn't watch the videos then - because the spurious signals are worst at low gain settings, which is one of the things I was demonstrating.

Yes I'm quite aware that it's best to use the minimum gain that will give you the best SNR for a signal of interest. This is more important with a wide bandwidth SDR than it is with a traditional superhet receiver which does relatively narrow bandpass filtering at every stage of conversion and therefore suffers a lot less from adjacent channel overloading, which is always going to be more problematic on a wide bandwidth SDR unless you have it switched into a narrow bandwidth mode with actual analogue filters.

As I noted, switching the device into a narrow bandwidth Low IF mode solved most of the problems, but at the expense of losing 80% of the 10Mhz of bandwidth that you paid for.

I have several lime sdr minis and they have a large DC spike, it dosnt bother me as I tune round it. I think you need to try it on another PC or use a better USB cable, perhaps try ferrites on the USB cable.

It's not the PC. I've also brought it into work and tried it on a completely different PC, the symptoms with the "wobbly spuri" and clock spur are the same. The USB cable is the recommended cable that is bundled with the device.

The DC spike might not bother you depending what type of signal you're trying to tune or what software you're using but for me its a big headache which makes the 3-10Mhz modes useless for many applications.

Some software seems to have DC compensation - it seems to work reasonably well in SDRAngel and SDRUno, however a lot of other software doesn't, for example SDR++, SDR Console.

SDR Console seems particularly poor in this regard as there is only one check box to choose whether to use DC compensation in the "SDR Play API", or use built in DC compensation, however neither option makes any difference and you are left with a 20-30dB spike right in the middle of your usable bandwidth. The SDR Console author goes so far as to say:

Bandwidth
For best performance use a bandwidth of 2.048 MHz or lower. Bandwidths greater than 2.048 MHz have a spur in the centre of the display which is generated by the SDRplay hardware and cannot be eliminated. If you listen to a signal in the centre with a bandwidth greater than 2.048 MHz the audio will be distorted and have many unwanted artefacts.

So it seems that he's basically washing his hands of trying to find any way to compensate for the DC spike from SDR Play units.

From an end user perspective this is frustrating when my cheap rtl-sdr device does not have this issue because it does not use Zero IF, and being forced to switch to 2Mhz or lower in Low IF mode to eliminate this problem makes buying a device with 10MHz of bandwidth a bit pointless.

Even SDRUno shows a significant DC spike in Zero IF modes which the controls in the settings part of the app do not seem to be able to correct for, and I notice that the program deliberately "side tunes" to try to avoid this - for example if you're in LSB and have it set to track the current frequency it always offsets it enough to keep the DC spike on the "wrong side" where it can't be heard - if you try to click the cursor directly onto the spike it doesn't let you.

If the Airspy Mini can provide its full 6Mhz of bandwidth (or even 5Mhz usable) without any DC or IQ imbalance spike (which it claims to do) that's a big win for me.

I was aware that the Zero IF architecture of the RSP1A can cause a DC spike but I was under the impression (before testing it first hand) that it would be relatively easy to cancel/correct in software, but practical testing says otherwise.

 

[ultrajv]

You probably didn't watch the videos then - because the spurious signals are worst at low gain settings, which is one of the things I was demonstrating.

Yes I'm quite aware that it's best to use the minimum gain that will give you the best SNR for a signal of interest. This is more important with a wide bandwidth SDR than it is with a traditional superhet receiver which does relatively narrow bandpass filtering at every stage of conversion and therefore suffers a lot less from adjacent channel overloading, which is always going to be more problematic on a wide bandwidth SDR unless you have it switched into a narrow bandwidth mode with actual analogue filters.

As I noted, switching the device into a narrow bandwidth Low IF mode solved most of the problems, but at the expense of losing 80% of the 10Mhz of bandwidth that you paid for.

It's not the PC. I've also brought it into work and tried it on a completely different PC, the symptoms with the "wobbly spuri" and clock spur are the same. The USB cable is the recommended cable that is bundled with the device.

The DC spike might not bother you depending what type of signal you're trying to tune or what software you're using but for me its a big headache which makes the 3-10Mhz modes useless for many applications.

Some software seems to have DC compensation - it seems to work reasonably well in SDRAngel and SDRUno, however a lot of other software doesn't, for example SDR++, SDR Console.

SDR Console seems particularly poor in this regard as there is only one check box to choose whether to use DC compensation in the "SDR Play API", or use built in DC compensation, however neither option makes any difference and you are left with a 20-30dB spike right in the middle of your usable bandwidth. The SDR Console author goes so far as to say:


So it seems that he's basically washing his hands of trying to find any way to compensate for the DC spike from SDR Play units.

From an end user perspective this is frustrating when my cheap rtl-sdr device does not have this issue because it does not use Zero IF, and being forced to switch to 2Mhz or lower in Low IF mode to eliminate this problem makes buying a device with 10MHz of bandwidth a bit pointless.

Even SDRUno shows a significant DC spike in Zero IF modes which the controls in the settings part of the app do not seem to be able to correct for, and I notice that the program deliberately "side tunes" to try to avoid this - for example if you're in LSB and have it set to track the current frequency it always offsets it enough to keep the DC spike on the "wrong side" where it can't be heard - if you try to click the cursor directly onto the spike it doesn't let you.

If the Airspy Mini can provide its full 6Mhz of bandwidth (or even 5Mhz usable) without any DC or IQ imbalance spike (which it claims to do) that's a big win for me.

I was aware that the Zero IF architecture of the RSP1A can cause a DC spike but I was under the impression (before testing it first hand) that it would be relatively easy to cancel/correct in software, but practical testing says otherwise.

Again youre focusing on faults and not solutions. Youre finding faults with everything including software. Gain staging on SDRs are critical and youve just messed with all the settings rather than follow the guide i gave you from the manufacturer. You cant be helped because you think theres a design problem. So you tried it on another PC, probably with the same USB cable. I suggest you send it back and forget about SDR. Good luck. 73

 

[DBMandrake]

I noticed you avoided my post but in your case, youre problems are user error. It will take you time to get used to the world of SDRs, youre analogue knowledge is fooling you and isnt impressive (its just wrong in this case). Youre obsessed with finding faults but you cant see the biggest of all is you. Im still a ham by the way

Wow, totally unhelpful and obnoxious mate. How did I avoid your post ?

1) I was already in the middle of composing a long reply to iMONITOR when you posted the post that you claim I didn't respond to (but which I later did before you posted the above diatribe chastising me for "avoiding" your post) so of course I finished writing and posting that before I moved on to reply to your post.

2) I'm a new forum member so my posts have to be approved by a moderator before they appear. So you may or may not see them appear in the correct order depending on how the moderators approve my posts.

As for the technical part of your comment - wait, there isn't one. You're basically just here to tell me I'm an idiot that doesn't know what he's doing. Righto then, thanks for that, glad you know my entire life history and what experience or qualifications I do or don't have.

I'm not obsessed with trying to find faults, I'm just trying to use the device as it should work, however the flaws with the device are so glaring that its clear within a couple of days that it's not satisfactory for the use cases I have in mind.

The suitability of the device is obviously going to depend a lot on the type of software you use with it, how compatible that software is, and what type of signals you're trying to listen to or decode. For some purposes it's absolutely fine. For other purposes not so much. If you're primarily using it in Low IF mode at 2Mhz or below bandwidths it will probably be absolutely fine for any use cases that will fit into that bandwidth. But I didn't buy a 10Mhz bandwidth device to use only at 2Mhz because the higher bandwidth Zero IF modes are hobbled with undesirable spurries and a DC spike which can't be removed in most software I want to use.

If you have actual specific suggestions on what I'm doing wrong in my examples that would cause these spurries please do tell, I'm interested in any feedback that's useful. But if the sum total of your useful feedback is "user error" and "you're an idiot who doesn't have a clue" then you'll very quickly find yourself in my blocklist.

 

[DBMandrake]

Again youre focusing on faults and not solutions. Gain staging on SDRs are critical and youve just messed with all the settings rather than follow the guide i gave you from the manufacturer. You cant be helped because you think theres a design problem. So you tied it on a nother PC, probably with the same USB cable. Good luck. 73

What "guide I gave you from the manufacturer" ? You've posted no such thing. Maybe you're a new user whose posts are also being moderated ? Consider that.

Thanks, but I have not "just messed with all the settings". In the videos I took I was just showing a variety of combinations for the purposes of illustration. I know what gain staging is thanks very much, besides, there are only two gain adjustments exposed in SDR Console, and obviously I know how to optimise them on real world signals. The videos were just to show the effect of various combinations of gain staging and sample rate / IF mode on the undesirable spurries and DC spike.

One of the points of the videos was that gain settings that are optimised for reception (relatively low IF gain and low to medium LNA gain) unfortunately also coincide with settings where the various spurious responses are worst.

You seem awfully defensive so I'm guessing you're an RSP1A owner who doesn't like his device being criticised.

 

[DBMandrake]

Is there anyone else out there with constructive feedback who isn't just going to tell me I'm an idiot who doesn't know what I'm doing ? Just checking. Because as it stands at the moment this thing is being sent back on Monday, and that's a shame. I really did want to like it.

 

[RFI-EMI-GUY]

I noticed you avoided my post but in your case, youre problems are user error. It will take you time to get used to the world of SDRs, youre analogue knowledge is fooling you and isnt impressive (its just wrong in this case). Youre obsessed with finding faults and blaming them on poor design but you cant see the biggest of all is you. Im still a ham by the way

Lack of shielding is a terrible design whether the receiver is analog or digital. Those are valid complaints.

 

[ultrajv]

Lack of shielding is a terrible design whether the receiver is analog or digital. Those are valid complaints.

If he is to believed, then it depends on where the shielding is. My limesdr mini has no metal case but the relevant section is shielded. Has he opened the unit to check? and voided the warranty? The man clearly has a problem.

 

[RFI-EMI-GUY]

If he is to believed, then it depends on where the shielding is. My limesdr mini has no metal case but the relelvent section is shielded. Has he opened the unit to check? and voided the warranty? The man clearly has a problem.

You are doubting the OP and have not looked yourself?

Here are some pictures of the inside. No filtering between any internal stages of any sort.

SDRPlay RSP1A Receiver Review. – Mersey Radio

www.merseyradar.co.uk

 

[ultrajv]

You are doubting the OP and have not looked yourself?

Here are some pictures of the inside. No filtering between any internal stages of any sort.

SDRPlay RSP1A Receiver Review. – Mersey Radio

www.merseyradar.co.uk

He says he did extensive research on many SDR units before he bought it, if you found it that easy - why didnt he? - caveat emptor. Ive seen this before where people rant on and on about problems. The problem remains that he didnt do enough research. he wants a pro SDR at a cheap price and is bitter. Dont we all. Im more than happy with my limesdr mini. I wouldnt dare recommend that to him because its a dev board without filtering as many are.

 

[DBMandrake]

Lack of shielding is a terrible design whether the receiver is analog or digital. Those are valid complaints.

I didn't take any pictures of mine when I opened it, but here is a picture from a review online which is identical to mine:

Just metalized paint sprayed onto the plastic case which then makes contact (hopefully) with the earth pads around the screw holes. I knew this before buying but I suppose I should have thought more about it.

And here is a nice close up of the PCB top side when it was reviewed by rtl-sdr blog:

Most of the bottom side is ground plane apart from a few via interconnects.

On this top side all of the circuitry in the top middle, top right and right hand side is the 11 preselection filters, 3 notch filters and RF switching chips to switch them in and out. As I said, more than half the foot print of the board and that is an awful lot of components and PCB traces on the input signal before it even gets to the first buffer. If anything on that unshielded board like a SMPS is radiating RF harmonics its just going to bounce around inside the metalized case and be picked up by all the traces in the filter circuitry. Same for the crystal oscillator.

The input filters at the very least really needed to be in separate shielded can sections.

If he is to believed, then it depends on where the shielding is. My limesdr mini has no metal case but the relevant section is shielded. Has he opened the unit to check? and voided the warranty? The man clearly has a problem.

If I'm to be believed ? Pictures of the inside of the device are all over the internet. SDRPlay themselves say that the plastic case has a conductive metalized spray inside, which is better than nothing but not as good as a metal case, otherwise their higher end models wouldn't have a metal case.

But I believe the real issue here is lack of segregation between different sections of the circuit. The input filters because they are so physically large and complex and have so many traces acting like antennas needed to be in their own shielded can sections, a SMPS generating the supply rails (if it has one, but it probably does) needed to be in its own shielded can with feed through capacitors to keep any unstable free running "hash" well away from anything else.

This has not been done and I believe what I'm seeing is the result. The DC spike is a different issue - that's due to the Zero IF architecture they've chosen and is more of a fundamental design choice rather than an implementation. The first issues could be fixed with a revision where the board is separated into can shielded sections but the DC spike is fundamental to the design.

Voided my warranty ? Pfft. Four tiny screws and it comes apart with ease. There are no warranty stickers nor are such stickers legally enforceable anymore. (That's why manufacturers don't generally use them anymore) I've repaired devices hundreds of times more complex than this with no service data available, I think I can open a plastic box with four screws and close it again...

By the way the only reason I opened my device at all was to check that it wasn't a counterfeit! SDRPlay themselves say specifically on their website that there are many convincing looking counterfeits of the RSP1A for sale and to be careful where you buy from.

Because it had significant performance issues I wanted to check that I had not somehow received a counterfeit device even though I had bought through one of their recommended resellers, just in case.

However my unit matches exactly internal photos of legitimate devices so that's not the case.

 

[DBMandrake]

He says he did extensive research on many SDR units before he bought it, if you found it that easy - why didnt he? - caveat emptor. Ive seen this before where people rant on and on about problems. The problem remains that he didnt do enough research. he wants a pro SDR at a cheap price and is bitter.

I knew what the device looked like inside before buying yes, of course, however it's hard to know how much effect the lack of shield cans would have ahead of time because RF circuitry can be very finicky. Depending on the design it's not always a major issue and it can be difficult to predict just by looking at it without knowing the fine details of the design topology which aren't always easy to find.

Other SDR's like the RTL-SDR I have now, or indeed the Airspy mini also don't have any shield cans over different sections of the circuit. They're just one admittedly much smaller PCB.

However they use a very different down conversion topology (Low IF instead of Zero IF) and they don't have that gigantic switched 14 section filter hanging off the input taking up half the PC to act as an antenna. The signal on those comes in from the connector and pretty much goes directly into the chip through a few tiny traces and a couple of components. Here's the PCB of an Airspy Mini for comparison:

Very short signal path from the antenna socket on the left and the tuner chip (small square chip on the middle left) on the order of 10mm.

In a Low IF design like the RTL-SDR and Airspy both the local oscillator for the mixer and and any free running SMPS oscillator are both going to below the IF frequency, so even though the ADC will digitise them they will be very low in level (they're only spurries) and can then be removed using digital filters in the digital domain - which I believe is what the Airspy does with its combined ADC/DSP chip, before it digitally shifts the signal down to the final baseband while simultaneously rejecting any spurious baseband frequencies which entered the ADC.

Similarly the 24Mhz main crystal oscillator is going to be above the passband of the filter feeding the ADC so cut off by the that low pass filter. The end result should be very clean as well as having no DC spikes.

On a Zero IF down conversion system the mixer is converting down directly to baseband before sampling. That means any spurious signals picked up on the board from say the SMPS radiating inside the box is going to be sampled by the ADC and appear directly in the output as there is no additional digital downmix involved.

Zero IF down conversion can be made to work well in principle but the analogue performance requirements to avoid things like spurious signals being radiated from one part of the board to another and then sampled as baseband frequencies are much more stringent than a low IF configuration, and that is patently obvious by how much better the RSP1A performs when you switch it into Low IF mode using the exact same hardware and PCB design.

Am I bitter ? A bit, yes. More disappointed than bitter though probably. Too trusting of favourable reviews from non-technical people, probably.

Until researching an upgraded SDR receiver I hadn't really had anything to do with Direct Conversion receivers - they weren't very practical in the analogue domain and had limited use, it's only digital sampling that makes them useful at all but now that I'm more up to speed on them and their limitations I'm a bit more wary. I was actually previously under the mistaken impression that the RTL-SDR used direct conversion, it's only when researching this further that I've realised that's not the case. (I should have guessed though when the ADC samples the tuner output at 28.8Mhz for a 2.4Mhz final bandwidth!) This was partly due to me confusing DC offset error with IQ imbalance errors which can look similar on a spectrum display. An RTL-SDR can have a spike due to IQ imbalance but not due to DC offset, even though it looks the same to the user.

I'll take it as a lesson learned and that I'm more up to speed now with the capabilities and limitations of the different devices.

Whether my expectations were too high or reviews etc were too forgiving and generous doesn't really matter, the device doesn't suit what I want to do. I'll send it back and give the Airspy Mini a try, however I'm just as willing to send that back too if it turns out that it has major issues of its own. Maybe the level of performance I'd hope for isn't available in the £100 range, if not, I'll just have to stick with my current RTL-SDR for now and revisit the "higher end SDR radio" scene at a later date.

 

[buddrousa]

And most people will not read a post that long when the op joined today

 

[PDXh0b0]

I had never tried my rsp1a on sdr++ , sdrconsole, etc before, just tried, while I didn't experience the issues you have shown, the performance wasn't the same as using it with SDRuno. Have you tried sdruno? The rsp1a coupled with sdruno is my preference for HF/shortwave/medium wave, rtl's & airspy for everything else

 

[ultrajv]

What "guide I gave you from the manufacturer" ? You've posted no such thing. Maybe you're a new user whose posts are also being moderated ? Consider that.

Thanks, but I have not "just messed with all the settings". In the videos I took I was just showing a variety of combinations for the purposes of illustration. I know what gain staging is thanks very much, besides, there are only two gain adjustments exposed in SDR Console, and obviously I know how to optimise them on real world signals. The videos were just to show the effect of various combinations of gain staging and sample rate / IF mode on the undesirable spurries and DC spike.

One of the points of the videos was that gain settings that are optimised for reception (relatively low IF gain and low to medium LNA gain) unfortunately also coincide with settings where the various spurious responses are worst.

You seem awfully defensive so I'm guessing you're an RSP1A owner who doesn't like his device being criticised.

You need glasses



its possible that these are coming from your PC or USB. Different clock speeds on SDRs produce different spurii. You should not be using high gain, on SDR. less is better. The spurii might be a result of too much gain. You should know that gain is best near the antenna, not the SDR. I have several lime sdr minis and they have a large DC spike, it dosnt bother me as I tune round it. I think you need to try it on another PC or use a better USB cable, perhaps try ferrites on the USB cable. Also, realise that gain should be adjusted to give best signal and least noise. If you keep turning it up, you will cause overload and that will cause trouble such as images, spurri, excess noise.

Microsoft Word - Gain and AGC in Uno .docx (sdrplay.com)


Please block me, I dont want any more OCD based rubbish. Others are querying youre results as well. You are trying to appear professional but youre at best an idiot, at worst a troll. Please seek help. My recommendation is a proper SDR from Flexradio, not cheap but you get what you pay for. Im done.

FlexRadio | Leaders in Software Defined Radios & Technology

Software defined radios have arrived, and FlexRadio is leading the charge. We are on a mission to change commercial and amateur radio.

www.flexradio.com

 

[PDXh0b0]

I didn't take any pictures of mine when I opened it, but here is a picture from a review online which is identical to mine:



Just metalized paint sprayed onto the plastic case which then makes contact (hopefully) with the earth pads around the screw holes. I knew this before buying but I suppose I should have thought more about it.

And here is a nice close up of the PCB top side when it was reviewed by rtl-sdr blog:


Most of the bottom side is ground plane apart from a few via interconnects.

On this top side all of the circuitry in the top middle, top right and right hand side is the 11 preselection filters, 3 notch filters and RF switching chips to switch them in and out. As I said, more than half the foot print of the board and that is an awful lot of components and PCB traces on the input signal before it even gets to the first buffer. If anything on that unshielded board like a SMPS is radiating RF harmonics its just going to bounce around inside the metalized case and be picked up by all the traces in the filter circuitry. Same for the crystal oscillator.

The input filters at the very least really needed to be in separate shielded can sections.

If I'm to be believed ? Pictures of the inside of the device are all over the internet. SDRPlay themselves say that the plastic case has a conductive metalized spray inside, which is better than nothing but not as good as a metal case, otherwise their higher end models wouldn't have a metal case.

But I believe the real issue here is lack of segregation between different sections of the circuit. The input filters because they are so physically large and complex and have so many traces acting like antennas needed to be in their own shielded can sections, a SMPS generating the supply rails (if it has one, but it probably does) needed to be in its own shielded can with feed through capacitors to keep any unstable free running "hash" well away from anything else.

This has not been done and I believe what I'm seeing is the result. The DC spike is a different issue - that's due to the Zero IF architecture they've chosen and is more of a fundamental design choice rather than an implementation. The first issues could be fixed with a revision where the board is separated into can shielded sections but the DC spike is fundamental to the design.

Voided my warranty ? Pfft. Four tiny screws and it comes apart with ease. There are no warranty stickers nor are such stickers legally enforceable anymore. (That's why manufacturers don't generally use them anymore) I've repaired devices hundreds of times more complex than this with no service data available, I think I can open a plastic box with four screws and close it again...

By the way the only reason I opened my device at all was to check that it wasn't a counterfeit! SDRPlay themselves say specifically on their website that there are many convincing looking counterfeits of the RSP1A for sale and to be careful where you buy from.

Because it had significant performance issues I wanted to check that I had not somehow received a counterfeit device even though I had bought through one of their recommended resellers, just in case.

However my unit matches exactly internal photos of legitimate devices so that's not the case.

aftermarket aluminum cases were out of stock, so I used aluminum tape lol

https://imgur.com/S7LRgQD