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Artefacts in new Airspy Discovery !? #sdrsharp #airspyhfplus #sdrconsolev3 #airspy

Uwe S.
 

Artefacts in new Airspy Discovery !?

Incidentally, SDRConsole has the same interference peaks, in exactly the same places with exactly the same behavior as in SDR#




Gruß Uwe

Simon Brown
 

I don’t think so. This is coming from your PC. Try a decent / good USB cable. Disconnect the antenna, put a pad on.

 

Simon Brown, G4ELI

https://www.sdr-radio.com

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Uwe S.
Sent: 25 August 2019 11:34
To: main@SDR-Radio.groups.io
Subject: [SDR-Radio] Artefacts in new Airspy Discovery !? #airspy #airspyhfplus #sdrconsolev3 #sdrsharp

 

Artefacts in new Airspy Discovery !?

Incidentally, SDRConsole has the same interference peaks, in exactly the same places with exactly the same behavior as in SDR#




Gruß Uwe

Guenter Fred Mandel
 

Hallo Uwe,
i experienced similar results at my device if the antenna input is left open or terminated with a 50 Ohm Dummy load. You will find these occurances only if you careffully search the spectrum in the area of 5MHz and 14,5 MHz.

After some experiments i am now quite confident that these Signals are real RF spurs and no digital Artefacts. If you connect the Discovery to the Input of another SDR you probably receive the same Frquencies coming out of the Discovery.  I also could  confirmed the real existence of these small (less than -110dBm) RF Spurs with a sensitive Spectum Analyzer. Not a big issue at all for reception, because the exernal noise of an Antenna is much higher than these bumps.

The spurs do not disappear - as previously assumed - when a real antenna signal is present. With a Signal 50dB above noise floor from a Signal Generator applied, the spurs are still visible.

Besides these occurences, the Airspy Discovery is a great litlle device with tremendous reception quality. A lot of Bang for the Bucks

 

regards

Guenter





Guenter Fred Mandel
 

Definitely not, Simon.
It is real RF that is not only present in the spectum. It can be received and measured by another receiver connected to the Discovery. Seems something parasitic.

Guenter

Uwe S.
 

Thank you for your prompt reply,

we have tested everything extensively, the error does not come from the outside.

The error was detected on 5 Discovery's.

Apart from this error, this is a top SDR receiver

Gruß Uwe

Kriss Kliegle
 

See my post this AM below:
Not all USB cables are equal? (Some notes while using my Airspy Discoveries...)

At first, I thought it was the Discovery rig, but found the QRM on the neighboring SDR-IQ as well. Using my little whip off the antenna port of both rigs yields the same pattern. Appears to be from the 
USB cable.

Kriss KA1GJU

Simon Brown
 

If you have this problem with 5 Discoveries and no-one else does then it’s your system.

 

Have you tried a Discovery with a different USB cable on a different PC – for example a laptop which is out of the building, away from noise?

 

Simon Brown, G4ELI

https://www.sdr-radio.com

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Uwe S.
Sent: 25 August 2019 15:36
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] Artefacts in new Airspy Discovery !? #airspy #airspyhfplus #sdrconsolev3 #sdrsharp

 

Thank you for your prompt reply,

we have tested everything extensively, the error does not come from the outside.

The error was detected on 5 Discovery's.

Apart from this error, this is a top SDR receiver

Gruß Uwe

Henry
 

These "artifacts" are definitely not caused by the USB cable or the PC or any neighbouring rigs. They are generated inside the HF+ Discovery. And they are no artifacts, they are real RF.
Some of them seem to be fixed like those around 4.7 MHz posted by Uwe. Others can easily be generated by switching off the automatic AGC and moving the HF ATT slider. You can almost give the "noise hills" any shape and shift them around over almost the complete SW spectrum.
When you connect a second SDR or a spectrum analyzer directly to the antenna input of the Discovery, you can "receive" the noise spurs with these devices. They are coming out of the antenna socket of the Discovery.
In the attached images you can see one where an SDRPlay RSP "receives" the spurs coming out of the Discovery's antenna socket. The others show more examples of spurs. You can monitor them all on a second SDR or spectrum analyzer.
I own a couple of different SDRs, but none of them procduces such spurs.
Although they may not bee seen at first glance in all every day reception secenarios, I think that a receiver with such a good sensitivity should not produce RF spurs up to a level of -110 dBm on its antenna socket and interfere with itself.

73s, Henry

Henry
 

Sorry Simon, but please read carefully:
Several owners of different PCs and systems have these RF spurs. They do not go away with 10 snap on ferrites on the USB cable and they do not go away when connecting the Discovery to a different PC, laptop or tablet. You can reproduce them identically in the same way on each system.
73s, Henry

Simon Brown
 

So,

 

No antenna, so the gain is set to the max? When an antenna is connected what happens?

 

Simon Brown, G4ELI

https://www.sdr-radio.com

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Henry via Groups.Io
Sent: 25 August 2019 17:13
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] Artefacts in new Airspy Discovery !? #airspy #airspyhfplus #sdrconsolev3 #sdrsharp

 

These "artifacts" are definitely not caused by the USB cable or the PC or any neighbouring rigs. They are generated inside the HF+ Discovery. And they are no artifacts, they are real RF.
Some of them seem to be fixed like those around 4.7 MHz posted by Uwe. Others can easily be generated by switching off the automatic AGC and moving the HF ATT slider. You can almost give the "noise hills" any shape and shift them around over almost the complete SW spectrum.
When you connect a second SDR or a spectrum analyzer directly to the antenna input of the Discovery, you can "receive" the noise spurs with these devices. They are coming out of the antenna socket of the Discovery.
In the attached images you can see one where an SDRPlay RSP "receives" the spurs coming out of the Discovery's antenna socket. The others show more examples of spurs. You can monitor them all on a second SDR or spectrum analyzer.
I own a couple of different SDRs, but none of them procduces such spurs.
Although they may not bee seen at first glance in all every day reception secenarios, I think that a receiver with such a good sensitivity should not produce RF spurs up to a level of -110 dBm on its antenna socket and interfere with itself.

73s, Henry

Guenter Fred Mandel
 

Simon and All,
Due tu my experiments i am very sure, it is no Software or digital signal processing or USB related issue.

It is parasitic RF-Spurious Signals (below -110dBm) which can be easily measured with a second receiver or a sprectrum Analyzer connected to the Airspy Discovery. It ist RF-Power (< -110dBm)  coming out of the Discovery Antenna Connector. And the Discovery itself receives those real Signals as it would be the case if those signals are fed in from an external source. 

These RF-spurs are not related to USB Emissions.. They exist also if the discovery ist powered by a clean Battery supply. And it is easy to measure these spurious emissions with a second receiver.

Please think RF  :-)
It likely could be a parasitic oscillation of the input stage or a crosstalk effect of an internal oscillator or PLL. Maybe caused by a unwanted ground loop on pcb or something similar.

Instead of guessing around guies, please do the follwoing experiment:
- Search the Spurs in the spectrum with the DicoveryAntenna Connecotr open or with 50 Ohm terminated. You probably will find them at 5 MHz and at 14.5MHz. (See screenshots in Posts above)
- connect then the Discovery to the Antenna Input of a second Receiver or SDR
- you will wath the same signals as shown in the spectrum of the Discovery. They are coming out of the Antenna Connector of the Discovery

Hence it is a real RF Signal emitted out of the Antenna Input of the Discovery. No digital artifact.

Most users won't recognize these spurs. Because external noise of a real antenna is higher, than the level of the spurs. They are normally covered by noise and have no negative effect on reception. But they still exist.

regards
Guenter

Henry
 

On Sun, Aug 25, 2019 at 06:18 PM, Simon Brown wrote:

No antenna, so the gain is set to the max? When an antenna is connected what happens?

The gain is not always set to the max. The spurs around 4.9 MHz occurr all the time reguardless of how the gain or AGC is set.
The other spurs suddenly come up when reducing the gain manually to certain levels, mostly around -20 dB, -24 dB or less. I originall thought they were self-oscillation in some kind of RF stage, but they do not respond to body capacity. You can touch the Discovery at any point with your fingers, the "oscillation" is not affected. Thus it cannot be self-oscillation.
When a powerful antenna is connected (e. g. an active one with high output) the spurs are suffocated by the local environment noise most of us have. When a small passive antenna is connected, the spurs are still noticeable. When a signal with various levels is injected from a signal generator, the spurs remain the same.

It is a pity that a receiver with basically a big potential creates such spurs and makes its good sensititiy partly useless.

73s, Henry

MadMike
 

Just wondering why this thread is on the SDR-Console group? Surely this should be on an Airspy group, it would not appear to be at all connected to Simon's excellent program.

Regards, Mike Simpson
South Penrith, NSW, Australia


jdow
 

Perhaps you should trundle over to the AirSpy list and make these observations over there. There is not much Simon can do to remove them.

{o.o}

On 20190825 09:51:09, Guenter Fred Mandel wrote:
Simon and All,
Due tu my experiments i am very sure, it is no Software or digital signal processing or USB related issue.
It is parasitic RF-Spurious Signals (below -110dBm) which can be easily measured with a second receiver or a sprectrum Analyzer connected to the Airspy Discovery. It ist RF-Power (< -110dBm)  coming out of the Discovery Antenna Connector. And the Discovery itself receives those real Signals as it would be the case if those signals are fed in from an external source.
These RF-spurs are not related to USB Emissions.. They exist also if the discovery ist powered by a clean Battery supply. And it is easy to measure these spurious emissions with a second receiver.
Please think RF  :-)
It likely could be a parasitic oscillation of the input stage or a crosstalk effect of an internal oscillator or PLL. Maybe caused by a unwanted ground loop on pcb or something similar.
Instead of guessing around guies, please do the follwoing experiment:
- Search the Spurs in the spectrum with the DicoveryAntenna Connecotr open or with 50 Ohm terminated. You probably will find them at 5 MHz and at 14.5MHz. (See screenshots in Posts above)
- connect then the Discovery to the Antenna Input of a second Receiver or SDR
- you will wath the same signals as shown in the spectrum of the Discovery. They are coming out of the Antenna Connector of the Discovery
Hence it is a real RF Signal emitted out of the Antenna Input of the Discovery. No digital artifact.
Most users won't recognize these spurs. Because external noise of a real antenna is higher, than the level of the spurs. They are normally covered by noise and have no negative effect on reception. But they still exist.
regards
Guenter

Henry
 

On Mon, Aug 26, 2019 at 10:22 AM, jdow wrote:
Perhaps you should trundle over to the AirSpy list and make these observations
over there. There is not much Simon can do to remove them.
a) I never wanted Simon do to anything against it!
b) Posting the subject in the Airspy group is not possible because the moderator there does not allow to discuss the matter. The corresponding posts, requests and comments were deleted or not allowed. We have tried!!!

Of course Simon cannot do anything against this. But the group here allows free speech and allows to speak out what we see and hear with the rig. No one of us wants to talk the Discovery bad. I personally regret that a receiver with such a high potential is not completely stainfree.

73s, Henry

Alan
 

Perhaps you should trundle over to the AirSpy list and make these observations over there. There is not much Simon can do to remove them.
Yes, I expect "prog" will have a suitable comment.
On the other hand is there any radio that is absolutely perfect? SDR processing is an ideal way of showing the slightest deficiency.
If these products are the only problem the Discovery has then it is still very good..

73 Alan G4ZFQ

jdow
 

Precisely - and if connecting an antenna swamps out the spurious who cares?
{^_^}

On 20190826 01:36:31, Alan via Groups.Io wrote:

Perhaps you should trundle over to the AirSpy list and make these observations over there. There is not much Simon can do to remove them.
Yes, I expect "prog" will have a suitable comment.
On the other hand is there any radio that is absolutely perfect? SDR processing is an ideal way of showing the slightest deficiency.
If these products are the only problem the Discovery has then it is still very good..
73 Alan G4ZFQ

Henry
 

In the meantime further investigations have shown that the "old" HF+ Dualport shows a similar behaviour when this not officially available preselector addon board ist installed. Not exactly on the same frequencies, but very close.
The "old" HF+ does not have the spurs without the preselector addon.
The issues must have come along with the input filters. Leif Asbrink assumes DC-DC converters there cause the spurs.

When an antenna is connected the spurs do not really go away. They are just covered by local RF noise and strong signals. But they are still there. And spurs up to -110 dBm can very well cause interference with weak signals in quiet locations.

73s, Henry

Henry
 

On Mon, Aug 26, 2019 at 10:53 AM, jdow wrote:
Precisely - and if connecting an antenna swamps out the spurious who cares?
I would not take this so easy. A spur with -99 dBm (this is S5!) is not a bed of roses.
And again: It does not go away when signals are present. I have tested this a lot with carriers of different levels injected from a signal generator. The spurs remain!
73s, Henry

Martin Ewing AA6E
 

General note: With complex digital systems and sensitive receivers, I'd be surprised if there were no "spurs" above the noise level at some frequencies. There are many digital clock and data signals in the box (in the chip). The question is just where and how strong the spurs are.

In practice, all we can expect is that they are weak enough or outside our bands of interest so they won't affect our operations.