SDR and signal-noise ratio

[Brookline]

Hello,
As you know signal- noise ratio is an important parameter in signals receiving. So i would like to compare the noise level with different sdr dongles. Noise can come from different origins: the antenna, the dongle receiver, atmospheric noise, domestic noise from 220v and probably others... My goal is to compare the noise level created by the sdr dongles.
I am using a MSI sdr panadapter with sdr uno. The noise i have, ANTENNA NOT CONNECTED, is s3 at 6 MHZ and s5 at 125 MHZ. My good old R7A trafic receiver has a noise at s 2 ( but his limit range is 30 MHZ). This is important for weak signal, as radioamateurs for ex. If you have some comment to this opinion you are welcome.
So i would like to know what is the noise level coming from your sdr dongle. I think the best is to see the strength value with antenna not connected, at 6 Mhz and 125 mhz...
thank you for your attention.

 

[KB4MSZ]

Shown below are what I have on my Sdrplay RSP2. Included are two screen captures for each of the two frequencies you requested. First set, 6 MHz with a 50 ohm load on the antenna port, then another with the port left unterminated.

Next set, 125 MHz with a 50 ohm load on the antenna port, then another with the port left unterminated.​

Not much difference between the terminated ports and the unterminated ports. What I found interesting with this test was that I had to remove all other antennas from the SDR unit, otherwise I could still receive a broadcast station that was in the upper 5 MHz range. I guess this demonstrates that the isolation between the different ports (3 in this case) isn't perfect.

Hope this helps.

 

[boatbod]

One of the challenges with SDR is that the signal level displays are uncalibrated and cannot be used for absolute measurement. Best case you may be able to draw some relative conclusions between hardware if everyone is using the same software, but unless you can attach lab equipment and inject a known signal level you are just guessing.

 

[Brookline]

Shown below are what I have on my Sdrplay RSP2. Included are two screen captures for each of the two frequencies you requested. First set, 6 MHz with a 50 ohm load on the antenna port, then another with the port left unterminated.

View attachment 80823
View attachment 80824
Next set, 125 MHz with a 50 ohm load on the antenna port, then another with the port left unterminated.
View attachment 80825View attachment 80826

Not much difference between the terminated ports and the unterminated ports. What I found interesting with this test was that I had to remove all other antennas from the SDR unit, otherwise I could still receive a broadcast station that was in the upper 5 MHz range. I guess this demonstrates that the isolation between the different ports (3 in this case) isn't perfect.

Hope this helps.

hello kb4msz,
first thank you for the pictures.
It seems at 6mhz you have s1 level. However it seems at this 6mhz you have a small signal, so the noise level should be a few lower... At 125mhz you are about s4...
I send a copy of the msisdr -sdruno screen also at 6 and 125mhz ( not exactly because you will see at these frequencies i have some signals,
mainly at 6 mhz although the antenna is not connected.. where does this signal comes from? SDR mysteries...) You will see my noise level is about s3 - s4 so not very different with you. I never did some smeter calibration on the sdruno...I have to say the msi-sdr dongle is a low cost model, about 50$ at amazon... I think with low cost we can t hope high perfomances... Bus this msi seems not so bad...in the evening i can hear amateurs in the 80m band, but i think only the strong ones, here not far from Paris......
I have to say i am used to my trafic receiver which is an r7a from Drake. I bought it in 1983 ant the price today would be about 500$! So it is difficult to compare msi and r7a! Problem with r7a is the range is limited at 30 mhz... The noise level r7a is at s1 or 2 ay 6 mhz...
So my goal is to compare different sdr dongles because i plan to buy an other... maybe the ''ham_it_up_plus'' from nooelec... Do you know something about it?
So thank you again and best 73's...

 

[Brookline]

hello kb4msz,
first thank you for the pictures.
It seems at 6mhz you have s1 level. However it seems at this 6mhz you have a small signal, so the noise level should be a few lower... At 125mhz you are about s4...
I send a copy of the msisdr -sdruno screen also at 6 and 125mhz ( not exactly because you will see at these frequencies i have some signals,
mainly at 6 mhz although the antenna is not connected.. where does this signal comes from? SDR mysteries...) You will see my noise level is about s3 - s4 so not very different with you. I never did some smeter calibration on the sdruno...I have to say the msi-sdr dongle is a low cost model, about 50$ at amazon... I think with low cost we can t hope high perfomances... Bus this msi seems not so bad...in the evening i can hear amateurs in the 80m band, but i think only the strong ones, here not far from Paris......
I have to say i am used to my trafic receiver which is an r7a from Drake. I bought it in 1983 ant the price today would be about 500$! So it is difficult to compare msi and r7a! Problem with r7a is the range is limited at 30 mhz... The noise level r7a is at s1 or 2 ay 6 mhz...
So my goal is to compare different sdr dongles because i plan to buy an other... maybe the ''ham_it_up_plus'' from nooelec... Do you know something about it?
So thank you again and best 73's...

sorry i made a mistake... the r7a today corresponding price wouls be 5,000$ (five thousand, because have still some problem with my english...)and not 500$....

 

[Brookline]

One of the challenges with SDR is that the signal level displays are uncalibrated and cannot be used for absolute measurement. Best case you may be able to draw some relative conclusions between hardware if everyone is using the same software, but unless you can attach lab equipment and inject a known signal level you are just guessing.

hello boatbod
sorry to be a few late... i agree the sdruno smeter is quite relative... but what i did was to compare the sdr uno smeter with the one on my Drake r7a trafic receiver... and i have seen the smeter values are about the same. Ant i do not have a lab at home! But my concern is not to have an exact smeter value but to know why the noise level is so high without the antenna, s3 to s4...The reason probably is it is a low cost device, about 50$... I never did smeter calibration on sdruno, do not even know if it is possible... But my goal is only to compare with other sdr dongles... I plan to buy
an ''Ham it up plus'' from nooelec dongle which is working with a converter for low frequencies. Do you know this device?

 

[DRL-XM43]

I use this to try and see relative ratio with different set up's

 

[Brookline]

I use this to try and see relative ratio with different set up's

View attachment 80942

hello drl xm43, thanks for the picture... it seems it is from an rtl802T and i dont know this device.But as i know this is no more on the market, I looked at the rtl sdr.com web page and have to tell honestly i did not understand very much what they are making... They write about RTL820T2 but no frequency range.... Maybe i missed something... however i m mainly interested in medium waves, sW receiving... My goal was to compare signal-noise ratio between different sdr dongles. But after thinking a few more to that, i think it is not possible. The smeters calibration could be different from one model to an other... the only way is to buy the device... and find before some opinion on the web...
thank you again.

 

[Brookline]

hello boatbod
sorry to be a few late... i agree the sdruno smeter is quite relative... but what i did was to compare the sdr uno smeter with the one on my Drake r7a trafic receiver... and i have seen the smeter values are about the same. Ant i do not have a lab at home! But my concern is not to have an exact smeter value but to know why the noise level is so high without the antenna, s3 to s4...The reason probably is it is a low cost device, about 50$... I never did smeter calibration on sdruno, do not even know if it is possible... But my goal is only to compare with other sdr dongles... I plan to buy
an ''Ham it up plus'' from nooelec dongle which is working with a converter for low frequencies. Do you know this device?

hello boatbod, this is a continuation of my previous post to you... I have thought to your post where you said signal-noise ratio should need a lab... And i think that is unfortunately right. The smeters calibration could be different from one dongle model to an other, depending the lab maker... More, in hdsdr there in an option to re-calibrate the smeter....So the only way is to buy the device... and find before some opinion on the web...

 

[DRL-XM43]

hello drl xm43, thanks for the picture... it seems it is from an rtl802T and i dont know this device.But as i know this is no more on the market, I looked at the rtl sdr.com web page and have to tell honestly i did not understand very much what they are making... They write about RTL820T2 but no frequency range.... Maybe i missed something... however i m mainly interested in medium waves, sW receiving... My goal was to compare signal-noise ratio between different sdr dongles. But after thinking a few more to that, i think it is not possible. The smeters calibration could be different from one model to an other... the only way is to buy the device... and find before some opinion on the web...
thank you again.

Standard RTL2832U chipset - common and recent V3 NooElectric