CLARIFICATION ON SENSITIVITY PERFORMANCE COMPARISON RSP-1A VS. RSPduo & FOCUS ON NEGATIVE S/N
I believe the previous two posts have introduced confusion on several important questions and with this post I wish to clarify some ESSENTIAL concepts.
1. RSP-1A and RSPduo Sensitivity & Noise Figure specifications
The beauty of handling equipment by SDRplay is that you do not have to speculate on performance parameters, because they are readily supplied by the Manufacturer. Here we are concerned with the sensitivity & NF specifications of the above mentioned RSp's and here is the data readily available from the RDSplay site.
From this table it is evident that at LF the RSPduo HI Z input has a 10 dB Noise Figure advantage over the RSP-1A.
2. Significance of Noise Figure
If a device, any device, receives a signal with a S/N ratio of 10 dB and has a Noise Figure of 8 dB, then the device will provide at its output the same signal with a S/N ratio of: 10-8= 2dB. If the same device receives a signal with a noise ratio(S/N) of -10 dB, it will provide at its output the same signal with a noise ratio (S/N) of: -10-8= -18 db.
In other words the device DEGRADES the received S/N by an amount in dB EQUAL TO ITS RATED NOISE FIGURE.
3. Significance of the advantage of the RSPduo over the RSP-1A in WSPR reception
If I am receiving a WSPR signal with the RSP-1A and the S/N coming from the antenna is -20 dB, the total S/N ratio will become: S/N= -20-21.2 = -41.2 dB.
If I am receiving a WSPR signal with the RSPduo and the S/N coming from the antenna is -20 dB, the total S/N ratio will become: S/N= -20-11.75 = -31.75 dB.
Thus the RSPduo has an extremely significant advantage (10 dB!) over the RSP-1A.
4. Significance of receiving bandwidth
The detection bandwith is neutral in the comparison. If we go from the 1800 Hz referred to in the SDRplay specifications, to, for example 800 Hz, the noise figure in both receivers will improved by:
NF1800 = 10*LOG(10) (1800) = 32.55 dB
NF800 = 10*LOG(10) (800) = 29 dB
Improvement = 32.55 - 29 = 3.55 dB
So, at the end of the day, the RSP-1A NF will become: 21.2 - 3.55 = 17,55 dB and the RSPduo NF will become: 11.75 - 3.55 = 8.2 dB and the corrected S/N's will become:
RSP-1A: -20 - 17.55 = -37.55 dB
RSPduo: -20 - 8.2 = -28.2 dB
AND THE SDRduo will still give an ADVANTAGE ON WSPR RECEPTION OF 10 dB as before!!
It is not true that with negative S/N the receiver sensitivity has no relevance: in fact the contrary is true and surely the RSP2 and the RSPduo have the potential of providing an extremely significant advantage of a 10 dB Noise Margin on WSPR reception.
6. Unexplained anomaly
If, as reported by vk7jj, it is possible to detect and confirm an improvement in WSPR reception results, not because of a restriction of the DETECTION BANDWIDTH, but because of a selectivity improvement at the receiver's input, then we are in presence of an unexplained anomaly that needs further investigation.
For further reading on these ESSENTIAL concepts, please read the thread shown below, which includes an extremely clear, masterful and praiseworthy tractation on Noise Figure measurement and how SDRplay interacts with S/N, NF and Noise Floor by Roger.
https://www.sdrplay.com/community/viewt ... =assessing