sdrom33 wrote:Hi z inputs cannot be compared with 50 ohm in of rsp1a. Better compare 50 ohm of all sets to have best idea.
Sabrina1984 was wondering why the performance of the RSP1A was not doing as well as the NRD525 and looking for tips on how to improve performance. I made a few suggestions like using Low IF, Setting the LO to 1000 kHz and using external MW reject filters and preselectors.
However there is only so much you can do with a receiver that has a high noise figure (NF) below 500 kHz when you use a poor antenna. The lower the Noise Figure the better when looking for weak signals under these conditions. SDRplay has published data that shows the 50 ohm ports of the RSP1A, RSP2 and RSPduo have about a 10 dB higher noise floor than the HiZ port of an RSP2 or RSP duo at 1 MHz. The NF will be even worse below 500 kHz. Here are some specs comparing the RSPduo with the RSP1A. This data is from the SDRplay data sheets for each product.
Noise Figure @ 1 MHz. - with maximum gain
RSP1A 21.2 dB
RSPduo Tuner 1 SMA 20.77 dB
RSPduo Tuner 2 SMA 19.33dB
RSPduo Tuner 1 HiZ 11.66 db ****
Sensitivity for AM signal @ 136 kHz, - with 60% Mod - 12 dB SINAD
RSP1A 6.02 microvolts
RSPduo Tuner 1 SMA 6.16 microvolts
RSPduo Tuner 2 SMA 5.36 microvolts
RSPduo Tuner 1 HiZ 0.37 microvolts ****
Sensitivity for SSB/CW signal @136 kHz, - 1.5 kHz. BW - 12 dB SINAD
RSP1A 2.26 microvolts
RSPduo Tuner 1 SMA 2.29 microvolts
RSPduo Tuner 2 SMA 1.99 microvolts
RSPduo Tuner 1 HiZ 0.18 microvolts ****
**** HiZ port is 1000 ohms but microvolt sensitivity has been converted to 50 ohm
SDRplay do not publish detailed NF specs for the RSP2 but in my experience I find slightly worse performance than the RSPduo but better than the RSP1A.
The RSP1A is a good SDR receiver but it has some limitations compared to the RSP2 and the RSPduo. It is the lowest cost member of the family but offers great value. For serious LF DXers the duo is the best choice. The HiZ port and the built-in MW rejection filter give the best weak signal reception below 500 kHz.