SDR VLF, LF and MF comparison
Posted: Fri Oct 02, 2020 7:56 pm
Hi all.
Long message follows!
I made some comparison on VLF, LF and MF (ITU designations) on
AFERDI NET
RX-888
AirSpy HF+ (2 connector)
and AirSpy HF+ Discovery
on my 135m BOG in 0 deg (due North) direction.
I made 1 1/2 minutes IQ recordings on each covering 10 kHz to ~250 kHz.
I also compared them on MF (= MW) 1440 kHz on Radio 208 in Köbenhavn/Ishöj 0.5kW at about 202 km distance from me in broad daylight (abt 12:20Z). The antenna used here was a 40 m Beverage in 310 deg.
I do have some local QRM from self guiding lawn mowers (Tx'ing at ~50 kHz with a broadband modulation as well as plenty of harmonics) about 60 m away (closest neighbor).
It is not a very scientifically made comparison, but you can listen to the IQ recordings yourself and make your own judgement.
While listening to Radio 208, I could not detect any clear difference between the different SDR's. Very much the same readability on all four SDR's. I had not expected anything else. It might be different at night when the band is full of strong signals. I will try to make the same comparison under these conditions at a later stage.
Recording VLF and LF, I just switched the antenna connector between the different SDR's and recorded for 90 seconds.
They show quite different spectrum's, I must say. Quite surprising, actually. I have no expatiation to the difference in recorded spectrum between the different SDR's. No filters were used in front of the SDR's, just the antenna right into the SDR. If anyone has an explanation to the differences in the shown spectrum, please post it.
I enclose pictures of the spectrum in this posting and will try to up-load the IQ-files somewhere you all can access them. Is there any space on this forum where I can put them? It was not possible to attach them to this posting.
The files are:
01-Oct-2020 140906.185 0.119MHz, AirSpy HF+ Discovery (Screenshot-2020-10-02-211002.png)
01-Oct-2020 141347.908 0.119MHz, AirSpy HF+ (2 connector) (Screenshot-2020-10-02-211258.png)
01-Oct-2020 141837.636 0.125MHz, RX-888 (Screenshot-2020-10-02-211351.png)
01-Oct-2020 142336.198 0.120MHz, AFEDRI Net (Screenshot-2020-10-02-211439.png)
You can clearly see that the AirSpy HF+ (2 connector) roles off below 40 kHz while the AirSpy HF+ Discovery holds all the way down to below 20 kHz.
You can also see that the RX-888 has a big hump at 40 to 120 kHz that is not as pronounced at the other SDR's. It also has a dip at about 180 kHz that you do not see on the other SDR's.
Interesting. I do not know how to interpret it.
73 / Ingolf, SM6FHZ
Long message follows!
I made some comparison on VLF, LF and MF (ITU designations) on
AFERDI NET
RX-888
AirSpy HF+ (2 connector)
and AirSpy HF+ Discovery
on my 135m BOG in 0 deg (due North) direction.
I made 1 1/2 minutes IQ recordings on each covering 10 kHz to ~250 kHz.
I also compared them on MF (= MW) 1440 kHz on Radio 208 in Köbenhavn/Ishöj 0.5kW at about 202 km distance from me in broad daylight (abt 12:20Z). The antenna used here was a 40 m Beverage in 310 deg.
I do have some local QRM from self guiding lawn mowers (Tx'ing at ~50 kHz with a broadband modulation as well as plenty of harmonics) about 60 m away (closest neighbor).
It is not a very scientifically made comparison, but you can listen to the IQ recordings yourself and make your own judgement.
While listening to Radio 208, I could not detect any clear difference between the different SDR's. Very much the same readability on all four SDR's. I had not expected anything else. It might be different at night when the band is full of strong signals. I will try to make the same comparison under these conditions at a later stage.
Recording VLF and LF, I just switched the antenna connector between the different SDR's and recorded for 90 seconds.
They show quite different spectrum's, I must say. Quite surprising, actually. I have no expatiation to the difference in recorded spectrum between the different SDR's. No filters were used in front of the SDR's, just the antenna right into the SDR. If anyone has an explanation to the differences in the shown spectrum, please post it.
I enclose pictures of the spectrum in this posting and will try to up-load the IQ-files somewhere you all can access them. Is there any space on this forum where I can put them? It was not possible to attach them to this posting.
The files are:
01-Oct-2020 140906.185 0.119MHz, AirSpy HF+ Discovery (Screenshot-2020-10-02-211002.png)
01-Oct-2020 141347.908 0.119MHz, AirSpy HF+ (2 connector) (Screenshot-2020-10-02-211258.png)
01-Oct-2020 141837.636 0.125MHz, RX-888 (Screenshot-2020-10-02-211351.png)
01-Oct-2020 142336.198 0.120MHz, AFEDRI Net (Screenshot-2020-10-02-211439.png)
You can clearly see that the AirSpy HF+ (2 connector) roles off below 40 kHz while the AirSpy HF+ Discovery holds all the way down to below 20 kHz.
You can also see that the RX-888 has a big hump at 40 to 120 kHz that is not as pronounced at the other SDR's. It also has a dip at about 180 kHz that you do not see on the other SDR's.
Interesting. I do not know how to interpret it.
73 / Ingolf, SM6FHZ