Re: Receive Antenna & Impedance "Matching"
Posted: Mon Jul 15, 2019 10:54 am
.. pity about the page break, I'd better post the comparison pic again
Here is the Kenwood Here is the RSP1A c) From the spreadsheet analysis of the many hundreds of spots from the last 24 hours it appears the RSP1A's WSPR noise floor is -29dB as compared with -33dB from the Kenwood so there is not much in it otherwise as you can see from the stronger SNRs above.
Thoughts:
I don't believe the difference is lack of RF gain.
Months of testing of the Kenwood on it's own (and an FT-991 and an FT-857) shows that turning their built in preamps on or off makes no difference at all to their ability to hear WSPR spots down to the -33dB WSPR noise floor which all 3 achieved.
RF bandwidth does matter.
I tried the RSP1A with and without the toroid preselector illustrated above and the preselector improved it's performance by around 4 to 6dB.
My impression is that the AGC action was moderated by the preselector, ie. strong adjacent stations on 40m caused more AGC action on the RSP than on the other radios. Of course that's only my impression and there may be other factors might make a difference, eg. I'm not sure what part the ADC resolution might play.
--
Because my Windows box is limited to a VM on a Mac I have not been able put two independent RSPs running SDRuno up against each other so that I could test out the twin coil preselectors, the differences in the dynamics of the RSP against an analogue radio make it too hard to properly analyse the anticipated results.
It's been fun.
Here is the Kenwood Here is the RSP1A c) From the spreadsheet analysis of the many hundreds of spots from the last 24 hours it appears the RSP1A's WSPR noise floor is -29dB as compared with -33dB from the Kenwood so there is not much in it otherwise as you can see from the stronger SNRs above.
Thoughts:
I don't believe the difference is lack of RF gain.
Months of testing of the Kenwood on it's own (and an FT-991 and an FT-857) shows that turning their built in preamps on or off makes no difference at all to their ability to hear WSPR spots down to the -33dB WSPR noise floor which all 3 achieved.
RF bandwidth does matter.
I tried the RSP1A with and without the toroid preselector illustrated above and the preselector improved it's performance by around 4 to 6dB.
My impression is that the AGC action was moderated by the preselector, ie. strong adjacent stations on 40m caused more AGC action on the RSP than on the other radios. Of course that's only my impression and there may be other factors might make a difference, eg. I'm not sure what part the ADC resolution might play.
--
Because my Windows box is limited to a VM on a Mac I have not been able put two independent RSPs running SDRuno up against each other so that I could test out the twin coil preselectors, the differences in the dynamics of the RSP against an analogue radio make it too hard to properly analyse the anticipated results.
It's been fun.