RX-888: sensitivity report

[NO6B]

NBFM 12 dB SINAD level is 0.9 uV from 144 through 450 MHz, +/- 1 dB or so. Funny thing is that optimum sensitivity is achieved with the VHF gain slider set to 15 to 17, anything higher & the sensitivity degrades badly. I have my sig. gen. connected directly to the VHF input of the RX-888 so I don't see how it can be overloading with the gain set only just above mid-range. At 52 MHz it gets better: ~0.4 uV, & optimum sensitivity is with the gain slider in the low to mid-20s. The same thing happens at 927 MHz, where the 12 dB SINAD is 0.35 uV - slightly better. I also notice that if I change the bandwidth, the sensitivity gets very poor until I bump the VHF gain slider one way or another. It's almost as if changing the BW or some other SDR parameters messes up the VHF gain & it has to be reset. FWIW the 12 dB SINAD at 16 & 29.6 MHz is ~1.0 uV. Maybe not that meaningful a measurement at HF but at least it's comparing apples to apples. I understand the RX-888 has no HF preamp so this is probably normal.

I wanted to try HDSDR to compare the performance, but I can't get it to go above 30 MHz. I do see the entire 0.5-30 MHz spectrum (impressive), & the SDR control has a VHF-UHF button but nothing happens when I click it. It does have a LW-MW button, which lets me see down to near DC although I see a lot of extraneous noise coming out of my 8640B below 1 MHz. I've never used it that low so I have no idea how well it works there. Just for fun I tried my function generator & I can see signal all the way down to ~20 kHz.

Is the "hacked" version of HDSDR the only one that works above 30 MHz, or is there something else to try? The ExtIO_sddc.dll version I'm using is 0.96, file date 3/2/2018.

Thanks

Bob NO6B

[fei666888]

In fact, I found that the UHF effect is not very ideal. It may be related to the sensitivity of the R820T2 itself. I have compared AIRSY R2 with RX888. R820T2 performs better on R2. We tried to set the internal IF filter bandwidth of R820T2. But it seems to have no effect?
But the RX888 effect is very good in terms of HF effect, better than the official SDRPLAY 1A in my hand. Although RX888 only has a 64M LPF filter, it shows a better SNR value when receiving the same DRM signal.

[NO6B]

OK I found the v0.98 DLL that enables VHF/UHF for the RX-888 in HDSDR. I was using v0.96 which only had HF enabled.

It's the first link on Oscar Steila's blog page: <http://www.steila.com/blog/index.php?co ... id_post=32>

I remeasured the UHF sensitivity using HDSDR & it seemed to be 1 to 2 dB better than what I could achieve in SDRC given the same IF bandwidths & audio shaping. The attached MP3 file is SDRC for the first 6 seconds & HDSDR for the rest, both with VHF gains set for best S/N.

[NO6B]

Tried the ExtIO DLL posted by fei666888 in a previous thread here, & was able to squeeze out another dB of S/N, so we're down to 0.55 uV for 12 dB SINAD at 440 MHz. This is 2 dB better than what I can get out of SDRC & its single gain slider, though 0.55 uV is still at least 7 dB off of what I think it should be given the R820T2 front-end.