FInding the best SDRC settings for the RX888

[HB9VQQ]

Here is an attempt to find the best settings in SDRC by comparing WSPR decode performance. This is my test setup

Station setup at HB9VQQ.jpeg (67.57 KiB) Viewed 30494 times

First, I created a baseline to see how much the DX (Spots > 3000 km) WSPR decodes differ from each other with the same SDRC configuration during 10m band peak propagation

SDRC settings.PNG (6.38 KiB) Viewed 30494 times

Baseline.jpeg (110.08 KiB) Viewed 30494 times

Deviation < 1%

Next I will change the gain setting on one of the RX888 and see if there is any change. Stay tuned

[HB9VQQ]

I changed the gain setting (HF Gain) on HB9CU/4 from 50 to 20 dB, which degraded the decoding performance by about 5%. No settings changed on HB9CU/5

20dB_Gain.PNG (6.21 KiB) Viewed 30484 times

20dBSpots.PNG (11.3 KiB) Viewed 30484 times

20dB_10mDXSpots.PNG (126.46 KiB) Viewed 30484 times

Next, increase the gain on HB9CU/4 to 70 dB and see if there is any positive change in the number of DX decodes.

[jdow]

If sensitivity at any cost is your requirement then increase gain until the spectrum display splashes full of junk. Back off one step and live with it. For a more balanced approach set gain high, tune a signal with constant or no modulation, and adjust gain downward until the SNR perceptibly changes. Leave it there for balanced weak signal and strong signal performance. Back off the gain reduction one step to favor signals. The gain steps you SHOULD use are each perhaps 5dB or 6 dB. And I suspect changing to 70 dB caused problems or at the very least showed no more than an imaginary improvement. The 20 dB to 50 dB step is staggeringly large for showing such a small change in performance.

Note that front end attenuation will change most likely change the performance of the splitter.

{^_^}

[HB9VQQ]

Noted, thanks. I don't see any improvement with higher gain settings.

[jdow]

That suggests that if there is a 30 dB setting use that for the last little bit of sensitivity since it seems to work without spurs for you. Otherwise use the 20 dB setting for normal use. (Even 25 dB would probably get you to a gnat's whisker of as good as it gets.)

(I don't remember what the RX666 MKII has for gain settings so I sure as heck do not know what the RX888 has.)

{^_^}

[HB9VQQ]

I don't understand how the SDRC gain settings correlate with the capabilities of the RX888..

SDRC-RX888_gain.PNG (45.03 KiB) Viewed 30411 times

https://www.rx-888.com/rx/

RX-888_specs.PNG (13.7 KiB) Viewed 30411 times

I am confused

[KA1GJU]

Not having one, I suppose higher the number, higher the gain?
On a similar note, the SDRPlay "RF Gain" numbers (0 to 9) have weird effects. In the attached image I went from a RF Gain level of "3", "5", and "7" in that order. One would think the noise floor would be highest on the "7", but the noise floor is -98dBm on "3", dropping to -120dBm on "5", and further dropping to -121dBm on "7" (along with all the AM BC garabge/products).
I don't think there's a correlation between gain numbers and 'real gain'.

[HB9VQQ]

I still wonder how the HF Gain in SDRC influences the gain level of -10 to + 33dB of the RX-888 Mk2

[jdow]

Considering there is no HF Gain within SDRC.... That menu item you see is the RX888 MKII gain.

1. Hook up the system and get it started.
2. Set front end gain about mid range. You should see a spectrum.
3. Move gain up and down until you see all the stations and the noise level changing the same.
You should be able to increase gain until the spectrum seems to splash full of grass.
4. Reduce gain until the grass is gone.
5. Tune to a signal on which you can hear a little noise. An unmodulated signal is most ideal.
6. Enable the SNR meter.
7. Reduce gain until the SNR meter just shows a reduced SNR. As long as the overload grass is not present you are done.
8. If the overload grass is still present reduce gain until it vanishes. You are done.

Any further fiddling should be in small steps to fit the particular situation you have. For example, usually you can set the gain maybe 10 dB below where the grass vanishes and do very well if you are diving way into the noise to catch really weak stations.

{o.o}