Problem with the Gain Control setup in ExtIO 3.5

[DaveB]

Hi Tech support - one to look at after the holidays.

The way in which the total system gain is controlled when turning on or off the LNA has totally changed - I hope due to an oversight. This gives rise to a big issue when running with the AGC turned off. There are good reasons to run with AGC off if you want to compare signals across a wider spectrum and you don't want the base line noise floor changing all the time. This is particularly so if running a frequency scanner that is looking at the signal strength.

I've attached three screen shots with explanatory notes - unfortunately there is a limit to three so you'll have to trust me that the LNA off settings look the same on both ver 3.3 and 3.5

ver 3.3 LNA ON

SDRPlay_ExtIO_3.3_LNA_Gr0.jpg (158.4 KiB) Viewed 23768 times

in ver 3.5 the total system gain shows as 57 dB

ver 3.3 LNA OFF

SDRPlay_ExtIO_3.3_LNA_GR24.jpg (133.15 KiB) Viewed 23768 times

in this version the Gain Reduction on the right appears to be the total system gain reduction

ver 3.5 LNA off

SDRPlay_ExtIO_3.5_LNA_GR24.jpg (168.68 KiB) Viewed 23768 times

in this version the Gain Reduction on the right appears to be the IF Gain reduction and we now have a separate line for showing the total system gain reduction.

Basically in the new version when you turn OFF the LNA the overall system gain goes down 24dB. In the old version the overall system gain stayed the same and the IF gain was reduced by 24 dB to compensate. The effect of this was that a small increase in signal to noise ratio could be obtained with the LNA without having to make other adjustments

What that means is that if you are in a strong signal situation and need to turn off the LNA to avoid inter-modulation products you suddenly lose 24dB of gain and signal to noise ratio drops dramatically - a manual adjustment of the IF gain is then needed to bring the signal to noise ratio back up.

In my particular case with different aerials it means that instead of simply being able to turn off the LNA to compensate for one having a pre-amp and the other not - I now have to make a massive adjustment to the IF gain to try and balance things out when switching aerials. My immediate solution is to re-install version 3.3

I hope I've explained the issue clearly

Having read your post I don't think you meant this to happen. With AGC on you can see the total system gain reduction jump by 24 dB when turning the LNA on/off on ver 3.5.

BTW I do like the on/off button to control the LNA - much better

Regards

David

SDRplay user for almost a year

[Tech_Support]

Hello David,
This was in fact a deliberate choice as we thought it better to separate the LNA from the remainder of the gain control. We can change this in a future release if people prefer it as you suggest.

Sincerely

SDRplay Tech_Support

[DaveB]

Hopefully people will play with this and post comments.

What I think is that instead of a smooth transition in gain under the old method - you are now introducing and abrupt 24dB change in gain. For me that is not good as under certain circumstances - and my situation can't be unique - beaming towards a strong transmitter site will result in mixer overload with the LNA on. As already stated - in the old gain model turning the LNA off removed the mixer overload but preserved the overall gain setting. With the new method turning the LNA off, unless AGC is on, results in a 24dB drop in overall gains which needs to be manually compensated.

I always run with AGC off to give a stable noise floor for judging signal strengths when DXing and run with less gain than the AGC would set but without losing s/n ratio on weaker signals. That way overload is avoided.

Please note that when mixer overload occurs when LNA is on a pointing at a strong station - no amount of overall gain reduction gets rid of the inter-modulation. Which is as expected as we have no control over mixer gain.

If SDRPlay users could reply to this thread with a simple "Like it" or "Don't like it" then TechSupport will know what is best for most people.

Thanks

David

[WhoaNellie]

I don't like it (v 3.5) because I too always have the AGC off and like being able to manually adjust the LNA threshhold and also the gain reduction (I usually am at 80 or 85 db reduction on the AM BCB). So I went back to using v 3.4.

[F1BJB]

I too have a problem with the new EXTIO3.5.
Using SDRsharper I cannot go below about 12.4MHz of center frequency tuning.
I have a box saying "Warning out of range"
This is with Wxp It seems OK with Window 7 /64
version 3.0 is OK in both cases.
Same problem with sodira 0.99
I could use W7 but the drivers of my hardware are marginal at best and this PC is not very stable.

[wd8kel]

So, how about a compromise?

There are times I like to run with the AGC off and others to have it on, depending on what I'm up to. Some days, manually fiddling with the gains would be OK. Others times would not. I may just elect to stick with the older version. (Though I just noticed it's been a while since I've been over here and am still running v3.0. <sigh> I guess I need to look at the site more often.)

Can you put a switch in the interface to chose the method of operation?

Rick