It's raining elephants – VA2GKA / F4GKA

To follow up on some questions about my QRSS grabber setup, I decided to write this short article focuses on some SpectrumLab tricks.
I tried to answer these questions :

• Get different speeds & captures using a single receiver
• Get extra high screenshot resolutions with SpectrumLab
• Use best practices with an SDR-IQ receiver

1. If you want get two or more sceenshots with SpectrumLab (at different speeds or settings), you need start two instances of the software because the program do not allow multiple captures at the same time or different FFT sizes. The main problem with a standard setup using Windows is that when you open a peripheral, (in this case, your sound card) it is locked and you cannot open it a second time. Many sound card have this problem.

The solution that I choose is to use a virtual audio pipe. VAC (Virtual Audio Cable) is a software that allows to create many virtual soundcards on your system, usable as pipes. Moreover, the developer gives tiny software called “Audio Repeater”. His name speaks for itself. You just need to open your sound card with this application and redirect the flow on a pipe. This pipe can be opened by different programs and/or different instances of SpectrumLab.

After, you just need to define 2 different configurations and start 2 instances of your analysis program.

VAC main control panel  – 6 stereo pipes used (some errors reported on the right side after a long time of use)

The control panel of  Audio Repeater – Reading data flow on the sound card and redirecting this flow on my first virtual pipe – 16bits used on this setting for a comparison

But you can also make a data treatment in the first program, redirect the output on another virtual pipe and reopen this second pipe with another instance of SpectrumLab. This case is interesting if you want downsample your primary signal to save CPU resources (FFT on high bandwidth take a lot of calculation) on post processing programs.

2. SpectrumLab periodic captures are based on the view of the main screen.If you define an extended resolution using the configuration file, the software will automatically adjust these settings to the maximum windows size of your display. So, you just need to increase your screen resolution, but everyone does not have a display that allows 4096 by 2048 pixels… This is not a problem because you can use an extended virtual area with Windows. The true resolution is kept for your monitor, but if you move your mouse on a side, you can push the screen to access to this extended area. It’s very boring if you use this trick on your primary computer, but it’s perfect for a QRSS grabber running in the garage :)

The alternative way is to use “RemoteDesktop“. In this way, you can define a big resolution and use the scrollbars to access to the entire area (just check the advanced settings). But use this option carefully if you access to your remote computer over the Internet. If your bandwidth (of your modem) is too low, the refresh rate may prevent you to access to your remote application/computer and the control will be lost.

Below, the details for an nVidia video card :

Add resolutions on the main control panel – nVidia drivers

Another clic…

Follow the steps – In this way, your can create a virtual extra resolution

3. SDR-IQ receivers have excellent performance and low costs. But it is more suitable to avoid the area around the central frequency (BF) and the border frequencies just below the Nyquist frequency. So, you can start a first instance of SpectrumLab to offset the signal, redirect the output to a virtual pipe and use two other instances of the program to display the waterfalls at two different speeds. You can also apply an I/Q amplitude and phase correction. These next pictures illustrate these process.

Spectrum Lab Components box – IQ amplitude & phase correction

Spectrum Lab Components box – Frequency offset using IQ mixer – Alternatively, you can use the filter to create an offset (caution to the FFT size)