Front-End Files

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Front-End Files

Post by Sam » Mon Jun 14, 2010 11:36 pm

Hi All,

I want to update you on a new feature of the MSA software. While there is not yet a new release, we can do a release whenever there is sufficient interest.

In spectrum analyzer modes, there are various possible probes, amplifiers, attenuators and other devices that may be used to interface a signal source to the MSA. These are referred to as front-end devices. If such a device, such as an amplifier, has a flat frequency response, it is easy to mentally adjust the displayed signal strength to subtract out the amplifier gain, thereby finding the true strength of the signal source. But front end devices rarely have flat response over a broad frequency range. As a simple example, you might create a probe that puts a 1k resistor in series with the signal, to avoid excessive loading of the signal source. The response of such a probe will change significantly over frequency.

The new feature allows the use of "front-end files", which describe the frequency response of a given front-end device. The net effect is to make the front-end device "invisible" to the MSA, so it does not distort the displayed signal strength.

It is simple to create a front-end file. In transmission mode, you calibrate with the TG cabled to the MSA input. Then insert the front end into the signal path and do a scan. Save the scan results as a front-end file. When you are using that front-end device, you simply load its front-end file to do the necessary compensation.

All this is relevant in SA mode, and in SA+TG mode. In VNA modes, the normal VNA calibration takes care of the necessary compensation. VNA mode is needed only to create the front-end file, with a transmission scan. Or, if you don't have the PDM to measure phase (which is irrelevant), the file is created by a scan in SNA mode (scalar network analyzer).

All this is described in

Sam W.

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