Re: Difference between S-Meter and Spectrum readings


Alberto I2PHD
 

On 2019-05-22 22:22, Marcus D. Leech wrote:

The Perseus has some kind of log-amp RSSI unit in the "front end".

I don't think so. Between the antenna and the ADC (an LTC2206-14) the only active component is a THS4509 Wideband, Low-Noise, Low-Distortion, Fully-Differential Amplifier. The incoming signal is then converted by the ADC to the numeric realm, and any subsequent processing, S value computation included, is performed by the accompanying Perseus software, which knows which bandwidth has been selected by the user, and of course the S value reported is referred to this bandwidth.

There are no uncertainties, as no analog stages are involved in this process, all is done numerically.
If you don't believe me, ask Leif Asbrink, who has performed extensive measurements with the Perseus hardware. And also the Perseus HW/ Linrad SW combo is capable of accurately measuring the incoming dBm value at the antenna terminal, which then relates directly to the S value.  

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73 Alberto I2PHD
<<< http://www.weaksignals.com >>>


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