Mercury - Frequently Asked Questions

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These are the questions regarding the Mercury receiver board which qualify as 'frequent'.

Why are there no input RF filters on the Mercury PCB?

This is due to the multi-function nature of the Mercury board. Whilst primarily a high performance HF (and VHF/UHF in alias mode) receiver, Mercury can also be used for other functions. For example, it can be used as a high performance 0-55MHz spectrum analyzer, sampling oscilloscope and VNA (by using Penelope as the signal source for the VNA and also as a tracking generator). In these cases it is desirable not to have any RF filtering before the ADC on Mercury.

When used as a receiver the amount of filtering will vary depending on the antenna system the user has. For most situations with say an HF beam or dipoles the natural frequency response of the antenna may provide adequate filtering. For the user with a high performance broadband antenna e.g. a rhombic, or very strong local signals, then additional filtering may be required.

An external set of filters will be provided as part of the Alex project.

We expect higher performance ADCs to be come available in the future. These newer devices will still require some form of input filtering. By using external filters the cost of replacing the ADC board is reduced.

ADC Overload

The ADC overload alert displayed in PowerSDR and KISS Konsole are to alert the user to possible "spurious signals in the bandscope".[1] They are not a warning of any danger to the receiver or the ADC - which are well protected. "The primary protection is the the clamp diode at the input connector, which hard clamps at 5 volts peak to peak".[2]

Notes

  1. http://lists.openhpsdr.org/pipermail/hpsdr-openhpsdr.org/2009-August/010396.html
  2. http://lists.openhpsdr.org/pipermail/hpsdr-openhpsdr.org/2009-August/010406.html