[hpsdr] Bug in Hermes Gigabit Jack Choice

[Steve Haynal]

Hi,

I am working on the Hermes-Lite V2 gigabit ethernet and have been reviewing
the Hermes design. The current Hermes BOM specifies this rather expensive
RJ45 jack:

http://www.trpconnector.com/pdfs/6605444.pdf

If you look at the schematic in that pdf, the center taps are shorted
together via pin 1. This works for PHYs with current-mode transmit drivers,
but is not recommended at gigabit speeds for voltage-mode transmit drivers
as used in the KSZ9021. Although there is no discussion regarding this in
the KSZ9021 datasheet, there is in the KSZ9031 datasheet. This may be why
some people have trouble with gigabit speeds on the Hermes.

I'm using a different jack on the HL V2 that we've proven elsewhere, so do
not face this problem, but wanted Hermes users to beware.

73,

Steve
KF7O
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