[Elecraft] KPA1500 Ethernet port RFI, cause and cure

[Bob Wilson, N6TV]

I forgot to mention, if it's not practical to replace a long unshielded
Ethernet cable, you can easily install these effective Ethernet RFI filters:

https://www.dxengineering.com/parts/dxe-iso-plus-2

Long ago I attempted to use turns of Ethernet cable wrapped around Mix #31
split ferrite beads on both ends of a long 100 Mbps unshielded Ethernet
run, but it didn't help much.  These DXE filters worked much better.

73,
Bob, N6TV


On Thu, Jun 11, 2020 at 12:50 AM Bob Wilson, N6TV <n6tv at arrl.net> wrote:

> *Summary*:
>
> To avoid 20m narrow band RFI generated by the KPA1500 and other Ethernet
> devices, use shielded Ethernet cables, CAT5 STP or CAT6 STP, instead of
> CAT5e UTP or CAT6 UTP.
>
> *Details*:
>
> The KPA1500 and some SDRs provide a 100 Mbps Ethernet port, which may be
> tempting to use instead of USB in some situations.   However, if you
> connect an "ordinary" CAT5e UTP Ethernet cable (unshielded twisted pair)
> to the amplifier, and your antenna is anywhere near the shack, you will
> probably hear steady carriers around 14.029.5 MHz (plus carriers from any
> other Ethernet devices in your house, or your neighbor's house, that are
> connecting at 100 Mbps).  I have not observed any HF carriers from
> devices connecting at 1 Gbps, but the KPA1500 does not support 1 Gbps.
>
> This is illustrated by the following P3SVGA screen capture (the unshielded
> Ethernet cable was short, only 1m long):
>
> https://www.kkn.net/~n6tv/KPA1500_RFI_from_3_ft_UTP_Ethernet_Cable_N6TV.
> png
>
> My 20m antenna was cranked down, located 9m directly above the amplifier.
>
> The (weak) Ethernet carriers are visible even when the amp. is OFF.   They
> disappear completely when either end of the Ethernet cable is disconnected.
>
> I replaced the 1m CAT5e UTP cable with a slightly longer 1.5m CAT5 STP
> cable (*shielded* twisted pair), and the KPA1500 carriers were not
> detectable..
>
> *How to tell if an Ethernet cable is UTP or STP*:
>
> Often it is printed on the cable, but it's easier to simply look at the RJ-45
> connectors.  If you see clear plastic on three sides instead of shiny
> silver metal on three sides, it is unshielded (UTP) not shielded (STP).
> Most Ethernet cables are UTP, because STP costs more.
>
> *How to tell if a device is connecting at 100 Mbps or 1 Gbps*:
>
> Implementations vary, but most modern Ethernet switches and Routers have
> one or two LEDs on each jack that indicate the current link speed.  My
> Netgear GS105 switch is clearly labeled (both LEDs green = 1000 Mbps, one
> LED green = 100 Mbps).
>
> 73,
> Bob, N6TV
>