KPA1500 Ethernet port RFI, cause and cure

[Bob Wilson, N6TV]

*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
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

[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 <[hidden email]> 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
>

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]