[Elecraft] ELecraft K2 DATA port IMPORTANT update

[Don Wilhelm]

Jean-Francios,

Congratulations on identifying and resolving the ground loop problem.

For those situations where a separate power supply is either required or 
desirable, the use of an optoisolator instead of the more simple 
transistor PTT/KEYING arrangement can also cure the ground loop 
problem.  However, one must be careful not to unintentionally power the 
optoisolator in such a way to make that 'sneaky' gound loop path 
re-appear.  In most cases, the optoisolator should be powered from the 
same supply that powers the device on the 'transistor' side of the 
optoisolator.

73,
Don W3FPR

Jean-François Ménard wrote:
> Hi everybody,
>
> Since my first prototype of the K2 DATA port implementation, I did 
> some extensive test today during an outdoor portable operation.
>
> I found that ground loop can occur on lower band... 40m or lower... 
> And the problem come from the PTT line.... that goes to ground during 
> TX. Even if the line IN and OUT are both isolated with an audio 
> tranformer.
>
> I also test today my DATA port with my SCS PTC-IIe modem and had the 
> same problem.
>
> I finally found the problem and solved it !!
>
> Like SCS (PTC-IIe manufactuer) said in their user manual. If you 
> tranceiver have an external power option, like found on Yaesu FT-8XX 
> data connector, YOU SHOULD USE IT. Do not power your modem from 
> another power source, but from the transceiver port itself. Like for 
> the NUE-PSK, PTC-IIe or any other TNC... always power your device with 
> power from your transceiver.
>
> This way, you will avoid ground loop that will harm your signal 
> quality for sure.
>
> I just add one wire inside my K2 to the DATA port. I took the 12V line 
> from the AUX 12V connector inside the K2. This way, you will not have 
> any more problem and finally have an universal DATA port ffor almost 
> any kind of external device.
>
> I will post a revised schematic on my website this week.
>
> Like my previous modification, I always use RG-174 for inside wires. 
> It does prevent RF pickup during transmit and keep the signal as clean 
> as possible.
>
> I will also post a few more pics.
>
> Another tip, apply acrylic coating spray on the back of the amplifier 
> board before applying the two way tape. It will prevent short circuit 
> with any electronic part with the chassis.
>
> Best 73,
>
> de J-F VA2SS
> ===
>