[Elecraft] [K3] RFI Problems - HELP!

[Don Wilhelm]

Gray,

Does your term "serial grnd" mean the RS-232 Signal Ground?  If so, that 
should not be connected to the enclosure ground.

As far as the K3 grnd goes, "bond" the K3 enclosure to the outside of 
your interface box, and then on to the computer - follow the audio and 
serial lines with the bonding.

Bond the K3 also to your station ground.

You might also want to add good current mode chokes to your feedlines.
If your end-fed antenna is of the type which uses the coax shield as the 
'counterpoise', then either add a wire counterpoise that is 0.05 
wavelength long (at the lowest frequency of operation) at the junction 
of the radiator and coax and place the choke also at that junction - or 
- place the choke 0.05 wavelength from the junction.

73,
Don W3FPR

On 5/28/2017 11:50 AM, G Wood wrote:

> 
> I decided to rebuild my CW/FSK/PTT interface, the old one was done for IC7000 with audio isolating trannies etc. The new circuit uses 3 opto-couplers, built in a small diecast box, at the moment the input serial grnd goes to input of opto's and the K3 grnd goes to output of opto's, the box is connected to station grnd.
> 
> Question:
> A) should the serial grnd go to the box.
> B) should the K3 grnd go to the box.
> C) or should they all be connected to the box. How does this affect the isolation of input/output of opto's?
> 
> Recently keying the rig from the computer, the K3 would lock up, if I keyed using paddle and K3 keyer no problem also discovered turning off K3 port on computer(no CAT to K3), no other changes, keyed OK.
> 
> The K3 serial lead used an old serial mouse lead all connections at both ends. I read Jim K9YC's article on RFI and followed his suggestion, made up a new lead using 2 twisted pairs for TxD & RxD, 1 lead from each to grnd. The first time I tried this running 10w the computer switched off and rebooted. With the K3 serial lead disconnected I could run 100w no problem.
> 
> I can run 100w on all bands, with full Cat to K3, on dummy load.
> 
> Everytime I try something new it gets worse, more questions than answers. I've hit a brick wall.