[Elecraft] RF into K3 via serial port?

[Jack Brindle]

What kind of cables are you using between the PC and the K3? If shielded, are you sure the shields are connected to the DE9 shell at both ends? The RF _could_ be getting into the conductors and causing problems in the computer/serial card and not actually the K3. The computer could then be asserting or negating the handshake lines, killing K3 transmission, or causing the software to send a stop data transmission to the K3. We have found the usually the RFI problems are outside of the K3.

Be sure to read the RFI info at K9YC’s site. It provides a lot of good details about the problems of RS-232 cabling and connections. Also, even though you may not detect “hot RF” in the shack, it just might be there. RF likes to ride on the outside of the coax going from the antenna to the radio, causing problems. Thus good choking is needed to eliminate the problems. Again, K9YC’s document has some really good info.

http://www.audiosystemsgroup.com/K9YC/K9YC.htm

73!

Jack B, W6FB



On Apr 5, 2014, at 5:39 PM, Don Wilhelm <w3fpr at embarqmail.com> wrote:

> Bill,
> 
> It is usually more effective to put the ferrite on the feedline.  A good current choke at the antenna feedpoint, and perhaps another at the shack entry end.
> If the feedline runs away from the radiator at right angles and is not otherwise run in the field of the antenna, the one at the shack end is normally not needed.
> 
> Of course, if the shack is in close proximity to the radiator, all bets are off because the shack is being bombarded with RF and ferrites on the various devices in the shack is the only choice.
> 
> Yes, my perception is that many electronic devices (notably computer peripherals) are getting more and more susceptible to RF.
> 
> 73,
> Don W3FPR
> 
> On 4/5/2014 8:10 PM, Bill Davis wrote:
>>   In my transition to Win7, I added a 2 port serial PCI card (NewEgg purchase -- Sunix 5037A) to my Dell PC. I was going to use one of these 2 ports to communicate with my K3 Utility terminal program. Very handy CW / RTTY application. Shortly after installation I made a nice contact on 30m RTTY and then moved to 80m RTTY. SURPRISE!!  During TX the K3 hung in TX and only a couple of characters (if that) were ever transmitted. I was attempting to run about 70watts or so. Only by reducing power to a few watts would the RTTY transmission seemingly be successful.
>> 
>>   The 80m antenna is resonate and very low SWR even without the KXPA100 tuner. (My K3/10 is for VHF/UHF/Microwave IF use mostly, hence the external PA/Tuner).
>> 
>>   So RF is getting back into the K3 .. odd ... nothing is "hot" in the shack at all. My workaround is to use the new serial ports for other hardware/applications and use the one serial port in the Dell Dimension 4700 for the K3 / terminal program. Things are happy that way.
>> 
>>   I may investigate and try a ferrite core on the serial cable. But I will need to get an "HF" core since all of mine are for higher freq use. I just thought this was really odd. My serial cable is "homebrew" minimum conductor cable and I don't recall if it is shielded or not.
>> 
>> 
>>   Anyone else had any similar experiences??
>> 
>> 73 Bill  K0AWU
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