K3 RFI Susceptibility
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While using my shunt-fed tower and amplifier on 80 and 160 CW, the K3 keying became erratic. The problem went away when I unplugged the spare headset from the rear panel jacks. The front panel jacks aren't a problem, no doubt because their shields go right to the chassis. If you use the rear panel ones at high power, it would be wise to wrap the cord around a ferrite core. I didn't have any trouble with the other rear panel cables, but I put cores on them anyway.
My shack is a high-RF environment on those bands, as it's only about 10 meters from the tower, but it's probably not the worst the K3 is likely to see. (Field Day, expeditions?) I've had to take measures to keep RF out of other equipment, though not the 60 pound behemoth next to the K3. I haven't looked into it, but maybe there's an easy way to ground those rear panel jacks more directly to the chassis. (This is a classic cause of RF susceptibility.) If not, a few ferrite cores is a small investment. 73, Scott Scott Ellington Madison, Wisconsin USA ______________________________________________________________ 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 |
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From: [hidden email] To: [hidden email] Subject: RE: [Elecraft] K3 RFI Susceptibility Date: Wed, 22 Dec 2010 10:13:49 -0600 I have had similar issues with my K3/10, but I was asking for trouble. I have an involved external sequence switcher and band decoder for all the VHF/UHF/Microwave transverters. Involved is an unshielded wire that runs between my sequencer switcher and the PTT circuit, accessed at a mike cable extension on the K3. The TX function for the K3 is operated by the sequencer. On 6m when running the 250w, the amp RF gets into the keying circuit. With a bit of lead dressing I have been able to avoid the problem, but I need to do something a bit more "evolved" for the problem. 73 Bill K0AWU (EN37ed Minnesota) ------------------ > Date: Wed, 22 Dec 2010 09:33:51 -0600 > From: [hidden email] > To: [hidden email] > Subject: [Elecraft] K3 RFI Susceptibility > > While using my shunt-fed tower and amplifier on 80 and 160 CW, the K3 keying became erratic. The problem went away when I unplugged the spare headset from the rear panel jacks. The front panel jacks aren't a problem, no doubt because their shields go right to the chassis. If you use the rear panel ones at high power, it would be wise to wrap the cord around a ferrite core. I didn't have any trouble with the other rear panel cables, but I put cores on them anyway. > > My shack is a high-RF environment on those bands, as it's only about 10 meters from the tower, but it's probably not the worst the K3 is likely to see. (Field Day, expeditions?) I've had to take measures to keep RF out of other equipment, though not the 60 pound behemoth next to the K3. > > I haven't looked into it, but maybe there's an easy way to ground those rear panel jacks more directly to the chassis. (This is a classic cause of RF susceptibility.) If not, a few ferrite cores is a small investment. > 73, > > Scott > Scott Ellington > Madison, Wisconsin > USA ______________________________________________________________ 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 |
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I have to shield all my control cables, etc. In fact, I think the only unshielded ones connected to the K3 are the power cable and headphones. I'm not worried about the power cable, as it's very well grounded and bypassed, as it should be.
73, Scott K9MA On Dec 22, 2010, at 10:15 AM, Bill Davis Jr wrote: > > From: [hidden email] > To: [hidden email] > Subject: RE: [Elecraft] K3 RFI Susceptibility > Date: Wed, 22 Dec 2010 10:13:49 -0600 > > > I have had similar issues with my K3/10, but I was asking for trouble. I have an involved external sequence switcher and band decoder for all the VHF/UHF/Microwave transverters. Involved is an unshielded wire that runs between my sequencer switcher and the PTT circuit, accessed at a mike cable extension on the K3. The TX function for the K3 is operated by the sequencer. On 6m when running the 250w, the amp RF gets into the keying circuit. With a bit of lead dressing I have been able to avoid the problem, but I need to do something a bit more "evolved" for the problem. > > 73 Bill K0AWU (EN37ed Minnesota) > > ------------------ > >> Date: Wed, 22 Dec 2010 09:33:51 -0600 >> From: [hidden email] >> To: [hidden email] >> Subject: [Elecraft] K3 RFI Susceptibility >> >> While using my shunt-fed tower and amplifier on 80 and 160 CW, the K3 keying became erratic. The problem went away when I unplugged the spare headset from the rear panel jacks. The front panel jacks aren't a problem, no doubt because their shields go right to the chassis. If you use the rear panel ones at high power, it would be wise to wrap the cord around a ferrite core. I didn't have any trouble with the other rear panel cables, but I put cores on them anyway. >> >> My shack is a high-RF environment on those bands, as it's only about 10 meters from the tower, but it's probably not the worst the K3 is likely to see. (Field Day, expeditions?) I've had to take measures to keep RF out of other equipment, though not the 60 pound behemoth next to the K3. >> >> I haven't looked into it, but maybe there's an easy way to ground those rear panel jacks more directly to the chassis. (This is a classic cause of RF susceptibility.) If not, a few ferrite cores is a small investment. > >> 73, >> >> Scott > >> Scott Ellington >> Madison, Wisconsin >> USA > > > ______________________________________________________________ > 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 Scott Ellington Madison, Wisconsin USA ______________________________________________________________ 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 |
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In reply to this post by Bill Davis Jr
On 12/22/2010 8:15 AM, Bill Davis Jr wrote:
> I have had similar issues with my K3/10, but I was asking for trouble. I have an involved external sequence switcher and band decoder for all the VHF/UHF/Microwave transverters. Involved is an unshielded wire that runs between my sequencer switcher and the PTT circuit, accessed at a mike cable extension on the K3. The TX function for the K3 is operated by the sequencer. On 6m when running the 250w, the amp RF gets into the keying circuit. With a bit of lead dressing I have been able to avoid the problem, but I need to do something a bit more "evolved" for the problem. YES! Here's the problem -- while that PTT line IS a DC line, because it is a WIRE, it is also an ANTENNA, so it will carry RF current from your TX and put it into the K3 PTT circuit (and into whatever is driving the PTT circuit). That means we CANNOT treat it as a DC circuit. It is an RF circuit, and must be wired with coax (or something like coax), with the shield bonded to the chassis at each end. Now, the RF current flows on the coax shield to the chassis at each end, so it does not cause problems with the keying circuit. 73, Jim K9YC ______________________________________________________________ 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 |
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However, if the connector is grounded to a PC board, rather than directly to the chassis, the current on the shield ends up getting INSIDE the radio. This is the problem with some of the rear panel jacks on the K3. However, I understand why Elecraft mounted those connectors on the PC board, and simply wrapping the cable around a ferrite core should solve the problem. (If that works in my shack, it should work almost anywhere.)
73, Scott K9MA On Dec 22, 2010, at 12:18 PM, Jim Brown wrote: > YES! Here's the problem -- while that PTT line IS a DC line, because > it is a WIRE, it is also an ANTENNA, so it will carry RF current from > your TX and put it into the K3 PTT circuit (and into whatever is driving > the PTT circuit). That means we CANNOT treat it as a DC circuit. It is > an RF circuit, and must be wired with coax (or something like coax), > with the shield bonded to the chassis at each end. Now, the RF current > flows on the coax shield to the chassis at each end, so it does not > cause problems with the keying circuit. Scott Ellington Madison, Wisconsin USA ______________________________________________________________ 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 |
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