K3 - bad CW note
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I have K3 SN 469, a kit K3-100 with transverter interface, tuner,
several filters, and a recently added subreceiver. It's updated with the latest beta firmware. This K3 works well at home, but I am having some trouble using it at the KH6LC station. Those of you who operated the Cal QSO Party and worked KH6LC heard my K3, and it is bad signal reports from this operation (Thanks AF6EV!) that prompt this message. The bottom line is that when the K3 is connected to the antenna at KH6LC there is a significant modulation of the output amplitude, synchronous with the power line, and independent of power level. It seems to be a buzz (square wave) rather than a hum (sine wave). Replacing the antenna connection with a dummy load removes the buzz. Turning the TX AGC off has no effect. The K3 is grounded to the station ground bus via the rear panel ground screw. There is some evidence that simply connecting a long coaxial cable (from the radio room to the garage at KH6LC) terminated in a dummy load can introduce the buzz. So what, you say, there's a ground loop and when you find it you'll be fine. Well, Ken N6KB and I have spent a fair mount of effort on just that and so far we have come up empty handed. In the interest of brevity I won't list all the things we tried. The reason why this might be interesting to K3 owners is that no other radio that we have tried seems to be affected by whatever condition is causing the problem. So I wonder if there is an assembly error that might be a contributing factor. What I'm looking for is some internal part that should be grounded but isn't, or vice versa. Before I dig into it I'm hoping that those of you with more K3 experience than I have can suggest a place to look. In the meanwhile, we are going to try for symptomatic relief by using isolation transformers, etc. Curt AH6RE _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Curt Knight wrote:
> >So I wonder if there is an assembly error that might be a contributing >factor. What I'm looking for is some internal part that should be >grounded but isn't, or vice versa. Before I dig into it I'm hoping >that those of you with more K3 experience than I have can suggest a >place to look. In the meanwhile, we are going to try for symptomatic >relief by using isolation transformers, etc. > You might also try a few diagnostic tests using a clamp-on RF current meter. You can probably make one in a half-hour from materials on hand, like this: http://www.ifwtech.co.uk/g3sek/clip-on/clip-on.htm#Constr This meter will show whether or not you really do have significant amounts of stray RF; and it will let you measure how much effect your treatments are having. It's so simple, and so effective. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Curt Knight
Interesting problem. It would be helpful if you told us more about
operating mode, band, type of antenna, etc and, most important, a complete list of the things you have already tried. I'm sure you have already ruled out the usual culprits (power supply, rf in the microphone or keying circuit, etc). The fact that you have problems at KH6LC but not at home and that the problem in independent of power level makes this problem unique in my experience. It would be very interesting to know if the problem occurs on all bands or not. Is there something else different at the KH6 location such as microphone or keyer .. even antenna tuner? Don K7FJ >I have K3 SN 469, a kit K3-100 with transverter interface, tuner, > several filters, and a recently added subreceiver. It's updated with > the latest beta firmware. > > This K3 works well at home, but I am having some trouble using it at > the KH6LC station. Those of you who operated the Cal QSO Party and > worked KH6LC heard my K3, and it is bad signal reports from this > operation (Thanks AF6EV!) that prompt this message. The bottom line > is that when the K3 is connected to the antenna at KH6LC there is a > significant modulation of the output amplitude, synchronous with the > power line, and independent of power level. It seems to be a buzz > (square wave) rather than a hum (sine wave). Replacing the antenna > connection with a dummy load removes the buzz. Turning the TX AGC off > has no effect. The K3 is grounded to the station ground bus via the > rear panel ground screw. There is some evidence that simply connecting > a long coaxial cable (from the radio room to the garage at KH6LC) > terminated in a dummy load can introduce the buzz. > > So what, you say, there's a ground loop and when you find it you'll be > fine. Well, Ken N6KB and I have spent a fair mount of effort on just > that and so far we have come up empty handed. In the interest of > brevity I won't list all the things we tried. The reason why this > might be interesting to K3 owners is that no other radio that we have > tried seems to be affected by whatever condition is causing the > problem. > > So I wonder if there is an assembly error that might be a contributing > factor. What I'm looking for is some internal part that should be > grounded but isn't, or vice versa. Before I dig into it I'm hoping > that those of you with more K3 experience than I have can suggest a > place to look. In the meanwhile, we are going to try for symptomatic > relief by using isolation transformers, etc. > > Curt AH6RE _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Curt Knight
Is there a difference in the power supplies at the two stations? I had a very similar bad CW report when I first got my K3 which was due to a switching power supply that I was using. The note was bad at all power levels on several bands. I bought an Astron RS-35A and the reports were good. I still wonder why the switcher didn't work well since it was a 12V, 24A supply.
Good luck. John W2XS |
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In reply to this post by Curt Knight
Hello Curt!
> This K3 works well at home, but I am having some trouble using it at > the KH6LC station... I don't know of any incorrect assembly step that might result in this. I'm sending you a private email to see about some steps to take and to try and help you solve this mystery. 73, Lyle KK7P _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by John W2XS
I recently completed building my K3 and listening on a different transceiver in the shack, I also noticed a light hum/buzz superimposed on my 18-24 MHz CW signal at levels above 12, up to 100 watts, into a dummy load. Also using a switching power supply, Astron SS-30. I don't own a linear power supply to substitute. However when I switch to battery-only, the buzz is still present. So over time I'll try to verify with stations if this is just a "local", in-station phenomenon, or truly going out on the air. Propagation hasn't actually been good for these upper frequencies...
73 Rick N6CY
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