Re: [Elecraft] [K2] External Fan Hum
Most "DC" fans used for equipment cooling use what are fundamentally synchronous AC motors, but with the twist that the the AC frequency is adjusted to match the rotation rate. (You can also consider them as stepper motors, operating at maximum slew rate.) That's what "brushless DC motor really means". I'd expect to see an AC field, although at a multiple of the rotation rate, and with quite small gaps between stator poles, so with the 1/3 power near field fall off, quite weak at distances. On the other hand, they will be square wave, before the inductances gets to them. -- David Woolley Owner K2 06123 On 07/11/18 14:56, Don Wilhelm wrote: The DC fan may have a magnetic field, but it would be constant instead of alternating polarity 120 times a second. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] [K2] External Fan Hum
I tried an AC muffin fan on my KPA100 ... while it worked wonders keeping the heat sink cool when I was using the K2 for RTTY, it induced hum. I switched to a brushless DC fan from an old computer and it solved the problem. I can't tell you if the K2VCOSHLDKIT would work or not since I opted for another solution. The DC fan was inaudible acoustically. I fastened it down with a little tab of velcro, blowing down onto the heat sink. 73, Fred ["Skip"] K6DGW Sparks NV DM09dn Washoe County On 11/7/2018 6:24 AM, eru...@att.net wrote: On Wed, Nov 7, 2018 at 7:51 AM, Steve Kavanagh via Elecraft wrote: I was experimenting with an external 120V AC fan to improve the cooling of the KPA100 during CW Sweepstakes this past weekend. The cooling worked fine but the fan caused some hum on received signals (and presumably my transmitted signal as well). Placing the fan towards the right and back (away from the speaker) reduced the hum to a pretty-much unnoticeable level for CW, though through careful checking on a very strong signal I could still detect it by ear. I haven't tried it yet but I suspect it isn't good enough for FT8. I assume the K2VCOSHLDKIT would fix this. But I also noticed, going through the archives that Eric had suggested a DC fan in the same location. Does anyone know if I might expect less hum from a 12V DC fan? 73, Steve VE3SMA __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] [K2] External Fan Hum
Steve, Yes, an AC fan would induce alternating magnetic fields in the K2 L30 and T5 VFO inductors. The K2VCOSHLDKT will eliminate it, as will a DC fan. The DC fan may have a magnetic field, but it would be constant instead of alternating polarity 120 times a second. 73, Don W3FPR On 11/7/2018 7:50 AM, Steve Kavanagh via Elecraft wrote: I was experimenting with an external 120V AC fan to improve the cooling of the KPA100 during CW Sweepstakes this past weekend. The cooling worked fine but the fan caused some hum on received signals (and presumably my transmitted signal as well). Placing the fan towards the right and back (away from the speaker) reduced the hum to a pretty-much unnoticeable level for CW, though through careful checking on a very strong signal I could still detect it by ear. I haven't tried it yet but I suspect it isn't good enough for FT8. I assume the K2VCOSHLDKIT would fix this. But I also noticed, going through the archives that Eric had suggested a DC fan in the same location. Does anyone know if I might expect less hum from a 12V DC fan? __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] [K2] External Fan Hum
Steve,When I had my KPA100 I had a small I think 4" diameter 12v dc fan to which I added some small rubber feet and placed it flat on top of the heatsink. I never had any hum issues. Russ, N3CO Sent from Yahoo Mail on Android On Wed, Nov 7, 2018 at 7:51 AM, Steve Kavanagh via Elecraft wrote: I was experimenting with an external 120V AC fan to improve the cooling of the KPA100 during CW Sweepstakes this past weekend. The cooling worked fine but the fan caused some hum on received signals (and presumably my transmitted signal as well). Placing the fan towards the right and back (away from the speaker) reduced the hum to a pretty-much unnoticeable level for CW, though through careful checking on a very strong signal I could still detect it by ear. I haven't tried it yet but I suspect it isn't good enough for FT8. I assume the K2VCOSHLDKIT would fix this. But I also noticed, going through the archives that Eric had suggested a DC fan in the same location. Does anyone know if I might expect less hum from a 12V DC fan? 73, Steve VE3SMA __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to eru...@att.net __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
[Elecraft] [K2] External Fan Hum
I was experimenting with an external 120V AC fan to improve the cooling of the KPA100 during CW Sweepstakes this past weekend. The cooling worked fine but the fan caused some hum on received signals (and presumably my transmitted signal as well). Placing the fan towards the right and back (away from the speaker) reduced the hum to a pretty-much unnoticeable level for CW, though through careful checking on a very strong signal I could still detect it by ear. I haven't tried it yet but I suspect it isn't good enough for FT8. I assume the K2VCOSHLDKIT would fix this. But I also noticed, going through the archives that Eric had suggested a DC fan in the same location. Does anyone know if I might expect less hum from a 12V DC fan? 73, Steve VE3SMA __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
