Re: [Elecraft] K3 hum problem - not the usual? [Try CONFIG:AFSK TX = FIL ON]
Wayne, Thanks for that suggestion - it worked!! One starts to wonder if there is any thing that this radio can't do! 73 -- Brian -- K1LI On Mon, Sep 28, 2009 at 5:58 PM, Wayne Burdick n...@elecraft.com wrote: The K3 has a CONFIG menu entry called AFSK TX. If you set it to FIL ON, a 400-Hz transmit-mode audio filter is inserted, centered around the mark/space tones. This is only available when the rig is set for AFSK A mode. It should be effective against low-frequency hum coming in through the mic or LINE IN connectors. 73, Wayne N6KR __ 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
[Elecraft] K3 hum problem - not the usual?
After enjoying my K3 for about nine months, I was recently alerted to audible 60-Hz hum on my transmitted audio signal. After reading the many hum related posts on the reflector, I began investigating. Step 1 was to remove all connections to the rig except the DC power and the coax to the external PA (I placed a direct short on the keying line input at the PA). Without a mic connected, the indication of the problem is that the PA registers output power with no audio input. The problem only occurs in an SSB mode when the nearby PA is both on and enabled (i.e., not on standby) and when the K3 is both within about 8-in of the PA and parallel or at right angles to it; rotating the rig about 15 degrees around the z-axis eliminated the hum. All in the usual vein, so far. There are several aspects of this problem that I find hard to understand: - With all conditions apparently constant, the problem is at least somewhat intermittent and will build up to full output over about a 3 second period when it does occur - When hum is being produced, the K3 output power meter reads zero while the external PA is putting out something near full power! (Ordinarily, it takes 20 watts of output power from the K3 to drive the external to this power level) - Lowering the output power setting on the K3 reduces the amount of hum power registering on the PA output power meter; there is a marked reduction in hum power when I pass the K3's internal PA power threshold and the hum power goes to zero when the K3 power output is set to zero - There is hysteresis in the output power registered by the external PA vs. the output power setting on the K3; i.e., starting with K3 output power set to zero, the K3 output power setting which produces the onset of hum power as shown by the external PA is a larger value than the K3 output power setting at which the external PA hum power decreases / disappears. I am space challenged inasmuch as I have an SO2R setup, so moving the K3 will be difficult. Any thoughts on what's going on? -- 73 -- Brian -- K1LI __ 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
Re: [Elecraft] K3 hum problem - not the usual?
On Mon, 28 Sep 2009 13:29:54 -0400, Brian Machesney wrote: The problem only occurs in an SSB mode when the nearby PA is both on and enabled (i.e., not on standby) and when the K3 is both within about 8-in of the PA and parallel or at right angles to it; rotating the rig about 15 degrees around the z-axis eliminated the hum. All in the usual vein, so far. Magnetic field coupling from the power supply to the K3's input circuitry, probably due to the use of unshielded audio transformers in the K3. This is a well known problem. One good band-aid is to go to the TXEQ1 settings and fully cut the three lowest octave bands. There's little communications value to the speech below 300 Hz anyway, and it burns TX power, so it's a win-win. Also, the acoustic stuff in that lower frequency range includes breath pops and room noise. It's also possible to have magnetic coupling on input wiring if you've managed to form it into a big loop, but the transformers are the more likely cause. I ran into the loop problem once when I jury-rigged a headphone amp for SO2R. No problem in TX audio, but it was in my phones. One of my neighbors had so much magnetically coupled hum into the Line In transformer that it regenerated to full output power when he tried to run RTTY in AFSK mode. 73, Jim Brown K9YC __ 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
Re: [Elecraft] K3 hum problem - not the usual?
Would wrapping some of this Ultraperm 80 shielding around the K3's audio transformers be a solution? (http://www.goldmine-elec-products.com/prodinfo.asp?number=G16600A) 73 -- Joe KB8AP On Sep 28, 2009, at 12:06 PM, Jim Brown wrote: On Mon, 28 Sep 2009 13:29:54 -0400, Brian Machesney wrote: The problem only occurs in an SSB mode when the nearby PA is both on and enabled (i.e., not on standby) and when the K3 is both within about 8-in of the PA and parallel or at right angles to it; rotating the rig about 15 degrees around the z-axis eliminated the hum. All in the usual vein, so far. Magnetic field coupling from the power supply to the K3's input circuitry, probably due to the use of unshielded audio transformers in the K3. This is a well known problem. One good band-aid is to go to the TXEQ1 settings and fully cut the three lowest octave bands. There's little communications value to the speech below 300 Hz anyway, and it burns TX power, so it's a win- win. Also, the acoustic stuff in that lower frequency range includes breath pops and room noise. It's also possible to have magnetic coupling on input wiring if you've managed to form it into a big loop, but the transformers are the more likely cause. I ran into the loop problem once when I jury-rigged a headphone amp for SO2R. No problem in TX audio, but it was in my phones. One of my neighbors had so much magnetically coupled hum into the Line In transformer that it regenerated to full output power when he tried to run RTTY in AFSK mode. 73, Jim Brown K9YC __ 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 __ 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
Re: [Elecraft] K3 hum problem - not the usual?
Jim K9YC wrote: Magnetic field coupling from the power supply to the K3's input circuitry, probably due to the use of unshielded audio transformers in the K3. This is a well known problem. One good band-aid is to go to the TXEQ1 settings and fully cut the three lowest octave bands. ... One of my neighbors had so much magnetically coupled hum into the Line In transformer that it regenerated to full output power when he tried to run RTTY in AFSK mode. Note that the upcoming firmware upgrade will reportedly eliminate TXEQ in AFSK (and other audio-based digital modes), and it apparently may be some time before another update provides true per-mode TX/RX EQ. So people with hum will need another solution, except for the voice modes. I tried wrapping the component side of the transformers in a sheet of Mu-metal (actually, a competitor, not Mu-brand) and noted no difference. It was probably a futile effort anyway as it didn't wholly enclose the transformer; probably I need to complain to Maxwell about this. Leigh/WA5ZNU __ 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
Re: [Elecraft] K3 hum problem - not the usual? [Try CONFIG:AFSK TX = FIL ON]
The K3 has a CONFIG menu entry called AFSK TX. If you set it to FIL ON, a 400-Hz transmit-mode audio filter is inserted, centered around the mark/space tones. This is only available when the rig is set for AFSK A mode. It should be effective against low-frequency hum coming in through the mic or LINE IN connectors. 73, Wayne N6KR On Sep 28, 2009, at 2:45 PM, Leigh L. Klotz, Jr. WA5ZNU wrote: Jim K9YC wrote: Magnetic field coupling from the power supply to the K3's input circuitry, probably due to the use of unshielded audio transformers in the K3. This is a well known problem. One good band-aid is to go to the TXEQ1 settings and fully cut the three lowest octave bands. ... One of my neighbors had so much magnetically coupled hum into the Line In transformer that it regenerated to full output power when he tried to run RTTY in AFSK mode. Note that the upcoming firmware upgrade will reportedly eliminate TXEQ in AFSK (and other audio-based digital modes), and it apparently may be some time before another update provides true per-mode TX/RX EQ. So people with hum will need another solution, except for the voice modes. I tried wrapping the component side of the transformers in a sheet of Mu-metal (actually, a competitor, not Mu-brand) and noted no difference. It was probably a futile effort anyway as it didn't wholly enclose the transformer; probably I need to complain to Maxwell about this. Leigh/WA5ZNU __ 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
