Low Frequency Modulation of Side Tone.
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Low Frequency Modulation of Side Tone.
 
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I just noticed that on 80 and 17m the side tone in my K2 has a low frequency
modulation superimposed over the normal frequency. When I discovered this I was trying to call a Panama station on 80m. I cranked the power up to 100w and started my call. The rig sounded like it was going nuts. It even locked into a repeating string of dits or das. I do not remember which. I turned the rig off to get it to stop. I suspect the repeating transmission is unrelated to the side tone problem because I found that my computer keying cable was part way out of the jack. It must have been bad timing that it came out just as I was calling. The amplitude of the modulation on the side tone increases with power output, and is only noticeable at ~60 to 100 w. On 80m if I key down for several seconds the modulation decreases. It sounds like a capacitor charging. On 17m, the sound is much louder and does not decrease with time. The output signal sounds fine in another receiver. I tested using a dummy load. I also turned off my power supply and computer monitor, and used a battery to power the K2. Neither helped. I built the KPA100 this last spring, and have not noticed this before. However, I have been running mostly QRP so I do not know when this problem showed up. KPA100 is located in an EC2 with the KAT2. The connecting cable is 32 inches long. What should I look for to fix this? Jeff Burns AD9T _______________________________________________ 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 |
RE: Low Frequency Modulation of Side Tone.
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Problem found. I added a fixed audio out port to the K2. Disconnecting the
wire to the sound card stopped the modulation. An audio transformer in line also eliminated the problem. Jeff Burns AD9T -----Original Message----- From: [hidden email] [mailto:[hidden email]] On Behalf Of [hidden email] Sent: Saturday, January 22, 2005 12:16 PM To: Elecraft List Subject: [Elecraft] Low Frequency Modulation of Side Tone. I just noticed that on 80 and 17m the side tone in my K2 has a low frequency modulation superimposed over the normal frequency. When I discovered this I was trying to call a Panama station on 80m. I cranked the power up to 100w and started my call. The rig sounded like it was going nuts. It even locked into a repeating string of dits or das. I do not remember which. I turned the rig off to get it to stop. I suspect the repeating transmission is unrelated to the side tone problem because I found that my computer keying cable was part way out of the jack. It must have been bad timing that it came out just as I was calling. The amplitude of the modulation on the side tone increases with power output, and is only noticeable at ~60 to 100 w. On 80m if I key down for several seconds the modulation decreases. It sounds like a capacitor charging. On 17m, the sound is much louder and does not decrease with time. The output signal sounds fine in another receiver. I tested using a dummy load. I also turned off my power supply and computer monitor, and used a battery to power the K2. Neither helped. I built the KPA100 this last spring, and have not noticed this before. However, I have been running mostly QRP so I do not know when this problem showed up. KPA100 is located in an EC2 with the KAT2. The connecting cable is 32 inches long. What should I look for to fix this? Jeff Burns AD9T _______________________________________________ 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 _______________________________________________ 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 Jeff Burns-3
In a message dated 24/01/05 02:07:20 GMT Standard Time, [hidden email] writes: Problem found. I added a fixed audio out port to the K2. Disconnecting the wire to the sound card stopped the modulation. An audio transformer in line also eliminated the problem. -------------------------------------------------------------- A similar solution was of value in clearing up my problems in using Spectrogram. I was getting spikes on the Spectrogram display at 50Hz (our power freq) and every 100Hz from 150Hz upwards. This was believed to be due to my PC having a power line filter installed to clear hash from the PC switch mode PSU and this left the PC case floating above ground at RF. Series capacitors had no effect, where a transformer placed in the audio path completely cured the problem. Used a miniature audio transistor interstage transformer for the purpose with the higher impedance side to the PC sound card. Would guess a transistor output transformer with the usual 1.2K to 4 ohms windings may have been even more suitable, but did not have one in the junk box. The only proviso in going down this path is to use a transformer that has a response well below 300Hz and 50 Hz if possible to ensure correct placement point of the BFO is seen. A totally different problem, though in the end with the same solution. Bob, G3VVT _______________________________________________ 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 |
Re: Low Frequency Modulation of Side Tone.
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In reply to this post by Jeff Burns-3
Jeff and all,
For a source of decent audio transformers for low power applications like that, look at defunct computer modem cards. I have salvaged transformers from them for computer to audio equipment isolation for some time now - small and quite inexpensive (i.e. 'cheap', 'free', etc.) Of course the more sophistocated way of handling such problems is with optoisolators, but they are not usually free, and they require a voltage source - transformers require no voltage. 73, Don W3FPR ----- Original Message ----- > Problem found. I added a fixed audio out port to the K2. Disconnecting the > wire to the sound card stopped the modulation. An audio transformer in > line > also eliminated the problem. > > Jeff Burns > AD9T > _______________________________________________ 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 Jeff Burns-3
I'm happy to report KX1 #959 is now sporting options KXB30 and KXAT1...and all is working as one seamless unit! I must admit that the dinky KXB30 is a deceiving little board! By the time you route the wires down through the main KX1, you've earned your stripes on this puppy. The detail work required isn't difficult but if you've got all thumbs, good luck! One note; the rubber pads for the 30 meter module had me scratching my head. My soldered leads were pretty darn 'flush' but certainly not flat or smooth enough to have those pads adhere worth a hoot. I ended up cutting the rubber pads into slimmer strips that were then strategically placed in between solder points so as to get a nice flat bond to the pcb and still offer rubber bumper protection. Second note: the manual states that one of the 30 meter alignment trimmers may be 'broad'; in my case, broad meant finding 'no' peak on the one nearest the bandwidth pot. I used my K2 as a reference signal and could not determine any peak what so ever. Tomorrow when I can hear WWV, I'll try to peak it again. The other 30m trimmer peaked nicely. As far as the KXAT1, the optional power calibration will be performed tomorrow as well. Can't believe the P6.3 it's saying for output...this is with pots R1 and R2 set to 60% as per errata sheet... All in all, a delightful trip down kit building lane...with a few detours along the way! 73 John K7FD _______________________________________________ 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 |
Re: Low Frequency Modulation of Side Tone.
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In reply to this post by Don Wilhelm-3
On Jan 23, 2005, at 10:30 PM, W3FPR - Don Wilhelm wrote: > For a source of decent audio transformers for low power applications > like that, look at defunct computer modem cards. I have salvaged > transformers from them for computer to audio equipment isolation for > some time now - small and quite inexpensive (i.e. 'cheap', 'free', > etc.) I'll second this. In fact, if you can find an older Hayes modem, like one of the 2400 bps full-sized modems -- the transformers are very high quality. They are physically large, about 3cm on a side and 1cm high (for through-hole board mounting). Hayes persisted in using these large transformers for years because they provided a low-distortion coupling to the phone line. Some of the teeny 1cm cube transformers you find in cheap modems aren't nearly as nice, but will work as well. Bill Coleman, AA4LR, PP-ASEL Mail: [hidden email] Quote: "Not within a thousand years will man ever fly!" -- Wilbur Wright, 1901 _______________________________________________ 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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