Clean CW signal
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I notice when I listen to my CW on a separate reciever that there appears to be a slight husky modulation to the carrier. It's not located near a power supply - so I've eliminated magnetic field interference. I do have a manual MFJ tuner located 3 ft away. My antenna is a G5RV that runs across the roof of the house. I have a 6:1 balun at the 300/50ohm junction.
I was wondering if this slight raspy noise on the carrier is normal or if I have some issues with my setup. Tonight I will set my K2 up to beacon and go for a walk 400m away from the house to see if it shows up further away. But any advice from you guys would be appreciated. It might save me a lot of time :-) I do not recall noticing this before I did the CW shaping upgrade, so I am wondering if I am just noticing this now. Dave SN#3222 _______________________________________________ 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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Thanks Alan. I will check that soon. When I moved away from my property the raspy sound faded. So I am wondering whether my FT-817 is having phasey PLL noise being so close to the antenna. I will get an on air check to see if others notice it before I open up the rig again. I have had it open and closed alot lately since I installed the KPA-100 last week.
I will let you know my result. Thanks for the tip of RFC15. I will check that for sure. Dave. On Tue, 25 Jul 2006 04:20:13 -0400 "w1hyv" <[hidden email]> wrote: > Check RFC15 on the bottom of the board. I will bet a donut that is open. > Let me know. > > 73 > Alan > W1HYV > ----- Original Message ----- > From: "David Walker" <[hidden email]> > To: <[hidden email]> > Sent: Tuesday, July 25, 2006 3:44 AM > Subject: [Elecraft] Clean CW signal > > > >I notice when I listen to my CW on a separate reciever that there appears > >to be a slight husky modulation to the carrier. It's not located near a 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: Clean CW signal
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In reply to this post by David Walker-8
Dave Walker wrote:
>I notice when I listen to my CW on a separate reciever that there appears >to be a slight husky modulation to the carrier. It's not located near a >power supply - so I've eliminated magnetic field interference. I do have a >manual MFJ tuner located 3 ft away. My antenna is a G5RV that runs across >the roof of the house. I have a 6:1 balun at the 300/50ohm junction. > > I was wondering if this slight raspy noise on the carrier is normal or if > I have some issues with my setup. -------------------------------------------------------------------------------- Does the modulation of the carrier change in any way if you change the sidetone frequency significantly and do you hear the same husky modulation on all bands? Is the modulation still there when transmitting into a dummy load and not your antenna? My K2/100 is #3255, same vintage as yours but unmodified except for some receiver birdie killers, and on CW the sidetone generator frequency / phase modulates the carrier slightly. With the sidetone frequency that I usually use, approx 400 Hz, the first set of sidebands is approximately 90db below carrier which should not be an issue running barefoot, but could be with a linear. After building my K2 the problem had been worse, caused by U10 on the Control Board not meeting its crosstalk spec. - an unusual case I believe. Although this might not be the cause of the modulation that you hear, the sidetone generator, the BFO varicap tuning and receiver IF filter varicaps circuits all share the Quad DAC chip U8 on the Control Board. Ideally each DAC should be completely isolated from the others, but in practice this is not the case which results in some sidetone signal hopping across to the BFO varicap circuit U10D during transmit, modulating the BFO. The same crosstalk problem can exist within the Op-amp U10 (Control Board), the cause of my problem. If your other receiver can tune to the BFO frequency, it would be worthwhile to listen to the BFO signal during CW transmit into your antenna and into a dummy load. 73, Geoff GM4ESD _______________________________________________ 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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Geoffrey Mackenzie-Kennedy wrote:
> Although this might not be the cause of the modulation that you hear, > the sidetone generator, the BFO varicap tuning and receiver IF filter > varicaps circuits all share the Quad DAC chip U8 on the Control Board. > Ideally each DAC should be completely isolated from the others, but in > practice this is not the case which results in some sidetone signal > hopping across to the BFO varicap circuit U10D during transmit, > modulating the BFO. As Geoff knows, I had this problem. I was alerted to it by someone whom I was working who could hear the sidebands. They were 50-60 db down, but as everyone knows even QRPp gets out! I tried various things suggested by Elecraft but finally the solution turned out to be to replace U8. The way to check for this is to listen for sidebands +/- your sidetone pitch on another receiver. If you hear them, try turning the sidetone volume up and down and see if the strength of the sidebands varies. Of course you have to be careful not to overload the other rx. -- 73, Vic, K2VCO Fresno CA http://www.qsl.net/k2vco _______________________________________________ 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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Listening to the on-air signal on a nearby receiver is a really *tough* test
of the transmitter. Things such as hum or noise on the signal that someone a short distance away would never hear will blast out loud and clear. That can be good. If the signal is clean on a nearby receiver, it's c-l-e-a-n!! On the other hand, it can be difficult to determine just what is of real concern and what isn't and, often, what is or isn't being created in the monitor receiver itself. With many receivers, just grounding the antenna input is not enough when dealing with anything above QRPp levels. The usual approach for serious monitoring is to put the monitor receiver in a completely shielded container, so it only gets a normal level of signal: a few microvolts at most. Of course any control lines and power lines have to be very well shielded. A battery-operated receiver is easiest to use. Tune in the signal, then button up the receiver is a tightly shielded box with a fine screen mesh opening to let the sound out. Many years ago, when Hams were first trying to accomplish a clean "d-c note" there was a popular little monitor receiver published in QST called "The Growler". It got its name because it was built into a popular all-metal lunch pail of the 1920's and 30's called a "Growler". Another approach that many of us are equipped to use is to look at the signal on an oscilloscope. Amplitude modulation can be observed directly. Amplitude modulation is what we're most often concerned with. Our receivers are rather insensitive to frequency or phase modulation. One can make a rough check for frequency or phase modulation by using a sharp filter and tuning in the signal right on the edge of the filter bandpass to produce "slope detection" of any FM present. If the frequency or phase is changing significantly, noise will appear when the signal is right on the steep slope of the bandpass. What's happening is that any change in the frequency of the signal moves it up and down the steep filter slope is producing amplitude modulation that the receiver can detect. (It's called, appropriately enough, slope detection.) Once again, that is also a rigorous test of the monitor receiver. Any frequency or phase modulation of the local oscillator or BFO in the receiver will have the effect of moving the signal along the slope of the filter bandpass too, producing the same noise. You can't tell which is the result of your transmitter and which is the result of your receiver. Most modern receivers use phase-locked-loop oscillators and many of those have a significant amount of phase jitter in those oscillators as they are constantly being corrected by the loop. That jitter is indistinguishable from FM on the signal being received. If the signal sounds bad, compare it with a known clean source such as the Elecraft XG1 or XG2 test oscillators set on the filter slope in just the same way. Don't be too surprised if it also sounds rough in many receivers! Ron AC7AC _______________________________________________ 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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