K2 ALC problem
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Hi,
I've noticed that my power output on 40 meters LSB is a lot higher than expected. I get four to five bars or more on the peaks in the ALC mode. I even got a high current reading last night and I then turned the power back from 12 watts to 10. I get 4 to five bars even at five watts. It didn't make much difference and I've found that I need to hold the mic further away. I switched to USB on 40 meters and it looks fine. It looks good on the higher USB frequencies also. I've noticed that it is around 2 to three bars on 80 meters LSB which is normal according to the manual. I'm wondering if it could be a carrier balance adjustment? Any ideas would be greatly appreciated. Everything else appears normal. I've checked all solder connections on the SSB board several times and re-flowed the connections I considered suspect. Thanks, Gary, N7HTS _______________________________________________ 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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Gary D Krause wrote:
> > I've noticed that my power output on 40 meters LSB is a lot higher than > expected. I get four to five bars or more on the peaks in the ALC > mode. I even got a high current reading last night and I then turned The number of bars in ALC display mode does not indicate the output power; it indicates the transmit chain gain (more accurately the excess gain over that needed to achieve the demanded power). The K2 does have more or less maximum gain on 40m. I suspect that the gain drops with increasing frequency because the transistors' gain reduces with frequency, and it drops with decreasing frequency because the coupling transformers are less effective. The ALC is greatest on 40m to stop the output power being greater. > the power back from 12 watts to 10. I get 4 to five bars even at five > watts. It didn't make much difference and I've found that I need to > hold the mic further away. I switched to USB on 40 meters and it looks > fine. It looks good on the higher USB frequencies also. I've noticed That's weird. Any difference between USB and LSB should switch between USB and LSB on the higher frequency bands. > that it is around 2 to three bars on 80 meters LSB which is normal > according to the manual. > > I'm wondering if it could be a carrier balance adjustment? Any ideas A severe carrier balance problem would result in their being ALC bars lit when there was no audio. As the carrier is also suppressed by the filter, I'm not sure that you would get enough leakage to trigger this, though. If the sideband switched at higher frequencies, I would suggest the problem was that your filter 1 wasn't correctly aligned for one of the sidebands, but if it is always the one sideband that needs more ALC, I have difficulty in imagining a mechanism that would cause that. > would be greatly appreciated. Everything else appears normal. I've > checked all solder connections on the SSB board several times and > re-flowed the connections I considered suspect. -- David Woolley "The Elecraft list is a forum for the discussion of topics related to Elecraft products and more general topics related ham radio" List Guidelines <http://www.elecraft.com/elecraft_list_guidelines.htm> _______________________________________________ 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 Gary D Krause
Gary,
I would expect two possible causes. One is the carrier balance adjustment. Use a band below 21 MHz when adjusting and adjust for LSB first. If you have an oscilloscope, the procedure is easy - connect a dummy load to the K2 and connect a paddle or straight key to the key jack. The oscilloscope is to measure the RF output voltage, so connect it across the dummy load with a 10x probe and set the vertical sensitivity to its greatest setting. In LSB mode, close the key (which activates PTT) and adjust the carrier balance for minimum RF. That setting should occur close to the center of the trimpot. Then check USB If the USB carrier is greater than that for LSB, adjust the pot a very small amount to see if you can reduce the carrier. You may have to make some compromise to get the amount of carrier the same between LSB and USB. Note, if you use this method, do not connect a microphone to the K2 and you do not have to set the menu for "SSBA bal". You can use a separate receiver to detect the minimum carrier in place of the oscilloscope as indicated in the KSB2 manual, but I suggest using the key to activate the PTT circuit rather than plugging in a microphone. A mic with its PTT button pressed can pick up residual noise and cause a false indication. This is easier done than to write about it. The second possible problem is alignment of the SSB filter. Use Spectrogram and set the BFO to position the OP1 filter passband between 300 Hz and 2600 Hz markers (use 300 and 2300 if you have the 2.1kHz filter width or 300 and 2800 if you have the 2.6kHz filter width). Center the passband between the two markers. Check both LSB and USB. If you moved the SSB passband in the step above, re-visit the SSB carrier balance adjustment. If those steps do not correct the imbalance between LSB and USB, you may have some fault on the KSB2 board. A very small difference may exist, but not to the extent that you have indicated. 73, Don W3FPR Gary D Krause wrote: > Hi, > > I've noticed that my power output on 40 meters LSB is a lot higher > than expected. I get four to five bars or more on the peaks in the > ALC mode. I even got a high current reading last night and I then > turned the power back from 12 watts to 10. I get 4 to five bars even > at five watts. It didn't make much difference and I've found that I > need to hold the mic further away. I switched to USB on 40 meters and > it looks fine. It looks good on the higher USB frequencies also. > I've noticed that it is around 2 to three bars on 80 meters LSB which > is normal according to the manual. > > I'm wondering if it could be a carrier balance adjustment? Any ideas > would be greatly appreciated. Everything else appears normal. I've > checked all solder connections on the SSB board several times and > re-flowed the connections I considered suspect. > > Thanks, > Gary, N7HTS > > > > _______________________________________________ > 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 > ------------------------------------------------------------------------ > > > No virus found in this incoming message. > Checked by AVG - http://www.avg.com > Version: 8.0.169 / Virus Database: 270.6.19/1661 - Release Date: 9/9/2008 4:58 AM > > 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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