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Post by Bigears on Apr 28, 2010 1:27:23 GMT -5
Hi, I have seen different Bias level settings mentioned for the MB8719 and UPD2824 Uniden radios, and even for the same chassis?
I am confused...can I set the bias correctly (for best linearity on SSB) by using a scope?
I can't seem to notice much difference on-air, or with a scope when I try different current settings.
Cheers
BigEars
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Sandbagger
Administrator/The Boss 
Posts: 6,247 
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Post by Sandbagger on Apr 28, 2010 7:36:23 GMT -5
Hi, I have seen different Bias level settings mentioned for the MB8719 and UPD2824 Uniden radios, and even for the same chassis? I am confused...can I set the bias correctly (for best linearity on SSB) by using a scope? I can't seem to notice much difference on-air, or with a scope when I try different current settings. Cheers BigEars Yes you can. You can input a 2-tone test signal and set the bias to eliminate the sharp cutoff at the zero power line, similar to the negative trough when setting 100% AM modulation on the scope. Typically the final bias on most standard power SSB radios is between 10 and 25 mA. If you're in that range, chances are you'll be fine. |
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Post by Bigears on Apr 28, 2010 23:55:28 GMT -5
Thanks Sandbagger. I have yet to try the "standard" 2-tone test, so once I have a suitable audio gen set that will be great!
Another question; Does the bias settings have any effect on AM?
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Sandbagger
Administrator/The Boss
Posts: 6,247
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Post by Sandbagger on Apr 29, 2010 7:24:00 GMT -5
Thanks Sandbagger. I have yet to try the "standard" 2-tone test, so once I have a suitable audio gen set that will be great! Another question; Does the bias settings have any effect on AM? That depends on the radio. Some radios only apply bias in the SSB mode. Other's leave it there all the time. You don't need to bias the driver and final on AM if the modulation is applied there as part of a high level scheme. On the other hand, if it's a low-level AM modulator (like the HR 2510 and President Jackson etc.), then the final and driver need to be biased in the linear range just like SSB. Adjusting the bias can affect the total current the final and driver draw (and how hot they can get), and may have a small effect on power output. But I wouldn't set it with AM in mind. If the bias is properly set for the SSB mode, it shouldn't have an adverse efffect on AM |
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