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Author Topic: ALC and power  (Read 9649 times)
W8JI
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« Reply #15 on: August 21, 2012, 05:44:52 AM »

I just did some more testing and now see I'm only getting about 20% max output in all modes - even built-in RTTY, FM, and when tuning. I'll try it on a dummy load (as soon as I track one down), but barring a miracle, it seems to be an issue with the finals or something else internal.

Thank you all for your help.

I looked at the manual for the PRO II and see nothing that indicates this is normal behavior, unless the meter in yours is wired wrong (or the switch isn't working) or you have too much gain someplace earlier.

It is probably NOT a final amplifier problem, because to the ALC system the final is just one more stange in the chain. I think some pro's had stability issues in an early stage, and certainly a stage oscillating could cause abnormal ALC.

If someone closeby had an identical rig, I would just swap it into my setup.

ALC works because the radio's POWER limit control is set lower than the detector's output voltage. The only things that can generate ALC is when the **gain** and signal level of the entire system ahead of the RF output detector tries to exceed the power level setting of the radio's power limit control, or SWR. Since the ALC is dependent on the entire system from audio source level to power control setting, it is tough to get a single cause.  

A spurious signal could trigger it, or too much gain/drive, SWR, or an excessively low radio power limit setting. The entire system is equally involved.

73 Tom
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N7SMI
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« Reply #16 on: August 21, 2012, 08:56:57 AM »

As I said, the first thing to do is to get it on a dummy load in order to eliminate variables in the antenna like high SWR.

I'm hoping to get one today and will report the results.

Tomorrow I'll have a chance to swap the rig into the location of the identical rig that is working normally. That should be a surefire test as to whether it's internal or not.

Quote
You might also try working the RF power control back and forth a few times to wipe the contacts clean. A poor connection in this control could cause it to be at a very low level even though it is physically set fully clockwise. You might try turning it while transmitting to see what the ALC reading does.

The connection seems to be good. Power (from my max of 15% to 0) and ALC (from max of about 45% to 0) both decrease as RF power control is decreased while transmitting in USB-D mode. When keying in USB, FM, or RTTY mode, power decreases (from my max of 20% to 0) while ALC decreases only slightly (from about 60% which is just into the red to about 45%) as RF power control is decreased from max to 0.
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K5TED
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« Reply #17 on: August 31, 2012, 08:55:03 PM »

A less challenging hobby might be in order
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VE3FMC
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« Reply #18 on: September 01, 2012, 04:34:51 AM »

A less challenging hobby might be in order

Thanks for your helpful input on this subject.  Roll Eyes
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N7SMI
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« Reply #19 on: September 14, 2012, 08:47:08 PM »

As an update and for posterity's sake, the rig came back from Icom and is now working splendidly. I now get full power where I'm supposed to. The repair report indicates "Adjusted PA biasing and APC on main board." Cost was $84 plus shipping.
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