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Author Topic: AM Modulation Drops  (Read 458 times)

KJ6TSX

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AM Modulation Drops
« on: April 22, 2022, 12:25:25 PM »

Hope I am posting in the right place?

Put my radio in AM mode and get about 100 watts with carrier only, Upon modulating (talking) the power output drops?? Shouldn't the power increase??

Thanks
George KJ6TSX
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WB8VLC

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Re: AM Modulation Drops
« Reply #1 on: April 22, 2022, 12:31:37 PM »

If your radio is only rated for 100 watt maximum then you need to set the carrier power to 1/4 or less of this maximum rating.

Set the AM carrier to 25 watts and then when 100% modulated with a 1 KHz test tone for example your radio willl produce 100 watts PEP.
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KJ6TSX

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Re: AM Modulation Drops
« Reply #2 on: April 22, 2022, 05:07:11 PM »

Thanks for the help
Did as you suggested everything as it should be
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W5HRO

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Re: AM Modulation Drops
« Reply #3 on: December 28, 2022, 07:33:43 PM »

Hope I am posting in the right place?

Put my radio in AM mode and get about 100 watts with carrier only, Upon modulating (talking) the power output drops?? Shouldn't the power increase??

Thanks
George KJ6TSX

The reason most of the newer radios modulate downwards on AM has to due with the fact companies like Kenwood and the other radio makers have the ALC's set to do that nowadays, but it's mainly for SSB. Unfortunately doing that screws them up when on AM. They actually have them regulated too far for AM and that's the problem. When you modulate on AM the power tries to go up until the ALC starts cutting it back so it drops backwards instead. It requires figuring out a way to internally disable the ALC when on AM. The ALC is only really needed for SSB operation and some of the other modes to protect the radio and they set those for that. Unfortunately they just forget about what it does when on AM.

I have the ALC on my TS-590SG disabled when on AM for example, but it required an internal modification across a resistor on one of the PC boards inside.

And yes like the other guy said, don't run that 100W radio at more than 25W carrier when on AM.
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SWMAN

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Re: AM Modulation Drops
« Reply #4 on: December 28, 2022, 07:54:04 PM »

 Kenwood cuts the AM mode back to 25 watts automatically anyway. So no danger to the radio at all.
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K1KP

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Re: AM Modulation Drops
« Reply #5 on: December 29, 2022, 03:55:39 AM »

W5HRO is on the right track. To get decent AM out of a modern radio you have to defeat the ALC. I operated W1AW/1 on AM with my 756Pro2, with the ALC externally controlled by a 9V battery and potentiometer. It produced excellent AM and got lots of kudos from the Old Buzzards on 3885.

see: http://amfone.net/Amforum/index.php?topic=25323.0

-Tony, K1KP
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W5HRO

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Re: AM Modulation Drops
« Reply #6 on: December 29, 2022, 06:15:16 AM »

Kenwood cuts the AM mode back to 25 watts automatically anyway. So no danger to the radio at all.
Yeah, the older Kenwoods like the 440 and the 940 and a few models after would allow you to adjust it up to the full 100W. The other thing is those older ones would put out 100W on SSB when your external wattmeter was on the AVG/RMS scale and not on the Peak or PEP scale. What they are doing with the newer ones now like the 590SG is they are adhering to that silly PEP rule which leaves a lot to be desired and you will only see the 100W when on the Peak or PEP scale. And a lot of the time those PEP meters are just reading a crude Peak measurement and it's not really PEP. On the AVG scale you now only get 50W on SSB and it’s all because of the way they have the ALC set internally and it’s usually one setting that is set for all modes and that’s the problem. Yeah, they are adding AM to all of the newer radios again, but they still consider it a non-important issue if it doesn’t work on AM correctly 100% On my 589SG I’ve added a switch in back now for AM so I only turn off the ALC when on AM. The radio will do almost 175W Peak on SSB with it off which might damage some of the internal filters and etc. over time, but on AM the ALC is not needed.
« Last Edit: December 29, 2022, 06:32:26 AM by W5HRO »
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