AM Controlled Carrier

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  • Updated 3 years ago

In a previous post I mentioned this topic but somehow it skewed off in another direction. For AM operation we normally maintain a 1:4 power ratio, where 25W of carrier peaks to ~100W. When I operate AM, I adjust my 6500’s output to produce 200W out of my Acom 1000. This produces a solid 800-900W output on peaks. I did some experimenting and decreased the AM Carrier setting on the 6500 to reduce the resting carrier (no modulation) to 100W out of the Acom 1000. The peak power still achieves the same 800-900W output. This lowers the operating temperature of the Acom by 8-10 degrees C. Further experimentation verified that at this 1:8 ratio, both legacy and SDR receivers did not have any problem locking on the signal. Has anyone else tried this, and does anyone know of any down side to doing this? I’ve mentioned it on the air a few times and the only comments I’ve received is that most transmitters don’t have an AM CARRIER adjustment that’s accessible to the end user. This might be a viable suggestion for those using less capable amplifiers on AM.

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WA2SQQ

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Posted 3 years ago

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Mike W9OJ

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How does it sound on the received end? Some of the controlled carrier rigs had kind of a "pumping" sound .

Mike W9OJ
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WA2SQQ

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No decernable difference. Without the amplifier I don't think this would work as well.
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Barry N1EU

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The down side is the possibility of over modulation.  I would be closely monitoring my modulation if I was lowering the carrier level adjustment.

Personally, if I was getting 800-900W on peaks with 200W carrier, I would NOT be lowering my carrier level.

Barry N1EU
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W7NGA

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I operate, almost, AM exclusively with my Flex 6500. With an oscilloscope and spectrum analyzer I simply observe that as you reduce the AM carrier you unbalance the relationship between carrier and modulation sidebands. That is, reducing carrier increases the modulation index and results in over-modulation .. as expected. I used this to my advantage with my 6300 and the ACC port, where I found the gain less than optimal for 100% modulation. I could reduce the carrier somewhat and gain a fully modulated AM signal. I think you will find that the peak-power can be maintained but distortion products increase dramatically.

I do not experience any issues or restrictions on the 6500 using the Balanced-Input. A 100% modulated signal is easy to attain and a beauty to behold.

W7NGA  dan
San Juan Island, Wa.
(Edited)
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WA2SQQ

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I agree. All looks OK on the scope. My adjustments are made by the scope, and not necessarily by the 6500's GUI. My goal was to see how much I could decrease the Acom's heat dissipation. I shared this with Acom and they were very interested in trying it.
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Barry N1EU

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We should start a Flex AM Net and behold all our beautiful AM signals!  ;-)

Barry N1EU
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WA2SQQ

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Might be interesting. Most evenings I hang out in the AM window of 75 (3870-3885) or 160 (1.885) with the nightly suspects from the New England area. Next time you get on shoot me an e-mail. The Flex radios, if set up correctly, will stand up to the best boat anchors on the band!
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W7NGA

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21.430 Mhz ... every day, all the time. 
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Barry N1EU

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I'll keep an eye/ear out for you guys!