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Swan 500CX on AM?

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Author Topic: Swan 500CX on AM?  (Read 287 times)
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« on: August 10, 2019, 08:53:13 PM »

Hi, I am trying to get on the AM frequencies on 80 and 40 meters and having just acquired a Swan 500CX, I was wondering if it would be sufficient to start out with. It does SSB with Carrier. I can hear others using AM with this rig, but I am wondering if my transmission would be sufficient. Thanks for any advice or comments. N2IU
AC0OB - A Place where Thermionic Emitters Rule!
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« Reply #1 on: August 10, 2019, 11:10:08 PM »

You certainly can get on AM with about 150 Watts (and good finals) and many people have been able to do AM with 100 to 150 Watts. How well you can communicate depends on the conditions of propagation.

Atmospheric noise in the AM mode requires a good modulation percentage and a bit more power of at least twice what you have there.

But try it and see what kind of responses you get.

Phil - AC0OB

"What kind of Koolaid do they make you drink in the Physics Department?" Charlie Epps to Dr. Larry Fleinhardt, NUMB3RS   Smiley

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I modulate, therefore AM

« Reply #2 on: August 11, 2019, 09:28:26 AM »

Using carrier inserted SSB nobody can tell the difference without a scope, however the difference lies in the audio. A transmitter designed for SSB has an audio chain designed for SSB, what Timtron WA1 Henry Yell Arr would call "telephonium audio". Unfortunately modifying it for AM Gangsta audio makes SSB sound muddy. I'd leave it alone and join the gang, but first invest in a good mic that can make all the difference in the world.

73 de Warren KB2VXA
Station powered by atomic energy, operator powered by natural gas.

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« Reply #3 on: August 14, 2019, 08:33:17 AM »

Be aware that this transceiver is rated at 125 watts INPUT in the AM mode, not output. That input level is based on about 150ma final cathode current. I would not recommend running at that level, as these finals are 6LQ6 sweep tubes that are under a high level of stress in this mode.

Your carrier output will not/should not be high, efficiency will be roughly 60% at 150ma. at tune up. However, at these lower power levels, your steady state (un-modulated) carrier output will be closer to only 25 watts (about 20% efficiency) at the 150ma level.

If you want to save those $$$ finals, running 100ma cathode current is recommended. Doing that will further reduce your steady state carrier to about 10 watts.

The carrier balance control sets the carrier insertion level and resulting cathode current.

Low power AM with current band conditions will not be too effective, however, if you intend to use this rig for extensive periods, I would highly recommend installing a fan behind or on the side of those finals. Of course a linear amp is a power option.

Modulation peaks should only be set (via mic gain) 10ma max above the carrier level. Also, keep in mind that your audio will be restricted by the 2.7Khz network, great for sideband but obviously not the bandwidth/audio you will typically hear from the guys in the AM window. Audio with desired lows (i.e < 300Hz) or highs (>3000Hz) will not be passed anyway, so your microphone requirements may not be so critical...

FWIW, I have a box full of sweep tubes that I driven into oblivion over the years, learning the hard way...ka8gef
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