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ALC question




 
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N2DTS
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« on: January 28, 2014, 12:16:16 PM »

This is more modern radio BS, but its technical...

I got a Ten Tec Argonaut 5 off QRZ, and its a fun little rig to play with.

I can not figure out the ALC though, with a tone into the mic, I get a nice looking waveform on the scope, about 100% mod in both directions. With speech, I get 100% in the negitive, and about 50% positive, and pep power goes up to maybe 10 watts.
5 watts carrier, 20 watt pep rig, I get about 22 watts on CW, about 15 watts pep on ssb.

The ALC light does not light up on AM, so maybe the ALC is not what is limiting the power?

If it is, would putting a small cap on the ALC buss smooth out the ALC action?
Its got a .1 uf on it now.
Or should I reduce it? .1 does not seem like much.


Since it does very well with a tone into the microphone, I can not figure out what goes wrong with speech...
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n1uvi
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« Reply #1 on: January 28, 2014, 01:09:41 PM »

I thought the Argonaut 5 was only a 20 watt rig
so a 5 watt AM carrier would be full power
as to why the higher negative peaks..maybe the microphone phase?
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W2VW
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« Reply #2 on: January 28, 2014, 02:06:59 PM »

The ALC loop may be faster than the lamp.

You could figure out where the control voltage is and probe it or just try reducing power.

Narrow, peaky frequency response can make ALC reduce positive peaks way below what looks like 100% positive mudulation.

Some of these rigs also get worse in the ALC department when the antenna load is not a perfect 1:1 SWR.

Modern? These designs are way older than ham plate modulated rig designs were back when a lot of us started using them.
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N2DTS
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« Reply #3 on: January 28, 2014, 09:03:52 PM »

20 watts pep, so yes, 5 watts carrier.
I switched to a balanced mic and checked the phasing and its quite a bit better.

It does not seem to be the alc, or the vr reference, or the final current, I measured them with and without modulation, my guess is the dsp does something when it sees the modulation get down to about 95% negative, it adjusts things or something...

I was amazed I could make a lot of contacts on 40 meters with 5 watts.
I might build a plate modulated 2E26 or something...6l6 modulators...


 

I thought the Argonaut 5 was only a 20 watt rig
so a 5 watt AM carrier would be full power
as to why the higher negative peaks..maybe the microphone phase?
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W2VW
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« Reply #4 on: January 29, 2014, 09:49:56 AM »

You could be right Brett. The DSP may be looking at modulation waveforms. The specifications don't state what is used as an AM modulator.

The Kenmore TS-2000 will not modulate positive beyond 90% positive even it it's threatened with violence.

How does it behave with a 1 khz tone?

Some guys have installed modulators and piped them right into the I.F. of plastic radios.

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Steve - K4HX
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« Reply #5 on: January 29, 2014, 10:04:46 AM »

Just remember that a 1k tone is static and voice is a dynamic waveform. Any settling time or over/undershoot in the ALC will not be seen with a tone.
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« Reply #6 on: January 29, 2014, 10:53:22 AM »

Just remember that a 1k tone is static and voice is a dynamic waveform. Any settling time or over/undershoot in the ALC will not be seen with a tone.

Hence the question of how it behaves with a tone  Wink
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Steve - K4HX
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« Reply #7 on: January 29, 2014, 11:53:27 AM »

I think he answered that question in his first post.

Quote
I can not figure out the ALC though, with a tone into the mic, I get a nice looking waveform on the scope, about 100% mod in both directions.
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N2DTS
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« Reply #8 on: January 29, 2014, 02:32:12 PM »

Yes, with a tone, it seems to do 95% in both directions, and looks very good on the scope.
With voice, phasing the microphone correctly makes a BIG difference, but it still has some sort of gizmo in there that limits things.

It seems it will not distort on AM, even with the mic gain all the way up, but if you hit it hard on SSB, it does distort.
On ssb, you adjust the gain so the alc light just lights up a little from time to time, it never lights up on AM...

On a pep watt meter, at 5 watts carrier, a tone makes about 15 watts pep, with voice, phased wrong, 10 watts, phased correctly about 13.

I was using some old electret condensor mic (cheap, unbalanced) because it has a lot of output and a lot of mid range, but it is phased wrong. The old radio shack dynamic is balanced, but sounds stuffy I suspect.

The radio will do 10 Kc wide on TX (5000 Hz audio).
For many years, Ten Tec did not put AM on their radios, but iits quite good on this one, the RX audio is very nice.

The receiver gets torn up a bit from close strong signals, but that may be why it sounds better then it should, the filters are not brick wall.
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