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   Home   Help Search  
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Author Topic: Why are there recommendations both for/against use of ALC with amps?  (Read 18035 times)
KM3F
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Posts: 908




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« Reply #45 on: June 24, 2015, 06:28:33 PM »

Some can manufacture various scenarios all day long to justify there positions.
If my equipment was shot gunning anyone, I would have been told about it looong ago.
I have heard others doing it but was no use to tell them with the attitudes they display.
Ever hear the response 'it must be your receiver' or get a new radio!
I say yep!    It's you trash my receiver is hearing.
Good luck.
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W1BR
Member

Posts: 4179




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« Reply #46 on: June 25, 2015, 09:26:27 AM »

I haven't looked at my signal on the scope yet (lazy) but I get lots of unsolicited compliments on my audio.

That statement shows the problem with your position. You could be running near Class C, and still receive good audio reports. Truth is, unless you test and monitor, you will never know how garbage the other guy is hearing is actual IMD products from your transmitter, or RX overload on his end.
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AF6LJ
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Posts: 580




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« Reply #47 on: June 25, 2015, 10:40:02 AM »

I don't know about other rigs, but I do not like the Yaesu reliance on ALC.

My ICOM IC-706MKII put out a 140-watt 2-ms spike regardless of the transceiver's power setting.  I.e., even at the normal 100-watt power level, there would be the 140-watt spike.  And if I set the transceiver to minimum power (about 5-watts), there would still be a 140 watt spike.  After the spike, the transceiver's ALC would control the output to the power set-point during the transmission period.  Once you had about 5-seconds of transmission inactivity, you'd get another 140-watt spike.  My IC-706MKIIG was a little better.  It would spike to 110 watts regardless of the power setting.

All easy to see on a good peak-reading power meter (I have an Array Solutions Powermaster) and/or a good oscilloscope (like my Tektronix TDS-2022B).

Phil - AD5X

I have two Icoms an IC-745 and an IC-756 The 745 doesn't generate the spikes it is a very well behaved radio. The IC-756 (non pro) generates 150W+ spikes and I wouldn't run it on a modern amplifier, not even on a bet. As for using the ALC connector on the back of my SB-220 I don't see any use for it here in this shack.
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Take Care
Sue,
AF6LJ

Don't Kalifornicate My Life
WA7PRC
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Posts: 2319


WWW

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« Reply #48 on: June 25, 2015, 10:45:05 AM »

I haven't looked at my signal on the scope yet (lazy) but I get lots of unsolicited compliments on my audio.
Distortion has to be almost gawdawful before someone can tell by ear. However, it doesn't take much nonlinearity before your signal is as wide as the broad side of a barn. Odd-order distortion products are usually the most prevalent. Listening OFF FREQUENCY will give an idea of how bad a station is flat-topping.

A spectrum analyzer is the tool to use to get a definitive look at how wide a signal is. However, most SAs are not cheap and not the most convenient tool. The next-best is an oscilloscope. They're easy to use and can be inexpensive. I prefer a lab scope because they almost always have triggered sweep that blanks the display until a signal is present.

vy 73 es gl.
Bryan WA7PRC
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N3DT
Member

Posts: 1655




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« Reply #49 on: June 25, 2015, 10:54:41 AM »

I have listened to my signal on another RX right here in the shack and it sounds fine, even tuning around. I'm certain I'd hear splatter with an S9+20 signal if it were there. I've also looked at my signal on my Moto spectrum analyzer and it looks fine thank you very much.
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W1BR
Member

Posts: 4179




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« Reply #50 on: June 25, 2015, 05:35:51 PM »

Transmitter IMD measurements require something a bit more substantial than the all-in-one two-way service boxes.
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KM1H
Member

Posts: 5096




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« Reply #51 on: June 25, 2015, 05:49:37 PM »

Quote
Some can manufacture various scenarios all day long to justify there positions.

Yep and some do the ostrich thing and deny everything.

Quote
If my equipment was shot gunning anyone, I would have been told about it looong ago.
I have heard others doing it but was no use to tell them with the attitudes they display.
Ever hear the response 'it must be your receiver' or get a new radio!
I say yep!    It's you trash my receiver is hearing.
Good luck.

Do you have the equipment to evaluate your own signal?  If not you have no idea what is going out. Expecting someone to tell you on the air just doesnt happen these day of a PC world, same if you had BO....

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N0SP
Member

Posts: 0




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« Reply #52 on: June 25, 2015, 08:15:10 PM »

    VERY few transceivers have fast enough ALC output to prevent overshoot and the resultant buckshot and dirty amplifier output.  The best and easiest method to absolutely limit the output of your exciter is to place an external negative voltage on the ALC terminal of your transceiver.  Use a 9v battery, wired through a 10 or 20-turn pot and place the adjustable -voltage on the ALC pin.  Key the transmitter in CW or TUNE position with the power control on the radio set to maximum, then adjust the pot until the power reduces to the level you want.  Then NO MATTER what you do with the audio or power control of your radio, it will never exceed the desired value.
    Another method used very successfully with many radios with RF processors (RF PROCESSORS only!, not "compressors") is to engage the RF processor and turn the processor level down to the desired output while whistling/yelling in to the mic.  I know this method works with many Yaesu radios. (generally not Kenwood, since they mostly use audio "compressors")  Hint: Turn down the processor's compression level (separate from the main front panel processor control) to a very low compression value to make it sound natural, not muddy/contestie.  This control is usually a seldom-used setting that is in the back of the radio or a more "hidden" menu. Set it to maybe 8 to 10db max.  The front panel processor control is the one you set while screaming at the mic.   This method works well with FT-102, 1000D, and later radios.  I have not tried it on others with RF processing.  These true RF processors pre-limit output without waiting for the radio's internal ALC to do the work.
   Others have suggested using audio limiting, but this is much trickier to do effectively unless you have some good equipment to monitor and carefully control the audio level in to the radio, many hams don't have the necessary tools to do this.
   All this being said, there are a few radios out there with a problem sending out a high power "spike" at key-up.  Make sure you don't have one of these radios, most that do have this issue have fixes for it available from creative users who have published them on the web. 
  I have never relied on ALC to tame an amplifier, but have heard hundreds of signals on the air with awful signals from people who do.  Meters will not tell you this problem is happening, only a properly connected scope with someone observing who is capable of interpreting the readings.
73,
Dennis
N0SP
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G3RZP
Member

Posts: 1225




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« Reply #53 on: June 26, 2015, 12:52:12 AM »

 
Quote
The best and easiest method to absolutely limit the output of your exciter is to place an external negative voltage on the ALC terminal of your transceiver.  Use a 9v battery, wired through a 10 or 20-turn pot and place the adjustable -voltage on the ALC pin.  Key the transmitter in CW or TUNE position with the power control on the radio set to maximum, then adjust the pot until the power reduces to the level you want.

Sadly, even that isn't foolproof. I found this with the FT102: the stage to which ALC is connected is also a receiver IF stage, and so has AGC. This means time constants are such that the externally applied voltage isn't there all the time in receive and the transition time is slow because of multiple time constants, allowing a power spike. The Yaesu method for not using the processor is to always drive to full power and have ALC control things - so some bright sparks wishing to reduce output power recommend reducing the loading, which of course, means splatter. Using the FT102 without the processor is a somewhat disastrous process as a result.

Quote
Another method used very successfully with many radios with RF processors (RF PROCESSORS only!, not "compressors") is to engage the RF processor and turn the processor level down to the desired output while whistling/yelling in to the mic.  I know this method works with many Yaesu radios.


It's an improvement, certainly, but doesn't always help on CW, where the drive control is sometimes implemented in a similar system to using the external ALC and it still spikes.

For CW testing, I use my pulse generator and relay switch on the key line and use the VOX with minimum delay: the oscilloscope then really shows the power spike on the first dit, especially if one triggers the scope from the pulse generator.

Quote
Others have suggested using audio limiting, but this is much trickier to do effectively unless you have some good equipment to monitor and carefully control the audio level in to the radio, many hams don't have the necessary tools to do this.

Very true.
Quote
I have never relied on ALC to tame an amplifier, but have heard hundreds of signals on the air with awful signals from people who do.  Meters will not tell you this problem is happening, only a properly connected scope with someone observing who is capable of interpreting the readings.

Also very true!
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