[Yaesu] ft 2000 and Alpha 8410

[Dennis]

   I have seen this problem in other (too many, actually) rigs.  The internal ALC (of the exciter) does not limit output power of the first syllable or two. The delay causes leading edge spikes to fault modern amps that are able to respond instantly.  I have fixed the problem two ways...
   Two Yaesu rigs I have (FT-102 and 1000D) will absolutely not overshoot if the processor is turned on and is set to limit output power to the desired amount.  Yea, I don't like using speech processors either, BUT I have the processing level turned way down (less than 10db) so my audio sounds natural, not all mushy.  On these rigs (and perhaps the FT-2000 if the design is similar) the processor limits ouput BEFORE the final amplifier so the radio's ALC is not involved. To properly set it up you should have a peak reading wattmeter available.  Start transmitting with full power, engage the processor then turn down the processing level until the desired peak reading is seen on the meter. (mic audio gain is not important, set it as high as you want) At this point you should see NO ALC action.  The ALC you read on the radio's meter is the action happening in the final amp, in this case there is none since the limting is occuring before the final stages. It works wonderfully on these two radios and probably any radio with a PROPER RF speech processor.  
  Few notes, I would first set the RF power control down to a level that's close to what you want anyway, (like 50 watts), then use the method described to get it down to the 35-ish watts you need. 
  Secondly ALL PROCESSORS do not work this way! (like many Kenwoods) Some only work at audio level, not the early RF stages.  This method will not work with them.
   In this case I use a little external box with a 9 volt battery and a 10-turn pot that puts a negative voltage to the radio's ALC connector.  I dial down this external voltage until the radio is putting out just the power I want.  At this point I can yell, scream, jump up and down and there is NO overshoot.
  With either method described above, there is no need to use the ALC line between the exciter and amplifier.  Those just don't work that well anyway.  Too much overshoot. I hear garbage signals all the time on the air where people are relying on simple transciever and amplifier ALC to do the work.
73,
Dennis
NØSP

--- w3bj at juno.com wrote:

From: "w3bj at juno.com" <w3bj at juno.com>
To: Yaesu at mailman.qth.net
Subject: [Yaesu] ft 2000 and Alpha 8410
Date: Thu, 19 May 2011 01:16:45 GMT

Run an ft 2000 into Alpha 8410. When I tune it up in cw, it is fine. The minute I transmit audio it kicks t into fault. Drive is only 30 watts rf. Has anyone had this problem before. IT seems like the audio spikes and faults the amp.

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