[Elecraft] ALC: issues raised almost 2 month ago + answer from Elecraft

[Greg - AB7R]

There are amps out there that will do full legal limit in RTTY all day long with the 
exciter at 30-50W. Some of these amps are not stressed at all at that level and are 
just loafing along happy as can be.   :)

-------------------------
73,
Greg - AB7R
Whidbey Island WA
NA-065
K3#0009

On Mon Dec  3 17:18 , David Wilburn  sent:

>I admit, I may not be the sharpest knife in the drawer, but to see a
>reference to an amp, and the words 'full power' and RTTY, all together?
>Wow.  That raised my eyebrows.  
>
>With the power density of RTTY, isn't that a full blown stress test of
>your complete RF system, at 100% duty cycle, or so...?  Any standing
>waves on the thing would be huge, and wouldn't the safety factor would
>be a negative number?
>
>Aren't you taking on a bit of risk to your system?  Please don't take
>the wrong way, I am trying to learn.  Being one of those no-code techs
>we hear so much about.  I am just rationalizing the described activity,
>with all these warnings I see on various equipment, about high duty
>cycle modes.
>-  
>
>David Wilburn
>k4dgw at k4dgw.com
>K4DGW
>K2 S/N 5982
>
>
>On Mon, 2007-12-03 at 16:43 -0500, Jerry Flanders wrote:
>> At 02:59 PM 12/3/2007, Enno, PF5X wrote:
>> >Hi gang,
>> >
>> > A very
>> >quick response from Wayne gave the following info. Sufficient to cool the
>> >discussion for a while I would say ...
>> >
>> 
>> Not so - Wayne's comments seem directed at those who might want to 
>> use ALC as if it were a substitute for the mike gain control.
>> 
>> It worries me when I see the discussion wander away from amplifier 
>> safety in an antenna catastrophe situation, which is my main concern. 
>> I once blew up the output circuit of an AL1200 due to an intermittent 
>> in an antenna coax while running full power on RTTY.
>> 
>> Please see my other in-line comments below.
>> 
>> >--
>> >
>> >
>> >From: wayne burdick n6kr at elecraft.com
>> >
>> >Date: Fri, 12 Oct 2007 14:12:24 -0700
>> >
>> >To: elecraft at mailman.qth.net, cw at dx.nl
>> >
>> >Subject: regarding external ALC
>> >
>> >
>> >
>> >Hi Enno,
>> >
>> >Transmit power control via the ALC input (AUX I/O pin 15) is planned, but
>> >not finalized. We're mindful of the negative impact ALC can have on transmit
>> >signal purity, a subject of recent debate within testing organizations.
>> 
>> Speaking only for myself, I do not intend to adjust the ALC to 
>> provide normal level control - only a crisis shutdown function. 
>> Quoting from my Quadra's manual p4.:
>> 
>> "The ALC cable must be connected between
>> the transceiver and VL-1000 to
>> prevent overdrive of the amplifier, and especially
>> to facilitate the proper operation of the
>> protection circuitry if sudden antenna system
>> problems should cause the SWR to rise to dangerous
>> levels."
>> 
>> Rightly or wrongly, Yaesu (and probably ICOM) engineers have presumed 
>> the ALC would be functional and could cut back exciter drive in the 
>> event of an antenna catastrophe. Other main-line rigs that I am 
>> familiar with are compatible. I think it is reasonable to assume the 
>> world-class K3 would have provided for this also.
>> 
>> BTW - It is worrisome that ALC was only planned, but still not 
>> finalized, as of Oct 12.
>> 
>> 
>> >  Once ALC is working to our satisfaction, we'll provide simple interfacing
>> >information that will allow the use of negative control voltages ...
>> 
>> I, and perhaps other Solid State amp users, would prefer a definite 
>> calendar commitment, if that is possible. If not possible, please 
>> state so. I would hope for a working, properly engineered 
>> negative-going ALC fix within a few months.
>> 
>> >Meanwhile, the K3's DSP-based early-stage ALC is very effective at
>> >preventing amplifier overdrive, and should suffice in nearly all cases.
>> 
>> I repeat -  my concern is amplifier safety, not a substitute for a 
>> mike gain control. Sooner or later, the antenna will fail, but we 
>> don't know when,  and we probably cannot manually cut back drive 
>> quickly enough to protect those expensive SS finals when it occurs.
>> 
>> >73,
>> >
>> >Wayne
>> >
>> >N6KR
>> 
>> 
>> Jerry W4UK
>> 
>> 
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