[Elecraft] linear amp shutdown (was ALC)

[Joe Subich, W4TV]

> 2   ALC has its problems and thus not always connected, but 
> everyone uses PTT which can be very easily disabled (allow 
> the rig to self protect) or tx inhibit, tx enable, or others?

I STRONGLY disagree ... I WANT a graceful foldback if the antenna 
SWR is slightly out of range.  10% reflected power should not take 
an amplifier off line.  However there should be some way to cause 
the exciter to reduce its power output so the amplifier does not 
generate voltages or currents that will cause the demise of the 
active devices.  

Unless one has an amplifier and exciter that share a common 
control microprocessor with data feedback or the amplifier has 
an extremely sophisticated and FAST attenuator in the drive 
line, ALC (e.g., an external gain control) is the appropriate 
means of reducing power gradually.  

Sure, if the reflected power is so high that it indicates an 
antenna failure (50% reflected power), the appropriate action 
is to disable the amplifier and potentially even the exciter 
but that's over the top for 10% reflected power (2:1 SWR) or 
even 20% reflected power (3:1 SWR).

73, 

   ... Joe, W4TV 
   



> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of David Cutter
> Sent: Monday, December 03, 2007 5:55 PM
> To: Elecraft Reflector
> Subject: [Elecraft] linear amp shutdown (was ALC)
> 
> 
> In my view there are 2 issues here:
> 
> 1   in my view the amplifier should be self-protecting 
> against overloads, eg 
> antenna fault (I am mindful of virtually any other equipment 
> which must be 
> tested by law with overload conditions)
> 
> 2   ALC has its problems and thus not always connected, but 
> everyone uses 
> PTT which can be very easily disabled (allow the rig to self 
> protect) or tx 
> inhibit, tx enable, or others?
> 
> ALC is an analog signal for gradually reducing drive, which 
> might not be 
> appropriate for shutdown.
> 
> David
> G3UNA 
>