[Elecraft] linear amp shutdown (was ALC)

[David Cutter]

Joe

I take your point entirely which is why I said

"ALC is an analog signal for gradually reducing drive, which
 might not be appropriate for shutdown."

Shutdown for me is for protection against gross overload and for this 
another signal might be more appropriate.  Since many users do not connect 
ALC, some other signal for protection should/could be provided.  The problem 
yet again is that users might still ignore what the manufacturer offers, so, 
the amplifier must protect itself.

 David
G3UNA

----- Original Message ----- 
From: "Joe Subich, W4TV" <w4tv at subich.com>
To: "'David Cutter'" <d.cutter at ntlworld.com>; "'Elecraft Reflector'" 
<elecraft at mailman.qth.net>
Sent: Tuesday, December 04, 2007 2:03 AM
Subject: RE: [Elecraft] linear amp shutdown (was ALC)


>
>> 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
>>
>