[AMPS] Alpha 91b Metering Question

[John Fielding]

I don't know the amp in question but from your description I think I know what is going
on. 

I suspect from the power meter readings you are getting the meter reads peak power.  If
so it is fairly easy to explain why the measurements are different.

An average reading wattmeter would indicate 100% for full key down, about 30% for dots
and about 60% for dashes.  A peak reading (holding) wattmeter reads the same for either
condition.

1.	Most transceivers put out a narrow leading edge spike of power when the key is first
pressed.  This can be 50% or more of the average power depending on the rig and how
quickly the internal ALC drags the power back to what it is set for.  A peak reading
wattmeter will see this as the full peak power.  One way to reduce this error is to
reduce the hold time of the meter.

2.	In a typical tube amplifier the ht sits higher when in idle mode than when full key
down.  So fast keyed cw would allow the amp to attain a slightly higher peak power than
full key down.


Hope all of this makes sense.

John	ZS5JF
----------
> From: Tim Mitchell <tim.k9tm@totalink.net>
> To: amps@contesting.com
> Subject: [AMPS] Alpha 91b Metering Question
> Date: 27 May 1999 11:19
> 
> 
> I have a 91b and am observing the following:
> 
> I have the 91b driven by a FT1000D to a dummy-load.  To tune the amp, I put
> the 1000D into CW mode.  I turn the keyer off.  Press the paddles and tune
> the amp.  No problem so far.  It tunes up fine and indicates 1000 watts (on
> the internal watt meter).  Next, I turn the keyer on and generate CW
> characters and now the watt meter indicates close to 1400-1500 watts.  The
> drive is about 60/65 watts.
> 
> I am suspicious of the 1000 watts indicated.  This seems too low for the
> drive level.  The 1400-1500 is more believable.  Also, I can not seem to
> drive the watt meter (builtin Alpha LED meter) beyond 1000w during cw
> keydown.
> 
> I then put a Daiwa power/swr meter in line and it shows 1200w when the Alpha
> shows 1000w during cw keydown.  I have no idea how accurate the Daiwa is.
> 
> I ran this past K8CC and his 91b does not act this way.  I called Alpha
> and they claim to have no idea why it is doing this and say that they have
> never heard or this.
> 
> Any ideas why the metering acts this way ?  Am I doing something wrong ?
> 
> Thanks 73 Tim K9TM  tim.k9tm@totalink.net
> 
> 
> 
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