Carl:
A caution on running a transformer beyond its original
design. After "processing" the audio response in the
modulator must be flat flat flat and if the iron
has poor response as a result of your stretching things
you may be in for an awakening!
Hold on to your hat here but I'm going to reveal a
spec that the shortwave broadcasters generally include
in their contracts when they buy a "big rig". They specify
not only the frequency response of the transmitter's audio
input but also how it handles a 50 Hz squarewave. And
that squarewave must have less than 5% tilt. This is so
that peak clipping won't be "tilted" or "canted" and so
require the output of the clipper to be reduced in level.
And they commonly specify overshoot ("ringing") on an
applied squarewave of 1000 or 2000 Hz. Again less
than 5%.
They also commonly specify that the transmitter run for
a short period of time without overheating when a sinusoid
that has been clipped 10 dB is used to modulate 100%.
These are how I remember things at Continental, from
which place I retired 5 years ago. But I am certain that
other manufacturers follow the same approach.
So the modulator in a transmitter using low-level clipping
should pass both a 50 Hz squarewave and a 1000 Hz
squarewave nicely.
- Jim WB6BLD
----- Original Message -----
From: "jeremy-ca" <km1h@jeremy.mv.com>
To: "Barry Kirkwood" <barry.kirkwood@gmail.com>; <amps@contesting.com>
Sent: Saturday, November 10, 2007 6:57 PM
Subject: Re: [Amps] Over running modulation /AF transformers
> Well, limiting may be a limiting factor; pardon the pun. Since I'm going
> to
> be using some audio processing and negative peak limiting my average power
> will be up a fair amount. Im also going to be boosting the bass a bit
> since
> my voice lacks lows and Im aiming for a solid AM sound.
>
> I'll be happy with 30-40% over ratings as long as I can keep it from
> overheating and it doesnt add distortion. Im just starting to read up on
> audio transformers and relearn things I forgot decades ago.
>
> Carl
> KM1H
>
>
>
>
> Carl
> KM1H
>
>
> ----- Original Message -----
> From: "Barry Kirkwood" <barry.kirkwood@gmail.com>
> To: <km1h@jeremy.mv.com>; <amps@contesting.com>
> Sent: Saturday, November 10, 2007 4:10 PM
> Subject: Over running modulation /AF transformers
>
>
>> Usually easy. First limiting factor is power at lower audio frequency.
>> If for speech only, simply ensure a falling frequency response below
>> say 800Hz, with lots of attenuation below 200Hz or so.
>> 73
>> Barry ZL1DD
>>
>> --
>> Barry Kirkwood PhD ZL1DD
>> barry.kirkwood@gmail.com
>>
>
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