----- Original Message -----
From: "Tom Rauch" <w8ji@contesting.com>
To: "bumerang boom" <bumerang.boom@yahoo.com>
Cc: "Amps Amps" <amps@contesting.com>
Sent: Wednesday, September 12, 2007 9:59 AM
Subject: Re: [Amps] Load Pulling
>> Thanks Tom for your reply. To my reconing the output
>> is a carrier of 2MHz pulses (500nS period) with a very
>> low duty cycle (20nS). The pulse, at least
>> theoretically, carries a lot of harmonics extending up
>> to 30MHz.
>
>> Perhaps an antenna tuner, a 50 OHM dummy load, a
>> current metter for the amp suply, and an osciloscope
>> to watch the magnitude of the output pulse could
>> provide a clue where the output impedance lies, but I
>> am not sure about the acuracy of such a measurement
>
>
> If the signal is broadband you cannot use a tuner. By
> definition all matching circuits and the load must have
> negligible impedance change over the signal bandwidth. Since
> the carrier is at 2MHz and the pulse duration is only 20nS
> the narrowest BW would be 100kHz (50kHz up and down) with a
> raised sine waveshape. This alone rules out use of a "tuner"
> since the BW is almost certainly hundreds of kHz with a
> 20nS pulse of any decent waveshape.
Tom,
Something doesn't make sense here. 1/20ns = 50 MHz, not
50 KHz!! The period of a 2 MHz carrier is 500ns, so with a
pulse width of 20ns, you are only transmitting a small fraction
(4%) of a single RF carrier cycle. That sounds more like a
sampling process than it does pulsed CW (as if you were
sampling a 2 MHz signal with a 50 MHz A/D converter).
I just worked a 20 hour day, so I am too tired to think about
this anymore. Maybe tomorrow :-)
73, Mike W4EF..........................................
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