Hi Marv,
When I saw your post, I also thought of using class E as well, since you have
to restore anyway. More efficiency = smaller heatsinks, smaller powersupply,
less expensive parts.
But my guess is that engineerig costs to produce a bullet proof militarized amp
such as this in a commercial venture would still exceed the $1/watt goal.
Paul
> From: Radio WC6W
> Subject: [Amps] Some thoughts on a transistorized legal limit
> amplifier...
> To: amps@contesting.com
> Message-ID: <924973.94241.qm@web63908.mail.re1.yahoo.com>
> Content-Type: text/plain; charset=iso-8859-1
>
> In order to meet the price, weight and broadband
> requirements discussed herein the past few days, I
> offer the following approach:
>
> Start with the 1500 watt peak output amplifier
> described in the old APT application note, APT9701,
> which posits 25?/watt for a Class C amplifier section
> with 70% efficiency at 27 MHz (ISM band, not CB!). Add
> some ferrite to the transformers for wideband
> operation.
>
> Connect a double pi-net (3C's & 2L's) to the output
> of the above amplifier for both impedance matching and
> harmonic suppression -- No filter bank required.
> Switching the pi-net into 7 or 8 band segments (the
> L's and one of the C's) plus padders for 160 should be
> about right. These components, including the
> switch(es), will have to handle some high currents
> but, only the center C will need to be rated for more
> than 1KV so, reasonably sized air variables will
> suffice for the two variable C's.
>
> Employ a power factor correcting (PFC) front end and
> a single ended pulse width modulated (PWM) regulator
> for the power supply. This will be a direct off line
> unit with AC isolation provided by the RF input &
> output transformers. A line input of 12 amps at
> 120VAC should be sufficient for 1500W PEP (750W
> average) out.
>
> The heaviest part of the unit will be the heatsink &
> fans which will be required to remove about 600 watts
> of heat, figuring an overall wall socket to antenna
> efficiency circa 55%.
>
> Now, recall this started with a class C amplifier,
> so a bit of inexpensive Digital Signal Processing
> (DSP) will necessarily be inserted between the mike
> and the exciter to provide for envelope restoration
> (linearization) of the amplifier via the PWM
> modulator. The exciter will only be required to
> provide around 30 watts drive for this scheme to
> function. Note that the exciter must be operated
> without compression, limiting, or ALC in this system.
> Those functions may be included in the DSP section.
>
> The above numbers are figured for SSB operation. AM
> could be implemented by setting a CW carrier at 375
> watts output (which will coincidently be the SSB tune
> point) and directly modulating the final with the PWM
> regulator. For CW/FM/FSK, the capacity of the
> heatsinking and the PFC section would have to be
> doubled.
>
> 73 & Good morning,
> Marv WC6W
>
> http://wc6w.50webs.com/
>
>
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