Marechiare wrote:
>
> Yes, I noticed it, not too many active linear 800W parts are priced
> under US$1 regardless of the working frequency.
>
> But if it were acceptable to stay in Big Mac price region, I'd choose
> MRF1513NT1:
>
> http://parts.digikey.com/1/parts/1426213-ic-mosfet-rf-n-chan-pld-1-5-mrf1=
513nt1.html
>
> Specified Performance @ 520 MHz, 7.5 Volts
> Output Power =97 8 Watts
> Power Gain =97 14 dB
> Efficiency =97 70%
>
> Priced	US$3.62 (for 1000)
> #
>   =

nice for a handheld :) It's not really 70% efficient. That depends on =

circuit and modulation.

Battery portable you want about 25W out. For safety you want a PA with =

pair transistors rated maybe 40W each. VSWR and over current circuits =

take a finite time to detect a mismatch. A short or open coax at just =

the wrong fraction of wavelength can dump all the "aerial" power into =

the PA transistor. If you want very linear operation for QAM or =

sustained FM, AM or SSTV also you you don't skimp.

My 25W HF manpack uses "24V" battery pack and 50V bipolar RF PA =

transistors (About $50 each, obsolete). My experimental 100W MOSFET amp =

needs maybe 90V for full power (IRF740, works OK to 30MHz). Generally =

above 10W and using TO220 type SMPU MOSFETS a higer voltage is needed, =

24V to 90V. So to run off 12V you need a SMPSU too!

So that leads to thought of a SMPSU output stage driven direct by FPGA =

PWM signal representing amplitude (only on/off) powering 5V to 90V from =

12V supply to a class C AMP driven direct by (only on/off) N.C.O phase =

modulated inside FPGA. you then use two cheap simple circuits driven by =

FPGA and have any arbitrary modulation. Polar Amp implemented in FPGA.


-- =

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