[AMRadio] Transmitter Efficiency [Was: Power Levels]

[Steve Cloutier, 978-597-3311]

>I THINK Efficiency is in the eyes of the beholder! Power is power,
>the entire transmitter needs about 2500 watts to provide the above
>levels
>about as efficient as any class E setup. What is your point.

Efficiency is not an abstract concept or a feeling.  It is a very 
quantifiable paramater, because everything can actually be measured and 
calculated.

Vacuum transmitters operating at 100% duty cycle (they are always 
transmitting - which is their most efficient operational state) are 
terribly inefficient.

If I use rough numbers for a BC610, the final consumes 5V. @10A - 50 watts 
for the heater.  The modulators, 5V @6A each - 60 watts for both 
heaters.  Then there is probably some type of audio driver - using, say 75 
watts, then an RF driver which (conservatively) uses 100 watts (or 
MORE).  285 watts.  Using published numbers for RF efficiency (I have the 
book right in front of me) - 2000V @ 500 ma = 500 watts DC input, 335 watts 
gross output.  There must be some tank circuit losses, but for the moment 
we'll ignore them.  Now we're modulating too, so using the IDEAL class B 
figure for efficiency - 60%, we need 416 watts input to the modulator (for 
250 watts audio out).

Let's add it up: 1201 watts (let's just call it 1200) for 350 watts out
                          - that's 29% efficient!!! -
If you don't transmit all the time, the efficiency figured over time will 
be considerably less than 29%, since the standby power is consumed 100% of 
the time that the transmitter is actuall turned on.

Even if we remove all of the standby power from the efficiency calculation, 
it's still very inefficient - less than 70% for the RF stage and 60% for 
the ideal modulator.  The driver power is 100% loss, since it does not add 
to the power output, further reducing the efficiency.

As to the assertion (quoted at the top of this post, from a previous 
thread) that this [the BC610] is as efficient as any class E setup - the 
numbers do speak for themselves :-)

The DC carrier efficiency, input to output of class E transmitters *is* 
around 90%, and there is almost no standby power consumption at all - when 
you're not transmitting, there is no power usage whatsoever by the RF 
amplifier or driver, and approximately 5 watts used by the PDM 
generator.  The VFO and associated circuitry consume around 10 watts in 
standby.  When transmitting, the drive for a class E transmitter operating 
at 350 watts carrier output is around 20 watts on 75 meters.  The pulse 
width modulator, operating at around 95% efficiency, wastes very little 
power.  So, such a setup is HIGHLY efficient.

As a practical matter, for Amateur operators, maybe efficiency is not a 
critical factor, and whether one chooses to operate any type of transmitter 
is a matter of personal choice.  One type of transmitter is not "better" 
than another.  What matters is if it suits the purpose of the operator :-), 
and that's really the bottom line! :-)  We're supposed to be having FUN - 
isn't the word Amateur derrived from the word "to love" :-)

Regards,

Steve WA1QIX