On Fri, 4 Mar 2005 16:11:50 -0600, "Richard Fry"
wrote:

"Richard Clark" wrote regarding Harris "Z" FM broadcast transmitters:
"For even greater reliability, any
PA module can be used as an IPA module,
with absolutely no modification."

It is quite obvious that as an IPA, that in the lower wattage systems
it represents overkill at 845W to generate drive to final PAs to 2.2
KW output. Hence the lower total efficiency. On the other hand,
an IPA driving 845W to generate 22KW obviously makes better
efficiency sense and is found in the overall 64.5% figure.

Yet another case where you write with guesswork, not knowing the facts.

Hi OM,

How amusing. :-)

Obviously you do not understand the architecture of this line of
transmitters, even though what I am about to write is available on the
Harris website.

Yes it is, isn't it. What that has to do with MY intimate knowledge
of them is hardly the point when I asked YOU for details. But this
posting only gets better.

The PA and IPA modules are the same,

As already noted in my direct quote above.

and consist of two, independent amps--each amp capable of 425W output.

Not being particularly knowledgeable, and taking your advice about the
information's availability (seeing that I provided the link, not you):
"Each module is conservatively rated to produce
850W of power into a system VSWR of 1.5:11"

AH! there we are with that errant SWR again. I wonder how you
explained that without noting this other egregious error of 850W?
What is even more amusing is that either way (425/850) it has
absolutely no impact on the outcome. But this gets better, after the
snooze that follows:

Their actual output
power depends on the tx they are installed in, and the power level required
from it. The only thing they have in common is a heat sink. An IPA at any
power level uses only one of these amps per 5kW (or less) block of PA amps.

How boringly trivial. Does the recitation of irrelevant facts bear
on some point being drawn here?

The other amp of the IPA remains unpowered and in reserve, and autoswitches
on line if the active one fails.

Op. Cit.

The lower AC input to RF output efficiency of the lower powered transmitters
arises from the fixed overhead in all units for losses OTHER than in the RF
amplifiers, i.e., power supply losses, exciter and controller power, RF
combiner and harmonic filter losses, and cooling power--the AC consumption
for which in low power units is a larger proportion of the total.

I said as much in the top section. However, if you enjoy your own
words that's fine, but it is becoming repetitive barring any obvious
point. (Both my and your entry could have as easily been left out -
did you say you were an editor?)

NOW, if the PA finals, accounting for 22KW are 80% efficient, that
must mean that they only consume 27.5KW of power to do so, and that
with a power input rating of 31KW then leaves the IPA (an identical
80% efficiency module) and control circuitry to absorb 3.5KW to
deliver the drive of .845KW.
It follows that for an 80% efficient IPA, it accounts for 1KW power
consumption. This remainder is easily attributable to power supply
losses (if we simply assign an industrial average efficiency of 95%
for power conversion) otherwise the system TTL circuits and LCD meters
suck down 2.5KW on their own.

Your analytical skills are seriously wanting. Please re-read my response
above.

Let's see, I have offered an analysis that supports your thesis that
the efficiency of this transmitters elements are ballpark 80% and you
say I am WRONG?

What a hoot!

I can only wonder why you can't offer your own numbers to show my
error. :-)

I originally wondered why you couldn't offer your own numbers and
carry your own water. Go figure....

Like I said, this has been one wild ride.

It is quite evident that such transmitters are no where
near these vaunted examples - but few dare venture into these
dissections.

It is "evident" only to those who don't understand the subject. Others have
not dared to venture into these dissections probably because THEY know
better.

I cannot say that I have enjoyed a more droll posting from your hand.

73's
Richard Clark, KB7QHC