I think more is being made of this then what it is - the reason why it was
defined as "supplied to the antenna" is that is indeed simple - and doesn't
necessitate any math/measurements beyond that single connection. I'm sure -
or better stated my guess would be the feedline is considered part of 'the
antenna' in their eyes - how ever that might branch out... thus making it
very simple for them. If they show up at Joe Dumbstuff's house who is
running 4000W to a feedline with losses of over 4db and putting 1500w at the
antenna TERMINALS - I'd bet he'd get a citation.
As for contests - that is a whole 'nother story ... I know of one guy that
is PROUD of his contest wins... and runs 6000W. I was told by the owner of
one antenna supply house that baluns in the 5kW range are quite common ...
and he's done as high as 20kW baluns.
... for me - legal limit is legal limit - period.
Gary
K9RX
-----Original Message-----
From: jimlux
Sent: Monday, September 26, 2016 10:47 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Legal Power measurement Discussion
On 9/26/16 6:05 AM, Ed Sawyer wrote:
Clearly, this is "settled science".
Actually, no it's not.
Sure, if you want to measure the "output power" of an amplifier, the
obvious reference plane for the measurement is the connector on the
amplifier.
But I think as we get to more and more complex antenna systems, some
with multiple amplifiers feeding multiple antennas, the "reference
plane" is harder to define. Particularly when you start getting away
from the 50 ohm connector with coax model.
Take two cases:
Case 1: If I built an amplifier with a 1200 ohm output impedance that
varies with frequency and load, and then some transmission line that's a
few meters long to an outboard matching network to ladder line to a
non-resonant dipole
Case 2: The amplifier has the matching network inside.
Case 3: what about case 1, with the line between amplifier and outboard
matching network is 50 meters long?
Where is the measurement plane? at the output of the amplifier before
the matching network? Or at the output of the matching network?
Why would the different physical configuration make a difference from a
regulatory standpoint?
I can think of other schemes where the distinction between "transmitter"
and "antenna system" is less obvious, or, at least doesn't provide a
convenient measurement point. What if I have two 3.7 MHz amplifiers in
the shack, phased 90 degrees from each other, then a couple 100 foot
transmission lines, and a hybrid coupler to combine them before the run
up the tower?
Topologically, this is a very common microwave system (90 degree hybrid,
2 PA devices, 90 degree hybrid), and in a microwave system, the
transmission lines might be several wavelengths long.
Is the power measurement at the MMIC device (that's what the mfr of the
MMIC will ask for), or is it at the output of the hybrid coupler (that's
what I, as a system engineer, care about)?
- if you're selling amplifiers, then clearly you want a "at the output
of my box" kind of spec
- if you want a simple to implement requirement that covers 99.9% of the
cases, "stick the power meter in the feedline at the end next to the
amp" is easy.
- But I'm exploring the 0.01%
Let's be clear.. nobody is going to be hunting down someone running
1900W into a 1dB loss transmission line, with 1500W showing up at the
load end. We're not talking here about "active antenna tuners" that
"seem" to radiate a signal equivalent to 5kW.
Nor are we talking about contest rules - which by definition are
arbitrary.. if the rules say "all transmitters within 1000 ft are to be
considered as one", then that's what the rule is.
This is sort of an academic discussion - but one of some importance in
the long run as more sophisticated radio systems start to be built. The
idea of amplifier per element hasn't got a lot of traction yet, but it's
coming. - SW broadcasters do it, why not hams. Particularly with solid
state devices, the losses in a combining network in a SSPA with a single
output jack are substantial, particularly with microwaves. Spatial
combining (which has essentially no loss) is pretty attractive, when
you're ganging up 20 100 watt modules to get 1500W out. Why burn the
extra 5 modules just to overcome the combiner loss.
https://en.wikipedia.org/wiki/ALLISS for an interesting take on this..
their power levels are substantially above what hams do, but the
architecture is interesting..
They use a variety of basically high power digital sources that are
combined to make a low distortion, high power RF signal.
The Harris AM broadcast transmitters are sort of similar: essentially a
giant power Digital to Analog converter, but without the spatial combining.
And shouldn't we be looking at architectures that have better "wall plug
to Radiated RF" efficiency.. That's part of "advancing the state of the
art" that's one of the purposes of ham radio.
Power is measured at the final of the
radio or amplifier, whichever is last. 1500W max PEP from the transmitter
is clearly in the rules - as its quite clear how the FCC states ERP for
other services. And they don't mention ERP except for the new VLF.
This dialog reminds me of the splitting hairs a decade ago of whether
1500W
was "per antenna" in the contest rules and rules finally settled the issue
by rewording that its 1500W total power - regardless of number or
direction
of antennas.
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