On 5/18/2015 12:57 PM, qrv@kd4e.com wrote:
PEP is not the same thing as key-down RTTY by a long shot.
How many switches, feedlines, and antennas, external to the
a
mp can survive 1500
w carrier for long?
I'm sorry, but I have to disagree
It depends on the switches. Most RG-8 size feed lines will handle much
more than 1.5 KW continuous. Other than the baluns, many non trap
antennas will handle substantially more than the legal limit
continuous. Look it up! Tube amps that will handle 1.5 KW out
continuous will have an ability to run as much as 2500 to 3 KW PEP,
unless computer controlled. Solid state amps are generally heat limited
for longer and higher duty cycle modes. SSB is typically 20%, unless
overly processed. CW is usually figured at 50%, but with break-in
conversations, transmissions are relatively short. Digital and AM are
100%. I know what that does to plate voltage, what does it do to the HV
on a SS amp? What's the IM numbers on the SS amp? What does continuous
duty modes do to that?
Operating a tube amp meant for the legal limit on 20% duty cycle SSB on
100% digital or AM will likely drag the HV down so it is no longer
properly tuned. Many of today's amps are over rated at the legal limit
on SSB The tubes, PS and components are all light duty in those amps
and trying to get what the manufacturer says they will do, does more
than cause the users to complain about short tube life
I think you will find that the Alpha Delta mechanical switches will more
than handle 1.5 KW continuous.
A little consideration, research, and asking those who are doing it
regularly what they are using, before purchasing the components that
follow the amp will likely find components rated well more than 1.5 KW
continuous. There are some hams with big home brew amps as well as
imported ones that can and do run the legal limit on digital and AM with
long transmissions without failures. I assume they might be able to
point the way to reliable components. One thing with SO2R and remote
switches is the isolation. If the components will handle the power,
will they give enough isolation so the second station can operate on the
second harmonic through the same switch?
It's more than just handling the power. When I shell out that much
money, I want two things. The full legal limit, any mode, no time limit
AND an IM3 of 40 db or better. Collins could do an IM-3 well more than
40 db (more like 50) in the 1960s. It's only recently that the solid
state rigs have approached that and it's with their top end (expensive)
rigs.
The receiver sections have long since passed the useful levels in
dynamic range, selectivity, adjacent frequency rejection, and
sensitivity far beyond the noise floor on low bands. They are into the
bragging rights only realm because these amazing numbers do little when
the noise floor is 10X the sensitivity. Ham 10 KHz up or down has an
IM-3 of 30 db, and a rig driving the amp using ALC derived power control
with a huge leading edge power spike that can easily be heard +/- 50 KHz.
Selectivity does little good when your neighbor on the bad has a wide
signal that covers your frequency.
The antennas, coax and switches are available to handle the power, and
it would help greatly if a number of hams learned how to properly set up
the functions of the driving rig to drive an amp and how to tune the
amp. There are a number of tetrode amps that are very clean when
properly driven and properly tuned. It's the users who have given some
of the larger amps a bad rep. Tetrodes do not tune up the same as
Triodes. Similar, but different
So, yes, there are many components, connectors, feed lines, switches,
and antennas that will handle the legal limit all day long. It's where
they cut corners the problems arise.
73
Roger (K8RI)
Especially heating at imperfect and/or marginal contacts
and connections?
I'm seeing estimates of 5 seconds, 10 seconds, and 15 seconds
of 1500w output in RTTY continuous-duty mode - but unlimited
at 1KW.
Most vendors will be cautious about running-at-the-edge as
they know that some Hams will push that margin then blame
them when something breaks.
Question:
Is RTTY so inefficient that one really needs 1500w output?
There are many other keyboard-keyboard digi modes that can
hold a qso under poor conditions at 30-50w.
Just wondering ...
David KD4E
I asked this very question from one of the two SPE vendors at Dayton.
I got very evasive responses until I insisted on a plain and simple
answer. Finally, the vendor stated that if you start at 1500 w out on
RTTY, the power will cut back to 1200 watts after ten seconds. I was
disappointed in his rather defensive posture on the question of
headroom. Yet there was a sign up that said the power out was 2000
PEP CW/SSB.
73, Dennis W0JX
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