Poppycock Phil....
73
Jim W7RY
-----Original Message-----
From: Phil Sussman
Sent: Saturday, May 27, 2017 2:57 AM
To: David G3YYD
Cc: rtty@xxxxxxxxxxxxxx
Subject: Re: [RTTY] Power
My thoughts on RTTY and RF power are below:
1. A 'clean' signal will provide significantly better results than an
overdriven one.
The ability to decode an RTTY signal, first and foremost, benefits
from FSK rather
than AFSK when setting up a station. Yes, AFSK, when properly
adjusted, will mirror
FSK, but ask yourself how many times a poorly shaped signal is the results
of
misadjusted AFSK.
2. I agree with David that power can have an effect; however, it is an
order of
magnitude. I disagree that a 2db increase in power will significantly
decrease the
error rate. Depending upon propagation and general background (e.g. a
contest going
on or a misadjusted adjacent signal) modestly increasing transmitter
power will have
little, if any, effect.
3. Antenna efficiency and feedline loss are far more significant that
transmitter
power. Improving copy at the other end, in my opinion, requires perhaps a 6
db
improvement. As an added benefit reducing losses also improves your
receive sensitivity.
4. There is no doubt that running 100w (e.g. full power on a 100w rig)
is better than
running 50w. But only slightly better, 3bd. Running full power reduces
the duty cycle
and while you may not "burn out" your finals in the short run, you
will induce more heat
and shorten overall life. Oddly enough, reducing power by 50%
increases life and reduces
duty cycle (considering RTTY to be 100% duty cycle) by more than 50%.
5. Propagation conditions are far more important than a 3db increase
in RF power. When
conditions are optimum I have run 1w (or less) with the same results
as 50w. Under less
than optimum propagation conditions, I have tried using 1Kw when 50w
was marginal and
I was advised that my signal went from barely copyable to readable but weak.
6. Some RTTY operators run lots of power which (unfortunately) causes
other stations to
also have to increase power, just to compete. When that does is drive
the lower power
signals away.
So, my suggestion is to improve efficiency of feedlines and antennas.
Raising an antenna
by only a few feet or replacing a lossy feed line will accomplish far
more than 3db.
'End of soap box'
73 de Phil - N8PS
Quoting David G3YYD <g3yyd@xxxxxxxxxxxxxx>:
There has been recent discussion about power and the difference it will
make. Unless you have studied this before you may be amazed at what sort
of
difference power can make to RTTY decode error rate.
A received signal with decode errors cause by noise and not by propagation
effects like selective fading, flutter etc has a character error rate of
10%. By increasing power by 2dB, e.g. 100 watts to 160 watts the error
rate
will drop to about 1% or for most amateur purposes perfect copy.
So changing that long run of RG58 coax to RG213 or putting the antenna up
a
bit higher or turning the power up from 50 watts to 100 watts can
significantly improve copy at the far end. Better copy at the far end =
more
QSOs.
I note many run their 100 watt rigs at around 50 watts because they think
the rig cannot take the full power on RTTY. I have news for you all the
rigs
I have ever had I have run at full power on RTTY without ever having blown
the PA devices. The typical 13.8v 100 watt AB class PA has similar device
dissipation at 50 watts out as at 100 watts out. Some PAs will have less
dissipation at 100 watts than 50 due to the PA being in gain
compression(saturation). The PSU will be supplying more power but again
all
of the commercial 13.8v SMPSU I have used have worked perfectly at 100
watts
output.
73 David G3YYD
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