[RTTY] Power

[Phil Sussman]

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 at btinternet.com>:

> 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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