Steve
I think you will find 50 to 100 watts will give good comms over the first
60 or so miles and with 'arq' over a couple of hundred the deep fade
pattern and high noise level , really prevent the simple broadcast operation
of the newer multi tone systems,
, Gary g4wgt and my self g0nbd have run various tests over the year , in
normal rtty 85 hz shift gave very good results local and over distance. The
85 hz shift was the result of a selective fading test , where 200 Hz
separation looked to increase the possibility of loosing one (the hf) tone
before the lower one, 23 hz shift also gave good results but benefitted
from a reduction in baud rate.
psk31 was a magnitude better over any path, good results can be obtained at
range with the mulit tone systems , eg Olivia , but in qsb the long out
times result in quite high data loss due to re-lock time
I would think, but have not been able to try it yet , as not found any
other station with a pk232 , the original amtor system would provide quite
a robust link over distance due to its very short tx/rx cycle time and
data frame of only 3 letters , but at a loss of noise immunity compared to
the psk systems.
the mail handling arq psk systems fail due to the length of the
transmitted data word and the reliance on a statistically 'high' level of
confidence in the reception of the 'echo' pulse, which cannot be archived on
500, then end result usually a lock up !
Amplifier , As you are nearly fixed tuned, its quite possible to modify a
set that works on 160 mtrs by discreet lumped inductance and capacity ,
with the original power level of some 25/30 watts , I used a simple parallel
tuned atu , not out of palce on 160 mtrs , the 4 gang 1000 pf capacitor was
a spare for a Marconi cr100 rx , the coil a ww2 bc640 2 mhz tank coil , i
also found my weltz sp220 swr bridge worked fine on 500 khz as well .... no
more than 25 watts or it heats up ..
with the increase of power the atu flashes over , I had to construct a
variometer , and oddly , I found the coaxial dynamics 8200G 2/30 mhz 250
watt bird insert gave reliable results on 500 , it reads a bit low 170 for
220 ish , but it doesn't produce a phantom reflected reading and once i had
made a calibration chart , proved quite usable , notably none of the 'bird'
slugs in the hf range , 50, 100, 500, 1000 w, worked without giving a false
return reading ,
Good luck with the system
G ..
I will begin construction shortly on something basic that will give me
around 100W for starters and then begin transverter construction in order
to
run some fsk modes.
Our experimental licences will be geared towards
fleshing out 600m for regional emergency networks reliability over various
paths and conditions. It is also looking as if we will be able to work
other
stations within the amateur service, either directly on 600m or via
crossband but nothing has yet been written in stone.
|
