In a message dated 13/08/2005, gcouger@.......... writes:

To beat  long cable runs and the associated problems wireless data links 
are just  becoming a reasonably priced off the rack solutions that is 
reasonably  easy to put in to practice. Using directional antennas Zigbee 
and  BlueTooth can work several hundred yard in the clear. 
Maxsteam has good  off the rack stuff that I know works.  
http://www.maxstream.net/products/index.php If you want plug and  play.
Cheers
Gordon



Hi Gordon,
 
    Thanks for the feedback.
    I am aware of the radio links that have been / are  becoming available. 
If you really need a long link and are happy to fund it,  fine, but do consider 
all the options.
    UHF radio links do require some skill to implement  and are not entirely 
'fit and forget'. They may impose limits on the receiving  computer, both for 
RAM provision and on the processing rate, particularly when  using encrypted 
data. You are usually running several linked applications for  seismic data 
recording. Check that you can have full 'preset' control of the  transmitted data 
rate. This is not always available. (e.g. If I run my 56 K  modem at more 
than 38 K, it 'drops out' several times an hour / performs like a  geriatric 
snail - due to the length of the line - according to the sevice  provider.) You 
need the link to work 100% in all weather conditions. High  speed UHF signals 
may become garbled in woodland locations, especially during  rain or snow / 
where you get strong reflected multipath signals.
    However, it still leaves you with a remote power  supply problem and you 
may need links both ways for seismic work. The link to an  ADC is usually two 
way. Low noise amplifiers tend to have significant power  consumption. Do you 
need to buy battery operated power supplies /  batteries / solar panels? You 
may then fit an ADC and send digital signals,  or you can generate a frequency 
modulated signals which are demodulated at  the receiver, but this may require 
several channels of additional electronics. 
    Somewhere along the line you have to have  a time reference on a 24/7 
basis to 1 second, or preferably to 0.1  second, linked to the ADC sample timing. 
GPS receivers tend to be power hungry,  location sensitive and still 
moderately expensive. The internal software  clocks which are usually fitted to 
computers are nowhere near accurate  enough. On my 'new' computer, I can't rely on 
it to within 20 secs per  day. Updating the clock every hour is just not 
adequate. Some of the web  time services have significant and variable signal 
delays. (I bought a radio  corrected LCD quartz clock.) A 1 sec error on a seismic 
signal represents about  10 km uncertainty.
    Do check on the total $$$ cost / benefit if you are  considering a radio 
system. Check if there are similar radio systems operating  locally over 
similar distances? Are there any adverse local problems, like other  radio 
transmitters / interference sources / obstructing metal mesh fences? Try  to avoid 
'buying trouble'.
 
    Regards,
 
    Chris Chapman






In a message dated 13/08/2005, gcouger@.......... writes:
<=
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  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>To beat=20
  long cable runs and the associated problems wireless data links 
are ju=
st=20
  becoming a reasonably priced off the rack solutions that is 
reasonably=
=20
  easy to put in to practice. Using directional antennas Zigbee 
and=20
  BlueTooth can work several hundred yard in the clear. 
Maxsteam has goo=
d=20
  off the rack stuff that I know works.=20
  
http://www.maxstream.net/products/index.php If you want plug and=20
  play.
Cheers
Gordon


Hi Gordon,
 
    Thanks for the feedback.
    I am aware of the radio links that have been /=20=
are=20
becoming available. If you really need a long link and are happy to fund it,=
=20
fine, but do consider all the options.
    UHF radio links do require some skill to implem=
ent=20
and are not entirely 'fit and forget'. They may impose limits on the receivi=
ng=20
computer, both for RAM provision and on the processing rate, particularly wh=
en=20
using encrypted data. You are usually running several linked applications fo=
r=20
seismic data recording. Check that you can have full 'preset' control of the=
=20
transmitted data rate. This is not always available. (e.g. If I run my 56 K=20
modem at more than 38 K, it 'drops out' several times an hour / performs lik=
e a=20
geriatric snail - due to the length of the line - according to the sevice=20
provider.) You need the link to work 100% in all weather conditions. Hi=
gh=20
speed UHF signals may become garbled in woodland locations, especially durin=
g=20
rain or snow / where you get strong reflected multipath signals.
    However, it still leaves you with a remote powe=
r=20
supply problem and you may need links both ways for seismic work. The link t=
o an=20
ADC is usually two way. Low noise amplifiers tend to have significant power=20
consumption. Do you need to buy battery operated power supplies /=20
batteries / solar panels? You may then fit an ADC and send digital sign=
als,=20
or you can generate a frequency modulated signals which are demodulated=
 at=20
the receiver, but this may require several channels of additional electronic=
s.=20

    Somewhere along the line you have to have=20
a time reference on a 24/7 basis to 1 second, or preferably to 0.1=
=20
second, linked to the ADC sample timing. GPS receivers tend to be power hung=
ry,=20
location sensitive and still moderately expensive. The internal softwar=
e=20
clocks which are usually fitted to computers are nowhere near accurate=20
enough. On my 'new' computer, I can't rely on it to within 20 secs=
 per=20
day. Updating the clock every hour is just not adequate. Some of the we=
b=20
time services have significant and variable signal delays. (I bought a radio=
=20
corrected LCD quartz clock.) A 1 sec error on a seismic signal represents ab=
out=20
10 km uncertainty.
    Do check on the total $$$ cost / benefit if you=
 are=20
considering a radio system. Check if there are similar radio systems operati=
ng=20
locally over similar distances? Are there any adverse local problems, like o=
ther=20
radio transmitters / interference sources / obstructing metal mesh fences? T=
ry=20
to avoid 'buying trouble'.
 
    Regards,
 
    Chris Chapman