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Author Topic: HF or VHF wifi  (Read 7361 times)
Ivan
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« on: March 18, 2009, 05:15:41 PM »

Is there any such thing? Not really bothered about whether it is legal or not. More interested in whether it is possible to reliably link two non-line-of-sight sites with a reliable data connection that could transmit data (temperature data, for example, or pictures - even if it took 30minutes to send a picture), with relatively low power. I've played around with low power transmitters (15mW or so), and found it's relatively easy to pick up the signal in an urban environment without high antennae over a distance of a mile or so.
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Justme
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« Reply #1 on: March 18, 2009, 05:53:10 PM »

Become a radio ham?

Use a microwave link?

Bounce the non line of site using a repeater?

Use a mobile phone for batch transmisions via the web browser?

Get a 3 G dongle?


Justme
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guydewdney
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« Reply #2 on: March 18, 2009, 06:23:49 PM »

go to a different old standard (RS232 or 485) THEN go wireless?

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=230326787623&cguid=32a508bb11f0a0aad4b6b2c6ff6c4d8b

for a rs485 wireless doohicky?
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Justme
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« Reply #3 on: March 18, 2009, 06:32:10 PM »

Estimated range 300m. That can be done with standard wifi gear.


Justme
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30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
Victron 12v 3000w 120a
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24 x 2v cells 700amp/h 5C
Total bank 4350 amp/h 5C
stephend
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WWW
« Reply #4 on: March 18, 2009, 07:40:23 PM »

Might have some luck searching for "general packet radio".  E.g. came across this: http://en.wikipedia.org/wiki/D-STAR
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The Crofter
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« Reply #5 on: March 18, 2009, 07:45:00 PM »

Google "Radio modem".

Quite a few devices around with varying data rates. Distances of several miles can be achieved with higher power systems (100mw ish) and directional yagi aerials. Serial comms only but modern ones may accept usb instead of using a usb/rs232 converter. However these are cheap and cheerful. You can pay good money for a system but the more expensive ones have more facilities.

Try this link for starters:

http://www.rfsolutions.co.uk/acatalog/High_Power_RF_Modem.html

Drop me a line if you need more help.
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Cheers

Pat
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« Reply #6 on: March 18, 2009, 07:58:26 PM »

Doh just re read your post....

As it happens I built a radio modem system using HF radios (squadcall) in the Antarctic many years ago. The front end was a BBC micro connected to a Maplin RTTY modem which produced tones transmitted by the radio. We achieved comms from several hundred miles away but the data rate was quite slow. Can't remember the actual rate but it was something like 50 to 100 baud - conditions dependent.

One of the reasons for the low rate was lack of effective bandwidth. The audio input could not handle fast data as it could not work fast enough switching between tones. Modern HF sets will probably have a dedicated data input which will be far more efficient.

I also built another system that used packet radio to transmit data. These may be of more interest as there is the possibility of creating a network from many devices.
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Pat
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« Reply #7 on: March 18, 2009, 08:19:05 PM »

If you really want to go hi-tech then there is alway the option of an Argos satellite system or Irridium - world wide coverage. I have a contact who has developed Irridium data links so PM if interested.
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Pat
wdh
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« Reply #8 on: March 18, 2009, 08:57:10 PM »

For anyone wanting a line of sight data link, it might be well worth checking out
http://www.digi.com/products/wireless/point-multipoint/xbee-pro-868.jsp
specifically the "development kit" which includes a pair of the xbee modules and an assortment of aerials, an other goodies for just $99.
Euro legal too.
Potentially, 24 kbps over an 80 km  Shocked  link.

And you can, if I've got it straight, set up a network fairly simply (given the sites) so as to go round corners.
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EccentricAnomaly
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« Reply #9 on: March 22, 2009, 12:35:53 PM »

Here's a page which mentions more powerful versions of the Xbee modules than Digikey carries:

http://ladyada.net/make/xbee/modules.html
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PhatBob
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« Reply #10 on: March 23, 2009, 09:11:47 AM »

I don't know if anything here will be of use to you:
http://www.coolcomponents.co.uk/catalog/index.php?cPath=25&osCsid=eda504364edafdf105c38a3c7dab1899
But I can never resist looking at Cool components' website.

Theres also this:
http://www.sparkfun.com/commerce/product_info.php?products_id=559
Which is said to have a range of 1.5km, at 915MHz feasible to make a compact high gain directional antenna


Although for the cost its got to be worth playing with :
http://www.coolcomponents.co.uk/catalog/product_info.php?cPath=25&products_id=238
and
http://www.coolcomponents.co.uk/catalog/product_info.php?products_id=239
And making a 1/4 wave yagi for the transmitter and a quad dipole for the receiver.
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