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Author Topic: Long Distance RF Link  (Read 5921 times)

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Offline airman00Topic starter

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Long Distance RF Link
« on: December 29, 2008, 06:27:19 PM »
Hi guys,
I'm looking for a long range version of the Sparkfun RF Link ( http://www.sparkfun.com/commerce/product_info.php?products_id=8947 )
I need a transmitter and receiver pair with really long range.

Heres the specs I need:
  • Maximum voltage I can give it is 12V
  • Maximum amperage I can give is 5 amps
  • Minimum baud rate should be 2400
  • Range of around 1/2 mile ( 805 meters or 2640 feet)
  • UART data transmission

I do not need bidirectional communication , only one way is fine. I don't need any fancy features like a signal strength pin. Also , if you can't give me an exact link or part number , what do you estimate the cost of the transmitter and receiver to be?

Thanks,
Eric
« Last Edit: December 29, 2008, 06:28:22 PM by airman00 »
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Offline bldavis

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Re: Long Distance RF Link
« Reply #1 on: December 29, 2008, 11:25:54 PM »
I was working on something of the sort, I believe that I once stumbled on a OEM Chip that might work for you check out Xstream:

http://www.digi.com/products/wireless/point-multipoint/xstream-modulespecs.jsp

take a look on here, i think that there was one in the 900mhz range that have an urban range of like 1500ft, i know that's less than what you are looking for but, i don't know what your situation is and the outdoor range exceeds what you are looking for so this mightb e a good starting point, keep up posted if there is any other way that we may be able to help! Good Luck!
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Offline hgordon

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Re: Long Distance RF Link
« Reply #2 on: December 30, 2008, 12:48:36 AM »
Digi/Maxstream XBee-Pro-900 has good specs, but I don't know if it is yet shipping.

Another possibility is
    http://www.meshnetics.com/zigbee-modules/zigbit900/
which supports 38kbps throughput and should have good range

I will be using Avalan AW900mUART on a new project - throughput is 1Mbps.
    http://www.avalanwireless.com/product_list.htm
Click on the OEM Radio Modules tab.  They only show the SPI version on the website, but the UART version is shipping.
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Offline bulkhead

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Re: Long Distance RF Link
« Reply #3 on: December 30, 2008, 04:45:39 AM »
How about the XBee-Pro? http://www.digi.com/products/wireless/point-multipoint/xbee-series1-module.jsp  This one should be currently available.  Their max distance rating ("up to 1 mile") is under ideal conditions, something like transmitting a few meters above water, line of sight.   Two of these RF modules can be used to "simulate" a wired serial port connection.

Offline dunk

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Re: Long Distance RF Link
« Reply #4 on: December 30, 2008, 05:41:53 AM »
i don't recommend you use them because there are cheaper 2.4GHz transceivers on the market these days but i used a pair of these for my first prototype RC system:
http://ie.farnell.com/quasar/t7g-434-225/transmitter-narrow-band-434-225/dp/1200994
http://ie.farnell.com/quasar/r7g-434-225/receiver-narrow-band-434-225/dp/1200995

range of the modules is advertised as 1 mile.

as long as you don't need super low latency a pair of XBee-pros would be around the same price and easier to use.


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Offline airman00Topic starter

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Re: Long Distance RF Link
« Reply #5 on: December 30, 2008, 06:09:16 AM »
Thanks for all the replies

These modules are all pretty expensive - is there anything cheaper?
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Offline dunk

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Re: Long Distance RF Link
« Reply #6 on: December 30, 2008, 07:25:22 AM »
Quote
These modules are all pretty expensive - is there anything cheaper?
heh. you remind me of the old network engineering joke:
"""you can have only 2 of the following 3 in any network: Reliable, Fast & Cheap."""

if you want long range and easy to use then you will have to pay a lot.
if you don't mind sacrificing range then the price will come down.
likewise if you want to build the module yourself from tiny surface mount components and laser etch tuning circuits then the price of the components will come down. (but obviously the price of the lab required goes waaay up,)

if you want "easy to use" at the range you are looking at then the XBee modules are some of the best i've seen.
if you need lower latency or don't mind putting a lot of work in there are some CYRF6936 based modules out there that do what you are asking but the development time will be much longer.

search DigiKey for all it's RF modules.
the toughest thing is working out what range a particular transmit and receive power will give. i've only reserched this on 2.4GHz modules so can't comment on other bands but here's some numbers ***for 2.4GHz only*** to get you started:
to get the range you are talking about at 2.4GHz from a DigiKey search you will need a Transmit Power of at least +8dBm or more
and a Receive Sensitivity of under -90dBm.

obviously a module with a lower sensitivity will not need such a high transmit power at the other end.
modules with between 100dBm and 130dBmdifference between Transmit Power and Receive Sensitivity will be worth investigating.

to add to the confusion power levels are measured in dBm (DeciBels per Meter) which have a logarithmic scale so although i'm putting numbers on the difference between TX and RX power, they don't actually make any sense.

the XBee-pro: range 1mile. Power output: +17dBm. Receiver sensitivity: -102 dBm.
the UGWJ 4US module i am using: range over 1mile. Transmit Power: +23dBm. Receive Sensitivity: -97dBm.

you might just get lucky and find a long range module on DigiKey at a reasonable price. if there is one it will probably operate on a low frequency and so relatively low bandwidth.
i'm guessing this is for a RC UAV right?


dunk.


[EDIT]
hmm, now i think about it, i should have mentioned, Transmit power can also be measured in mW (mili Watts) so you will also need to work out the mW to dBm conversion for transmit powers.
« Last Edit: December 30, 2008, 07:27:04 AM by dunk »

Offline airman00Topic starter

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Re: Long Distance RF Link
« Reply #7 on: December 30, 2008, 06:03:32 PM »
thanks for the reply dunk , it really helped in my researching out all the RF solutions

The application of the RF module is for a product I am working on for a client. We are just in the planning stage to see if the product is cost worthy to produce and sell. We really need the transmitter and receiver to cost approximately $10 each - but keep in mind we would order in quantities of at least 5000. I was hoping there would be a longer range version of the Sparkfun transmitter and receiver for approximately the same price.
The closest module to my specs is the XBee Pro Module - which is $32. The Xbee Pro is a tranceiver - which means its both receiver and transmitter. I feel it is because it is able to do 2 way communication , the price is $32. I believe if I make a similar module , but only do 1 way communication I could reduce the cost greatly.

So the questions I have now are the following:
1. Would I be able to design a RF transmitter and receiver with the specs that I gave above , so that the final production cost of the transmitter and receiver would be around $10 each ? ( assuming order quantities of 5000 )
2. Do you think I can get the price of an Xbee Pro module down to $10 if I order in quantities of 5000 ? Retail cost of the Xbee pro is $32
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Offline hgordon

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Re: Long Distance RF Link
« Reply #8 on: December 30, 2008, 06:11:41 PM »
There is a lower cost, lower power (1mW) version of XBee-Pro called just XBee.  Pricing used to be around $16 in volume, but I think the prices were raised earlier this year.  I used to pay $28 for the XBee-Pro and bought more than 1000 of them.  XBee is based on a chipset that integrates xmit and recv functions - you won't get them separately.

By the way, for xmit power, 1dBm = 1mW, 10dBm = 10mW, 20dBm = 100mW, 30dBm = 1W, etc
« Last Edit: December 30, 2008, 06:15:51 PM by hgordon »
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Offline airman00Topic starter

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Re: Long Distance RF Link
« Reply #9 on: December 30, 2008, 06:13:34 PM »
But XBee only has 300ft (100m) range , I need the range that the Xbee Pro offers - up to 1 mile range

XBee is based on a chipset that integrates xmit and recv functions - you won't get them separately.
Guess I'll use a different ( and cheaper) chipset
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Offline hgordon

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Re: Long Distance RF Link
« Reply #10 on: December 30, 2008, 06:17:16 PM »
But XBee only has 300ft (100m) range , I need the range that the Xbee Pro offers - up to 1 mile range
Good luck getting 1 mile range with 2.4GHz unless you have directional antennas and clear line-of-sight.  You need to drop to 900MHz or 450MHz for that kind of range.
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Offline airman00Topic starter

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Re: Long Distance RF Link
« Reply #11 on: December 30, 2008, 06:19:46 PM »
Oh right , forgot about that high frequencies get lost with objects blocking them.

Guess I'm stuck with only one remaining question:
1. Would I be able to design a RF transmitter and receiver with the specs that I gave above , so that the final production cost of the transmitter and receiver would be around $10 each ? ( assuming order quantities of 5000 )
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Offline hgordon

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Re: Long Distance RF Link
« Reply #12 on: December 30, 2008, 08:30:46 PM »
Radio chipsets are cheap and plentiful, but RF design is not cheap, and you have to get FCC type acceptance if you design your own module (not an issue if you purchase complete modules that already have FCC certification), which likewise costs a bunch of money.
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Offline dunk

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Re: Long Distance RF Link
« Reply #13 on: December 31, 2008, 05:13:37 AM »
Quote from: hgordon
but RF design is not cheap, and you have to get FCC type acceptance if you design your own module (not an issue if you purchase complete modules that already have FCC certification), which likewise costs a bunch of money.

i would speculate getting approval from the regulatory authorities would cost more than the cost of the components for a run of 5000 boards.
bear in mind you would need to do this for all the regions you want to sell the boards in, not just the FCC.

be careful choosing high power modules as well because a lot of the higher power ones are only legal in the US and a handful of other countries.


hey Airman00,
you were asking about RF amplifiers in another post but it fits better here.
i've never used one but go to DigiKey.com, search for the keyword "amplifier" and select "RF Amplifier ICs and Modules".
some of the DataSheets look reasonably straight forward once you understand the language.

i would guess some of the WiFi hackers will have documented some of these at 2.4GHz if you search around a bit.

bear i mind that if you use an amplifier you are altering the RF output so the device will need separate regulatory approval.

a bit more glossary for you: a concept you will need to understand is SNR or S/N (Signal to Noise Ratio).
at work i light a lot of long-haul fiber optic where this is very important but the theory is the same with RF transmissions.
SNR is how visible a signal is against the background noise expresses in the logarithmic decibel scale (dB).


on a different tack,
have you looked at my ongoing project yet?
i'm aiming for 1km rage LOS.
http://sites.google.com/site/mrdunk/ using this module: http://www.unigen.com/download/UGWJ4US%20User%20Manual_v09.pdf.
the modules i am using are around half the price of the XBee ones. my code would be easy to port to any other AVR and will eventually support bandwidth sharing and channel hopping.
feel free to use/sell something based on my platform if you want but bear in mind it (or anything based on it) must be kept open source.


dunk.

Offline Geir

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Re: Long Distance RF Link
« Reply #14 on: January 07, 2009, 02:52:35 PM »
This is an interesting project. Try looking in to FSK. Its what was used in the old modems. You can use this to send data on a normal audio line. Hook this up to a cheep walki talki or something like that. There is IC for this. Or you can build it from scratch FSK is pretty simple, but implementing it could be a little hard. Using this you don't have to build you're own receiver.
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Offline airman00Topic starter

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Re: Long Distance RF Link
« Reply #15 on: January 07, 2009, 03:57:24 PM »
This is an interesting project. Try looking in to FSK. Its what was used in the old modems. You can use this to send data on a normal audio line. Hook this up to a cheep walki talki or something like that. There is IC for this. Or you can build it from scratch FSK is pretty simple, but implementing it could be a little hard. Using this you don't have to build you're own receiver.
Hi, it looks interesting.

This project is not really a "throw-together" project. Rather its a prototype of a product to be mass produced for a client. That means I can't just hack walkie-talkies on a massive scale. Are there any long range FSK modules that I can use (simpler versions of walkie talkies basically)?
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Offline Geir

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Re: Long Distance RF Link
« Reply #16 on: January 08, 2009, 04:02:07 PM »
There probably is, I know radio amateurs use it. Try google. But I think there is a lot of DIY where they use old modems, and thats no god.
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Offline airman00Topic starter

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Re: Long Distance RF Link
« Reply #17 on: January 14, 2009, 04:10:59 PM »
 I'm gonna go with the TXLC-434-LR and RXLC-434-LR RF Modules - made by Linx
Before I go ahead and make my own PCB boards I'm gonna buy these breakout boards for the Link Modules
http://www.rentron.com/remote_control/RXLC-434LR.htm
http://www.rentron.com/remote_control/TXLC-XXX-LR.htm

Those are the same modules used on the Parallax Receivers and Transmitters - http://www.parallax.com/Store/Accessories/Communication/tabid/161/CategoryID/36/List/0/Level/a/ProductID/112/Default.aspx?SortField=ProductName%2CProductName

Now even though the Parallax one claims only 300 feet and the Rentron one claims 3000 feet , they are both correct. You might ask, " How is this possible if they both use the same chip ?". The answer is that the Parallax one uses a 2inch antenna and the Rentron one is supposed to use a 7 inch one - http://www.rentron.com/remote_control/434-RF-Antenna.htm. I called up Rentron a few minutes ago to verify this.

So I guess I'll be ordering these boards and I'll report back how that goes. Oh and the chips have built in RSSI pins so I don't have to use that method I described in another thread about RF ranging.
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