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el00
Joined: 27 May 2009
Posts: 5
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 27 May 2009 10:45 can over rf |
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Hello,
I am developing a communication between two units that need to talk over two wires, distance is 100 to 500m maximum. The carrier has to be greater than 100kHz, reason is that this is the Nyquist frequency for other analog signals running on wires close to those for the comminication. Main aim is to avoid cross talk between communication and sigals, choosing two bands that do not overlap.
For this reason I avoided modems like v32bis, the carrier is too low. I am evaluating powerline modems, carrier is 130kHz, not very far actually, but might be a solution even if slow.
The question is: is it possible to use two RF transceivers connected by two wires instead of using the antennas? For example, I am thinking about using two CC1000.
Notice that it is not possible to use a coax instead of the two wires, that eventually can be twisted.
Any suggestion?
Thank you.
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Awarapunshee
Joined: 11 Jul 2007
Posts: 455
Helped: 60
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27 May 2009 11:12 testing rf link coax cable |
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Why not you use RS-485?. It can go upto 1KM. I have tested even at 1.5KM twisted cable.
ENJOY!
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el00
Joined: 27 May 2009
Posts: 5
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27 May 2009 11:27 avoiding rs485 cross talk |
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| Awarapunshee wrote: |
Why not you use RS-485?. It can go upto 1KM. I have tested even at 1.5KM twisted cable.
ENJOY! |
Because using RS-485 we would fall inside the 0 - 100kHz band, where we are transmitting and sampling analog signals.
As I explained I need to modulate on a carrier higher than 100kHz to avoid cross talk. The two devices need to talk at a baud rate of 4800 (at least).
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Awarapunshee
Joined: 11 Jul 2007
Posts: 455
Helped: 60
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27 May 2009 11:52 27 mhz rf link |
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| Kindly recheck the data sheet, I have used it for baud rate of 4800, it has I think more than 1M, and RS422 has 10M, You have to check the data sheet. I have used ADM1485 (Analog Devices), just check its data sheet.
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el00
Joined: 27 May 2009
Posts: 5
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27 May 2009 12:04 communication distance using two cc1000 |
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| Awarapunshee wrote: |
| Kindly recheck the data sheet, I have used it for baud rate of 4800, it has I think more than 1M, and RS422 has 10M, You have to check the data sheet. I have used ADM1485 (Analog Devices), just check its data sheet. |
I think you did not read my original post, or I did not explay well enough.
The problem is that I need to modulate over a carrier which is higher than 100kHz to avoid cross-talk. This is the point. I cannot use RS485 because it generates cross talk. For the same reason I cannot use RS232, RS422 or whatever is not modulated over a high frequency carrier.
I hope now it is more clear.
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sau_sol
Joined: 27 Feb 2008
Posts: 249
Helped: 27
Location: India
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27 May 2009 12:31 communication between two cc1000 |
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think on connectivity over Ethernet
which can have a data rate of about 1Gbps
and normally about 10/100Mbps
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el00
Joined: 27 May 2009
Posts: 5
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27 May 2009 13:41 Re: rf link over two wires |
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| sau_sol wrote: |
think on connectivity over Ethernet
which can have a data rate of about 1Gbps
and normally about 10/100Mbps |
What do you mean exactly with "connectivity over Ethernet"?
Do you know any single IC to have a look at the datasheet?
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sau_sol
Joined: 27 Feb 2008
Posts: 249
Helped: 27
Location: India
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27 May 2009 14:09 Re: rf link over two wires |
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connectivity over Ethernet means data connection using Ethernet protocol
and we are using this IC with AVR atmega16
and other IC too but I dont know about them
also there are lot of other transceivers available for ethernet search the web you will get
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el00
Joined: 27 May 2009
Posts: 5
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27 May 2009 14:51 Re: rf link over two wires |
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| sau_sol wrote: |
connectivity over Ethernet means data connection using Ethernet protocol
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Thank you for the datasheets. However, I am not sure that 0-100kHz band is not affected by ethernet. I think it could be a problem, but I am not sure. The datasheeds you posted do not say much on this aspect.
Do you know more about ethernet frequency spectrum?
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abc123
Joined: 28 Mar 2002
Posts: 68
Helped: 2
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29 May 2009 6:44 rf link over two wires |
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| look at "Ethernet over AC power line" device on the market now, they are using OFDM modulation on the RF carrier signals in MHz over the home AC power lines, the distance can be 100meter. the data rate can be in 10 MBps or higher, For twist pair line, it should be much better in terms of distance.
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Google
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29 May 2009 6:44 Ads |
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FvM
Joined: 22 Jan 2008
Posts: 5160
Helped: 767
Location: Bochum, Germany
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29 May 2009 9:03 Re: rf link over two wires |
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Your original specification has been unclear regarding the 0-100 kHz band. Obviously, your requesting the carrier to have no residual signal in this band. This specification hasn't to do with Nyquist frequency, it's a simple interference problem.
You didn't specify the properties of your cable. Hopefully it's twisted pair, but it also matters if it's shielded (STP) or unshielded (UTP). You can expect a usable bandwidth of a few MHz up to a few 10 MHz, depending on the acceptable attenuation. Ethernet 10BASE-T could work up to 100 or 150 m, but it needs two pairs. It can't work over 500 m, however. Thus usage of MHz band powerline modems or similar devices is actually the best idea, to my opinion. It can be expected to send a bandpass signal, in other words have no low frequency components. An additional high pass filter may used otherwise to further reduce low frequency interferences. If you are designing somthing on your own, simple FM transmission (FSK modem) with an around MHz carrier should work.
As a professional equipment reference, take a look at ADSL technology.
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