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More powerful antenna

Added by jwp almost 6 years ago

Hi,

I was wondering if anybody here has experimented with more powerful antenna’s on Jeenodes. The project I’m working on currently consists of a master Jeenode/Jeelink broadcasting to a large number of custom designed boards that have a chip antenna. Although there are plans to transmit back from the custom boards to the master, our focus currently lies on transmitting from the master. Would the range be extended if I hook up a wifi-router type antenna (for 868Mhz) or even something bigger? Is there also an option/need to use some kind of amplifier?

Thanks,
JW


Replies (6)

More powerful antenna - Added by martynj almost 6 years ago

jwp, interesting issue.  Antenna’s can make a substantial difference to the effective radiated power, but remember it is a zero sum game.   The ERP can be increased in a certain direction, but only by diverting the energy that would have gone in another.  For example, a Yagi array is physically quite small at 868MHz and can give gains of 12-20db but only by focusing the energy in a narrow cone.  Does this match the layout of the many receivers w.r.t. the transmitter?

There are alternatives (e.g. phased dipole arrays) that give much less gain, but preserve a wide effective cone. These are physically quite big though.

RE: More powerful antenna - Added by jwp almost 6 years ago

You know the project, right ;), so a Yagi wouldn’t be very useful with nodes scattered around a nightclub. I’m looking for something that I can rig on the ceiling and gives a wide omnidirectional signal.

The problem with multiple transmitters is that some client nodes will receive messages twice, and we would have to filter those messages out. Not a big deal, but a change in software. Another issue is the latency between the master transceiver and the repeaters. We need synchronized signal throughout the whole area.

For people who don’t know the project: http://heinekenignite.tumblr.com

[edit]

I was just browsing around on the HopeRf site and found the RFM12BP, which sounds to me like a more powerful version of the RFM12B. Anyone has experience with this part?

RE: More powerful antenna - Added by dzach almost 6 years ago

One very interesting type of antenna, especially for the UHF frequencies, is a fractal antenna ; they can be made really small and wideband, and maybe exhibit better gain than a 1/4 wavelength monopole wound in a random helical form. I would have definitely tried to make one for the 3 bands the JeeNode + RFM12B supports, had I have access to some RF equipment that could measure impedance and SWR… ;-)

RE: More powerful antenna - Added by martynj almost 6 years ago

jwp, sounds like a phased dipole array will work well. The ceiling mounting would put the main lobe pointing down into the space beneath. Imagine a wide cone with the apex on the array mounting point.  There are good design references if you search with “phase array” and “Radio Amateur ” as tags.

RE: More powerful antenna - Added by jwp almost 6 years ago

A short update: I built a board with the RFM12BP, based on JeeNode and Matt Hodge’s RFM12BP shield schematics. It works pretty good! But I also modified one of our custom PCB’s to use a wire antenna instead of the chip antenna. That makes the whole setup work even better. If anyone is interested in building one, I have a Visio file for a stripboard build, but it became a bit messy. I hope to find time to make the design a bit cleaner and suitable for putting it in an enclosure.

s. it might be worth noting that for its purpose, this board always is connected to USB via FTDI. If you would want a standalone board, it would require a 12V -> 3.3V regulator to power the Arduino. Now the 12V is only used for the amplifier and 3.3V is taken from the 5V supply of the FTDI cable. Matt Hodge’s schematics cater for this.

RE: More powerful antenna - Added by plutonomore almost 6 years ago

Hi Jan,

Glad to hear you got your application up, successfully and thanks for finding a more exciting application
than just punching 32 channels of 10 bit analogue data through several floors of ferro-concrete. Am attaching
a photo of one of my shields which has been working away for a couple of years now. Please note the SMA
antenna, like the one pictured, it was used on both the transmit and receive boards.

cheers, no pun intended!

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