Hello - newcomer here. I'm trying to set up some JeeNode USBs (v2) to measure river water heights each side of a sluice gate. It turns out that my preferred loations are at the limits of the RF range back to my house, so I am looking to increase RF range. Has anyone experimented with using half or full wavelength antennae to see what increase can be achieved? I also wish to hide my JeeNodes a little to avoid theft - has anyone managed to site the antennae a few metres away from the JeeNode via some kind of coax cable?
RF range(24 posts) (12 voices)
Hello - newcomer here. I'm trying to set up some JeeNode USBs (v2) to measure river water heights each side of a sluice gate. It turns out that my preferred loations are at the limits of the RF range back to my house, so I am looking to increase RF range. Has anyone experimented with using half or full wavelength antennae to see what increase can be achieved? I also wish to hide my JeeNodes a little to avoid theft - has anyone managed to site the antennae a few metres away from the JeeNode via some kind of coax cable?Posted 2010-01-07 ago #
This is where mesh communication would pay off, which the RF12 driver doesn't do.
I'm hitting a similar limitation in a different context: can't get a signal from the garage, which is two reinforced-concrete floors away from the JeeLink in my office. One plan is to explore a simple relay placed halfway: receive packets in one network group, and resend them in another network group. Don't know yet how to handle acks, but maybe for simple broadcasting sensors with central acks it's all doable. Needs more thought.
Another option is try improving all the antenna's. I'm out of my league here, but there are directional antenna's and tuned antenna's. Maybe someone with more RF design experience can shed some light on how to go about impedance matching, connecting cables, and optimal matching of antennas... I admit that I stopped tinkering once the wire antenna worked, but surely there is room for improvement.Posted 2010-01-07 ago #
An interesting test would be to use a PCB edge mounted SMA connector and see how it compares to the wire antenna. You can see pics of someone using it here: http://blog.strobotics.com.au/2009/05/15/strobit-wireless-widget-photos/Posted 2010-01-10 ago #
have you looked at directional antennas for the frequency your RFM12s operate at?.
With "coax cable", one tends to limit the cable length to a minimum to avoid signal loss, though the loss can be compensated for by gains in the sending and receiving antennas.Posted 2010-01-14 ago #
My plan is to first test 1/4 vs full wavelength antennae, and then if still unhappy to try to build a "cantenna" (although a cantenna would be low priority compared to getting one site working fully, ie parallax ping -> jeenode -> jeenode -> web server (via php & mysql)). I hope to try the antenna length tomorrow, but no promises; however whenever I do I shall report the results here.
(The good news is that since my last post I have managed to get a parallax ping ultrasonic rangemeter working, and relaying over rf between nodes - not much to brag about, but fantastic progress for me! )
NickPosted 2010-01-16 ago #
OK - I've done a simple test. A jeenode USB v2 with an 85mm antenna competing with a jeenode v4 with a 345mm antenna. Both running the same sketch, both powered by 2 brand new AA batteries out of the same packet, both radioing a test signal back to a jeelink every 5 seconds.
And the result is that when I took them to a distance where the signal was intermittent (unfortunately roughly where I need to site one of my water level sensors) there was NO DISCERNABLE DIFFERENCE in signal quality between the two.
It may be worth noting that before I got to this point I made a lot of mistakes with my experimental setup, and as a result I suspect two other factors are important:
1) I think I got a little more signal with 3AA batteries (as opposed to two);
2) I think I got a better signal when all the antennae were absolutely straight and vertical.
But both these points need more experimentation. Also did I read somewhere that we can control the signal strength of the RF12? And of course the "cantenna" needs trying at some point.
For now I aim to move my receiver a bit closer to the transmitter, and get on with php and mysql and getting some kind of basic server up and running (the river has been up and down like a yoyo these last 24 hours and I had to get out of bed at 2am to check it, so I could really do with getting at least one station fully working asap).
All comments/suggestions gratefully received,
Quick experiment to get max range with what you have might be to add a ground plane: straight wire pointing up from the receiver, with entire JeeNode placed on a conductive ground plane (without shorting out any pins of course).
In ASCII art form: [code]__|__[/code]
Should get the most out of a simple quarter-wave wire antenna.
PS. indeed, I'd use 3 AA's, so that the voltage regulator does produce 3.3V, not less.
Thanks JC; I'm not following you about the detals of the ground plane - do I simply stand the jeeNode on a sheet of polythene and that on a sheet of metal? Do I connect the metal to a ground pin on the jeenode? Does the sheet have to be any particular size?
I'm not sure either :) - but yes, that's what I would try. Grounded to the JeeNode ground. Perhaps A4 sized, the larger the better as I understand it (at least half a wavelength on each side would be my guess). Take a baking plate or something, just to see whether it has a significant effect - you can always tweak and come up with a more elegant solution later. I'd try that on both ends, in fact.
Here's a link with antenna design notes for the RFM12's:
Also this one:
Lower baud rates get longer range according to HopeRF. Not sure if this always works out on FSK, though. Maybe you can slow down the RFM12B baud and extend your reach. Maybe you already tried this, though.
RFM12BP is a higher power module which might help. Bit late now, maybe.
A repeater sounds like a goode idea.
And I really like the idea of a mesh. Any plans for that, JC?