[TriEmbed] Di-Pole Dilemma

[Charles McClelland]

Jeff, 

Thanks for the response, very helpful.  I had not considered your point about the rubber ducky - I doubt my small sensor node will provide a very good or very large ground plane.  

As for height, I guess that getting the antenna off the ground would be helpful.  My sensor is i2C based so I don’t want to have too long a wire between the Moteino and the sensor.  At the same time, my understanding is that the longer the length of the cable that connects the board to the antenna the more losses there.  My first attempt will put the antenna close to the board (3-6”) and the sensor 6’ from the Moteino, If I place this well, that would place the antenna 4’-6’ off the ground.  Does that sound reasonable?

Based on your answer, it seems like the first option below may be preferable as it will include a full quarter wavelength ground and emitter arm and it could be “tuned” by trimming the wires.  Agree?

Thanks,

Chip


On May 28, 2014, at 10:17 AM, Jeff Highsmith <jeff at jeffhighsmith.com> wrote:

> Chip,
> 
> Forgive me for my rusty RF theory, but my understanding is:
> • Dipoles are still somewhat directional, just not as much as a "Directional" antenna like a Yagi. Your best radiation and reception is at 90 degrees to the wire. In other words, the performance drops in the directions that the tips of the wires point. If you are vertically polarized, this isn't as much of an issue, since you are unlikely to be above the tip of the antenna. 
> • Polarization matters. You lose 3dB or so when switching polarizations, so make all your antennas horizontal or make all your antennas vertical.
> • So-called "Rubber Ducky" dipoles rely on the radio's case or, more frequently, the human body holding the case to be the other side of the dipole. If you don't have a good ground like that under your rubber ducky, it won't do as well. 
> 
> At what height relative to the ground are you placing your antennas?
> 
> I hope that helps. Others, feel free to correct me-it's been awhile since my ham days.
> 
> Jeff :)
> WJ3FF
> 
> 
> On May 28, 2014, at 9:42, Charles McClelland <chip at mcclellands.org> wrote:
> 
>> To all,
>> 
>> I am playing with the Moteino and recently tested the range at a local park.  I was a bit disappointed and discussed this at the last meeting.  As with all things embedded, there seems to be a number of things that can be done to improve performance both hardware and software.  For this note, I wanted to ask for any advice on the hardware front.  Once I have that set, I plan to tweak the software settings (primarily data rate but some others as well) to see how much range I can get - ideally 1.5 miles outdoors through wooded terrain.
>> 
>> The Environment:
>> 	- Moteino base and sensor nodes 
>> 	- I went with the lowest frequency transmitter - 433MHz - and the highest power
>> 	- The Moteino site states that there is not much improvement from monopole antennas   
>> 	- In the forums however, there is a posting promising greater range from dipole antennas
>> 
>> I understand that a directional antenna would be better but my application would not easily support this as the sensors nodes may need to be moved frequently.
>> 
>> My limited understanding of a dipole antenna theory is that there are two elements - one with signal and one with ground with each sized to match the specific frequency.  I plan to add an SMA connector to the board so I can install a commercial antenna and I found two options that both claim to be sized to the 433MHz frequency:
>> 	- The first looks like what I expected a dipole antenna to look like and could be easily made
>> 	- The second would be much better for packaging and use on a sensor that may be moved often - but it does not look like a dipole antenna to me.
>> 
>> Any advice on which might be the better choice or whether I should look at other options?
>> 
>> Thanks,
>> 
>> Chip
>> 
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