Author Topic: Pocket Transceiver and antenna question  (Read 1335 times)

Zeph

  • Newbie
  • *
  • Posts: 9
Pocket Transceiver and antenna question
« on: September 21, 2014, 02:15:32 PM »
I've done some searching, but I'm not finding quite this topic....

What I want to do is have a pocket sized wireless transceiver with Arduino programmability, running on 2 or 3 AA's - a moteino would be perfect, except that I'm not sure how to handle the antenna.

My "default" solution would be an Arduino Pro Micro 3.3v + nRF24L01+, but I'd like the range of 433 MHz, and the compactness of the Moteino.  But I'm not sure about how to fit the antenna into a small package - which should certainly be smaller than a cigarette pack.

For a wireless sensor node a monopole wire antenna hanging out would often be no problem but in a pocket it would be.  Would I need to reserve a space inside the case for a coil similar in size to another AA battery?  Or what?

Moving to 915 MHz would cut the length/size of the antenna, at some cost of range, right?

Thanks for any experience or ideas.
« Last Edit: September 21, 2014, 02:22:31 PM by Felix »

Felix

  • Administrator
  • Hero Member
  • *****
  • Posts: 6409
  • Country: us
    • LowPowerLab
Re: Pocket Transceiver and antenna issues
« Reply #1 on: September 21, 2014, 02:22:11 PM »
I doubt your range will suffer significantly at 915mhz. I've not seen evidence of that. Coiling your antenna will definitely alter range very significantly. The best ideal antenna solution is to have it perpendicular to the GND plane (PCB) sticking straight up. And same on the other end.
In lack of a better solution it's better to have the antenna wrapped around the inside or outside of your package, but as non-coiled as possible (ie spread out). That seems to work pretty well for my MotionMotes where I don't want/need the antenna to stick out.

Zeph

  • Newbie
  • *
  • Posts: 9
Re: Pocket Transceiver and antenna question
« Reply #2 on: September 21, 2014, 05:19:22 PM »
Hmm.  So non-coiled is good?

I was thinking of the cheap, dumb 433 MHz tranmitter/receiver pairs, that often use a coiled antenna - at the same frequency.

Felix

  • Administrator
  • Hero Member
  • *****
  • Posts: 6409
  • Country: us
    • LowPowerLab
Re: Pocket Transceiver and antenna question
« Reply #3 on: September 21, 2014, 05:54:03 PM »
Oh yeah, those will often have helical antennas. Those are much different than the transceivers used with Moteino, not sure how much advice there is for those in this forum though.
Coiled/helical will not work well for RFM69.

Zeph

  • Newbie
  • *
  • Posts: 9
Re: Pocket Transceiver and antenna question
« Reply #4 on: September 22, 2014, 07:00:07 PM »
Coiled/helical will not work well for RFM69.

OK, that's very useful advice.  Scratch that idea.

I'm still pondering what a non-coiled monopole layout within a smallish case might look like - alas the MotionMote write-up (while cool) doesn't show much about the antenna.  It may be short enough to be stuffed in the case in an L shape.  A longer monopole antenna (I'd prefer 433 MHz) might need to be bent in some way - U shaped, or Z shaped or a full loop around the inside of the case (which is sort of a single coil albeit loose).  Any advice?

And - i anybody could explain why a 433 MHz helical would not work, it would help my understanding of these things.   I would have thought that an antenna for 433 MHz OOK transmitters and receivers, would also work for FSK transceivers.  The only thing which occurs to me would be if the helical has a much narrower hi-Q  bandwidth than is desirable for the more frequency flexible RF69's full range.  But that might mean it would work really well for some frequencies (and filter out others).

Felix

  • Administrator
  • Hero Member
  • *****
  • Posts: 6409
  • Country: us
    • LowPowerLab
Re: Pocket Transceiver and antenna question
« Reply #5 on: September 22, 2014, 07:31:27 PM »
Hmm .. not sure man. I know quite a bit what works and what not with the RFM69 FSK radios. Not much about anything else.