Antenna Tutorial or Antennas in a Mote

[Tommy T]

It looks like Mike over at www.airspayce.com also mentions attaching to GND.  Here's the link:

http://www.airspayce.com/mikem/arduino/RadioHead/classRH__RF69.html

The following is quoted from there:

10cm RG58C/U soldered direct to RFM69 module ANT and GND

10cm also sounds quite a ways off from the 82mm that's listed for 1/4 wavelength here: http://farm4.staticflickr.com/3818/10585364014_d028c66523_o.png

[Lensdigital]

Great info here!
So I have a question. Would I see any benefit if my transmitter's antenna is longer than receiver (T=1/2 with R=1/4)?  And vice versa, if my receiver's antenna is longer than transmitter (T=1/4 with R=1/2).  Which option is better?  Obviously I realize that if both have 1/2 antenna it would be the best, but might not be possible.

[Felix]

I think one of the more expert RF guys posted in one of the threads that odd number of quarterwaves lengths is better than even. So 1/4, 3/4 etc..
BTW the radios are both receiver and transmitter, unless you're using them only has RX or TX, but it still makes sense to listen for ACKs even when only transmitting.
I would just keep them all the same.

[KanyonKris]

The RF principal of reciprocity says it won't matter. However you may have some environmental effects (RF being absorbed by or bouncing off objects in or near the link path) may favor one  antenna setup over the other so you may want to try each and look at the RSSIs to decide which to use. But my gut feel is you'll only see a little difference, if any.

[john k2ox]

The length should be the same for both rx and tx.  The environment effects it equally in tx and rx.  Different lengths apply when rx and tx are on different freqs.

[Charly86]

Hi,

I'm using CAT5 network cable for my antenna (so single inside) but I don't know what is the best, single wire or multi-wire, any tough on this ?

By the way, I'm searching to thickness the wire and I don't know which one to buy, anyone as a good reference (ebay is okay) of thin wire to use a antenna ?

Thanks for your help.

[Felix]

Single core 22-24GA works well. Don't use stranded wire.

[Charly86]

Felix,

thank's for the tip about stranded wire, so much time I'm asking this question, it's good to know now 

So except the fact that Cat 5 wires are not the thickened one , they're good ?

[Felix]

Yes

[john k2ox]

Electrically or RF wise there is little difference between single and multistrand wire. Practically, single strand is preferred because it retains its shape. Stranded wire is floppy.

[joelucid]

Interesting antenna experience: With my Tino (https://lowpowerlab.com/forum/index.php/topic,1269.0.html) I've been experiencing sub par RF performance. RSSI was about 10-12 lower than with a regular Moteino with 9V battery.

I did some research and some experiments and found that:

1.) The Tino had great RF performance if powered from a cylindrical Lithium battery.
2.) Different environments (e.g. sizes of ground plane) sometimes lead to very significant resonance shifts.
3.) Resonance shifts can be compensated for by adjusting antenna length.

So I hooked a 25cm antenna to my 433mhz Tino and started clipping. Turns out the optimal antenna length with CR2450 mounted is 22-23cm instead of the around 17cm that work for a Moteino. At that length RF performance is similar to a Moteino with 9V battery. I would have never expected such a large divergence.

So if you've built elaborate enclosures etc and get RF problems, just attach a LONG antenna and take out your scissors.

[WhiteHare]

Would that have to do with item #8 in the OP?  I've read that even the PCB epoxy's dielectric constant can play a role in determining the impedance, so getting all the factors perfectly specified and built seems like it could be quite a challenge.

[TomWS]

Would that have to do with item #8 in the OP?

Ha!  Good one!  Maybe probably a lot!

Tom

[phil.bolduc]

I was wondering if anyone has tried to use a Molex Industrial, Scientific and Medical (ISM) Antenna before.  They look useful. The spec sheets describe radiation patterns and guidelines on bend and placement of the cable.  They are definitely more expensive than a 17.31 cm piece of solid copper wire.   

[Felix]

I have not tried that particular one. I doubt it's worth the expense.
Try the monopole and see how it performs. If it works and RSSI is satisfactory, don't "fix" it.
Dipoles would be next step up from the basic monopole wire.