Author Topic: Antenna recommendation for RFM69HCW  (Read 2699 times)

alexsh1

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Antenna recommendation for RFM69HCW
« on: June 26, 2016, 02:17:34 PM »
Hello,

I have searched this forum for this, but unfortunately was not able to find the answer. I am a noob and most posts go into the physics theory. I just need a simple recommendation. I have MoteinoMEGA USB with RFM69HCW 433Mhz and another node with RFM69HCW 433Mhz. Both will be used indoor or briefly outside. I have the following choice of antenna:

1) SMA -1.6mm + SMA Antenna - there are a few for sale. 5cm and a bit larger ones from NiceRF - http://www.aliexpress.com/item/2pcs-lot-straight-Rod-antenna-SW433-ZB165-433MHz-Aernna-free-shipping/32583093225.html?spm=2114.30010308.3.248.l6KzYA&ws_ab_test=searchweb201556_10,searchweb201602_5_10037_10017_405_507_10032,searchweb201603_2&btsid=6a59ad94-4679-4fae-8af1-88b58e8b82ac
2) Wire which comes with Moteino ~17cm I think
3) uFL
4) Can I use these helical antenna - http://www.aliexpress.com/item/High-Quality-10pcs-Spring-Antenna-433MHz-Antenna-Helical-Remote-Control-Network-Accessories-VE462-P/32436979740.html?spm=2114.30010308.3.10.l6KzYA&ws_ab_test=searchweb201556_10,searchweb201602_5_10037_10017_405_507_10032,searchweb201603_2&btsid=6a59ad94-4679-4fae-8af1-88b58e8b82ac
5) Your recommendation

There will be quite a few walls between the two nodes, so I have to get the best reception possible.
Apologies if similar topic exists - I was not able to find it.

Many thanks
Alex
« Last Edit: June 26, 2016, 02:21:39 PM by alexsh1 »

TomWS

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Re: Antenna recommendation for RFM69HCW
« Reply #1 on: June 26, 2016, 03:02:49 PM »
If you have room for it, the bare (insulated) wire is easy and will work with plenty of margin with an RFM69H.  Even detuned you'll be able to reach 150 feet with several walls in between.

u.fl works nicely on a MoteinoMega, but an R4  doesn't have the footprint for a u.fl.  The u.fl with a pigtail to SMA & rubber ducky is what I use on all my gateways.

Felix shows a way to mount an SMA on an R4 but I haven't tried it.  The post is somewhere on the forum - search for SMA would be my guess.

JoeLucid has done a LOT of testing so he can squeeze out about 257db link budget (or something close to this, I think  ;)  , but the only time I've really had an issue with a bare wire is when I tried to put a mote underground - that doesn't work so well...

Tom

alexsh1

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Re: Antenna recommendation for RFM69HCW
« Reply #2 on: June 27, 2016, 05:45:56 AM »
So the answer is either a wire or ufl with a pigtail to SMA and SMA Antenna.
I have 433Mhz transceiver so this means my insulated wire - antenna is longer. 

captcha

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Re: Antenna recommendation for RFM69HCW
« Reply #3 on: June 27, 2016, 06:45:41 PM »
What Tom said.

Plus:
At 433MHz the ~17cm wire antenna is for bare copper antenna radials. Using ~17cm single-insulated wire will mean the antenna needs to be shorter. This has to do with the Dielectric Constant of the insulation material and is different for every type and thickness of insulation. Just leave it a straight bare copper wire. If you want omnidirectionality and longest distance use this.

If you're going to use the ~17cm wire I would advise against curling it up to make it look neat or whatever. Keep it straight. With curling up the antenna you've created a helical antenna and due to the proximity of each winding (the curls) you've created an inductor which changes certain properties of the antenna which may perform worse and can even damage your radio.

Feeding antennas with a bit of coax needs to be thought through as well. If possible stick to multiples of half-wavelengths of coax between radio and antenna.

Felix

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Re: Antenna recommendation for RFM69HCW
« Reply #4 on: June 28, 2016, 09:56:05 AM »
Just adding my 2 cents,
The connectors on the MEGAs were added for convenience or when the antennas have to be exchanged or removed. They add to the cost of feeding an antenna but some folks prefer the flexibility of that.
Otherwise 50ohm RF coax to any external antenna will work, no need for a connector, it can be soldered right to the board.