Author Topic: RFM69HW Range issue 868MHZ  (Read 1183 times)

autobot

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RFM69HW Range issue 868MHZ
« on: March 14, 2019, 01:05:42 AM »
Hello,
       I'm using RFM69HW 868MHZ module transmitter and receiver. transmitter and receiver could not communicate with 4th floor to ground floor. i used this library "https://github.com/lowpowerlab/rfm69" and using his types of antenna.

Felix

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Re: RFM69HW Range issue 868MHZ
« Reply #1 on: March 14, 2019, 09:43:14 AM »
- Use the working library examples,
- Check your settings and code settings to match
- check your wiring and antenna position

HeneryH

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Re: RFM69HW Range issue 868MHZ
« Reply #2 on: March 14, 2019, 03:02:43 PM »
FWIW,

I was under the impression that a helix antenna was nearly as good as a straight one but in my experience it was significantly worse.

I took the standard wire antenna and when I coiled it around a pencil to make a compact coil it was MUCH worse than when I straightened out the wire antenna.

Felix

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Re: RFM69HW Range issue 868MHZ
« Reply #3 on: March 21, 2019, 04:01:48 PM »
Those helical antennas are quite good.

Around the pencil huh? Nice try...
::)  :'(  ??? when I see people coiling their monopole wire antennas thinking they are making it better.

HeneryH

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Re: RFM69HW Range issue 868MHZ
« Reply #4 on: June 11, 2019, 11:00:07 AM »
Those helical antennas are quite good.

Around the pencil huh? Nice try...
::)  :'(  ??? when I see people coiling their monopole wire antennas thinking they are making it better.
@Felix, So what is the physics difference between a helical and a monopole wrapped into a helical pattern?    Since you have so many emoticon emotions I am sure you can explain the error in my ways.

I'm not trying to make it better, I'm trying to make it fit into the enclosure.
« Last Edit: June 11, 2019, 11:02:32 AM by HeneryH »

Felix

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Re: RFM69HW Range issue 868MHZ
« Reply #5 on: June 11, 2019, 01:21:13 PM »
Folding the antenna is going to hurt the matching of that antenna.
Its still going to work, just not as good, and a bunch of signal will be reflected back into your RFM, meaning it will have to output greater power to get the same signal strength across the same distance.
Makes sense?

Making your helical antenna on-the-fly without any considerations is probably not a good approach. Size, diameter, gauge, length, all matter.

I hope that makes sense.

TomWS

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Re: RFM69HW Range issue 868MHZ
« Reply #6 on: June 12, 2019, 05:44:06 PM »
I'm not trying to make it better, I'm trying to make it fit into the enclosure.
The antenna referenced in this post (https://lowpowerlab.com/forum/rf-range-antennas-rfm69-library/antenna-recomendation-placed-inside-enclosure/msg21436/#msg21436) works well enough for me.  I'm using it in virtually every Mote I'm making now (unless it clearly requires max range on the radio, then it's monopole with a large ground plane).  I've used both 915MHz & 433MHz versions with equal success.

I've tried helical (mfrd and custom wound) and they were noticeably worse.

Felix

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Re: RFM69HW Range issue 868MHZ
« Reply #7 on: June 13, 2019, 09:25:47 AM »
I've tried helical (mfrd and custom wound) and they were noticeably worse.
I have tried some ceramic antennas myself and I found the exact opposite. I have had helical antennas completely enclosed in metal containers and they got the signal out at TXLVL=0 to a gateway nearby. I had another application where a TINY mote had to have a ceramic antenna similar to the above for compactness, and it had great difficulty getting the signal from the front of a car to the back of the car (behind the trunk). So the mileage varies, and there are lots of variables at play not just the antenna of course.

Again ... depends how you use the helicals and any antenna in general.
I know various use cases where these are deployed with great success and they are great performers.
I think any antenna can be made good if the matching and settings are right, and the enclosure plays well.
It's not an easy recipe like just saying "helical is better than ceramic" or vice versa, it's a lot more than that. We DYI-ers/hobbyists and RF amateurs can just try something that works and make it the preferable part for us which is great. If it works, dont change it. For very rugged applications any combination of parts and antenna needs extensive testing to determine what is optimal.

HeneryH

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Re: RFM69HW Range issue 868MHZ
« Reply #8 on: June 13, 2019, 10:10:37 AM »
My very quick research seems to show that helical might have a more directional beam pattern.  That might factor into any performance testing.