RFM69 antennas comparison
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I wanted to share my finding following my RFM69 signal scanner I previously built. I used 2 types of antennas:
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Hand made like the one mentioned by @sundberg84 in [his project](https://www.openhardware.io/view/389/EasyNewbie-PCB-RFM69-HWW-edition-for-MySensors
I let them run several hours reporting TX power since the new rfm69 driver adjusts power output to the default target RSSI of -80db
The test was done on the same spot (my desk) and the gw about 5 meters away (1 floor difference, and a couple of walls in between; gw running the coil spring antenna).
I am currently testing the SMA antennas and results are better than the hand made antenna with a TX power of 35/40% instead of 55/60%. My guess is the hand made antenna had to be squeezed inside the box getting a wrong orientation, while the SMA one is outside and it can stay perfectly vertical.
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I wanted to share my finding following my RFM69 signal scanner I previously built. I used 2 types of antennas:
-
Hand made like the one mentioned by @sundberg84 in [his project](https://www.openhardware.io/view/389/EasyNewbie-PCB-RFM69-HWW-edition-for-MySensors
I let them run several hours reporting TX power since the new rfm69 driver adjusts power output to the default target RSSI of -80db
The test was done on the same spot (my desk) and the gw about 5 meters away (1 floor difference, and a couple of walls in between; gw running the coil spring antenna).
I am currently testing the SMA antennas and results are better than the hand made antenna with a TX power of 35/40% instead of 55/60%. My guess is the hand made antenna had to be squeezed inside the box getting a wrong orientation, while the SMA one is outside and it can stay perfectly vertical. -
How do you interpret the results ? Which one is better ?
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@gohan could it be because it's longer and easier catch the wave length compared to the coiled?
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Im using this: https://www.ebay.com/itm/Antenna-433Mhz-3dbi-SMA-Male-Plug-Magnetic-base-with-2-9m-cable-for-Ham-Radio-/172360344112?hash=item28217a2230 antenna for my RFLink and this is by far the best I have used. (No hard evidence... but I have it on my GW for RFLink and its been working since day 1 with a great coverage).
Maybe you could test this :)
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Could be, I have to try the straight wire antenna for a better comparison. Either way they seem not that far away and depending on the node size I think the coil spring is still a good option.
@gohan A straight wire will always have greater actual gain than a coil even though a quarter wave electrically with minimal ground plane.
On your findings on commercial v DIY coils, they are unlikely to be designed for the same centre frequency, but also typical shrouded helicals tend to be manufactured with very thin wire. The larger wire diameter coil will (even at identical design centre frequency) exhibit a slower rate of mismatch (SWR) as you move away from the centre frequency.
Where the objective is to use minimal power consumption on a battery powered node, efficient antennae can have significant effect when transmit power can be reduced for the same effective radiated power with a dipole etc...
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@gohan A straight wire will always have greater actual gain than a coil even though a quarter wave electrically with minimal ground plane.
On your findings on commercial v DIY coils, they are unlikely to be designed for the same centre frequency, but also typical shrouded helicals tend to be manufactured with very thin wire. The larger wire diameter coil will (even at identical design centre frequency) exhibit a slower rate of mismatch (SWR) as you move away from the centre frequency.
Where the objective is to use minimal power consumption on a battery powered node, efficient antennae can have significant effect when transmit power can be reduced for the same effective radiated power with a dipole etc...
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@zboblamont so basically if I make a 66cm long straight wire is the best antenna I can make?
@gohan In comparison with a coil, the straight version will always behave more efficiently, but is also easiest to make correctly...
The issue I suspect your experiment uncovered is matching the exact wire diameter, turns and spacing to radiate precisely at the target frequency. You may find both are labelled as 433MHz for instance, but one is tuned to 470, the other at 435.... The 435 will be less a mismatch to the transmitter, thereby more efficient...
It is all a trade-off between location and how much intrusion into the space the antenna will be. You could have a node 100m away using minimal power into a full wavelength loop antenna (1/4 wave each side) using a metal shed wall as a reflector, there it does not intrude, in your kitchen it would....
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Actually the coil spring antenna work sufficiently well for my needs anyway, since it is compact while the half coiled half straight antenna it is harder to fit in a small box.
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@gohan Fair comment, as always it is a trade off...
@zboblamont @gohan (or anyone!) - could i ask your opinion about an PCB trace antenna (like a normal Nrf24l01+) would benifit in different orientations - and which one is the best?
For example, most of my MySensors nodes are laying down flat (and therefore the antenna is pretty much going through the horizontal plane). Would it benifit to have the radio standing so the PCB trace is in the vertical plane instead?
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@sundberg84
for "best" pcb antennas, I would say : monopole (meandered or not), and inverted F. they also need tuning of course, regarding board geometry, antenna design etc.
but a well tuned whip antenna (with a wire) will always radiate in a better way, sort of 3d antenna compared to a 2d pcb antenna. -
@sundberg84
for "best" pcb antennas, I would say : monopole (meandered or not), and inverted F. they also need tuning of course, regarding board geometry, antenna design etc.
but a well tuned whip antenna (with a wire) will always radiate in a better way, sort of 3d antenna compared to a 2d pcb antenna.@scalz - ok, but if you take the Nrf24l01+ radio with its PCB antenna - is the antenna performing worse if the radio is lying down compared to if I have the radio standing up?
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@zboblamont @gohan (or anyone!) - could i ask your opinion about an PCB trace antenna (like a normal Nrf24l01+) would benifit in different orientations - and which one is the best?
For example, most of my MySensors nodes are laying down flat (and therefore the antenna is pretty much going through the horizontal plane). Would it benifit to have the radio standing so the PCB trace is in the vertical plane instead?
@sundberg84 Not a great fan of PCB trace antennae, although I fully understand the advantage of small footprint. A whip or dipole antenna is problematic in terms of incorporating neatly, but will outperform the PCB a large factor.
Horizontal polarisation when received by a vertical cuts the gain considerably, at vhf/uhf etc up to 20dB, not sure the level at 2.4GHz as the wavelength is fairly short, but there will certainly be some attenuation on the outer fringes.
The other problem with horizontal polarisation is that the radiation lobe tends to be directional, so if nodes are at range you may have to compromise direction to 'catch' the edge of the radiation lobe. -
@sundberg84 Not a great fan of PCB trace antennae, although I fully understand the advantage of small footprint. A whip or dipole antenna is problematic in terms of incorporating neatly, but will outperform the PCB a large factor.
Horizontal polarisation when received by a vertical cuts the gain considerably, at vhf/uhf etc up to 20dB, not sure the level at 2.4GHz as the wavelength is fairly short, but there will certainly be some attenuation on the outer fringes.
The other problem with horizontal polarisation is that the radiation lobe tends to be directional, so if nodes are at range you may have to compromise direction to 'catch' the edge of the radiation lobe.@zboblamont - must admit I have a little hard time to fully follow your explanation and the terminology - but if I understand you correctly the answer is, yes I might have some loss if the radio is lying down.
Controller: Proxmox VM - Home Assistant
MySensors GW: Arduino Uno - W5100 Ethernet, Gw Shield Nrf24l01+ 2,4Ghz
MySensors GW: Arduino Uno - Gw Shield RFM69, 433mhz
RFLink GW - Arduino Mega + RFLink Shield, 433mhz -
@zboblamont - must admit I have a little hard time to fully follow your explanation and the terminology - but if I understand you correctly the answer is, yes I might have some loss if the radio is lying down.
@sundberg84 Sorry, yes there will be a loss.
This site may better demonstrate it graphically down the bottom...
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