433MHz antenna tests

[flegmatoid]

I've made few tests to compare 433 MHz antenna performance.

Test setup:

• RFM23BP module hooked to atmega238 (2x) (those are found in OpenLRSng transmitters)
• RF22 library
• OOK modulation / 2.4Kbps / 335KHz RX bandwidth

Uponsuccessfully received message RX DBi was red.
Receiver was only listening (uni-directional communication).

Stock antennas


Hand-built antennas




I've started with a LAB test. Antennas 2 meters apart, TX power 1DBm (1.26mW).

	two small spring antennas	two stock whip antennas	two omni antennas	two dipole antennas	two omni with spring antennas	omni vs v_shape	omni vs whip with gnd_plane	omni vs stock whip	omni vs custom spring
MAX / DB	-12	-30	-12.5	-4.5	-10.5	-6.5	-3	-12	-4.5
AVERAGE / DB	-24.5	-40.0	-21.6	-12.2	-18.6	-16.5	-10.6	-22.2	-10.1

*Average reading was achieved by trying to get max RSSI. Antenna was rotated in all directions possible. Consider it as real-life indication of how would such antenna perform on the flying aircraft.

CONCLUSIONS:

Omni antenna (TX) and Whip ground-plane antenna(RX) is the best combo.
Two Dipoles perform nearly identical to Omni (TX) and Custom Spring (RX).
V-Shape antenna is also a good candidate, however, average reading is the worst from the 4 top performers.

Stock antennas are good for nothing.


Then, the FIELD tests. Antennas 300 meters apart, 1 meter above ground. TX power 17DBm (50mW).

	omni vs omni	omni vs stock whip	omni vs stock spring	omni vs custom spring	omni vs wire with spring	omni vs dipole	omni vs wire with gnd plane	omni vs v_shape	dipole vs dipole	dipole vs v_shape	dipole vs wire with gnd_plane	dipole vs custom spring	v_shape vs wire with gnd plane
MAX / DB	-68	-70.5	-72.5	-69	-70	-73.5	-67	-66.5	-67	-62.5	-64.5	-66.5	-77
AVERAGE / DB	-71.04	-72.55	-74.94	-72.10	-75.56	-77.66	-73.54	-72.59	-75.15	-68.35	-72.04	-71.47	-108.42

CONCLUSIONS:

dipole(TX) and V-shape(RX) is best combo
dipole(TX) and wire with ground-plane(RX) is 2nd best combo
omni(TX) and V-shape(RX) or custom-spring(RX) is 3rd best combo

reverse combinations are bad performers (i.e. placing V-Shape on TX side)

Real ground-air performance should be few DBs higher, because my antennas were tested relatively close to the ground.

stock vs stock combinations were not tested due to conclusions made in LAB tests.

[salience]

Excellent post and research, thanks flegmatoid!
The V-shape mentioned was a tuned 120° inverted Vee I assume?
And the omni was exactly what?

[flegmatoid]

yes, correct, V-shape is 120 deg inverted Vee.

I've bought all these antennas on ebay. All are unbranded. Some sites claim 2.5DB gain for that Omnidirectional antenna (largest-one in the 1st photo).

I've disassembled the two stock-ones (which come free of charge with various receivers):


The wire length of the right-one is measured to be approx. 2.5cm. Not sure what type of antenna it is, but I'm suspicious it's really a 433Mhz-one.

[salience]

yeah, I think the right-hand is for 433 - saw some discussion on it awhile back somewhere I don't remember.
I bought one of the Diamond SRH771 for Tx, supposed to be very good.
It'd be interesting to see how a Tx/Moxon plus Rx/inverted Vee combination stacks up.
http://www.ebay.com/itm/Hawkeye-UHF-...item19fb133d74
These are pretty easy to build - I made one for 2.4GHz but didn't have enough instrumentation to test it properly. Did work fine however. Seems to be a good choice for Tx hand-held pointed roughly in the right direction, although beam width is quite reasonably wide. Nice to project most of the energy in the right direction rather than back through one's body as well!

[justin.mader]

I've got a couple of 433 antennas that look like the two in this picture. The shorter one worked great, the longer swivel one went into failsafe and crashed about 200' away when I went behind a tree. I have my suspicions it's not really 433, even though I got it from RMRC and was labeled as such.

yes, correct, V-shape is 120 deg inverted Vee.

I've bought all these antennas on ebay. All are unbranded. Some sites claim 2.5DB gain for that Omnidirectional antenna (largest-one in the 1st photo).

I've disassembled the two stock-ones (which come free of charge with various receivers):


The wire length of the right-one is measured to be approx. 2.5cm. Not sure what type of antenna it is, but I'm suspicious it's really a 433Mhz-one.

[SecretSpy711]

the short spring is called a Normal Mode Helical (as opposed to an Axial Mode Helical, as many of us use on video receivers). I can assure you it IS a 433MHz antenna. It can work in some circumstances, if whatever you're attaching it to has a large-ish internal groundplane. If it does not, then it's crap.

I did some experiments by adding my own groundplane and it worked MUCH better:
http://fpvlab.com/forums/showthread....l=1#post565947

I have a crapload of these, and even more of the springs without the SMA or plastic housing.

The swivel one on the left looks like a 2.4GHz antenna to me.

[flegmatoid]

yes, the short-one works fine, its 433Mhz.

A funny observation - I did get couple of those longer "crappy" antennas marked as GSM.
Wire length of 2.5cm translates to 12GHz. So, if, presumably, its a quarter wavelength thing, 10cm translates to 3GHz.

It explains bad 433Mhz performance as well as 0DB increase when I plug it into my GSM shield.

[flegmatoid]

yeah, I think the right-hand is for 433 - saw some discussion on it awhile back somewhere I don't remember.
I bought one of the Diamond SRH771 for Tx, supposed to be very good.
It'd be interesting to see how a Tx/Moxon plus Rx/inverted Vee combination stacks up.
http://www.ebay.com/itm/Hawkeye-UHF-...item19fb133d74
These are pretty easy to build - I made one for 2.4GHz but didn't have enough instrumentation to test it properly. Did work fine however. Seems to be a good choice for Tx hand-held pointed roughly in the right direction, although beam width is quite reasonably wide. Nice to project most of the energy in the right direction rather than back through one's body as well!

@Sailience, that Moxon thing seems attractive, but I'd suggest for you to save 10 bucks and go for this-one http://www.ebay.com/itm/Yagi-beam-antenna-pmr-446MHZ-tunable-4el-high-gain-professional-gammamatch-/291441611065?pt=LH_DefaultDomain_3&hash=item43db461139

I've got couple of those. After running initial test I thought there's some error in my measurements, cause I couldn't see a noise curve. Then I've realized its there, just the noise is virtually gone. Truth, that's not something one can place on the RC aircraft, but for ground-station its probably the best thing you can get for such a miserable price.

[salience]

Thanks for the link! At that price, I'll have to get one - but first I'll ask him if it can be tuned to 433, the offer says "Tunable 440-450MHz".
I wonder what beam width it has. I'll enquire about that too. It may be a little too narrow to use for Tx, risking signal loss unless it is accurately pointed. That seemed a strong point for the Moxon, it's radiation pattern is quite wide and probably you'd need only to be sure you are pointing within 45-60 degrees.

[slappomatt]

might be cool to run one of those on your tracker but after losing a $1000 ZII because of a GPS glitch I am scared to run the tracker anymore.