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[Pro2 Compact] Disappointing RF reliability
#1
Sad 
Hello All,

I have, finally, got my TX board completed (at least enough to do some testing) and I'm not too happy with the performance of the RF link between it and the RX. I'm hoping someone can give me some suggestions as to where I may have gone wrong or how to improve things. I have the TX board temporarily on a breadboard that has a 12V power supply. I'm using a small black antenna screwed directly to the SMA connector on the board.

If I have the TX and RX in same room about 2 meters apart, things seem to work great. I get about 98 or 99 % RF efficiency.
If I move the TX to another room about 8-10 meters away the efficiency drops to about 25%
If I move the TX outside to approximately where I want to mount the TX, about 16-20 meter away from the RX, the efficiency drops to about 14% and I can see the 'outside temperature' disappears on the RX at times. This was only a short test (about an hour) because it's not in a weather proof box and it was going to rain.

Any help appreciated.

Cheers,
Gord
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#2
(01-04-2020, 01:11)WetCoast Wrote: I have, finally, got my TX board completed (at least enough to do some testing) and I'm not too happy with the performance of the RF link between it and the RX. I'm hoping someone can give me some suggestions as to where I may have gone wrong or how to improve things. I have the TX board temporarily on a breadboard that has a 12V power supply. I'm using a small black antenna screwed directly to the SMA connector on the board.

If I have the TX and RX in same room about 2 meters apart, things seem to work great. I get about 98 or 99 % RF efficiency.
If I move the TX to another room about 8-10 meters away the efficiency drops to about 25%
If I move the TX outside to approximately where I want to mount the TX, about 16-20 meter away from the RX, the efficiency drops to about 14% and I can see the 'outside temperature' disappears on the RX at times. This was only a short test (about an hour) because it's not in a weather proof box and it was going to rain.

Hello Gord,

could you post some photos of your construction - the both ends? I am mainly interested in the size and type of antennas (ideally where you bought them) and the mutual position of the antennas towards each other. It's also important - aren't you or anyone around you using other devices operating in the same frequency band? (Devices should not interfere, but sometimes someone violates regulations.)

Good luck.
Best Regards
Zdenek

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My outdoor AQM-I: here
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#3
Thank you so much for the reply. I hope the following is what you need.
The antenna are from Ebay https://www.ebay.ca/itm/Antenna-433MHz-g...1a83b17c64
and I'll attach the photo you requested. The TX is not finished so please don't be too critical of my workmanship Blush
BTW, I used the wrong word in the subject, it's not reliability, I believe it's called efficiency.

   
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#4
Hello Gord,

If you have this device so close together, they will probably work without antennas (not recommended, the transmitter may be destroyed). But as soon as you zoom out, you have to set the axes of all antennas as parallel as possible. The picture from you is the worst possible case, when the signal is almost completely attenuated. (Conversely, in such close proximity, if the antennas are correctly adjusted, the signal strength may be too congested, so this adjustment is acceptable and perhaps the only possible at such a small distance.)

   

Please try and let me know if it helped. Good luck.
Best Regards
Zdenek

[Image: banner.php]
My outdoor AQM-I: here
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#5
Hi Gord,

think the best would be in your case if the antennas are parallel to each other.
Also, the transmitter module on your TX could also be of bad quality - sometimes the carrier frequency is drifting.
But I do not think that is the case because everything is good if you are close.

And in the end, the antenna could be of bad quality. Mostly you can say the smaller the antenna the result does not get better.
I use self made dipole antennas and I get an efficiency over 80% over about 50meters and one wall.
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#6
Thank you very much for the replies.
The way the units are shown in the photo is not the way I have been doing testing. It was just a way to have both units in the same photo.
I will keep in mind the suggestion of antenna orientation when I try more testing. I did not take note of the orientation when I made the previous tests.
Do you think the antenna are part/all the cause of the trouble? Do you think it would be wise to order another pair of antenna? perhaps of a different design?
I have very limited test equipment so I can't really see what makes a difference except to use the receiver and go by what it says.
Is there anything else I can try?

Thanks again,
Gord
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#7
(01-04-2020, 20:08)WetCoast Wrote: Thank you very much for the replies.
The way the units are shown in the photo is not the way I have been doing testing. It was just a way to have both units in the same photo.
I will keep in mind the suggestion of antenna orientation when I try more testing. I did not take note of the orientation when I made the previous tests.
Do you think the antenna are part/all the cause of the trouble? Do you think it would be wise to order another pair of antenna? perhaps of a different design?
I have very limited test equipment so I can't really see what makes a difference except to use the receiver and go by what it says.
Is there anything else I can try?

Thanks again,
Gord

Hello Gord,
I'd echo what the others are saying about antenna separation and relative orientation. I've found the Tx modules I buy on eBay can be unreliable, so I now mount them in a socket. Confession: I've also destroyed one by powering up a board without an antena connected. I've found you need to leave the system running for several hours for the RF efficiency values to stabilise, and even then, they seem to change for no apparent reason - maybe due to interference or weather conditions (rain?).

I've had three transmitters running successfully for a couple of years. Two using antennas from eBay that look like longer versions of yours (mine are c. 16cm), and the third using a 17.3 cm long piece of wire soldered to the inner core of a length of coax cable (17.3 cm = quarter-wavelength at 433 MHz). I'm using coax cable between the Tx board and the antenna because the Tx is several metres lower than the Rx, so there is no line of sight.

So, I wouldn't worry too much about the actual RF efficiency values, but maybe experiment with simple wire antennas to find a good layout that gives you RF values in the right ball park, then leave things alone for 24 hours to see what the actual data look like.

Good luck,
Ted
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#8
You could build such an antenna:
- https://crycode.de/diy-433-mhz-dipol-antenne

I use those:
http://der-bastelbunker.blogspot.com/201...ebaut.html

Links are German but I think you can figure out what is ment.

But in your case I think it is mostly the direction. You can imagine that the radio signals of come out of the antenna as like a torch. With the antenna you can influence the beam and each antenna type has a different kind of beam. Now if the two beams never meet you do not get any signal.

Cheers
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#9
Hi Gord,

I agree with all the suggestions done in the post above regarding antennas.
I just want to add something about the RF Efficiency. It isn't an instant measure like SNR, instead, it compares the number of data packets received during the last hour with the number of data packets sent by the receiver, and then computes the RF Efficiency. So, when one of the units is turned off or reset, the RF Efficiency value always start with low values, and start to increase until the first working hour. After that it should start to stabilize.

Another hints: Before buying any new antennas, specially on the TX, try something which was already suggested: Attach one single wire of around 17cm to the central pole of the SMA connector. From my experience, those small antennas aren't good for transmitting, while usually work well on the receivers.
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