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There is a task given to me that I have to investigate a problematic RF remote controller against its weakness and make a suggestion report how it can be improved. This RF remote controller is used with two hands like PS console remotes. While it is functioning normally, in some cases, signal is not correctly or completely received by the receiver. Edit: The receiver is under the bed controlling motors.

Here are my findings, considerations and modifications;

1. Hands or human body on the remote controller are causing attenuation over the transmitted signals significantly at some directional orientation. (Observed with RF spectrum analyzer in dBm). At those moments, sometimes data is not properly received by the receiver but not always, unpredictable.

2. Antenna is on the 4-layers PCB. This anteanna is working OK when there is no obstacle. See image.

3. RF circuitry and micro-controller are all together and no shielding on the RF side. See image.

4. I have cut out on-board antenna and added a smd female RF connector. This way I experimented these steps; a. with teflon brown cable and connected a 17.3 cm wire. Antenna is inside the box: More or less same dBm measured as the on-board one. Data lost is not checked yet since it is not always the case. b. with teflon brown cable and connected a 433Mhz whip antenna. This is shorter, most likely it has a spiral version of 17.3 cm antenna inside. Antenna is outside the box: 30% more dBm measured than the on-board antenna does. And most importantly, hands and human body factors are quite less effective over the signals.

5. My point of view, the RF circuit part standalone is looking OK to me in terms of proper matching and harmonic suppression.

So, After those info and the image, what mistakes are you seeing (if there are)? How can this RF circuitry be made more effective by all the RF design technics considered?

I hope that I could explain what I am up to.

enter image description here

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    \$\begingroup\$ Hopefully the user's hand is not near the antenna. 443 MHz remotes usually use robustly coded and repetitive transmissions; this may not be a purely RF problem. \$\endgroup\$
    – Chris Stratton
    Oct 16, 2016 at 23:41
  • \$\begingroup\$ Yes Chris, the antenna is partially covered by hand most of the time and even when you are holding the remote close to your body and turn opposite the receiver, signal lost is dramatic. And yes, you are right, continuous button push is not causing repetitive transmission, it is only one shot and stops. But there is a kind of ACK back to transmitter from the receiver in order to figure if a correct data is received or not. But, the code is also quite suspicious. \$\endgroup\$
    – Sener
    Oct 17, 2016 at 6:03
  • \$\begingroup\$ Thank you Chris, you gave a good tip, I will try to check the source codes. Especially that repetitiveness is not happening and when bad luck happens and the data is not receipt or corrupted, there is no code to fix the last transmission. \$\endgroup\$
    – Sener
    Oct 18, 2016 at 10:18

1 Answer 1

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How much is 30% more dB?

Ricean fading or (reflection cancellation) will be your dominant cause of dropout even if RSSI or SNR shows adequate but marginal signal, so reflective surfaces and people interfering with reflections can cause dropouts when a reflected signal is near equal amplitude but out of phase with the main signal path.

Keeping the whip antenna at right angles to the direction of propagation give the most signals. To see if you are in a Ricean Fading zone with weak signals, behind the Tx, move the unit on a table top slightly over a +/- 1/2 wavelength zone in small increments to FIND a dead spot and then you know you will get dropouts with random orientations at that distance or path loss. Try to get the RSSI or AGC signal out of the Rx to display on a scope to get better sensitivity to Path loss, interference and Ricean Fading Effects.

Then consider the best gain/dispersion antenna and location for the fixed receiver with an improved ground plane for the antenna.

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  • \$\begingroup\$ With the PCB antenna, without any obstacle between TX and RX, I read -50 dBm at most. But, with the antenna I mentioned in 1.b is about -35 dBm. \$\endgroup\$
    – Sener
    Oct 17, 2016 at 9:14
  • \$\begingroup\$ -60dBm should plenty of signal so if this causes issues, then quality of Rx is at fault in CNR to SNR IF filter etc.Rx threshold is too high \$\endgroup\$
    – Tony Stewart EE75
    Oct 17, 2016 at 14:55
  • \$\begingroup\$ Yes, I agree, -50dBm is a reasonable signal strength. But, this result is just sight of line from 2 meters. \$\endgroup\$
    – Sener
    Oct 17, 2016 at 15:08
  • \$\begingroup\$ Sorry, I hit the Enter key unwillingly and it is published in the middle. I continue where I left. When I use my two hands on the remote or hiding it behind my body, it goes down -75 dBm (again from two meters). It is still communicating with the receiver but causes some data loss. \$\endgroup\$
    – Sener
    Oct 17, 2016 at 15:12
  • \$\begingroup\$ use Friss loss calculators for reflection path length and reflection loss and examine Ricean loss below that \$\endgroup\$
    – Tony Stewart EE75
    Oct 17, 2016 at 15:14

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