Weak signal?

I have an installation with an EmonTX and a Raspi at 433MHz. The distance between TX and RX is about 3 floors, something like 20 meters (through the steps) and a few walls...

The RF69 module sitting on the Raspi allows you to measure the signal strength at RX. This value is around -80 dB in my case which is quite low. I use the small antenna (Miniature Stubby SMA) on the TX side from the OpenEnergyMonitor shop.

I wanted to improve the transmission. I had a Radio Amateur antenna lying around. It's a car antenna with a magnet mount, type MR77 from Diamond. It's slightly out of band but I gave it a try.

 
Surprise: I measured 10 dB more so the signal increased to -70 dB. This antenna has a 4 meters cable and you can play with it until you get the best signal.

Now, I can move the Raspi on the top of my roof :-)

Walter

 

Robert Wall's picture

Re: Weak signal?

I guess -10 dBm = the price of a small antenna. It would be very interesting to see what a 433 MHz Yagi could do (on the receiver - it's probably illegal on the transmitter).

pb66's picture

Re: Weak signal?

What a coincidence! I too improved reception of my weakest signal by 10dB today with an antenna mod  :-)

Based on something emjay commented about regards ground planes on another thread I decided to add a wire the same length as the antenna to the ground of my JeeLink to make a 1/4 wavelength dipole. I made the wire(s) slightly over size at 180mm with the intention of trimming to size and got an instant >10dB improvement from ~78 to ~66, placement and direction have an effect and I haven't trimmed yet!!

Paul

Bill Thomson's picture

Re: Weak signal?

I decided to add a wire the same length as the antenna to the ground of my JeeLink to make a 1/4 wavelength dipole.

Sounds like the result was a 1/2 wave dipole   ;-)

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