Time is running out.

I have managed to get data from a remote transmitter, but the range is poor. Might be the lack of LOS (Line of Sight) between the receiver and the transmitter, but I suspect something else.

I brought the receiver and the transmitter at close range (that is 10 cm).

The receiver displayed its RSSI: -44dBm.

I moved 3 m away: -57dBm.

I connected them together: -42dbm.

The transmitter should send out 20 dBm.

I fired up a spectrum analyzer at work and conected the RF output through -45dB attenuation. I centered the analyzer on 434MHzwith 100MHz span

The marker peaked at -27.98dBm.Let's call it -28. Add 45 and we get 17dBm. Not bad, it migh actually output 20dBm, but the attenuators definitely have some tolerance and the thin coax cable is certainly not loss-less. I bought it from ebay.

Let's try a different coax, maybe this one is of low quality and has high losses.

With a new coax, the result is very close, but the soldering job at the board certainly dropped 0.2dBm. So the module outputs a decent amount of power and the cable is not as bad as I thought.

Let's see what does the receiver receive. I borrowed a better pair of antennas from a colleague (thank you Marius):

And I connected it to the analyzer, with no attenuation. I got -3dBm. Quite a loss from all those 17dBm, but still far away from the -44dBm returned by the receiver.

And I tried several other antennas:

Right now I wish I paid more attention at the Microwave course at school. We also had a class for antennas, but only theoretically.

Something doesn't add up. The receiver's antenna gets around -1dBm with the better antennas, but is reports -44dBm.