Strange One Way Communication Problem

I’ve got 2 T-Beams, 1.1 boards.
Both of them are running on 433Mhz, LongSlow and 20 dbm.

I’ve got the same antenna on both. I mounted one on a 4th floor window and I took the other for a walk with me.

My friend and I were texting each other successfully for about 300m. Beyond 300 metres, I was able to receive messages up to 1km (didn’t try to go further) but none of my messages were going back.

If I’m understanding everything correctly, if there are 2 boards with the same antenna and transmitting power, and I can receive a signal, I should be able to send the same signal on the same path right? Given the same obstructions and transmission power, my friend should have received my messages too?

I will try reversing the situation tomorrow by taking his board for a walk, and leaving mine on the window.

What do you guys think?

It could be the RF noise level at one side deteriorating the reception. It sounds like this is the most probable answer if communication is affected only one way. Try to look at the SNR on both sides, see if they have a large difference…

Okay. I will be doing the test in a suburban/rural area today and see if it still happens.

Do the same test but swap the devices.
If you get the same result, it’s the environments not one of the devices, right?

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