I'm really puzzled about this. I have a simple transmission between two ATTiny85's going on with a 433MHz receiver and transmitter. The transmitter is in the basement so the signal is rather weak but here is weird thing. If I hold my USB to TTL cable, that connects the ATTiny to my PC, at a higher position like shown in image #1 I get a steady stream from my transmitter down stairs.
If I put the cable down (touching the cable isolation makes no difference) like shown in image #2 I get no signal AT ALL. Just nothing. I could repeat this behavior several times.
I really don't know much about antennas and radio transmission so this doesn't make sense to me in any way. I guess he USB cable must act as some sort of antenna/repeater but how? It only provides 5v power to the receiver and ATTiny and reads the serial output from the tiny.