Might be really dumb question, but just curios. (couldn't find anything useful).
Let's say I have two wireless devices, both have SMA connectors for external antenna. Can I connect them both with some form of coaxial cable together? Would they still work for like 100m, or would the signal be too week?

 

The problem is more likely to be that the signal would be too strong and swamp the receiver. A simple resistive attenuator would make it work.

 

Coax is an attenuator. The amount of attenuation depends on coax type, frequency and length.

A length of coax can make an excellent dummy load.

Depending on that frequency and power level, you probably can't get a signal thru 100 ' of coax.

 

The attenuation of 100' of RG58 at 443MHz is 10dB so a 10dBm transmitter level may still be too much for -110dBm receiver.

 

I am thinking of RFM69HW 868Mhz on both ends (tx @ +20dBm). 100m RG6 @ 868 has attenuation of 20dBm. I guess that's still too much power for receiver end?

 

If you haven't got a spec for the receiver max input power it's difficult to say for certain. 0dBm may well be OK - it's not going to damage anything so you can try it and it's easy enough to add some a couple of resistors to reduce it if need be.

 

Hello,

Have a look here for the calculation of an attenuator pad:
http://www.radio-electronics.com/in...sistor-pi-t-bridged-attenuator-pad-design.php

Bertus

 

I figured, I can always reduce RFM69HW output power if needed. Thank you guys, much appreciated.