Bad idea to use RG-6 coax for the VLF/HF loop antenna amp?

Eric Inloes


In light of the impedance mismatch issues I had a question. Would it be a bad idea to use RG-6 coax which is 75 ohm vs something that is 50 Ohm that would lead to problems? 


Chris Moulding

Either version of the Loop Antenna Amplifier will work well with 75 ohm coax.

What I would suggest at the receiver end would be to add a 75 to 50 ohm matching attenuator. This would give the coax a good 75 ohm load relatively unaffected by whatever the input impedance of the SDR receiver is.

A simple 10 dB tee attenuator would have a 47 ohm resistor from the 75 ohm input, 18 ohm resistor from the 50 ohm output with a 43 ohm resistor from the tee junction to ground. These are preferred resistor values so that it's easy to buy the parts.

Here's a very useful online calculator to calculate resistor values for other impedances or attenuation levels: