Coax cable portable magnetic loop for 80 and 160m 

It is a magnetic loop antenna. Exact same schematic as the MFJ 536B. Effectively it is a gamma match which in turn is an auto-transformer. Just as a transformer is still magnetically coupled when tapping the coil so is a mag loop and at low frequencies it is a lot easier to implement a gamma match than to try to have some sort of huge inductive small loop 20 feet in the air to couple to the loop. I also find the gamma match a LOT easier to achieve 1:1 SWR.

The diameter of the wire used in the loop is extremely important. Going from 1/4 inch to 1/2 inch approximately doubles its efficiency and effective transmit power. I'm not sure that it makes that much difference on receive but seems reasonable to assume it does. There's an online calculator for mag loop antennas and you can put in various parameters and it will tell you the efficiency but using ordinary wire your efficiency is going to be only 1 or 2 percent. 1/2 inch copper tubing gives about 52 percent.

15m long. Rest is in the video. Nothing is critical.

@@vk3ye thanks, I'll watch it again, I must have missed it.

At about 3:30 he says 95 foot to a guy he is talking too.

Mag loops often have two loops or a gamma match arrangement. This loop is different again with the loop fed at the capacitor end.

I still don’t understand. You showed a picture of a wire going up to a pole. But I didn’t see a circular loop.

@@hughbassoon There is no circular loop. See the diagram at 1:07.

Ok..I see the circular structure in the diagram. I just didn’t see your circular structure in subsequent slides I’ll look again.

I’ll take your word for it.