i am using a realistic dx-394 receiver, i am about to put a long wire antenna up outside which would be best to use a ATU or a BALUN chook or indeed booth, on the receiver there are two antenna connections hi-z and lo-z which of these should i be using ?

My preference is a longwire (9:1) balun (technically called an UNUN) installed as follows:



This has the advantage of keeping the end of the antenna that is most susceptible to man-made noise away from the house. Being coax fed this would plug into the 50ohms Lo-Z socket of the DX-394.

The alternative is to get string up a length of wire and connect it to the Hi-Z socket on the receiver. Or, to get an ATU and connect the wire to that and run a patch lead from the ATU to the Lo-Z socket. Using this method with the ATU will give better results than without, though having the antenna come into the house you always run the risk of interference.

Its debatable whether using an ATU with an UNUN is worth it, possibly if signal capture voltage is below the receivers capabilities (unusual with modern kit), or you need to peak a signal which is at a high impedance point on the antenna.

ATB

Hi

The balun to use is a 9;1 ratio, as this transforms the high impedance of the longwire from about 400 ohms'ish down by a factor of 9 to 50 ohms ish, which makes matches the aerial to the radio much better.

Personally , I'd much rather make my own( and have made several) its much cheaper.......
The diagram attached is a toroid ferreite one, but if you cant find one of these, a ferrite rod salvaged from an old bust AM radio will work just as well, ( if not better Ive found)
If you use the rod, you just need to replicate the windings on to that as in the diagram.

Its isnt essential to have an earth connection, but I find it boosts the signal slightly, and is supposed to reduce local interferance.
By experiment Ive found it does both.