Hello Brian...I do not know too much about longwire antennas, but I would say 
that it would depend upon whether you wanted it for transmit and receive, or 
just receive...I think someone told me that it should be at least 135 feet 
long for the optimum signals, but he said the longer the better...It wouldn't 
be too critical if you are only going to receive with it, but I think that 
you should go with wavelengths of the lowest frequency that you want to use 
it on if you transmit with it...Another antenna you could try, which seems to 
work just about as well is the 1/2 wave dipole...You take 465/center 
frequency of where you want it to be to use on transmit...at least I think 
that is the formula...Anyway, all I remember off the top of my head is for 
what is called 80 Meters, around the 3.5-4.0 MHz range, it works out to be 
about 66 feet on both legs. What you do then is feed it in the center, or 
rather feed one leg using the center conductor, and feed the other leg with 
the ground or shield or outside of the cable, if you use coax, so including 
the coax or feedline the antenna sort of looks like a letter "T" with the 
legs of the dipole as the top of the T and the coax being the "Leg" of the T 
if you know what I mean Brian? You can also use it as an inverted or upside 
down "V", but then it is recommened that you put the feed point at 35 feet 
off of the ground or so for optimum performance. I find the 1/2 wave dipole 
to work better for DX stations, stations in other countries, and the "V" 
antennas to work better locally...Have a good one and catch you 
ter...Bernie
--- Maximus 2.01wb
---------------