1 reply to this topic

[jwed]

Can anyone tell me about using 1/2 copper pipe for a quad? Do you increase/decrease the element sizes because of the large outside diameter by some factor? And when you measure the loop size do you measure the outside circumference (with the elbows in place), or in the middle somewhere?

Any thoughts would be appreciated

[Shortwave]

Hiya jwed

All the info I've read over the years points to the "length" of the elements being measured along their centre line.

If you are only deviating a small amount from the original design material diameter, then you could most likely go with the original lengths listed.

Of course, the higher you go in frequency so the more critical the length/diameter radio becomes. To get around "constructor introduced variations" the normal practice is to make the quad loops slightly smaller than they would otherwise be, and then add a small shorted stub section at some point around the loop to allow for fine tuning/length correction.

In fact, tuning stubs are a good idea all around on Quads, as there's nothing worse than building an antenna only to find that one of the elements is a few hundred kilohertz off resonance, thus rendering the antenna next to useless.

73, Mark.