TimH1971 wrote:Walruss wrote:TimH1971 wrote:Re: Quad Loops - any idea how quiet these are? QRM is the thing I am trying to lessen above all else.

Appreciate the help so far guys.

Tim

A balanced loop gives some immunity to local common mode interference - i.e. the equal and opposite currents induced in both arms cancel eachother out.

Note below attached the low gain of the square quad loop, and the gains and impedances of the various loop permutations.

Also below attached, design of a simple ferrite balun to balance loop and match 50Ù impedance of feeder to the 100Ù or so of the loop.

Thanks Chris.

Tim.

At 27.350 MHz one wavelength is 10.96m.

We must allow for the

*velocity factor* also called

*velocity of propagation* of the wire, which is a nominal 0.95 for a straight copper wire. (much less for some coaxial cables!) This is the speed that an electromagnetic wave travels down the wire compared with the speed of an electromagnetic wave in a vacuum. So slower down the wire.

10.96m times 0.95 is 10.41m. (10.88*0.95 = 10.41)

This 10.41m we would call the

*electrical length* of a wave of frequency 27.35MHz

Each of the four sides of a fullwave square quad loop would therefore be 10.41 divided by 4,

which is 2.6m.

A circular fullwave loop cut for 27.35 MHz and therefore having an electrical length of 10.41m will have a diameter of 3.31m - quite a big circle to keep in shape I'd say.