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On Mar 25, 6:19 pm, "art" wrote:
On 23 Mar, 21:29, "Bill Bowden" wrote: How much improvement can I expect using Litz wire to wind a AM ferrite Rod antenna as opposed to using solid copper wire? Is it worth the trouble to obtain Litz wire, or can I expect almost the same response at say 1 MHz using regular enamaled copper wire? -Bill Bill, to give you a better background so the answer is more understandable is to think about what Litz wire does for you. When are delving into lower frequencies than AM then the skin depth required of the wire is much deeper that at higher frequencies and if the wire diameter is relatively small then the resistance goes up because even if there was enough skin depth the circumference is small. If the wire was made of many strands insulated from each other then the resistance goes down since the wires are in parallel. As I stated earlier Litz wire is used below AM frequencies. So now let us examine what wire resistance does at A.M. frequencies say on your auto, do you think that you could tell the difference on the radio if you replace the stainless whip with say a copper wire? No I don't think so. So for starters the Litz wire is not relavent for your frequency of use and 2 the conductivity of the whip will not affect your radios performance unless you took liberties with the conductivity and replaced your whip with a wooden stick Art Well, according to this website, Litz wire will increase the Q factor of a ferrite rod antenna by 6 times or more at 943Khz. The attainable Q value is 141 with solid copper wire and 1030 using Litz wire. Quite a significant difference. Of course the bandwidth is is only about 500 Hz with a high Q value and much wider at the lower Q, which may be desirable. But it's much easier to start with a high Q and work down, than the other way around. Very easy to reduce efficiency, very hard to increase it. Quote from website: "Solid wire instead of litz?: Keep in mind that the work described here used close-wound 125/46 litz wire. If one duplicates 'Coil and Former B' in Table 2, except using 22 ga. solid copper wire (having the same diameter) as 125/46 litz, the Q values drop to about 1/6 of the values achieved with the litz wire. The cause is the large proximity effect resistive losses in the solid wire. The proximity effect, but not the skin effect loss may be much reduced if the wires are space-wound. New trade-offs now must be considered: Same wire diameter, and therefore a longer solenoid, or a smaller wire diameter and the same overall length? If one wishes to use solid wire, it should probably be wound directly on the ferrite, not on a former. The overall Q will still be much less than when using litz, but the loss from the high (tan δ) dielectric of the ferrite will be pretty well swamped out because of the now higher losses from the skin and proximity effect losses. The Q values, using a close-wound solenoid of 22 ga. solid copper wire on a polyethylene former, as in 'Coil and Former' B in Table 2 a 520 kHz: 130, 943 kHz: 141 and 1710 kHz: 150 when using the "best core". The Q drops only 3, 3, and 5 points respectively if the "worst core" is used. " -Bill |
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