Re: Kchibo antenna experiments installment 2 (trying to analyze Ray's loop)
Steve Ratzlaff
Ray can give details about his loopinductance, min/max of his
variable cap used to tune it, etc.
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I used a program by Reg Edwards to "reverse engineer" Ray's loop given the details Ray has already giventwo foot square box loop (610 mm/side), with 11 turns spaced 7 mm. Reg Edward's program "rjeloop3" (which will only run on older Win XP and earlier machines)can be downloaded at: http://g4gcp.sheard.org/antenna/download.htm . I entered 610 mm length of one side; 11 turns; 1 mm wire diameter (just a convenient guess); 7 mm winding pitch (7 mm spacing vs. 1 mm wire diameter); 531 kHz frequency (bottom of BCB for Ray's southern Australia location)that will give the max value needed for the variable cap to tune down to the bottom of the band. The program then calculated the loop as 156 uH; 574 pF needed to resonate at 531 kHz; Q at 531 kHz approx 238 (giving a bandwidth at 531 khz of 2231 Hz; 124.1 kohm impedance across the loop at resonance at 531 kHz; a one turn coupling loop would have 1 kohm output impedance (seen by the receiver) at 531 kHz. One can change the frequency to see how much capacitance would be needed at the top of the band, and change any of the other parameters as desired. So Ray can tell us how close his actual loop and variable cap comes to what the program calculated. Loop inductance given by the program is on the low side; maybe Ray's variable cap is a twosection cap in parallel to give more capacitance? Of course best Q for any loop will occur at minimum frequency (531 kHz) and will decrease (increasing bandwidth) as frequency rises. But Ray may already be able to tune one sideband by itself when tuned to the bottom of the band, assuming he has a station on 531 kHz he can receive. The software program doesn't differentiate types of wire used, just wire diameter. So switching to Litz wire would give lower RF resistance and higher loop Q, plus Litz can be wound with no turns spacing if desired since it has much lower turn to turn capacitance compared to nonLitz. But having some spacing between turns even with Litz will always give the lowest distributed capacitance compared to turns with no spacing. Best regards, Steve
On 3/16/2015 3:59 PM, Phillips
phillicom@... [ultralightdx] wrote:

