Re: Kchibo antenna experiments installment 2 (trying to analyze Ray's loop)


Steve Ratzlaff
 

Ray can give details about his loop--inductance, min/max of his variable cap used to tune it, etc.
I used a program by Reg Edwards to "reverse engineer" Ray's loop given the details Ray has already given--two 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 two-section 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 non-Litz. 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:

Thank you Everett,

I am trying to duplicate reports of box loop tuning so sharp that it is possible to select which sideband to use. The idea is to use cheap hookup wire to get as far as possible and then use expensive Litz for the final product if the hookup wire version is near the mark.

I don't have an RF meter but I do have an oscilloscope that covers the MW band. The CRO will measure the RF and only load it with 1MOhms and a few pF.
Winding a balun is easy enough.
I need to finish the ferrite experiments first but I will get working on the box loop again.


Ray
35S138E

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