Because it is very cold outside, recently, I moved from my shack into the other end of the house with my receiver. I regularly listen to the 80 and the 40-meter Ham bands.
I do not dare to run the outdoor antenna into the house permanently, so I tried to find a limited space solution for these frequencies. I remembered that if a transmission line with a shorted end is shorter then λ/4, it behaves like an inductance and this inductance can be resonated with a variable capacitor.
After a few calculations (*) I cut a some 5-meter long TV flat cable, soldered one of its ends, and made the folloving arrangement as it is shown in the fig.
With a 500pF broadcast type variable capacitor I could resonate the flat cable antenna. Connecting a buffer/amplifier with high input impedance to the resonant circuit, low impedance antenna inputs can be driven too.
I do not dare to run the outdoor antenna into the house permanently, so I tried to find a limited space solution for these frequencies. I remembered that if a transmission line with a shorted end is shorter then λ/4, it behaves like an inductance and this inductance can be resonated with a variable capacitor.
After a few calculations (*) I cut a some 5-meter long TV flat cable, soldered one of its ends, and made the folloving arrangement as it is shown in the fig.
With a 500pF broadcast type variable capacitor I could resonate the flat cable antenna. Connecting a buffer/amplifier with high input impedance to the resonant circuit, low impedance antenna inputs can be driven too.
(*)
Because the velocity-factor is around 0.85 for such domestic flat cables, λ = (0.85 * c) / f
The impedance of the cable inductance XL = Z * tg (360 * (L/ λ))
The cable inductance = XL / ω
Because the velocity-factor is around 0.85 for such domestic flat cables, λ = (0.85 * c) / f
The impedance of the cable inductance XL = Z * tg (360 * (L/ λ))
The cable inductance = XL / ω
For Qbasic platform a simple basic program:
Z = Ohm, L = meter, f = MHz
———————————————————————————————————————
INPUT “Z=”; z
INPUT “L=”; l
10 INPUT “f=”; f
IF f = 1 THEN GOTO 100
CONST PI = 3.141592
fi = 360 * l / (300 * .85 / f)
xl = z * TAN(fi * (PI / 180))
Ind = xl / (2 * PI * f)
C = 1000000 / (40 * f * f * Ind)
PRINT fi; ” “; xl; “ohm “; Ind; “uH “; C; “pF”
GOTO 10
100 PRINT
Z = Ohm, L = meter, f = MHz
———————————————————————————————————————
INPUT “Z=”; z
INPUT “L=”; l
10 INPUT “f=”; f
IF f = 1 THEN GOTO 100
CONST PI = 3.141592
fi = 360 * l / (300 * .85 / f)
xl = z * TAN(fi * (PI / 180))
Ind = xl / (2 * PI * f)
C = 1000000 / (40 * f * f * Ind)
PRINT fi; ” “; xl; “ohm “; Ind; “uH “; C; “pF”
GOTO 10
100 PRINT
