LF and MF mobile antenna

The inductance of the full wave wire equivalent, the lumped component radiator element, equates to an inductance at the lowest frequency of operation of a value of:

full wave length * inductance of wire per metre : (300/0·136) * 300nH = 660uH of inductance as a coil of wire.

The impedance match tuning of the 50Ω stub tuning are as follows with the calculated SWR matching values.

The lower end of the 50Ω stub tuning circuit must not be ground to earth, it must stay free of any grounding connection, while only the top end positioned to the 50Ω terminal connection, need only be connected to the tuning stub circuit.

In many regards, the 50Ω stub tuning circuit can be referred by other means as a counter-poise antenna load of a 50Ω impedance.

Text Box

10 Cshunt= 4700E-12

20 Lcoil = 100E-6

30 PRINT

40 PRINT

50

60

70

80 PRINT TAB(15);"LF / MF vertical antenna stub tuning Trapped"

90 PRINT TAB(15);"Cshunt = ";Cshunt/1E-12;"pF";" Lcoil = ";Lcoil/1E-6;"nH "

100 REM PRINT TAB(15);"leg_B = ";segments_B;"m"

110 PRINT

120 PRINT TAB(15);"performance spec's"

130 PRINT

140

150

160

170 FOR f = 0.35 TO 0.38 STEP 0.005

180 PROC_sums

190 NEXT

200 PRINT

210 FOR f = 0.47 TO 0.48 STEP 0.001

220 PROC_sums

230 NEXT

240 PRINT

250

260 PRINT

270

280

290 REM *CHDIR C:\Users\alastair\Pictures\antenna designs

300 REM *SCREENSAVE 50omh_mobile_phone_antenna.bmp 1,1,2000,1100

310

320 END

330

340

350

360 DEFPROC_sums

370 Xc=1/(2*PI*f*1E6*Cshunt)

380 Xl = (2*PI*f*1E6*Lcoil)

390

400 Trap_effect = ((Xc*Xl)/(Xc+Xl))

410

420 L_trap_effect_inductance = Trap_effect / (2*PI*f*1E6)

430

440 L_antenna_inductance = L_trap_effect_inductance

450

460 resonant_length = L_trap_effect_inductance/(0.3E-6)

470

480 wave_length = L_trap_effect_inductance * 2 * PI * f * 1E6

490

500 SWR_imped = (wave_length)/50

510

520 PRINT TAB(15);" freq = ";f*1000;"KHz";TAB(32)"eqiv. stub = ";INT(resonant_length * 100)/100;" m";TAB(59);"coax line = ";INT(50*SWR_imped*10)/10;" ohms";TAB(88);" SWR = ";INT(SWR_imped * 100)/100

530

540 ENDPROC

550