10m to 70cm mobile antenna
The full wave wire is in reality a lumped component inductance resonator. This section has an inductance required for the lowest frequency of band operation. In this regard the 10m band is the lowest frequency used, so the inductance of the full wave vertical section is as follows:
inductance antenna lumped component is ( 10m * 300nH ) = 3uH inductor as the radiating element
Note the bottom or negative end of the 50Ω tuning element must not be earthed to any grounding source, as the bottom end must see an high impedance load, so the terminal connection end the upper connection, reveals a 50Ω tuned load for the antenna.
As the antenna is used higher up the bands, the 3uH radiating element will be greater than a full wave length, equating to a signal gain of increasing degree higher up the bands. At the 10m band, the 3uH radiating element is one full wave, but five times full wave at the 2m band, and so on.
The matching section of the antenna, the lower section, retains a 50 ohm impedance, thus providing an impedance matching load for the complete operating range of the antenna.
The values for the tuning element and the band width of operation towards wide band coverage, are listed below. The 225MHz band is also listed for our neighbouring American Radio Ham operators.
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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= 8.2E-12
20 Lcoil = 0.3E-6
30 PRINT
40 PRINT
50
60
70
80 PRINT TAB(15);"VHF / UHF 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 = 28 TO 30 STEP 1
180 PROC_sums
190 NEXT
200 PRINT
210 FOR f = 50 TO 54 STEP 1
220 PROC_sums
230 NEXT
240 PRINT
250 FOR f = 70 TO 72 STEP 1
260 PROC_sums
270 NEXT
280 PRINT
290 FOR f = 144 TO 148 STEP 1
300 PROC_sums
310 NEXT
320 PRINT
330 FOR f = 220 TO 230 STEP 2
340 PROC_sums
350 NEXT
360 PRINT
370
380 FOR f = 430 TO 450 STEP 5
390 PROC_sums
400 NEXT
410 PRINT
420
430
440 REM *CHDIR C:\Users\alastair\Pictures\antenna designs
450 REM *SCREENSAVE 50omh_mobile_phone_antenna.bmp 1,1,2000,1100
460
470 END
480
490
500
510 DEFPROC_sums
520 Xc=1/(2*PI*f*1E6*Cshunt)
530 Xl = (2*PI*f*1E6*Lcoil)
540
550 Trap_effect = ((Xc*Xl)/(Xc+Xl))
560
570 L_trap_effect_inductance = Trap_effect / (2*PI*f*1E6)
580
590 L_antenna_inductance = L_trap_effect_inductance
600
610 resonant_length = L_trap_effect_inductance/(0.3E-6)
620
630 wave_length = L_trap_effect_inductance * 2 * PI * f * 1E6
640
650 SWR_imped = (wave_length)/50
660
670 PRINT TAB(15);" freq = ";f;"MHz";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
680
690 ENDPROC
700