Electronics & radio calculators
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Indicative calculation; verify before use.
Resistor color code
4, 5 and 6 bands. Colours to value and value to colours, with the nearest E12/E24/E96 value.
SMD resistor code
3-digit, 4-digit and EIA-96 markings like 472, 4R7, 1002 or 01C to ohms, and any value to its codes.
LED resistor
Series resistor for one or more LEDs, the standard value to buy, real current and resistor wattage.
Antenna length
Half-wave dipole and quarter-wave vertical from frequency, in metres and feet, with a shortening factor.
dBm to watts
dBm, dBW, W and mW both ways, with RMS, peak and peak-to-peak voltage in 50 Ω or any impedance.
SWR and return loss
SWR, reflection coefficient, return loss, mismatch loss and reflected power, or SWR from a power meter.
Capacitor code
Ceramic capacitor markings like 104, 4R7 or 2A104J to pF, nF and µF, with tolerance and voltage, and back.
Voltage divider
Output voltage from Vin, R1 and R2 with a load warning, and the E12/E24 R2 for a wanted output.
PCB trace width
Minimum trace width for a current, or the current a trace can carry, on outer and inner layers (IPC-2221), with voltage drop.
Toroid turns
Turns for an inductance on iron powder (T) and ferrite (FT) toroids, or the inductance for a number of turns, with AL in both units.
Coax loss
Cable loss in dB/100 m and dB/100 ft at any frequency, total loss with SWR, and the power that reaches the antenna.
Wire gauge (AWG ↔ mm²)
Diameter, cross-section and copper resistance for AWG 0000 to 40, the AWG size for a metric cross-section, and the nearest IEC 60228 size.
QSL card maker
A printable 140 × 90 mm QSL card for one QSO, in three layouts. Print it or download SVG or PNG; nothing is uploaded or saved.
LC resonance & RC/RL filters
Resonant frequency of L and C, or the L or C for a frequency, with XL and XC. RC and RL cutoff, time constant and gain at any frequency.
LoRa time on air & EU duty cycle
Time on air of a LoRa packet from Semtech's formula, and how many packets per hour each EU 868 MHz sub-band allows. Meshtastic presets included.
Series & parallel (R, C, L)
Total of up to 8 resistors, capacitors or inductors in series and parallel, and two standard E12/E24 resistors for any target value.
555 timer (astable & monostable)
Frequency, high and low time and duty cycle from R1, R2 and C, R1/R2 for a frequency and duty you choose, and one-shot pulse width t = 1.1 RC.
Antenna tables (NEC2)
Resonant dipole and ground-plane lengths and feed impedance for 160 m to 6 m, modelled in NEC2, in free space and over ground, against the 468/f rule.
CEPT licence: countries & prefixes
Where your amateur licence works under CEPT T/R 61-01 and the prefix to sign with (DL/, OZ/, OY/ …), searchable, from CEPT's own table.
Ferrite choke chart (RFI)
Which Fair-Rite mix (31, 43, 52, 61) gives the most common-mode impedance per turn on each band, 160 m to 6 m, on FT240 and FT140 sizes. Printable.
Printable charts
One to four pages each, readable in black and white. Print them or save as PDF.
- Resistor color code chart: 4, 5 and 6 bands, tolerance and tempco, all E12 and E24 values with their colours
- EIA-96 SMD resistor code chart: codes 01 to 96 with every multiplier letter, plus the 3- and 4-digit rules
- dBm to watts table: −30 to +60 dBm with mW/W and RMS and peak-to-peak volts in 50 Ω
- Dipole antenna length chart: half-wave dipole and quarter-wave lengths for every ham band from 160 m to 70 cm, metres and feet
- Antenna tables modelled in NEC2: resonant dipole length in free space and 10 m over average ground, feed-point impedance, quarter-wave vertical with 4 radials and wire thickness, 160 m to 6 m, with the 468/f rule beside it
- Region 1 HF band plan chart (unofficial): where CW, digimodes and phone sit on every band from 160 m to 10 m, with maximum bandwidth and centres of activity, A4 landscape
- Region 1 VHF/UHF band plan chart (unofficial): 6 m, 2 m and 70 cm segments, calling frequencies, FM simplex and repeater channels with shifts, and satellite sub-bands
- Coax loss chart: dB/100 m and dB/100 ft for common coax cables at the ham bands from 160 m to 23 cm, from the manufacturers' datasheets
- AWG wire gauge chart: AWG 0000 to 40 with diameter in mm and inches, mm², circular mils, copper Ω/km and Ω/1000 ft, and the nearest IEC 60228 size
- CEPT licence countries and prefixes: every country and territory in CEPT T/R 61-01 with the prefix to put before your call sign and the equivalent licence classes, searchable and printable
- Ferrite common-mode choke chart: calculated impedance per turn for Fair-Rite mixes 31, 43, 52 and 61 on FT240- and FT140-size toroids, 160 m to 6 m, from Fair-Rite's own permeability data, printable
- Q codes, RST and CW abbreviations: the Q codes amateurs use with their ITU meanings, the RST scale with S-meter levels, and CW prosigns
Why these calculators
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