STN M0PEE LOC JO01en POS 51.56°N 0.38°E UTC --:--:-- DATE ---- SUN -- —
M0PEE
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// Toolkit

Utilities

Small calculators I use at the operating position. Everything runs in your browser – nothing is sent anywhere.

01Greyline map

Day / night terminator · Maidenhead fields
AA AB AC AD AE AF AG AH AI AJ AK AL AM AN AO AP AQ AR BA BB BC BD BE BF BG BH BI BJ BK BL BM BN BO BP BQ BR CA CB CC CD CE CF CG CH CI CJ CK CL CM CN CO CP CQ CR DA DB DC DD DE DF DG DH DI DJ DK DL DM DN DO DP DQ DR EA EB EC ED EE EF EG EH EI EJ EK EL EM EN EO EP EQ ER FA FB FC FD FE FF FG FH FI FJ FK FL FM FN FO FP FQ FR GA GB GC GD GE GF GG GH GI GJ GK GL GM GN GO GP GQ GR HA HB HC HD HE HF HG HH HI HJ HK HL HM HN HO HP HQ HR IA IB IC ID IE IF IG IH II IJ IK IL IM IN IO IP IQ IR JA JB JC JD JE JF JG JH JI JJ JK JL JM JN JO JP JQ JR KA KB KC KD KE KF KG KH KI KJ KK KL KM KN KO KP KQ KR LA LB LC LD LE LF LG LH LI LJ LK LL LM LN LO LP LQ LR MA MB MC MD ME MF MG MH MI MJ MK ML MM MN MO MP MQ MR NA NB NC ND NE NF NG NH NI NJ NK NL NM NN NO NP NQ NR OA OB OC OD OE OF OG OH OI OJ OK OL OM ON OO OP OQ OR PA PB PC PD PE PF PG PH PI PJ PK PL PM PN PO PP PQ PR QA QB QC QD QE QF QG QH QI QJ QK QL QM QN QO QP QQ QR RA RB RC RD RE RF RG RH RI RJ RK RL RM RN RO RP RQ RR
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Sub-solar point
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Sun elevation at M0PEE
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Condition at QTH
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Along the greyline (the amber band) the D-layer is weak on both ends of a path, which often opens long-distance contacts on the low bands.

02Locator converter

Maidenhead ⇄ latitude / longitude
Locator → position
Centre
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Decimal
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WAB square
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Position → locator
Locator
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WAB square
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03Distance & bearing

Great-circle short and long path
Short path
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Beam heading
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Long path
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Reverse heading
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04Antenna calculator

Wire lengths from frequency

Cut a little long and trim – real lengths depend on wire, height and surroundings. 0.95 suits bare wire; leave at 1.0 for the free-space figure.

Results
Wavelength λ
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½λ dipole (total)
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Each dipole leg
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¼λ vertical / radial
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⅝λ vertical
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Full-wave loop
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05EFHW calculator

End-fed half-wave · corrected for wire velocity factor

Insulation slows the wave along the wire (a longer propagation delay per metre), so the wire is electrically longer than it looks and must be cut shorter. The end-effect factor covers capacitance at the wire ends; 0.95 is the classic 468/f figure.

Results
Free-space ½λ
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Bare-wire length
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Cut length (this wire)
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Shorter due to insulation
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Propagation delay
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Delay along the wire
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Counterpoise (≈0.05λ)
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Trim sensitivity
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Harmonic bandsestimate
×Bandn × fLikely resonanceFit

The end effect only happens at the two ends, not every half-wave, so the harmonics land a little high (ARRL long-wire rule: L = 492 (n − 0.05) / f ft). Trim for the band you use most, or add a small loading coil / capacitor to pull the upper bands down.

Setting it uptypical sloper · numbers follow the calculator
EFHW layout: rig, coax with choke, 49:1 transformer on a post, half-wave wire sloping up to a tree, short counterpoise RIG 49:1 counterpoise -- ½λ wire -- ⚡ high voltage 1 2 3 4 5 coax
  1. Transformer. Mount the 49:1 at the feed end, ideally 2 m or more up. The wire end carries several hundred volts of RF, so keep it out of reach.
  2. Radiator. Cut the wire to the cut length plus 2–3 %. Run it as straight as you can – sloper, inverted-L or inverted-V – and away from gutters and metal.
  3. Counterpoise. A short wire on the transformer's ground side. Often a metre or two of coax shield does the job.
  4. Choke. Put a common-mode choke on the coax at the rig so RF doesn't come back into the shack.
  5. Far end. Use an insulator and non-conductive cord. Fold the extra wire back here rather than cutting it, so you can lengthen it again later.

Tuning and on the air

  1. Put it up in its final position. Height and slope change the resonance.
  2. Sweep the fundamental with an analyser or low-power SWR meter. Is the dip below the band? The wire is long: fold more back, using the trim sensitivity figure. Is it above the band? Unfold some.
  3. Check the harmonic bands in the table above. If the upper bands land high, a 100–150 pF capacitor across the primary pulls them down.
  4. On the air you shouldn't need a tuner on the harmonic bands. It won't match bands that aren't harmonics (30 m, 17 m and 12 m on a 40 m EFHW). Use the end-fed long wire below for those.

06EFHW transformer

49:1 / 64:1 unun winding · core material & size

Winding
Core
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Turns (primary : total)
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Transformed impedance
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AL · primary inductance
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Primary XL at lowest band
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Core rating (est.)
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Secondary voltage
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Wire
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Wire to cut (secondary)
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Cap across primary
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    Wound as an autotransformer: the primary is a tap N₁ turns from the cold end of an N₂-turn winding. Aim for primary reactance of at least 3–4 × 50 Ω at the lowest band. Ratings are a rough guide from typical builds – check for heating with a long carrier on the lowest band.

    07End-fed long wire

    9:1 unun random wire · e.g. LWHF-160 · band-by-band check

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    A 9:1 unun turns about 450 Ω into 50 Ω. That works when the wire is not a multiple of a half wave on the band in use – there the end impedance rises to roughly 1–3 kΩ, an SWR of about 2–7:1 after the unun. Most ATUs will still match that, but more power is lost in the unun and coax. The trick is a length that misses every half-wave multiple on the bands you use most.

    Results
    Wire length
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    Bands clear of half-waves
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    Lowest band, electrical length
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    Counterpoise (suggested)
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    Coax choke
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    Best nearby length
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      Band by bandestimate
      BandLength in λHalf-wavesFeed pointExpect

      "Half-waves" shows how many electrical half wavelengths fit on the wire from the bottom to the top of the band. Close to a whole number = high impedance (high SWR, tuner needed). The count is only good to about ±2 %, so the error grows with it: past about 3½ half-waves it's bigger than the margin, and the band shows "can't call" instead of a verdict. Close to x.5 = an odd quarter wave, low impedance (≈ 5–15 Ω after the unun) – a tuner copes, but losses rise. In between is the sweet spot. The insulation slows the wave along the wire, so an insulated wire is electrically longer than it measures. How much depends on sheath thickness relative to the conductor and on the material, and it grows slightly with frequency. The velocity factor is worked out per band from the wire sizes above, using Regier's thin insulated-wire approximation. Copper weight and colour don't matter; sheath thickness does.

      Compare antennaseach with its maker's wire
      AntennaLength

      ● good   ○ low Z (odd ¼λ) – tuner copes easily   ◐ borderline, near a half-wave multiple   ATU on a half-wave multiple – works, but needs the tuner   ? too many half-waves for the model to call   · shorter than ¼λ. "Clear" counts bands that are not known to be on a half-wave multiple ("?" counts as clear). A band that isn't clear still works: it just needs the tuner to work harder. Each antenna is modelled with its maker's wire (hover a mark for details); "Your wire" uses the wire set above. Click a row to load it. Makers expect an ATU on most bands, and the coax and counterpoise shift real results.

      Length finder--

      How far each wire length stays from a half-wave multiple on the worst of your selected bands. Taller and greener is better. Drag the slider, or hover over or click the chart.

      Selected length
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      Tightest band
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      Margin
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      Verdict
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      #LengthFeetMarginTightest band

      This is not an SWR plot. Each column is one wire length (x axis). Its height is the margin (y axis): how far that length stays from a half-wave multiple on the worst selected band, in % of a half wave. Red = within 7 % of a half-wave (high impedance – needs the tuner), amber = 7–12 %, green = more than 12 %. The y axis scales to the best length in range. Click a length in the table to try it. Lengths assume the velocity factor above and do not count the coax, which also radiates on these antennas.

      Setting it uptypical inverted-L · numbers follow the calculator
      End-fed long wire layout: rig and ATU, coax with choke, 9:1 unun at the base with a counterpoise and ground rod, wire running up a mast then across to a tree RIG ATU coax 9:1 counterpoise -- wire -- (vertical + horizontal) 1 2 3 4 5
      1. ATU. You need one. A 9:1 brings the wire into tuner range but doesn't give 1:1 on its own. A remote auto-tuner at the unun works too.
      2. Choke. Put it at the rig end of the coax. The shield between the choke and the unun is part of the antenna.
      3. 9:1 unun. Fit it at the base of the wire, weather-proofed. The wire goes on the antenna post, the counterpoise and ground rod on the ground post.
      4. Counterpoise. Lay one or more wires on or just under the ground, and add a ground rod if you can. More radials make the low bands more efficient.
      5. Wire. Cut it to the length you picked here. You don't trim a long wire to resonance. Get it as high and clear as you can, and count every bit of wire after the unun.

      Tuning and on the air

      1. Pick a length with the length finder and check the band-by-band table. "ATU" bands need the tuner, and the worst may need an external one. "?" bands could go either way.
      2. On each band, tune the ATU at low power (5–10 W, or the tuner's tune button) before you go to full power. Write the settings down or let the auto-tuner store them.
      3. If a band won't tune, or RF gets into the shack, add or remove a metre of wire or improve the counterpoise. Don't keep raising the power.
      4. Every band works, but it's a compromise: expect a few dB less than a resonant antenna, with most of the loss on the lowest band.
      5. Be suspicious of a dead-flat 1:1 across a whole band with no tuner. Loss in the unun, the coax or a wet joint looks like a perfect match to the SWR meter. If the SWR drops on every band at once, check for water or heat before you celebrate.