Calculator Input
Example Data Table
| Band | Frequency MHz | Apex Angle | Velocity Factor | Typical Use |
|---|---|---|---|---|
| 40 m | 7.15 | 120 | 0.95 | General HF work |
| 20 m | 14.20 | 115 | 0.95 | DX and field stations |
| 10 m | 28.40 | 130 | 0.97 | Compact upper HF setup |
Formula Used
Wavelength: λ = c ÷ f
Straight half wave: L = 0.5 × λ × velocity factor
Angle factor: A = 1 − shortening% × ((180 − apex angle) ÷ 90)
Resonant wire: R = L × A
Starting cut length: C = R + trim allowance + two tail allowances
Per leg length: Leg = C ÷ 2
Horizontal half span: S = Leg × sin(apex angle ÷ 2)
Vertical drop: D = Leg × cos(apex angle ÷ 2)
SWR estimate: SWR = larger impedance ratio between coax and transformed feed impedance
How To Use This Calculator
- Enter the design frequency in MHz.
- Set the wire velocity factor for your conductor type.
- Enter the planned apex angle for the inverted V shape.
- Add a trimming allowance so the first cut is slightly long.
- Enter center height, feedline length, coax factor, and power.
- Press calculate to view length, span, impedance, and safety notes.
- Cut longer first, then trim equally from both ends.
- Use the CSV or PDF button to save the antenna plan.
Inverted V Dipole Planning Article
What This Calculator Does
An inverted V dipole is a half wave antenna. Its center is high. Its two legs slope down toward supports. This shape saves space. It also lowers the feed impedance when compared with a flat dipole. The calculator estimates wire length, each leg length, ground span, end height, feed impedance, current, voltage, and feedline electrical length.
Why Frequency Matters
Frequency controls wavelength. Lower frequencies need longer wire. Higher frequencies need shorter wire. A small change in frequency can move resonance. For that reason, the calculator uses the exact design frequency. It then applies the selected velocity factor. Bare copper, insulated wire, and stranded wire may behave differently. Nearby trees, roofs, soil, and metal can also shift tuning.
Angle And Height Effects
The apex angle changes the final layout. A wider angle acts more like a standard dipole. A narrow angle makes the antenna compact, but it can reduce impedance and efficiency. Center height also matters. A low antenna may radiate strongly upward. That can help local contacts. A higher antenna can improve lower angle radiation.
Trimming And Field Tuning
The result should be treated as a starting cut plan. Always cut the wire slightly long. Install the antenna in its real location. Measure resonance with an antenna analyzer. Trim both legs equally. Remove small lengths each time. Retest after every trim. The final value may differ from the estimate because the site affects resonance.
Feed And Safety Notes
The impedance and SWR values are estimates. They help with planning only. A 1:1 current balun is common at the feed point. It can reduce feedline radiation. Keep wire ends away from people, buildings, and power lines. RF voltage can be high near the ends. Good support, strain relief, and weatherproofing improve long term performance.
FAQs
What is an inverted V dipole?
It is a half wave dipole with a raised center. The two wire legs slope downward. This layout needs less horizontal space than a flat dipole.
Is the calculated length exact?
No. It is a starting estimate. Real resonance depends on wire insulation, height, soil, nearby objects, and installation details.
Why should I cut the wire long first?
A long wire can be trimmed. A short wire usually needs splicing. Small equal cuts from both ends give better tuning control.
What apex angle should I use?
Apex angles from 90 to 140 degrees are common. Wider angles usually improve impedance and efficiency. Narrow angles save space.
Does height affect performance?
Yes. Height changes radiation angle and ground loss. Higher installations often improve DX performance. Lower installations may favor local coverage.
Do I need a balun?
A current balun is recommended. It helps reduce common mode current on the feedline. It can make the pattern cleaner.
Can I use insulated wire?
Yes. Insulated wire often needs a different velocity factor. It may make the resonant length slightly shorter than bare wire.
Can this calculator replace an analyzer?
No. Use it for planning. Final tuning should be checked with an antenna analyzer or reliable SWR meter.