Calculator Form
Example Data Table
| Cable | Frequency | Length | Input Power | Extra Loss | Estimated Output |
|---|---|---|---|---|---|
| 1/2 inch Heliax style | 450 MHz | 100 ft | 50 W | 0.35 dB | About 25 W to 28 W |
| 7/8 inch Heliax style | 900 MHz | 150 ft | 100 W | 0.45 dB | About 44 W to 48 W |
| 1 5/8 inch Heliax style | 2400 MHz | 200 ft | 200 W | 0.50 dB | About 70 W to 80 W |
Formula Used
The calculator estimates cable attenuation with: Loss per 100 ft = A × √fGHz + B × fGHz. A and B are planning coefficients for the selected cable profile.
Cable loss is: Cable loss = Loss per 100 ft × Length ft ÷ 100. The condition allowance increases only the cable portion.
Total loss is: Total loss = Cable loss + Component loss + Mismatch loss + Safety margin.
Mismatch loss is: Mismatch loss = -10 × log10(1 - Γ²). For VSWR, Γ = (VSWR - 1) ÷ (VSWR + 1). For return loss, Γ = 10^(-Return loss ÷ 20).
Output power is: Output dBm = Input dBm - Total loss. Watts are converted with: W = 10^((dBm - 30) ÷ 10).
How to Use This Calculator
- Select the closest Heliax style cable size.
- Enter the operating frequency in MHz.
- Add cable length and choose feet or meters.
- Enter transmitter power in watts, kilowatts, or dBm.
- Add connector, adapter, jumper, arrester, and filter losses.
- Choose VSWR, return loss, or no mismatch allowance.
- Add antenna gain and a safety margin if needed.
- Press the calculate button and review the result above the form.
- Use CSV or PDF export for reports and records.
Why Heliax Loss Matters
Heliax style feeder is used where normal coax can waste too much power. It has a corrugated outer conductor, low resistance, and stable shielding. Even so, every feed line loses energy as frequency and length rise. A small loss at the shack can become a large heat load on a tower run. This calculator helps you see that loss before parts are installed.
Planning a Clean Feed System
The form separates cable loss from extra losses. Cable loss comes from length, frequency, and the selected cable profile. Connector, adapter, jumper, arrester, splitter, and mismatch losses are added after that. This gives a practical result, not only an ideal cable number. You can also add a safety margin for aging, moisture, bends, and field installation error.
Reading the Results
Total loss is shown in decibels. Output power is shown in dBm and watts. Efficiency tells how much transmitter power reaches the antenna port. Heat loss shows how many watts become heat in the feed system. EIRP and ERP include antenna gain, so they are useful for link budgets and regulatory notes.
Using Advanced Options
Use measured attenuation when you have a data sheet. Choose custom cable when a listed profile does not match your line. Select return loss or VSWR for mismatch. Return loss is often easier with network analyzer data. VSWR is common with radio meters. Both methods estimate the same reflection effect. For careful design, enter real connector counts and real jumper losses. Do not assume every short jumper is perfect.
Better Field Decisions
A lower loss cable may cost more, but it can reduce amplifier size. It can also improve receive sensitivity. At VHF, the difference may be modest. At UHF and microwave bands, it can be critical. Compare several lengths and cable sizes before buying hardware. Export the results for records, site proposals, or maintenance reports. Recheck the calculation after changes to antennas, filters, duplexers, or lightning protection. The best setup is not always the largest cable. Weight, bend radius, tower loading, and connector availability matter too. Use the numbers as a design guide. Then confirm limits with cable data sheets, radio ratings, and local installation practice before final work on any site.
FAQs
What is Heliax cable loss?
It is the signal power lost as RF travels through corrugated coaxial feeder. Loss depends on frequency, cable length, cable size, connectors, and installation quality.
Why does frequency change the result?
Higher frequency increases conductor and dielectric losses. A cable run that is acceptable at VHF may become inefficient at UHF or microwave frequencies.
Should I include connector loss?
Yes. Each connector adds small loss. Several connectors, adapters, arresters, and filters can create a noticeable total loss in real installations.
What is mismatch loss?
Mismatch loss estimates power not delivered because of impedance mismatch. It can be calculated from VSWR or return loss measurements.
What does feed efficiency mean?
Feed efficiency shows the percentage of input power that reaches the antenna port after cable, component, mismatch, and margin losses.
When should I use custom cable loss?
Use it when you have manufacturer data, field measurements, or a cable type not listed in the preset menu.
Is EIRP the same as output power?
No. Output power is power at the antenna port. EIRP also includes antenna gain, so it is higher when gain is positive.
Can this replace a cable data sheet?
No. It is a planning tool. Always verify final designs with official cable data, radio limits, and local site requirements.