How this tool calculates
Most antenna selectors use a lookup table. This one does not. It computes the free‑space path loss for
your distance and frequency, adds the receiver sensitivity and a system margin, subtracts your radio’s output
power and the feeder loss, and derives the antenna gain the link actually needs. It then searches the RF element
catalogue for models that cover your band and match that gain.
FSPL = 32.44 + 20·log10(dkm) + 20·log10(fMHz)
Grequired = FSPL + Srx + M − Ptx + Lcable
Grequired = (FSPL + Srx + M − Ptx + 2·Lcable) / 2
point‑to‑point, identical antennas at both ends
- Ptx — radio output power at the connector, dBm
- Srx — receiver sensitivity required for the modulation in use, dBm
- M — system margin covering fading, alignment and tolerances, dB
- Lcable — feeder loss at the centre frequency, dB
Two things follow from this. First, gain requirements are dominated by the receiver sensitivity, not by the
distance — a LoRa link at 5 km needs a fraction of the gain a WiFi link at the same distance needs.
Second, the feeder can silently consume more of the budget than the antenna adds: at 5.8 GHz it is entirely
possible to lose 12 dB in a thin 10 m cable.
Default assumptions per application
| Application | Radio power | Sensitivity | Margin |
|---|
| LoRa / LoRaWAN | 27 dBm | −129 dBm | 15 dB |
| IoT / M2M low-power | 20 dBm | −110 dBm | 12 dB |
| WiFi 2.4 / 5 GHz | 20 dBm | −85 dBm | 10 dB |
| 4G LTE / 5G NR | 30 dBm | −100 dBm | 10 dB |
| UHF / PMR / TETRA | 30 dBm | −116 dBm | 12 dB |
| Microwave / point-to-point | 23 dBm | −70 dBm | 10 dB |
These are starting points, not specifications of your equipment. Open
Advanced and enter your own numbers if you have the datasheet in front of you.
Feeder loss — dB per 100 m
| Coaxial cable | 150 MHz | 450 MHz | 900 MHz | 2.40 MHz | 5.80 MHz |
|---|
| RG-58 / RG-58A/U (Ø5 mm) | 18.5 | 33 | 47 | 79 | 128 |
| RG-8X / Mini-8 (Ø6 mm) | 12.5 | 22.5 | 32 | 54 | 88 |
| RG-213 / RG-8/U (Ø10 mm) | 7 | 13 | 19 | 33 | 55 |
| LMR-100A (Ø2.5 mm) | 24 | 43 | 62.5 | 105 | 170 |
| LMR-200 (Ø5 mm) | 13.5 | 24.5 | 35.1 | 58.5 | 95.1 |
| LMR-240 (Ø6 mm) | 11 | 20 | 30.3 | 50.5 | 82 |
| LMR-400 (Ø10.3 mm) | 5.5 | 10.2 | 14.8 | 24 | 38 |
| LMR-600 (Ø14.9 mm) | 3.4 | 6.1 | 8.8 | 14.1 | 22.6 |
| 1/2" corrugated copper (LDF4-50A) | 3.1 | 5.4 | 7.7 | 12.6 | 20.4 |
| 7/8" corrugated copper (LDF5-50A) | 1.9 | 3.3 | 4.7 | 7.7 | 12.4 |
Typical published attenuation at 20 °C; intermediate frequencies
are interpolated. Rigid corrugated lines such as LDF4‑50A are quoted for a straight run — every bend adds
loss. Values are indicative, not a substitute for the cable datasheet.
Frequently asked questions
Omni-directional or directional - which one do I need?
An omni antenna radiates 360° in the horizontal plane. It is the right choice when you do not know exactly where the other end is, or when many endpoints are spread around one site. A directional antenna concentrates energy into a beam: for the same gain it reaches much further, but it has to be aimed. As a rule of thumb, beyond three to five kilometres you want directional, unless the endpoints move.
How much antenna gain do I need for a given distance?
It depends far more on the receiver sensitivity and the radio output power than on the distance alone - and those vary enormously between technologies. LoRa’s sensitivity is around −137 dBm, WiFi’s around −85 dBm. That is a 52 dB difference, so the same 5 km link needs roughly 5 dBi with LoRa and 27 dBi with WiFi. That is why this tool asks for the application first and shows the arithmetic instead of a lookup table.
Does a longer coaxial cable really reduce my range?
Yes, and usually more than people expect. At 5.8 GHz, 10 m of RG-58 loses about 12.8 dB while 10 m of LMR-400 loses about 3.8 dB - a 9 dB difference, which is roughly the same as halving the distance. The feeder step quantifies this for your cable type and length, and tells you what a better cable would buy you.
My radio covers several bands. Which band should I select?
Select every band your radio uses - the band selector accepts multiple choices. The tool then recommends only antennas that cover all of them, and reports the exact gain at each band. Selecting both 2.4 GHz and 5 GHz, for example, surfaces the true dual-band models rather than a single-band compromise.
Why does the tool sometimes say a single antenna is not enough?
Because at some frequency and distance combinations the free-space path loss is larger than the entire link budget. At 5.8 GHz over 20 km, even a 34 dBi 90 cm parabolic dish falls short of a 10 dB margin with a typical 23 dBm radio. In that case the tool tells you how much extra gain, transmit power or how much shorter the path would need to be - rather than recommending an antenna that will not work.
What is the difference between the minimum required gain and the recommended target?
The minimum is what the link budget needs in order to close. The recommended target adds practical headroom - cable and connector tolerance, fading, imperfect alignment - typically 8 dB, and never less than a sensible deployment floor for the distance you selected.
Are the gain figures the headline gain of each antenna?
No. Every figure is read from the specification table of that specific model at the band you selected. Wideband antennas are rarely flat: a 698–4200 MHz panel may deliver 5 dBi at 700 MHz and 8 dBi at 2.6 GHz. Using the headline number would over-promise at the low end of the band, which is exactly where long-range links usually operate.
What if no antenna in the catalogue fits my requirement?
That is a normal result, not a dead end - the tool says so rather than pushing the nearest compromise. There are three situations where it happens: your selection spans several bands that no single model covers, the link needs more gain than the catalogue carries at that band, or the closest models cover only part of your band. RF element designs and manufactures antennas to specification, from a modified standard platform to a clean-sheet design, and verifies prototypes in our own microwave anechoic chamber. In those three cases the tool shows a custom-design panel that writes your application, band, distance, required gain and link budget straight into an email to sales@rfelement.com.
