Antenna cutting

Introduction:

Entel offers pre-cut and un-cut antennas for its radios.

Un-cut antennas can be optimised for your exact operating frequency, ensuring the very best range performance.

If the radios were programmed by Entel, to your frequencies, the antennas should have been cut to frequency prior to dispatch.

If programming the radios yourself, its very important an un-cut antenna is cut to the correct frequency. If left un-cut, or cut to the wrong length, the radios range can be significantly reduced.

Uncut antennas:

The following are all the un-cut antennas Entel offers and need cutting to your radios centre frequency.

CAT20 VHF HT radios
CAT80 UHF HT radios
CAT420 VHF HX, DX & DT radios
CAT480 UHF HX, DX & DT radios

If the antennas part number includes a frequency e.g. CAT480S/425, the antenna is pre-cut to this centre frequency (425 MHz in this example) and must not be cut.

Operating bandwidth:

Antennas operate best over a limited frequency range (bandwidth). For optimum performance the transmit frequencies should be within:

VHF antennas (CAT20 & CAT420) +/- 1.5 MHz
UHF antennas (CAT80 & CAT480) +/- 7 MHz

Its possible to operate outside these ranges, up to +/- 10 MHz, but this will result in reduced range (worsening the further outside the optimum frequency range you are).

How to calculate the centre frequency:

Note the lowest and highest transmit frequencies programmed in your radios, e.g.

Lowest TX frequency: 148.825 MHz
Highest TX frequency: 153.425 MHz

The antennas centre frequency is then calculated as follows:

148.825 MHz + 153.425 MHz = 302.25 MHz
302.25 MHz ÷ 2 = 151.125 MHz (Centre Frequency)

The operating frequency range in this example is +/- 2.3 MHz

Cutting the antenna:

Use the cutting chart supplied with your antenna, or from the download links below, identify the antennas cutting length for your centre frequency.
Remove the antennas top cap.
Measuring from the very bottom of the antenna’s connector and mark the exact cutting point.
Using suitable side cutters, cut the antenna.
Affix the top cap with ‘Ever Build Stick2’ superglue or similar (only 1 drop for UHF, 2 drops for VHF antennas are needed).

How to identify your antenna & cutting chart download links:

CAT20 & CAT80: