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ERP is a calculation done by the antenna designer when he has built the first one and the user then accepts the figure and does his own calculations based on the RFoutput from the radio. So, for example if Ofcom issue a license for 15w ERP and you want to use a 3dBD gain antenna you would attach your power meter to the end of the coax instead of an antenna and with the aid of a 50 ohm dummy load, adjust your power out to give a reading of 7.5W on the meter. This is because the figure of 3dBd is double 0dB, so, 15w ERP on a 0dB antenna is 15w into the bottom of the antenna. Or, 7.5w into the bottom of a 3dB gain antenna is 15w ERP and finally 3.75w into a 6dBd gain antenna will equal 15w ERP

ERP Calculator this is an external link and so we cannot guarantee its content.

We have found a little... how shall we say, perhaps “trick” is the right word, that will double the gain without doubling the ERP so you can use your 0.5W legal ERP modem and get a range that is around the same as you would if you were using 1W ERP. This is not suitable for true omni directional antennas, but many customers have found this useful, click here to find out how.

KGSX-600 Diamond VSWR/POWER Meter.power meter

 * 1.8-160MHz (S1) * 140-525MHz (S2) * Two Sensors * 5W, 20W, 200W * 13.8V DC Lamp * 155 x 63 x 103mm * Weight 630g

Note this is only suitable for the Epic range as it is a minimum of 5 W