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VHF Radios specs

The Receiver section costs more then the Transmission in a VHF Radio . Surprised, Read More.

 The specifications of greatest value in choosing a VHF set are those that describe the performance of the radio's receiver.

Although many people think that the majority of the cost of the radio is in the transmitter, the receiver accounts for about 75% of the cost. The two main measures of receiver performance are sensitivity and selectivity. It is easy to build a very sensitive receiver. In fact, it is easy to build a too sensitive receiver. Virtually every radio on the market will provide more than sufficient sensitivity (typically 0.30µV). The most significant receiver performance measure is its ability to ensure you to hear only the signal you need to hear and to reject all of the interfering signals that crowd the airwaves. The greater the receiver's selectivity, the greater the cost. How much selectivity you need depends on where you usually use  the radios. Three specifications define how well the receiver will do in ensuring that you hear what you need to hear; adjacent channel selectivity, intermodulation rejection ratio (IM) and spurious response rejection ratio. For a radio used in an unpopulated or radio interference free area ratings of at least 60db for each of these specifications will be satisfactory. If your area of operation  is near a large city or in a busy area you will want a receiver whose performance for these measures is at least 70 db. To ensure the best receiver performance buy a set whose specifications are 80 db for IM and 70 db for the other two measures.

Many of the other specifications are in the category of nice-to-have or bells-and-whistles. Radios will offer differing types of channel scanning, automatically listening to all or selected groups of channels and stopping the scan so you can hear what is being said on the first active channel found. Building the scanning capability into the radio is not at all expensive and in addition is usually of limited value.

They come equipped with a choice of transmitter power: one (1) watt for very close communication (approximately one mile or less) or twenty five (25) watts for extended communication (up to approximately twenty five miles). All of this is done usually with the push of a button. 

Important Specs of a typical  Fixed VHF radio.

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