Frequency band - what is it?

RECEIVER FREQUENCY BAND

When ordering tags we need to know the frequency band of your receiver. If you do not have a receiver then you will have to decide what frequency band to use before you order it.

Different receivers have different band coverage, though most are available on all the frequencies commonly used for radio-tracking. Our new Sika receiver overcomes this problem by covering the range 138.000 MHz - 173.999 MHz. However, most receivers only cover 1 MHz, e.g. 142.000 - 142.999 MHz or 150.500 - 151.500 MHz.

The band coverage has implications for the number of tags that can be used on a single study site. If all the tags are to be on distinct frequencies, they should be spaced by about 10 kHz. This means that a receiver covering 150 kHz can be used to track up to 15 tags. A receiver covering 1 MHz, as most frequency synthesis receivers do nowadays, has enough band for up to 100 tags.

When considering what frequency band a new receiver should cover, the following considerations apply;

1) If possible, you should use the frequency allocated to radio-tracking (or low power radio devices) in the country or region where the equipment will be used. To find out more information about radio-frequency allocations in your part of the world, please check the Low Power Radio Association’s website for relevant wesbites with contact information.

2) If no official frequency is allocated, a wider choice is available. However, the frequency band chosen must be one that is not in use for other purposes. Most other users of the radio spectrum operate very high power transmitters that will completely swamp the signals from radio tags. Your tags are very unlikely to upset other users, but the signals from powerful transmitters can have a profound impact on your tracking and your ears ! It is particularly important to avoid frequencies used for communications and public broadcasting.

When you have a free choice of frequency band, apart from the constraints mentioned above, you should choose one of the bands commonly used around the world for radio-tracking (these are 142, 148, 149, 150, 151, 165, 173, 216 or 230 MHz). If you are preparing a foreign expedition, you should give preference to the frequency allocated to tracking in your native country, so that when the expedition is over, the receiving equipment can be used at home without modification.

3) Some properties of radio propagation also affect the choice of frequency. High frequencies are attenuated by vegetation to a greater degree than lower ones. So, for example, lower frequencies are preferred for tracking in rainforest. On the other hand, at low frequencies, tracking antennas are larger and rather unwieldy. If you are tracking in densely vegetated habitats, you should consider using an antenna with flexible elements.