Frequency of operation
Often there is not a choice over operating frequency. In most countries frequency allocations are very limited, by way of example in Europe there is only
In order to generalise the choice of frequency should be based upon the distance of intended operation, power supply constraints, data rate, duty cycle, attenuation, portability (antenna size) and the presence of other users. The following table is produced to assist your choice:-
| VHF (10mW) | UHF (10mW) | UHF (500mW) | SHF (5mW) | SHF |
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| (500mW)* |
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| * |
Free Space Transmission | 5 - 10km | ||||
range |
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Industrial installation | |||||
In large buildings |
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Penetration through | ********** | **** | ****** | * | ** |
concrete walls |
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Ability to bend/ defract | ********** | ****** | ****** | ** | ** |
around obstructions |
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Antenna size (dipole) | 43cm | 17cm | 17cm | 8cm | 8cm |
Potential users in adjacent | Message pagers | Radio | Radio | CT2 | CT2 |
channels | Radio Microphones | Amateur on | Amateurs on | Mobile | Mobile |
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| 433MHz | 433MHz | telephones | Telephone |
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| Message |
| s |
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| Pages on |
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| 458MHz and |
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| TETRA on |
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| |
Transmission efficiency | ********** | **** | **** | *** | *** |
For battery operation |
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Relative cost | *** | ***** | ***** | ******* | ****** |
R.F path Surveys
The only certain way of determining the suitability of a communication channel is to conduct a radio path survey and spectrum scan.
The spectrum scan is something normally conducted prior to ordering a system. Normally this requires the use of a good quality scanning receiver such as an ICOM 8500 and a broadband antenna. Failure to use a quality scanner may result in signals being missed if channel resolution is too low and false signals being detected if
When scanning, both the desired and adjacent channels should be checked for signals. As transmissions may be intermittent it is important to take time with the scan, stopping for as long as possible on each channel and looking for at least
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