FAQ
1. HOW FAR DOES A VIDEO TRANSMITTER WORK?
The range of any given video transmitter can vary greatly with the type of terraine that it is used in. Because of this, most transmitter distance ratings are under "line of sight" conditions. Unfortunately most video transmitter use is urban in or among buildings and so a good quality 10mW video transmitter with a rubber duck antenna can expect the following results: line of sight 500 metres rural, but out of sight 250 metres urban brick/wood construction 30 metres modern steel frame building 20 metres
2. WHY IS THE TRANSMISSION DISTANCE SO MUCH LESS IN BUILDINGS?
Materials such as brick and concrete absorb RF transmissions and metal can completely block them.
3. HOW IMPORTANT ARE ANTENNAS?
Using an antenna which is correctly matched to the transmitter and receiver can extend transmission distances by up to 20%.
TX ------------------- RX at 1394MHZ "path loss" is 100dB for 1.6km (1 mile) if TX=20mW & RX = RV2000 13dBM NF 6dB
- Case 1: When antenna used at the TX has gain of 2.14dB (Coaxial Dipole) and that at the RX has 17dB (Hand-held LQ), this will give a just-breaking picture at 1.6km.
- Case 2: Changing the TX antenna to a Patch will further increase the range to 2.5km, over a similar uncluttered path.
- Case 3: Changing the TX antenna to another Hand-held (or Mast-mounted) will further invrease the range to 9km.
- Case 4: With the Coaxial Dipole on the TX and with a Patch on the RX, the range will be reduced to around 600m.
- Case 5: For a solid picture, these ranges will be considerably reduced especially under cluttered conditions - very likely to one-tenth of the range - i.e 160m in Case 1.
- Case 6: If the TX power is raised to 1W, then the ranges will be expected to rise by a little more than double.
4. WHY ARE SOME TRANSMITTERS MORE EXPENSIVE THAN OTHERS FOR THE SAME AMOUNT OF POWER?
There are several common reasons: some manufacturers are optimistic in their measurements transmitters which are crystal controlled or synthesised and incorporate a high quality voltage control oscillator are expensive to build but inherently stable and reliable a well-designed transmitter is more efficient in that less power is wasted on harmonics and other off-frequency transmissions picture quality, sound quality and build quality are also part of the overall cost.
5. WHY ARE SOME VIDEO RECEIVERS MORE EXPENSIVE THAN OTHERS?
quality video receivers have special video filters which optimise picture and colour quality. They also have much more sensitive receiving sections which means that they can pick up video transmissions from greater distances.
6. CAN HIGH QUALITY VIDEO TRANSMITTERS AND RECEIVERS SEND VIDEO SIGNALS FOR LONGER DISTANCES THAN SOME WHICH CLAIM THE SAME OUTPUT POWER?
Yes. Video transmitter/receiver systems which are properly designed and matched will be more efficient transmitters and more sensitive receivers than those without the more costly circuit refinements.
7. CAN HIGH QUALITY VIDEO TRANSMITTERS AND RECEIVERS SEND VIDEO SIGNALS FOR LONGER DISTANCES THAN SOME WHICH CLAIM THE SAME OUTPUT POWER?
High quality video receivers have special video filters which optimise picture and colour quality. They also have much more sensitive receiving sections which means that they can pick up video transmissions from greater distances.
8. WHAT FREQUENCIES CAN I LEGALLY USE WITHOUT A LICENCE?
This varies from country to country. For example, in the UK, the frequencies are: 1. DTI approved MPT 1394 1394MHz up to 500mW 2. DTI approved ES 300/400 2.42.483GHz 10mW
9. DO I HAVE TO HAVE A DTI AND CE APPROVED VIDEO TRANSMITTER AND RECEIVER?
Yes. You or your customers may be liable for penalties and fines if you are caught.
