simply RED
May 24th, 2006, 01:42 PM
VHF
100 - 1500 MHz is the most useful part of the VHF. 30-100 has majour drawbacks. Apparature for 30-100 is hardly available also it is difficult to make good mobile antennas for the range.
Propagation:
VHF propagates in the "visible area". Long propagations are very rare and useless for communication.
(approximated for urban areas)
1-5 W "gummy" (low quality) handheld antenna = 2-3 km
1-5 W high quality handheld antenna = 3-4 km
1-5 W high quality handheld antenna (30 meters above the ground) = up to 20 km
1-5 W groundpalne antenna (ground level) = 4-8 km
1-5 W groundplane (30m above ground) = 20-30 km
5-50 W "3*5/8" antenna (30 m above ground) = 30-100 km
50 W 5-10 element yaggie (100 m above ground) = up to 300 km
Apparature:
High quality handheld transcievers are available on the market (for 120- 175 MHz for example). The handheld transciever is the best choice here. It easily becomes mobile station by conecting to the power supply and antenna of a car.
When buying handheld transciever be on guard.
It should have:
- long transmitting range (at least 30 MHz - from 130 - 160 for example)
- option for external power supply
- good display
- detachable antenna with BNC
- DTMF encodind
Antennas used by enthusiasts are usually home made. Groundplane is the easiest - yet well working antenna for both 144 and 430. Yaggie is a standard choice for long distances. There are complicated systems like "yaggies in phase" or "mirth" that are seldom used.
Modulation:
FM is used here with 5 kHz deviation. The other good thing is digital modulation (on FM or SSB or directly).
Callsigns:
Usually:
Everyone in the VHF network has individual callsign. For example police or fire brigade work with numbers. "175 calling 12". Radio amateours used combination of symbols and numbers (like "LZ1KIL").
Repaters:
There are repeaters used by some amateours and majority of radio pirates. 144 - 146 and the upper band. See information in the internet or from some amateour or pirate for the frequencies of the repeaters. May be useful.
Practical issues:
There is generally no problem to transmit in the range of 144- 146 MHz. The only thing to worry about is beeing listened to :) . For this case, transmit near this range. For example 146.10. Or use some kind of encoding.
Scan and map the whole range your radio uses. Chose non - populated frequencies.
DTMF encoding is the simplest way to turn the radio into remote detonator. When the DTMF unlocking signal is received, a signal is send to the speaker. Cables are conected from the external speaker connector to an amplifier, which turns on a rellay - and the relay short circuits the detonator.
Practice is the key to effective radio communication. Without practice noone is able to work well "on air"...
100 - 1500 MHz is the most useful part of the VHF. 30-100 has majour drawbacks. Apparature for 30-100 is hardly available also it is difficult to make good mobile antennas for the range.
Propagation:
VHF propagates in the "visible area". Long propagations are very rare and useless for communication.
(approximated for urban areas)
1-5 W "gummy" (low quality) handheld antenna = 2-3 km
1-5 W high quality handheld antenna = 3-4 km
1-5 W high quality handheld antenna (30 meters above the ground) = up to 20 km
1-5 W groundpalne antenna (ground level) = 4-8 km
1-5 W groundplane (30m above ground) = 20-30 km
5-50 W "3*5/8" antenna (30 m above ground) = 30-100 km
50 W 5-10 element yaggie (100 m above ground) = up to 300 km
Apparature:
High quality handheld transcievers are available on the market (for 120- 175 MHz for example). The handheld transciever is the best choice here. It easily becomes mobile station by conecting to the power supply and antenna of a car.
When buying handheld transciever be on guard.
It should have:
- long transmitting range (at least 30 MHz - from 130 - 160 for example)
- option for external power supply
- good display
- detachable antenna with BNC
- DTMF encodind
Antennas used by enthusiasts are usually home made. Groundplane is the easiest - yet well working antenna for both 144 and 430. Yaggie is a standard choice for long distances. There are complicated systems like "yaggies in phase" or "mirth" that are seldom used.
Modulation:
FM is used here with 5 kHz deviation. The other good thing is digital modulation (on FM or SSB or directly).
Callsigns:
Usually:
Everyone in the VHF network has individual callsign. For example police or fire brigade work with numbers. "175 calling 12". Radio amateours used combination of symbols and numbers (like "LZ1KIL").
Repaters:
There are repeaters used by some amateours and majority of radio pirates. 144 - 146 and the upper band. See information in the internet or from some amateour or pirate for the frequencies of the repeaters. May be useful.
Practical issues:
There is generally no problem to transmit in the range of 144- 146 MHz. The only thing to worry about is beeing listened to :) . For this case, transmit near this range. For example 146.10. Or use some kind of encoding.
Scan and map the whole range your radio uses. Chose non - populated frequencies.
DTMF encoding is the simplest way to turn the radio into remote detonator. When the DTMF unlocking signal is received, a signal is send to the speaker. Cables are conected from the external speaker connector to an amplifier, which turns on a rellay - and the relay short circuits the detonator.
Practice is the key to effective radio communication. Without practice noone is able to work well "on air"...