AM/MW & VHF/FM how far the signal goes?
Posted: Fri Mar 01, 2024 11:38 am
Because the questions come up now and then... "What is the range of this or that transmitter" or "How far will this signal go..."
After 45 years of experiments with transmissions on AM (MW) & FM (VHF/UHF) here are some observations and assessments about transmitter range in my experience:
- FM has the potential to be received further, a) because it's not affected so much by interference, b) because most FM receivers are slightly more sensitive than the AM.
- In practice an AM signal may go further than an FM of equal transmitting power - if all other things are of equal quality - due to the time of the day, landscape and the environment. FM has some "line of sight" restrictions (although that's not absolute) while the AM/MW does not.
- Although one cannot know the range of a particular rig until one tries it there are some "rules of thumb" as baselines, to be used as guides: If one get less range then something could be improved by some change in the complex - transmitter, voltage, grounding, antenna, location, height, frequency etc. If one gets more, one should be happy then!
Example, a nearby RSL station transmits in both AM/MW (1W) and on FM (1-2W). The surrounding area is flat and both antennas are not very high. Reception by car radio on AM is decent even 6 miles away while on FM the signal becomes unintelligible at 3 miles.
During the last 45 years I had the chance to experiment and test low power transmitters on VHF/FM with powers from 50mW to 40 W, on AM/MW (5mW to 80W,) and on UHF (10mW to 0.5W) as well as other bands.
These are the best ranges I got
- FM, homemade transistor based 50-100mW, up to a 100yards with a simple 1ft wire antenna. Up to 300-500 yards with a proper FM dipole antenna at a height of 40ft (at 100-104 MHz). (Car radio)
- FM homemade 20-25W, valve based (EL504). 101-104MHz. Common range in an urban setting 2-3 miles (dipole antenna at a height of 90ft) greatest range recorded, line of sight, 35 miles (QSL reception with good quality). (Home radios)
FM homemade transistor based 1W, 104MHz, dipole antenna at 90ft urban setting 0.5-1 mile, dipole antenna at a height of 180ft countryside, 2-3 miles. (Car radio)
- FM semi-professionally made valve based (EL504) 40W, dipole antenna at 180ft, 15-20 miles depending on terrain. Dipole antenna at 500ft at least 40miles, 104 MHz, over water (sea.) (handheld radio)
- AM, homemade 5mW-50mW, depending on voltage (power,) grounding and antennas, from 1ft to 2 miles. (Car radios)
typical on "clear" channels:
10mW, small wire or telescopic antenna, no grounding 1-5ft. (Good for "broadcasting within a room,) with some grounding 20-30ft.
10mW 5-6ft simple wire antenna, water pipe grounding, 40-60ft. That's the ideal for "broadcasting" around a home.
10mW 20ft simple wire antenna metal railing grounding, 100 yards.
10mW 100ft simple wire antenna, water pipe grounding, 250 yards
10mW to 50mW, 150-200ft inverted L antenna, water pipe grounding, 0.5-2miles (by car radio.)
- AM, semi-professonal, valve based (807) 60-80W, inverted L wire antenna at 180ft (10ft from the ground), water pipes grounding, at least 20-30miles on a clear channel, 1566KHz and 1620KHz (behind mountain too.) (Card radio) No reception beyond 40miles.
- AM, professional exciter PLL 0-20W, (PEP,) inverted L wire antenna at 180ft (10ft from the ground), water pipes grounding, at least 20 miles on a clear channel, 1566KHz and 1620KHz (behind mountains too.) (Car radio)
SW using harmonics of above 10mW, depending on the antenna, telescopic, 20-40yards, wire antenna, from 50 to at least 200 yards.
- CB, various COBRA, EURO etc 1-4W, whip antennas, 0.1-1miles (from within a moving vehicle, never tested them in ideal conditions, as line of sight or from a height).
- Short range homemade CBs (10mW) 100 yards with a telescopic antenna.
- VHF transceiver, ICOM IC-A20 5W, whip antenna 5-10miles.
- UHF, Alan LPD433, 10mW, common range 0.1-1 mile, greatest recorded communication 20 miles, between one walkie-talkie at a plain, and the other 20 miles away at a height of 300ft overlooking the plain.
- UHF PMR446/LPD433 10mW-0.5W, various ALAN, COBRA, ALINCO models, usually 100 yards to 0.5mile inside malls or in the city downtown, up to 3miles (never tested them in ideal conditions, as line of sight from a height).
To summarise the above:
Fo low power transmitters on a clear from interference channel under normal and fair settings (both for transmitter and receiver) one can expect for 10mW 100 - 1000 yards, for 100mW 0.5mile-0.8mile, 0.5 W up to 1mile, for 1W up to 6miles, 4W 8-10 miles, 20W 15miles, 40W 20 miles, 80W 30 miles. Sometimes under ideal transmitting/receiving conditions those figures will be surprisingly greater, while under not ideal conditions (interference, low locations surrounded by obstacles) the figures may be substantially lower...
After 45 years of experiments with transmissions on AM (MW) & FM (VHF/UHF) here are some observations and assessments about transmitter range in my experience:
- FM has the potential to be received further, a) because it's not affected so much by interference, b) because most FM receivers are slightly more sensitive than the AM.
- In practice an AM signal may go further than an FM of equal transmitting power - if all other things are of equal quality - due to the time of the day, landscape and the environment. FM has some "line of sight" restrictions (although that's not absolute) while the AM/MW does not.
- Although one cannot know the range of a particular rig until one tries it there are some "rules of thumb" as baselines, to be used as guides: If one get less range then something could be improved by some change in the complex - transmitter, voltage, grounding, antenna, location, height, frequency etc. If one gets more, one should be happy then!
Example, a nearby RSL station transmits in both AM/MW (1W) and on FM (1-2W). The surrounding area is flat and both antennas are not very high. Reception by car radio on AM is decent even 6 miles away while on FM the signal becomes unintelligible at 3 miles.
During the last 45 years I had the chance to experiment and test low power transmitters on VHF/FM with powers from 50mW to 40 W, on AM/MW (5mW to 80W,) and on UHF (10mW to 0.5W) as well as other bands.
These are the best ranges I got
- FM, homemade transistor based 50-100mW, up to a 100yards with a simple 1ft wire antenna. Up to 300-500 yards with a proper FM dipole antenna at a height of 40ft (at 100-104 MHz). (Car radio)
- FM homemade 20-25W, valve based (EL504). 101-104MHz. Common range in an urban setting 2-3 miles (dipole antenna at a height of 90ft) greatest range recorded, line of sight, 35 miles (QSL reception with good quality). (Home radios)
FM homemade transistor based 1W, 104MHz, dipole antenna at 90ft urban setting 0.5-1 mile, dipole antenna at a height of 180ft countryside, 2-3 miles. (Car radio)
- FM semi-professionally made valve based (EL504) 40W, dipole antenna at 180ft, 15-20 miles depending on terrain. Dipole antenna at 500ft at least 40miles, 104 MHz, over water (sea.) (handheld radio)
- AM, homemade 5mW-50mW, depending on voltage (power,) grounding and antennas, from 1ft to 2 miles. (Car radios)
typical on "clear" channels:
10mW, small wire or telescopic antenna, no grounding 1-5ft. (Good for "broadcasting within a room,) with some grounding 20-30ft.
10mW 5-6ft simple wire antenna, water pipe grounding, 40-60ft. That's the ideal for "broadcasting" around a home.
10mW 20ft simple wire antenna metal railing grounding, 100 yards.
10mW 100ft simple wire antenna, water pipe grounding, 250 yards
10mW to 50mW, 150-200ft inverted L antenna, water pipe grounding, 0.5-2miles (by car radio.)
- AM, semi-professonal, valve based (807) 60-80W, inverted L wire antenna at 180ft (10ft from the ground), water pipes grounding, at least 20-30miles on a clear channel, 1566KHz and 1620KHz (behind mountain too.) (Card radio) No reception beyond 40miles.
- AM, professional exciter PLL 0-20W, (PEP,) inverted L wire antenna at 180ft (10ft from the ground), water pipes grounding, at least 20 miles on a clear channel, 1566KHz and 1620KHz (behind mountains too.) (Car radio)
SW using harmonics of above 10mW, depending on the antenna, telescopic, 20-40yards, wire antenna, from 50 to at least 200 yards.
- CB, various COBRA, EURO etc 1-4W, whip antennas, 0.1-1miles (from within a moving vehicle, never tested them in ideal conditions, as line of sight or from a height).
- Short range homemade CBs (10mW) 100 yards with a telescopic antenna.
- VHF transceiver, ICOM IC-A20 5W, whip antenna 5-10miles.
- UHF, Alan LPD433, 10mW, common range 0.1-1 mile, greatest recorded communication 20 miles, between one walkie-talkie at a plain, and the other 20 miles away at a height of 300ft overlooking the plain.
- UHF PMR446/LPD433 10mW-0.5W, various ALAN, COBRA, ALINCO models, usually 100 yards to 0.5mile inside malls or in the city downtown, up to 3miles (never tested them in ideal conditions, as line of sight from a height).
To summarise the above:
Fo low power transmitters on a clear from interference channel under normal and fair settings (both for transmitter and receiver) one can expect for 10mW 100 - 1000 yards, for 100mW 0.5mile-0.8mile, 0.5 W up to 1mile, for 1W up to 6miles, 4W 8-10 miles, 20W 15miles, 40W 20 miles, 80W 30 miles. Sometimes under ideal transmitting/receiving conditions those figures will be surprisingly greater, while under not ideal conditions (interference, low locations surrounded by obstacles) the figures may be substantially lower...