AM/MW & VHF/FM how far the signal goes?

[outis]

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...

[fmuser877]

think my problem is earth I have no water pipe small garden wish I could find another place to test it but don't know any one.

[Albert H]

I solved my earthing problem by burying a galvanised dustbin (later I added a second one for even more area contact with the ground). This is cheap and easy, and a galvanised dustbin won't rot!

In response to "Outis"'s extensive posting, I'll just point out that VHF signals always go to the horizon. The transmitter power just determines the signal to noise ratio at range.

We've all had freaky results due to tropospheric ducts ( I got from London to Morocco using 2½ Watts each way on 145 MHz), but the general rule at VHF is that the higher the transmitter power, and the higher the antenna (to extend the effective horizon), the further away the signal will remain usable.

I still fail to understand those people that Roger used to call "the Hackney 'mitter men" - they'll get a 200 - 500 Watt rig and then run it into a dipole! I remember demonstrating to the operator of a "London-wide" station that my 50 Watt test transmitter into my aerial went much further than his 250 Watt rig into a couple of stacked dipoles from adjacent sites.

Useful range can be wildly variable - my little 8 Watt carrier MW rigs went from East London to Cambridge and Reading in the daytime! At night, we couldn't hear them 200 m from the site.

[outis]

think my problem is earth I have no water pipe small garden wish I could find another place to test it but don't know any one.

Depends what you seek to achieve. But when it comes to range, grounding is a BIG make or break factor. Even for house "broadcasting" that same little low power AM (5-10mW) that without grounding (6ft antenna) wouldn't go further than a foot, with grounding (to a defunct metallic gas pipe) it really "took of" - I'm getting now 40 to 60ft. Nothing else changed!
No water pipe? Be creative! A radiator pipe will do, any kind of metal rod or piping will do. Recently I was at a place with nothing for grounding. I took a metal camping tent peg, connected a wire of a few feet to the peg and tapped it in the ground and had (for the same 10mW set up, 10ft antenna) "magically" transform the range from 10ft to 60yards.
So no matter how small is your garden a metallic tent peg in the ground will do. Perhaps not ideal but certainly effective at the end.
As for space for the antenna, I have tried (same set up and gas pipe grounding) an indoor "long" wire (30ft). It gave me 100ft, and stopped using it because it was going well beyond the property. In the past such a setup gave me 200yards (grounding to heating pipes). I fed that antenna/grounding set up from an AM PLL 0-20W at its lowest for the SWR tuner antenna setting and got too much range (beyond 300 yards, so I disconnected it!)

[radium98]

Is the AM wave propagate in day better then in night or i am wrong understanding ? i know that is goes up to the ionosphere and get back in fading so the only good thing this that noise caoul not or barely heard on the receiver , but the audio quality is nostalgic .

[outis]

Is the AM wave propagate in day better then in night or i am wrong understanding ? i know that is goes up to the ionosphere and get back in fading so the only good thing this that noise caoul not or barely heard on the receiver , but the audio quality is nostalgic .

Daylight AM propagation is normal, quite like FM - but better in the sense it can go behind hills and mountains and worse reception in the sense that inside houses and buildings there may be strong interference from computers, monitors, laptops, TVs etc.
Nighttime it gets interesting. Theoretically the signal goes further, much farther than FM, but every station's signal goes further, meaning that a Hungarian station at 1188KHz that no one can hear in the morning, so you think the frequency is empty, will come strong in the UK, and any low power station from 1179-1197 may suffer from interference and whistles, and if you are on 1188... the Hungarian 300KW will squash anything less than 60W and even those more powerful will see their range reduced from a potentially 30 miles to 3...
On the other hand if you have power (100W-400W or more) and a fairly clear channel (no really clear exists) the 50 miles daylight range can become 200 and more in the night. Just make sure that there are no Spanish stations near your frequency.
Nowadays, with the band emptying there are good frequencies to choose from.
The quality can be "nostalgic" (meaning bad?) but it can be excellent and FM-like with the right transmitter and the right radio receiver.

[87to108]

Daylight AM propagation is normal, quite like FM - but better in the sense it can go behind hills and mountains and worse reception in the sense that inside houses and buildings there may be strong interference from computers, monitors, laptops, TVs etc.

steel framed buildings will have a worse effect to MW/LW inside the building than FM/DAB/mobile (the latter can get in through windows etc to a better extent)

its also notable that MW will travel a lot better across sea water than land. If transmitting from a headland (or offshore!) you will have excellent coverage of places along the coast on a sea path

Even reception of distant inland stations during daytime (when its groundwave only, no or minimal skywave) get a boost in strength by being right beside the sea (even though the signal is not coming across the sea). Try tuning around MW the next time at a beach

[Gigahertz]

I still fail to understand those people that Roger used to call "the Hackney 'mitter men" - they'll get a 200 - 500 Watt rig and then run it into a dipole! I remember demonstrating to the operator of a "London-wide" station that my 50 Watt test transmitter into my aerial went much further than his 250 Watt rig into a couple of stacked dipoles from adjacent sites.

Didn't OFCOM do a presentation on this many years ago

[Albert H]

Not to my knowledge.

The cheapest power amplifier is often just a better antenna!

[radium98]

Thank you outis . I would like one day to build a 25w just to pleasure myself , as i never dream to build one with transistor . i found one of the czh rep , and by the way i am so far from spanish etc... problem will be filter and aerial , i have no garden here .

[outis]

Thank you outis . I would like one day to build a 25w just to pleasure myself , as i never dream to build one with transistor . i found one of the czh rep , and by the way i am so far from spanish etc... problem will be filter and aerial , i have no garden here .

basically the one-transistor helps as "proof of concept" and allows experimentation with antennas and groundings, and directionality of signal. Or, as I use it to send content to my vintage radios. To filter the signal is not necessary in such a low power case, but again one can experiment. 25W can be heard quite far with the right antenna, but the wrong antenna can damage it unless it's got SWR protection. In my one-transistor solution case no SWR protection is needed.

[Albert H]

If you're going to build a 25 Watt AM transmitter, you'll find that FET output is the best way to go. Luckily, modern FETs are very robust and can withstand mismatches without self-destruction. The negative temperature coefficient characteristic of FETs ensures that thermal runaway never happens.

[radium98]

If you're going to build a 25 Watt AM transmitter, you'll find that FET output is the best way to go. Luckily, modern FETs are very robust and can withstand mismatches without self-destruction. The negative temperature coefficient characteristic of FETs ensures that thermal runaway never happens.

feedback is welcome , Thanks .