Mini FM Radio station...need more range

[sram]

Hi folks. We have this mini radio station running for purposes I don't really need to mention here. We are using a FM transmiter which has according to its specs a maximum output power of ~340 watts. They have it set at about 282, and according to the users it covers 8 km radius. Now, I'm not into this, but I have been given the task of increasing this range. I don't remember the antenna gain out of the top of my head. They want to increase it to 100 km!

So, what are my options? Get a more powerful transmiter with the approriate gain antenna and fix it in a high enough place and call it a day?

The system they are using is MIZAR FM system.


Thanks

 

[audioguru]

The transmitter has excellent spec's but has very low power for a radio station.
A directional antenna might allow it to reach 100km but only in one narrow direction.

If the transmitter and its antenna are mounted on top of a mountain then its range will be increased a little.

 

[audioguru]

I forgot to say the range also depends on the sensitivity of the radio.
A garbage "radio" from The Dollar Store might pickup the transmitter across the street.
A cheap Sony Walkman radio might pickup the transmitter 1km away.
A very sensitive hi-fi tuner or car radio might pickup the transmitter 10km away.

 

[sram]

I myself forgot that FM is LOS communications, so no matter how much power you put into the signal, it will still be affected by the spherical shape of the earth. What do radio stations use for FM channels? What typical power? how long does their signal reach? Do they use repeators? I don't want the signal to travel only in one direction.........I want to use an omni antenna.

Should I switch to AM since it bounces back from the ionsphere?

 

[Nigel Goodwin]

Hi folks. We have this mini radio station running for purposes I don't really need to mention here. We are using a FM transmiter which has according to its specs a maximum output power of ~340 watts. They have it set at about 282, and according to the users it covers 8 km radius. Now, I'm not into this, but I have been given the task of increasing this range. I don't remember the antenna gain out of the top of my head. They want to increase it to 100 km!

So, what are my options? Get a more powerful transmiter with the approriate gain antenna and fix it in a high enough place and call it a day?

The system they are using is MIZAR FM system.

Essentially (and crudely) you need to increase the power ten times to double the range.

However, any changes will require your licence changing - and I would have thought the chances of been granted a licence for such a huge FM station is goijngto be pretty slim. As suggested, VHF FM is LOS, so to get those kinds of distances you need a tall aerial as well.

 

[RadioRon]

As Nigel says, a crude rule of thumb to start with is that you need to add about 3 zeroes to the amount of watts you are putting out to get to 80 km if you coverage now is 8km. However, looking at examples of existing FM stations, I notice that their coverage is often around 80km with about 50,000 watts (this is to the 60dBu contour which defines reliable reception on almost any receiver). However, the distance is strongly affected by the height of the antenna, at least for the first few hundred feet above ground. So, with the right antenna height, perhaps you can get away with somewhere between 10,000 watts and 100,000 watts, rather than the rule of thumb 340,000 watts.

AM may not be effective because the MW bands do not propagate well with ionospheric bounce. Most of the propagation at these low frequencies is ground wave. And besides, a good AM antenna has to be fairly large, like a 100 foot tower for example. Based on examples and assuming 1MHz frequency, you would need perhaps 3000 watts to a 240 foot tower to reach 80Km.

I suggest that if you are only reaching 8km with 340 watts, then perhaps your antenna is not so good.

 

[audioguru]

Haven't you heard that an AM radio station sounds awful but an FM radio station sounds almost perfect??
I think AM tried to do stereo a long time ago but FM radio stations are in stereo.

 

[Boncuk]

AM may not be effective because the MW bands do not propagate well with ionospheric bounce. Most of the propagation at these low frequencies is ground wave. And besides, a good AM antenna has to be fairly large, like a 100 foot tower for example. I suggest that if you are only reaching 8km with 340 watts, then perhaps your antenna is not so good.

The well known radio ham "W3DZZ-Antenna" has a length of 468.75m as an open dipole with a balun in the center. If it is suspended 100m above ground level you can have dx-connections (great distance) on the 80m band.

Local FM-transmitters power out between 1 and 10KW of RF-power and their range is usually between 10 to 15km.

I suggest the OP moves to Singapore and mounts his antenna on the world's highest tower of 955m height with a power output of 100 to 500KW.

Boncuk

 

[sram]

The well known radio ham "W3DZZ-Antenna" has a length of 468.75m as an open dipole with a balun in the center. If it is suspended 100m above ground level you can have dx-connections (great distance) on the 80m band.

Local FM-transmitters power out between 1 and 10KW of RF-power and their range is usually between 10 to 15km.

I suggest the OP moves to Singapore and mounts his antenna on the world's highest tower of 955m height with a power output of 100 to 500KW.

Boncuk

Correction: World's tallest tower is in Dubai, UAE. List of tallest buildings and structures in the world - Wikipedia, the free encyclopedia

Anyways, this is a serious issue on my part, so cut the sarcasm^_^. Hmmmmm, I'll just do the reasonable, so help me do that! I found this website and it seems like they have what I want. If 100km is not easily achieavable, then I guess 50km will suffice. How come this FM transmitter we are using reaches about 10km with only 282 transmitt power, and you are saying local fm transmitters tx power ranges from 1k to 10k watts and they can only achieve 15km? Can you please explain?

Like I said, they are now using 282 watts and the antenna is only 7 meters high I think. So if I get something like this :

**broken link removed**

with a good high antenna, I'll reach 50 km .............right?

 

[Nigel Goodwin]

Correction: World's tallest tower is in Dubai, UAE. List of tallest buildings and structures in the world - Wikipedia, the free encyclopedia

Anyways, this is a serious issue on my part, so cut the sarcasm^_^. Hmmmmm, I'll just do the reasonable, so help me do that! I found this website and it seems like they have what I want. If 100km is not easily achieavable, then I guess 50km will suffice. How come this FM transmitter we are using reaches about 10km with only 282 transmitt power, and you are saying local fm transmitters tx power ranges from 1k to 10k watts and they can only achieve 15km? Can you please explain?

Like I said, they are now using 282 watts and the antenna is only 7 meters high I think. So if I get something like this :

**broken link removed**

with a good high antenna, I'll reach 50 km .............right?

Try it and see? - a lot depends on what you mean by 'reach' - what sort of quality are you expecting?.

You also still appear to be totally ignoring licence restrictions - do you have a licence at all?, and if you do, does it allow you to use higher powers? (very unlikely).

 

[sram]

Try it and see? - a lot depends on what you mean by 'reach' - what sort of quality are you expecting?.

You also still appear to be totally ignoring licence restrictions - do you have a licence at all?, and if you do, does it allow you to use higher powers? (very unlikely).

No No, not ignoring anything. That is being taken care of by other parties. I'm taking care of the technical stuff. The technical solution will get adjusted as per the regulations.

 

[Nigel Goodwin]

No No, not ignoring anything. That is being taken care of by other parties. I'm taking care of the technical stuff. The technical solution will get adjusted as per the regulations.

You're going about it the wrong way - you need to see what the licence will allow, presumably it strictly limits the allowed power (and aerial system).

 

[sram]

You're going about it the wrong way - you need to see what the licence will allow, presumably it strictly limits the allowed power (and aerial system).

the wrong way? Why? I'm not buying anything yet, just looking, asking, and searching. No action is being taken. The license will be obtained from a government and given to another government. It is high level so I don't think there will be a problem.

 

[JimB]

Anyways, this is a serious issue on my part, so cut the sarcasm^_^. Hmmmmm, I'll just do the reasonable, so help me do that! I found this website and it seems like they have what I want. If 100km is not easily achieavable, then I guess 50km will suffice. How come this FM transmitter we are using reaches about 10km with only 282 transmitt power, and you are saying local fm transmitters tx power ranges from 1k to 10k watts and they can only achieve 15km? Can you please explain?

Like I said, they are now using 282 watts and the antenna is only 7 meters high I think. So if I get something like this :

**broken link removed**

with a good high antenna, I'll reach 50 km .............right?

I have sarcasm mode disabled for this post so here goes:

Discussion of what range can be obtained is rather pointless without an understanding of the local terrain.
You say the current antenna is 7m high, ok, but if your transmitter station is in a valley surrounded by hills, then your range will be restricted by the hills.
In such a situation, if you could move the transmitter station to the top of a hill, the range would increase considerably. How much it would increase would depend on the height of your chosen site and the other hills in the area.
If your current site is on a flat plane, your best option is to get a big mast and mount your antenna on top of it.

There are software which can predict the usefull radio coverage if you input your location map, details of transmitter and its antenna, and details of receiver and antenna.
Sorry I dont have a link to such software as I type here. I will see if I can find a link a bit later.

You dont give details of your location and seem to be working on behalf of a well funded organisation, are you stuck in a sandpit somewere?

JimB


OK, for radio coverage prediction software,have a look here:
**broken link removed**
It is rather involved and obscure to use, especially the first time or two! But it does work in a reasonable manner.

 

[Nigel Goodwin]

the wrong way? Why? I'm not buying anything yet, just looking, asking, and searching. No action is being taken. The license will be obtained from a government and given to another government. It is high level so I don't think there will be a problem.

You don't mention what country you're from, but in the UK you would be allocated a frequency, permissable power, and presumably permissable aerial array.

These things are critical to your licence conditions, and it's unlikely they would be prepared to increase them.

 

[sram]

Jimb, I wonder how your post would have been if sarcasm mode was on!

>>>>You say the current antenna is 7m high, ok, but if your transmitter station is in a valley surrounded by hills, then your range will be restricted by the hills.
In such a situation, if you could move the transmitter station to the top of a hill, the range would increase considerably. How much it would increase would depend on the height of your chosen site and the other hills in the area.
If your current site is on a flat plane, your best option is to get a big mast and mount your antenna on top of it.
>>>>>

It doesn't take a genius to understand that I think. It is an open area. I'll try my best to put the antenna on a communications tower. I thank you very much for your input. Can you recommend me a good long mast to put the antenna on?

 

[sram]

OK, for radio coverage prediction software,have a look here:
**broken link removed**
It is rather involved and obscure to use, especially the first time or two! But it does work in a reasonable manner.

Okay, I'll see how that goes. Thanks.

 

[JimB]

Can you recommend me a good long mast to put the antenna on?

Have a look at these guys:
ROHN Towers, Poles and Antennas | ROHN Products, LLC

JimB

 

[RadioRon]

We have touched on a number of key variables including tx power and terrain, but some additional attention should be paid to the antenna system as well. It is common in omnidirectionial applications to stack elements into vertically stacked, driven arrays to maximize gain towards the horizon. This additional gain helps a great deal, but there is a limit to how far you can go with this. For example, it is not unusual to achieve array factor gains of 9 dB, most often done by stacking dipoles. Properly phased, going from one to two dipoles will double the gain, hence will add 3 dB. Doubling the gain again by going to four dipoles will deliver a total array gain of 6dB. Another four dipoles, for total of eight will give you 9dB of gain over and above the gain of each individual element. If dipoles are used, your element gain will be roughly 2 dBi, so total gain will be about 11 dBi if losses are minimized. We run into practical limitations when trying to double this again to 16 elements so many stations stop at fewer than 16 elements in practice. The key point here is that it is much cheaper to add antenna gain than it is to add transmitter power. So, you should be maximizing your antenna gain first, plus your antenna placement (location and height above average terrain) before deciding on what your transmit power should be.

It is common practice to use circular, vertical and horizontal polarizations in FM broadcast. Circular has been popular because many stationary FM receivers have horizontally polarized antennas, while most car receivers use vertically polarized antennas. To service all of the listeners, circular polarization is a good compromise as it costs everyone -3dB of link budget but suffers no polarization mismatch losses other than that. However, vertical polarization is lower cost and services car radios well so may be the more common setup. You get to pick which polarization makes the most sense for your listeners.

I also want to mention that in all broadcast sitations of this magnitude, we are talking about a significant support structure (tower) to hold the antennas up. Towers of this size require proper engineering of anchors and foundation, structure, wind loading, earthquake resistance, corrosion protection (rust and electrolytic problems), lightning surge management, and aviation anti-collision lighting to name a few that I could remember. It would be wise to involve an experienced structural engineer with communications tower experience to deal with these issues. I have only been involved with these issues in designing grounding and lightning protection and even this one little topic is surprisingly complex. Get help if you are not competent in these areas.

Back on the topic of transmitter power, I had been looking at examples of FM stations in the USA, which have publicly available coverage contours and transmitter power specs. What they don't mention is that I think their transmitter power, for example 50,000 watts, is not the transmitter output power but rather the effective radiated power or effective isotropic radiated power. So, if we find through examples that 50,000 watts has provided good coverage for many FM stations in America out to at least 80 Km, and if we plan to use an antenna system with 10dB of gain, this would suggest that a transmitter with 5000 watts of output power is enough. Using a propagation analysis tool, like Radio Mobile, is a good way to test these examples because it will force you to develop a complete link budget including transmitter power, antenna gain, transmission line losses, and terrain losses too. We may find that 10,000 watts is overkill. Focus your attention and some money on the antenna system. Beware that in broadcast applications, the exact receiver antenna gain is not know, so broadcast engineers design to a goal of a particular field strength. In the US, for example, the 70 and 60 dBu contours define very good reception by most listeners, while field strengths of 54 dBu and lower may provide less than clear reception on the average consumer radio. You get to choose what level of field strength is good enough for your listeners. Alternatively, you could assume a receiver antenna gain (I suggest -6dBi) and receiver antenna height (suggested: 1m) for your analysis.

By the way, here is another estimation tool to check radius of coverage for flat topography: https://www.fcc.gov/mb/audio/bickel/fmpower.html
It is, unfortunately, somewhat USA -centric but it might be helpful as it is very easy to use.


This company may be helpful: https://www.electro-tech-online.com/custompdfs/2010/12/hpbcast.pdf

 

[sram]

I contacted this National Transmitter company and told them what I need and they send me this 8700 $ quotation and this is the Transmitter:
**broken link removed**

Uploaded with ImageShack.us

And they claimed it will do 50 mile range. But they didn't send me any details about the antenna system. How does that thing look? I sent them an email but they didn't reply yet.