FM range question - coastal mountainous terrain

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Deep Thought
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Re: FM range question - coastal mountainous terrain

Post by Deep Thought » Mon Nov 13, 2017 5:27 pm

dicky96 wrote:
Mon Nov 13, 2017 2:33 pm
Could you be so kind as to do that again for say 4kW in the same location, for 4 antenna bays instead of two, and for both those combined 4Kw + 4 bays?
Mr. Fry will probably answer you directly, but as a practical matter the number of bays is irrelevant, and the increase from 1 to 4 KW will just double (+ 6 dB) the signal levels, which is not enough to get past a major terrain obstruction.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

dicky96
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Re: FM range question - coastal mountainous terrain

Post by dicky96 » Tue Nov 14, 2017 4:35 am

Thanks for the reply

I was asking as the guy who originally owned the station (my partner now) is already convinced that increasing the power, even to 2kW, will fix the PDI problem. I honestly didn't know enough to comment on that, other than every 3dB doubles the signal level. So I googled around and found this

'To calculate the FM transmission range of an omni-directional antenna at 60 to 70 feet in height. A logarithmic formula is used to calculate the loss of a signal strength over a set distance. The basic formula is 10n * log10 (d) + C, where d is the distance of the transmission, n is the path loss exponent and C is a constant. For a broadcast of 6 watts, the transmission range will be 3 miles. At 15 watts, the range increases to 5 miles, at 40 watts to 10 miles and at 100 watts to 15 miles. The general rule of thumb is it will take four times the power to double the transmission distance.'
https://itstillworks.com/12439428/how-t ... nsmissions

But after joining this forum and reading the replies on here from you helpful guys I admit I am already convinced this does not apply to our situation. I hope to show him the charts from here to say 'look, this is what would happen with 4kW/more bays at the current location'. That is much better than learning the hard way!

I would be interested though to see how much of the blue 45-60 dBuv area turns to light red 60-70 dBuv. There is no way of knowing how much of that blue area is already 54-59dB

Also what dbuv level is needed for good reception of music?

Rich.

R. Fry
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Re: FM range question - coastal mountainous terrain

Post by R. Fry » Tue Nov 14, 2017 9:01 am

dicky96 wrote:
Tue Nov 14, 2017 4:35 am
... I googled around and found this: https://itstillworks.com/12439428/how-t ... nsmissions
Generally useful, but misses a lot of specifics.
I would be interested though to see how much of the blue 45-60 dBuv area turns to light red 60-70 dBuv. There is no way of knowing how much of that blue area is already 54-59dB.
The first graphic below shows the L-R coverage areas when using a 4 kW tx with a 4-bay transmit antenna similar to that shown in your previous pic.

Image

Another consideration in doing this is the increase in radiation near the earth, near the antenna site. It may be getting high enough to cause signal overload of some nearby receivers, at some distances (see graphic below).

Image
Also what dbuv level is needed for good reception of music?
The 45 dBuV/m lower limit for the L-R coverage areas shown in blue convert to a field intensity of about 178 µV/m. Probably in most cases that is high enough to drive an FM receiver into full limiting/quieting, but may also be susceptible to some multipath distortion, or in "picket-fencing" in mobile receivers at some locations.

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Re: FM range question - coastal mountainous terrain

Post by dicky96 » Wed Nov 15, 2017 10:04 am

Thanks everyone for the continued input. Special thanks to R Fry for your time generating those charts

Interesting, I thought from the discussion here that increasing the transmitter to 4kW 4bay wasnt' going to make much difference but it seems that the second chart has light red in most of Maspaolomas/PDI and also extends the light blue to San Agustin & Bahia Feliz which is as far as we would need to cover.

The gap in coverage between El Pajar and Pasito Blanco is not really an issue as this is really wild country and no one lives here

If, as you say, the light blue areas are probably strong enough to fully drive a FM radio then is this suggesting 4Kw/4 bay could do the job?

I was showing these charts to a veteran Ham Radio freind last night who is also an electronics engineer. The same guy who has loaned me the N Type Dummy load. He suggested that using an array of (for example) 2 or 4 x 3 element Yagi instead of our current type of antenna could give us enough range in that direction especially as we are wasting so much power going out to sea and into the uninhabited mountains.

We don't need to get good reception 'behind' us any further than Puerto de Mogan which sits on the coast in front of Lomo Quiebre on that map.

Are the current antenna type we are using really optimal for our requirements? Is there some milage in the idea of using a 4kW transmitter at Puerto Rico after all?

Cheers
Rich

COMMENG
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Re: FM range question - coastal mountainous terrain

Post by COMMENG » Wed Nov 15, 2017 11:03 am

Is there some reason you can't move the transmitting facilities to the Nieves Peak area somewhere along GC 134 (such as the San Bernardo refuge) and increase power to 5kW?

I concur with Deep Thought, your major problem here is obstructions from volcanic landforms with the resulting wave reflections, refraction, etc.

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Re: FM range question - coastal mountainous terrain

Post by R. Fry » Wed Nov 15, 2017 11:28 am

dicky96 wrote:
Wed Nov 15, 2017 10:04 am
... I was showing these charts to a veteran Ham Radio freind last night who is also an electronics engineer. ... He suggested that using an array of (for example) 2 or 4 x 3 element Yagi instead of our current type of antenna could give us enough range in that direction especially as we are wasting so much power going out to sea and into the uninhabited mountains. ...
A Yagi array could give you additional radiated power in some directions at the expense of having less radiated power in other directions. Here is a link to one possibility: http://omb.com/wp-content/uploads/2017/ ... _ING-1.pdf

At this point you might want to make use of a commercial broadcast consultant familiar with current antenna design configurations and their manufacturers, and having specific knowledge of the signal coverage needs of this FM station and the regulatory standards that apply. Those designs/configurations and their coverage capabilities need to be studied with respect to your various requirements, and a decision made.

IMO the choice of FM transmit hardware and the siting details most likely to serve your desired markets is a very complex set of issues that can't be addressed thoroughly/adequately on an Internet forum.

dicky96
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Re: FM range question - coastal mountainous terrain

Post by dicky96 » Wed Nov 15, 2017 3:25 pm

That's a very fair comment Mr Fry and I want to say that I very much appreciate your input to this point - I'm not sure I am totally clear in my mind of the best way to proceed but I am definitely feeling more educated regards the current situation and the options available.

So to yourself and others here who have been helpping me all that I can say is THANK YOU! Now.... where is that 'applause emoticon' when you really need one?

Richard.

dicky96
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Re: FM range question - coastal mountainous terrain

Post by dicky96 » Wed Nov 15, 2017 3:39 pm

COMMENG wrote:
Wed Nov 15, 2017 11:03 am
Is there some reason you can't move the transmitting facilities to the Nieves Peak area somewhere along GC 134 (such as the San Bernardo refuge) and increase power to 5kW?

I concur with Deep Thought, your major problem here is obstructions from volcanic landforms with the resulting wave reflections, refraction, etc.
Hmmm Riscos de Tirajana/San Bernado Refuge - That's a national park up there! World Biosphere Reserve or something.... Could be a problem

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