FM range question - coastal mountainous terrain

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dicky96
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FM range question - coastal mountainous terrain

Post by dicky96 » Thu Nov 09, 2017 5:40 am

OK guys I put this on a new thread to keep my other one on topic - hope this is OK

So I am now involved with this radio station in Gran Canaria. There are only 5 or 6 stations on the island - we are the only one catering for English language and Scandinavian tourists

I've attached a topographical map screenshot to this post. You can find the original link here http://en-gb.topographic-map.com/places ... a-1424037/ which you can zoom scroll and click on points to see the elevation. Also a map of the island - original is at http://www.orangesmile.com/common/img_c ... -map-0.jpg which you can zoom etc

The studio is located between Puerto Rico and Tauro on top of one of the highest hills in the area at an elevation of 554ft plus the mast height on top of that. The mast is maybe 30-40 feet I would have to go and get some pics. The transmitter is a 1kW OMB. The antennas are like a dipole but with a circular 'twist' in the middle. It looks like the attached pic and there are two of them one above the other. I will get some pics when i next go up there. I marked it's location on the topological map

With reference to the attached map - Our main audience is a town/resort called Puerto Mogan about 10Km/6 miles 'behind' us and all the touristic area in front of us from Puerto Rico as far as Bahia Feliz / Berri el Aeroclub. When I say in front of us I mean the antennas are on that side of the mast facing that way. The station is on the coast and to our right is open ocean which looks lovely but signal going that way is wasted. To our left is the interior of the island which is rural and mountainous and we have suprisingly (to me) good coverage up in the mountains though there is hardly anyone there to listen!

Currently we get decent reception in Puerto Mogan but the signal towards Bahia Feliz becomes patchy after Sonneland and just about reaches Playa Del Ingles but is too weak to be usable. So our usable range in in this direction is about 12 km/8 miles

We used to have another 1kW transmitter broadcasting the same station on a different frequency in Playa Del Ingles but that went off the air months ago due to problems with the owners of the property.

So we need to get back on the air in Maspalomas/Playa del Ingles/San Agustin area as this is our largest audience and brings in the most revenue.

The preferred solution for us would to be a more powerful antenna/transmitter at Puerto Rico as it costs a considerable amount of money each month to rent a suitable premise for a second transmitter in Playa del Ingles and this solution would also:

1. free up that frequency for a second 'oldies' station we want to start.
2. avoid the problem of folk driving up and down the motorway between Maspalomas and Puerto Rico having to retune their radio if it does not do it automatically.

So looking myself from the maps we need to roughly double our range in that direction while still having coverage in Puerto Mogan behind us. The ocean is just wasted power.

One thing possibly in our favour - our signal peters out at Sonneland which is on a bit of a hill but the resorts we want to cover after that are pretty much flat and near sea level.

I have been told the fact this is a volcanic island it dampens our transmission as the igneous rocks are conductive to RF energy or some such thing. Is that true?

OK I hope with the pics that this all makes sense. The photo shows the transmitter antenna its just visible as a white mast on the hilltop below what looks like a flock of birds but it actually dirt on my camera lens lol
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antenna.jpg
grancan.jpg
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TPT
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Re: FM range question - coastal mountainous terrain

Post by TPT » Thu Nov 09, 2017 7:18 am

Antennas: Those are circularly polarized antennas, dividing power between the horizontal and vertical plane. Two bays is usually unity gain. So, whatever power coming out of the end of the coax is what you are radiating. You loose some power in the coaxial cable--so your effective radiated power is probably in the range of 950 watts.

Looks like from where I am guessing your transmitter site is--by the time you get around the coast to "English Beach" you have a couple of mountain ridges in your way, the way the island curves.

Having a relay transmitter is a good--but as you note--expensive solution. Depending on what EU radiation regulations would permit, one solution might be a low power relay on the top on a high rise apartment or hotel building near the center of population. Playing around on Google street view I see lots of 4/5 story apartment buildings/hotels. A one bay antenna with a 50 watt exciter on the roof of one of these buildings would cover three or four miles in what looks to be the relatively flat area around the beach. Could be fed by internet.

dicky96
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Re: FM range question - coastal mountainous terrain

Post by dicky96 » Thu Nov 09, 2017 7:45 am

Thanks for the reply. The station used to have a 1kW transmitter on top of one of the hotels in 'Englishmans Beach' on 102.5 and the other transmitter here is on 99.4. The 102.5 transmitter was fed via internet. So I guess the emmisions were OK.

The PTX20 I am looking at actually came from that rig - I'm not sure what the status of the transmitter is. Problem as I mentioned it cost something like 600 euro a month to rent the premises plus cost of internet link so it soon adds up.

That's why we were wondering if (say) a 2-4Kw transmitter and maybe a better antenna system in Puerto Rico with more gain in that direction would be the better way to go in the long run. Plus it means we can use the 102.5 frequency allocation for something else

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Deep Thought
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Re: FM range question - coastal mountainous terrain

Post by Deep Thought » Thu Nov 09, 2017 9:56 am

Can you see the target area from the transmitter site? If not, there is little you can do to get past the terrain obstruction other than raising the antenna higher.

"we need to roughly double our range in that direction"

All else being equal, on flat terrain the 60 dBu contour of a station running 1 KW at 169 meters (554 feet) should be around 24 kilometers from the antenna. To double that distance, you'd need to increase your power to 24 KW at the same height. If you were to double the height to 1100 feet you'd only need 6 KW. You can see this is not going to be easy. Toss a mountain in the path and all the calculations go out the window.

The volcanic nature of the rock really isn't an issue except that it is probably a good reflector, making any terrain obstruction even more effective. The reason the mountain coverage is good is that the receive antenna is "looking down" at you with nothing in the way.

I don't have terrain data for that part of the world but if I had to guess based on looking at the maps, you've got some elevation issues. If I get some time today I'll try to pull some data off the terrain map you provided and run a couple path studies. It would help to have the geographic coordinates of your antenna site.
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 » Thu Nov 09, 2017 11:06 am

That is very kind of you to offer your time! :D

I think these are the co-ordinates 27.7901582,-15.7164727

Took these from google maps and I know our island is 27.5N 15.5W so that sounds right

The antenna mast is directly on top of the Barbacoa Restaurant and Show Bar

https://www.google.es/maps/place/Gran+C ... 15.5474373

I just did some distance measurements on google maps (didn't k now I could do this) we currently have about 12Km range to Faro maspalomas - would need 20Km to reach as far as Bahia Feliz

Cheers
Rich

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Re: FM range question - coastal mountainous terrain

Post by TPT » Thu Nov 09, 2017 4:36 pm

Load up Google Earth--has lots of handy tools & you can get coordinates easily if you can find your location.

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Re: FM range question - coastal mountainous terrain

Post by TPT » Thu Nov 09, 2017 4:44 pm

Google Earth sayeth thus:

27-47-24 N 15-42-59 W, 504' AMSL at the end of the bar

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Re: FM range question - coastal mountainous terrain

Post by TPT » Thu Nov 09, 2017 5:13 pm

Some links to play with, you need to take the results with several grains of salt:

https://www.fcc.gov/media/radio/haat-calculator (use the globar terrain data base)

https://www.fcc.gov/media/radio/fm-and- ... ion-curves

The first calculator, when you enter the height above sea level (in meters) of your antenna (with two bays you split the distance), & coordinates you get an Antenna Height Above Average Terrain--key word being "average" over 360 degrees

Let's say you have a flat plain at 200' AMSL, with a 1500' mountain smack dab in the middle. Take a 16 Km path, with a point every kilometer.
12 points at 200', 4 point at 1500' Add together the measurements, divide by 16, and the average terrain is 525 feet. Of course--you still have that 1500 foot mountain in the middle, so it is not a very good radio path even if your antenna is at 600 feet. Grain of salt #1

The other program gives you a predicted signal strength when you enter the AHAAT, distance in kilometers, and radiated power. From your transmitter site I ran a line on Google Earth to the Ecumenical Center in Play Del Ingles--15 KM @ a bearing 103 degrees, AHAAT 50 meters, projected field strength 57 dbu. Of course this chart is based on an antenna 30 feet in the air, and the signal level prediction is at 50% of the locations, 50% of the time. Large boulder of salt!

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kkiddkkidd
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Re: FM range question - coastal mountainous terrain

Post by kkiddkkidd » Thu Nov 09, 2017 6:49 pm

I just did a quick Google Earth path. It looks like there is a lot of dirt that is at least 200ft above line of sight between those coords and Playa del Ingles. I think that was the desired area.
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Re: FM range question - coastal mountainous terrain

Post by Deep Thought » Thu Nov 09, 2017 8:18 pm

Ha! I keep forgetting that's in Google Earth. Yeah, that's going to be nearly impossible to blast through. Best advice would be to find some midpoint along the coast that can "see" both areas to put up a booster aimed to the shadow area if those are allowed over there.,
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

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Re: FM range question - coastal mountainous terrain

Post by TPT » Fri Nov 10, 2017 7:00 am

Another problem--get back up those ridges (some of the roads show on Google streetview)--and you have a nice view of the ocean, but no electric.

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Re: FM range question - coastal mountainous terrain

Post by kkiddkkidd » Sat Nov 11, 2017 8:47 am

But there are several accessible ridges above and about 4 miles away from central PdI that probably do have power for a higher power tx. There are even more where a lower power solar power transmitter with a yagi pointed down into the target area would provide a much better signal than a kw trying to plow thru 9 miles of dirt. Sunlight doesn't seem to be in short supply there.

Waking up this morning to freezing temps in Middle TN.... I am available (at discounted rates) to do onsite consulting on a subtropical beach paradise.
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Re: FM range question - coastal mountainous terrain

Post by R. Fry » Sat Nov 11, 2017 9:32 am

Below is a Longley-Rice coverage estimate for the conditions shown. Other conditions can be modeled (within reason), based on further input.

Hope this helps...

Image

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Re: FM range question - coastal mountainous terrain

Post by dicky96 » Mon Nov 13, 2017 2:33 pm

Hola from cold England! So yes I am back in the UK for one week, I've been here for 4 days now and it's really is too cold here for me!

Hey guys thanks for all the hard work on this problem

In reply to a few points


The projected height of the obstacles in relation to the transmitter is probably slightly exagerated as the google maps altitude for the site of the transmitter does not include the fact the antenna mast is on top of a single story building and then there is the mast itself so we are probably 50ft higher. Not that this is enough apparently.

Another problem--get back up those ridges (some of the roads show on Google streetview)--and you have a nice view of the ocean, but no electric.
Yes some of nearby higher ridges have no power as a lot of the island interior is uninhabited - but there are probably some that do - maybe I should look around for any higher nearby alternative sites and then the same sort of analysis could be done again? If we only need a few hundred more feet that is.

Sunlight doesn't seem to be in short supply there.
You are right - We officially get over 320 full days of sunshine a year but it is probably nearer 350 days from my own personal experience. When we do get cloud it tends to be thin high altitude cloud. Actually here is an scientific explanation why South Gran Canaria is one of the sunniest places on earth http://www.gran-canaria-info.com/weathe ... f-sunshine I think you will find it quite interesting.

The almost permanently clear skies and lack of large population cenrtes are also why we have this at Montana Blanca, near Maspalomas. I drive by it on regular occasions and would love the opportunity to go visit it. The americans built it originally, by the way http://www.esa.int/Our_Activities/Opera ... as_station Hope you found that interesting too.

Waking up this morning to freezing temps in Middle TN.... I am available (at discounted rates) to do onsite consulting on a subtropical beach paradise.

So if i need a good RF engineer I know who to ask then :)


Below is a Longley-Rice coverage estimate for the conditions shown.
I've not seen one of these before - but I would say that is a damn good pictoral representation of our coverage from our 1kW transmitter!! We probably get a bit further towards Pasito Blanco before the signal drops out but then I think it reasonable to assume our antenna is about 50ft higher than assumed for the reasons explained above. 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?

Thanks for all the help guys - well done to you all!

Rich
PS - picking up the dummy load for the PTX 20 repair tomorrow and heading back to the island on Friday

dicky96
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Re: FM range question - coastal mountainous terrain

Post by dicky96 » Mon Nov 13, 2017 3:39 pm

Oops sorry I see that the chart is ALREADY for antenna 15m above grond level :oops:

Rich

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