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GR300 Help , Map included for reference

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GR300 Help , Map included for reference

Postby hfd921 » Tue Aug 06, 2013 7:28 pm

Hey guys looking for some help….

Currently I have a Motorola GR300 repeater. It will be located approximately 10 miles away from our office and coverage area. The proposed site is approximately 15 stories up. “I’m told the higher up the better, the location picked is the tallest around in the entire area, it just 10 miles away”.

Here is a photo of our coverage area. The Orange oval is the proposed repeater site. And the two blue ovals our two offices. The yellow represents our coverage area. We primarily use portable radios indoors. I made note of a couple job sites on the out skirts of our area. Almost 10 miles from our office and atleast 20 miles from the repeater.

As you can see we have a large area NORTH , SOUTH and EAST of the repeater site, that DO NOT need any coverage at all in the white area. We need to reach out 20miles from the repeater location in the yellow area.

Here is my question, Please forgive my lack of antenna knowledge.

1. Would a Yagi or directional antenna be better to project all its power towards our coverage area from the repeater?

2. If not a directional yagi antenna, what would be proper for our use? Our budget is under 200$.



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Re: GR300 Help , Map included for reference

Postby Bill_G » Tue Aug 06, 2013 10:02 pm

Shoot me the lat/long and rooftop elevation of the proposed rptr site either here or in PM along with your email addy. I'll make a coverage plot based on the following:

UHF 450-470 band
rptr pwr 25W (at the ant port after the duplexer)
rptr rx -114db
line loss 2db (50ft of LMR400)
ant gain 3db omni
port pwr 4W
port rx -114db
ant gain -1db omni

I'll send it to you via email as a kmz that you can load into Google Earth so you can determine if it will suit your needs at the job sites. A single yagi would serve one, but probably not everywhere you want to operate. An offset dipole (cardioid pattern) would, but not fit within your budget. Stacked yagis using a simple TEE would fit your budget and give an offset pattern, but making the phasing harness and spacing the antennas correctly could be tricky (but not impossible).

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Re: GR300 Help , Map included for reference

Postby Bill_G » Wed Aug 07, 2013 7:18 am

Plot sent as promised.

A suggestion - the building selected prides itself in being the tallest building in the parish (according to their web page). Looking at the rooftop on Google Earth, a lot of people have the same idea you have. I can see an antenna farm up there. You should consider upgrading the duplexer to a good pass/reject type over the standard reject only that comes with the model to help the radio operate in that environment.

You're in Jim202 country. Contact him for professional services to get this done right.

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Re: GR300 Help , Map included for reference

Postby d119 » Sun Aug 11, 2013 7:36 pm

Another important question - what type of radios are you using in the GR300?

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Re: GR300 Help , Map included for reference

Postby AEC » Mon Aug 12, 2013 12:11 pm

Good radios, with good shielding are a prerequisite in congested sites.
The use of a good duplexer, as already mentioned, is also necessary.
You can use Yagis with a power divider to cover your intended areas, but are costly over a single antenna configured to cover only your service locations.
A 3-way power divider from Telewave covers 350-600 Mhz. but will set you back about $200.00 (ANTPD34).
A good dipole antenna by the same mfr. is $622.00 (ANT450D3).
A dipole assy. will allow you to adjust your coverage according to location and direction, by moving the dipoles to favor specific areas, while creating a null over undesired locations. This is NOT the same as turning off a light, the signals will cover unintended areas regardless, but the higher signal level will 'favor' your needed locations, above those areas you do not require strong signals.
Your BEST start is with the antenna, then feed line, and duplexer. All other additions will add to selectivity, sensitivity and operational effectiveness. You may require the inclusion of a good GaAs FET preamp if your most distant site is in a fringe area, or a poor Fresnel zone.

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Re: GR300 Help , Map included for reference

Postby Bill_G » Mon Aug 12, 2013 12:36 pm

I kind of envy his service area. It's in SW Lousiana, and the plot looked like a pancake. I could have drawn it with a compass. Flat flat flat flat flat. OTOH, there are no naturally occurring heightenfiers. You either put up a tower, or you find a tall building, and they don't give you the advantage a mountain does. We put up 150ft towers to get above the canopy on top of a 1300ft hill. Our radio horizon is 50 miles away. His is 20 and hardly an inch more.

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