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Base Station Antenna Locations


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I have two possible base station locations that I'm considering. I did some basic gain/loss calculations for comparison. Which way would you guys go and how much difference in range over average rural terrain do you think there would be for the two locations?

 

Note: The 90 footer will be considerably more difficult to do

 

 

(Location #1 – Base of 16 ft antenna is 90 ft from the ground)

Cable Loss per 100 ft at Operating Frequency of (462 MHz) = 2.725 dB

Cable Length = 120 Ft.


Calculated Loss = 3.3 dB


Power into Cable = 50 Watts

Power out of Cable = 23.5 Watts

Gain of Antenna = 11.9 dBd

ERP of Antenna System = 364.7 Watts


(Location #2 – Base of 16 ft antenna is 36 ft from the ground)

Cable Loss per 100 ft at Operating Frequency of (462 MHz) = 2.725 dB

Cable Length = 50 Ft.

Calculated Loss = 1.4 dB

Power into Cable = 50 Watts

Power out of Cable = 36.5 Watts

Gain of Antenna = 11.6 dBd

ERP of Antenna System = 528.1 Watts
 

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To be perfectly frank, reception at your base/repeater is much more dependent on height than any other factor. While "power" might allow you to talk up to 13 miles, if you can only hear at most 3 miles what's the point?

 

Keep in mind that both mobile and HT radios will have on average 5' antenna height, so their LOS to your base/repeater is the true limiting factor to success. There are several web based propagation map generators that may be used to obtain a visual prediction of your system's performance.

 

I've found it very useful to work "backwards" and generate splatter maps as though the mobile/HT was the primary, and the actual base/repeater was the secondary. In other words, try to answer the question of "how high must my base/repeater antenna be to communicate with mobile/HT units..."

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To be perfectly frank, reception at your base/repeater is much more dependent on height than any other factor. While "power" might allow you to talk up to 13 miles, if you can only hear at most 3 miles what's the point?

 

Keep in mind that both mobile and HT radios will have on average 5' antenna height, so their LOS to your base/repeater is the true limiting factor to success. There are several web based propagation map generators that may be used to obtain a visual prediction of your system's performance.

 

I've found it very useful to work "backwards" and generate splatter maps as though the mobile/HT was the primary, and the actual base/repeater was the secondary. In other words, try to answer the question of "how high must my base/repeater antenna be to communicate with mobile/HT units..."

This is an excellent idea   the this is where I want to be   how high to phone home!

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This program will tell all you need about your system, its pretty accurate, its designed for Ham radio operators so the frequency max is 450mhz, but it will give you a very good idea of your system performance, and its PRETTY ACCURATE.

Just register for free http://www.ve2dbe.com/ and ENJOY. 

 

It's really sucks my HOME antenna propagation, because I live in a hole with hills around me, just 1/4 mile from my home I have a nice hill and I can hit repeaters everywhere with a 0db NMO car antenna, but at home I can't :( the program shows exactly where I can reach. and its very accurate.

 

 

 

range.jpg

 

mapgmrs.jpg

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height is you friend.

that being said I would look into a better cable for the 90 footer. 3.3dB loss to me not acceptable. I would at least entertain the idea of LMR400 at a minimum cable w/2.5 dB loss/100'.

as to the above post on the antenna propagation site it's close enough if you have the right numbers to plug in.

just my thoughts, JE

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height is you friend.

that being said I would look into a better cable for the 90 footer. 3.3dB loss to me not acceptable. I would at least entertain the idea of LMR400 at a minimum cable w/2.5 dB loss/100'.

as to the above post on the antenna propagation site it's close enough if you have the right numbers to plug in.

just my thoughts, JE

 

 

You can get 1/2" or 7/8" hard line New for $2 a foot...

 

Corey

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height is you friend.

that being said I would look into a better cable for the 90 footer. 3.3dB loss to me not acceptable. I would at least entertain the idea of LMR400 at a minimum cable w/2.5 dB loss/100'.

as to the above post on the antenna propagation site it's close enough if you have the right numbers to plug in.

just my thoughts, JE

 

Here's a couple of comparisons using LMR-400 & LMR-600. Larger, surplus cable is another thought (anybody know a good source)?. Also, an all weather repeater on a platform up near the antenna with only a short coax lead needed. Now the shortest I can get away with is 128 feet to the house.

 

(LMR-400) Cable Loss per 100 ft at Operating Frequency = 2.725 dB

 

Cable Length = 128 Ft.

 

Calculated Loss = 3.5 dB

 

Power into Cable = 50 Watts

 

Power out of Cable = 22.4 Watts

 

Gain of Antenna = 11.9 dBd

 

ERP of Antenna System = 346.9 Watts

 

 

(LMR-600) Cable Loss per 100 ft at Operating Frequency = 1.746 dB

 

Cable Length = 128 Ft.

 

Calculated Loss = 2.2 dB

 

Power into Cable = 50 Watts

 

Power out of Cable = 29.9 Watts

 

Gain of Antenna = 11.9 dBd

 

ERP of Antenna System = 462.9 Watts

 

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where?

 

Tessco has great deals on cable.

 

CommScope FXL-780 is a 7/8 smooth-wall aluminum shield and copper center conductor. I use this and swear by it, I have 2 sites that have 155' runs in service. Loss 100 ft @ 450 MHz 0.775 dB $1.99 per foot

 

CommScope LDF4-50A 1/2 Foam Heliax Cable Loss 100 ft @ 450 MHz 1.45 dB $1.98 per foot

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Thanks to all for all the information and suggestions.

 

So far I have had two (made in China) 16.6 foot antennas fail me on this project so I switched to a "DPD GMRS Vertical Outdoor Base Antenna". It's pre-assembled, weather sealed, and only 26" long. Right now its just hung on a cord off the porch roof but is performing very well with out a hint of SWR on 462-467 frequencies. Hopefully it will be up about 40 feet by this weekend.

 

My base station is now a refurbished Motorola CDM 1550 LS+ ,with power supply, cradle/speaker, and desk mike all from Motorola. This radio really seems to be solid and I'm loving it already.

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I got my base antenna up approximately 40 feet last weekend before all the weather and wind blew through. Strangely, I don't  seem to be talking any further than with the mobile on the ground, however I'm talking "better" if that makes any sense. What I mean is within a five mile circle, I've filled in a lot of "dead zones".

 

These were areas that I barely had a signal or had no signal at all. Some were explainable like low areas crossing a river bridge where you might expect to lose the signal, others were just places you couldn't talk for no apparent reason. Most of those have disappeared so I guess you could call the effort a partial success.

 

So far I've been able to push the signal out 12-14 miles to a mobile but only in certain places. Line of sight terrain models are usually reasonable predictors but not always. I have a clear line of sight over all terrain features to a small community 13.8 miles away and could not even break the squelch this morning.  

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