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Author Topic: Communication range help  (Read 2191 times)

Posts: 1

« on: March 03, 2002, 01:15:56 PM »

I dont know much beyond the basics of ham radio and I am going to test for my license soon, but I have a few questions.  I am trying to decide what type of radio to purchase.  There is a 50 watt desktop radio and a 5 watt handheld that I am trying to decide on.  How far will the 50 watt radio be able to communicate?  What about the 5 watt handheld?  Do I need an antenna to use the desktop station?  Can I buy another antenna for the handheld to enable further communication?  Thanks.

Posts: 10091

« Reply #1 on: March 04, 2002, 07:11:41 AM »

More important than power is the frequency of operation, the antenna and the antenna's intended location (how high). You need to consider that info.  And there are no hard numbers either. The same setup will have differing performance depending on terrain, weather, etc.  If on HF (which I suspect you are not operating), the time of day, sunspot cycle and other solar conditions all play a role.

All thing being equal, the 50W radio will allow you to be heard further away, but will not do anything to help you receive signals.  So without a decent antenna, the 50W radio might only make you an alligator (big mouth, no ears). Don't worry, many of us are!

Mike N2MG

Posts: 21764

« Reply #2 on: March 05, 2002, 05:20:04 PM »

I'm guessing you're talking about a VHF rig, like 2 meters.  You didn't say, but this is a very important factor.

The antenna plays a much more important role than transmitter power does.  50 Watts into a lousy antenna won't get you very far.  1 Watt into a great antenna will.

If you're really studying for your ham license (I hope you are!), this is handy information to know, and the theory behind this data is contained in many of the ham exams:

50W is 17 dB greater power than 1W (calculation is 10 x log P1/P2).

A "rubber duckie" flexible antenna, like that found on most hand-held transceivers, has approximately -10 dB gain (that is, 10 dB "loss") compared with a 1/2-wavelength dipole at the same elevation.  If that elevation is just your standing height, and you're six feet tall, that's -10 dB at 6 feet.

A 12 element Yagi ("beam," a directional antenna) installed at 50' above ground has approximately 14 dB gain (not loss), plus the added 12 mile horizon which equates to about another +13 dB on signals arriving from distances greater than 12 miles.  The cumulative gain of the antenna plus its height is about 26 dB.

Now, you're looking at +26 dB, opposed to -10 dB.  The difference is 36 dB, in favor of the beam up 50 feet, for distant signals.

36 dB gain is a multiplier of 4000.  If you run a 1W transmitter into an antenna system having overall gain of 26 dB, it will be as strong as a 4000W transmitter into a -10 dB gain antenna, like a "rubber duckie" flexible antenna.  That's quite a difference.

And, it's also an achievable difference, since a +14 dB gain 2m Yagi is something that can be purchased for about $150, and it is possible to install it 50 feet above ground and feed it with very low-loss transmission line.

A 4000W amplifier, on the other hand, is illegal to use, and even if one could be built or purchased, would cost many thousands of dollars.

The place to put the $$ is into the antenna system, almost always.

If you were speaking of 2 meters:

From an average location, at average terrain, in a flat (not mountainous) area, with 50W output to a good, well-installed directional antenna system such as the one described above (12L beam, 50' above the ground, unobstructed), using FM communications, normal range when contacting a similarly equipped station is about 100 miles over flat terrain, and >200 miles over water; however, if there are obstructions between the stations, including elevated terrain, this can be cut much shorter.  On the other hand, if you're atop a high hill with a 25 mile view and your antenna is the highest thing around for miles, that same 50W might land you consistent contacts in the 200+ mile region, without any special conditions to enhance signals.

Range for an average 5W hand-held 2m tranceiver with its little flexible antenna (rubber duckie) is only a few miles.  But if the station being contacted is a mountaintop repeater that's line of sight to you, the range is greatly extended by the capabilities of that repeater.  I've worked repeaters more than 250 miles away, using my little 5W 2m HT and "rubber duck" antenna, when I'm standing at the summit of Mammoth Mountain (CA) at 11,000 feet above sea level, and I can literally see that far.



Posts: 984

« Reply #3 on: March 16, 2002, 11:34:25 PM »

Well, Steve, you certainly "bagged" that answwer. Very good.
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