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Ham Operator Sets New Miles-Per-Watt World Record
DoctorPepper writes "A ham radio operator in New London, North Carolina correctly copied an 80 meter CW beacon in Wappingers Falls, New York, a distance of 546.8 miles. The kicker is, the beacon station, an Elecraft K1, was putting out 40.6 uW (40.6 millionths of a Watt) -- which works out to 13,467,980 miles per watt!"
Even most directional antennas will not give you linear 'watt to distance' amplification.
In worst case it is a power^1/3. So for 40 milliwatts to 1 watt amplification you'll get some 30x distance (at worst), but never 2500x, unless some wicked atmospheric conditions happen.
This seems an odd way to compare accomplishments. If you use this metric, then you reach the false conclusion that doubling wattage doubles distance. Since signal strength deteriorates with distance squared, a better metric might be miles^2 per Watt.
Example using round numbers. Philip transmits 10 miles using a 10W transmitter. Sally transmits 19 miles using a 20W transmitter. If you use miles per Watt to compare, it looks like Philip achieved better results, when in fact Sally did.
It's as sensible as measuring distance travelled/max acceleration of a car. There simply isn't a linear relationship between these things and so dividing one by the other doesn't give you anything interesting. If we start dividing random variables by each other and reporting the result on /. we'd never get to read any interesting news.
Doesn't it make you feel good to know that our freedoms are protected by politicans, lawyers and journalists.
The record is quite impressive given that there is more land and civilization between the new points of the new record. Still probably used ionsphere to bounce it forward, but there would be less ground effect in the new record than in the old.
These guys have advanced antennas but its still way cool that with a QRP rig and even a simple wire antenna, you can communicate over great distances with the juice of a 9 volt battery.
Here is a list of some famous hams
Pete Carr Owner Chatmag.com
The units here are watts per square mile. Your typical FM radio station has a range of maybe 50 miles and is running maybe 10 kwatts, so they're doing 4 watts per square mile. This guy is doing much better. My own power/distance record, back when I was active in ham radio, was 7000 miles on about 25 watts, or 5.10204082 × 10**-7 watts per square mile.
You might wonder how it's remotely possible for there to be a gap of seven to ten orders of magnitude. Why aren't we bothered by FM radio stations on the other side of the world? There is a qualitative difference between the behavior of radio waves above and below about 30-50 MHz (the FM band starts at 88 MHz). Conditions permitting, the lower frequencies can refract in the ionosphere and come back down to earth along non-straight-line paths. That's why shortwave radio stations on other continents can be heard.
WWJD for a Klondike Bar?
My cell phone can talk around the world on it's itty bitty power output.
No, it can't. That is why there are those little bars showing signal strength. You're lucky the newer digital units can get two miles to a tower (where it is then pumped thru an ATM link over a T-1 to the landline network).
Funny, fine. But to whomever modded that post "Informative" needs to go back to school.
-Charles
Learning HOW to think is more important than learning WHAT to think.
It's more like hearing a whisper across a huge crowded stadium.
The listener had really good ears and was able to pick out the code from a lot of background noise, with a really good antenna setup.
/sig
Outmoded you say? Here's a recent example that may make you change your mind on that one.
f m
http://www.voanews.com/english/2005-01-05-voa24.c
Now imagine how hard that is to see from 7 billion miles away.
Right...the power drops off as the square of the distance, when you are operating in the far field.
The far field of an antenna starts at a point where the radiated wavefront is practically flat. One such measure of this distance is
2* D^2
R = ----------
wavelength
where D is the largest dimension of the antenna. With a satellite dish, this is the reflector diameter typically; with a monopole ("stick") antenna it is the antenna length. There are other measures that are also used to calculate the start of the far field, but I can't recall them now; I will say that whichever one yields the furthest distance is the thumbrule used.
Your orientation to the radiating antenna also plays a role. A "stick" antenna (dipole or monopole) has more energy radiated perpendicular to the mast than along the mast axis. In free space with no reflections, you can stand at either end of a stick antenna and not receive squat, as long as you are in the far field. Thus, you must also consider the gain of your antenna in the direction of interest. A stick antenna has about 3dB gain perpendicular to it, and negative infinity gain along the antenna axis.
The actual equation to get the power density Pr when distance r from the source is:
Pt * Gt
Pr = ----------
4pi*r^2
Pt = Power radiated
Gt = Gain of your antenna
That's why the change in power to distance isn't linear. May have been long-winded but I spent most of the afternoon doing power density calculations so it was fresh in my head.
Government's idea of a balanced budget: take money from the right pocket to balance...oh who am I kidding?