Transmission range optimization

[chapi]

I noticed noaa’s satellite can reach a range of 1000 km with a 5w radio, and wonder how can I maximize the range of my 5w radio on earth, without tackling too much multi path.

Should I use it in an open area? Try to transmit from a high point to a lower one? Avoid power lines?

Thanks.

 

[mmckenna]

Which bands are you using?

Open area, highest antenna you can possibly get, good antenna, good coax, sensitive receivers and good transmitters. It all adds up.

 

[chapi]

Using 450 mhz fm.

Can you recommend a strong transmitter to max range?

 

[mmckenna]

Using 450 mhz fm.

Can you recommend a strong transmitter to max range?

OK, so 450MHz is public safety/business band, and power levels, antenna height and antenna gain are all dictated by the FCC issued license. All of those variables are not negotiable.

If you are talking about the GMRS channels, you are limited to 50 watts, no more. The only variables you can play with are antenna gain and antenna location.

If you are talking about the 440MHz 70cm amateur radio band, then getting the most range will depend primarily on the height of your antenna. UHF is ~usually~ line of sight, so getting the antenna up as high as you can will give you the best range. This is why a lot of amateur radio operators take their radios to mountain tops to try to see how much range they can get.
Transmitter power doesn't have as much to do with range as some might think. Since UHF tends to be line of sight, increasing transmitter power won't get you much more range.
If band/atmospheric conditions are good, you can sometimes use tropospheric ducting to get your signal farther, but that's dependent on things you have no control over.

So, get you and your antenna up as high as you can. Don't get hung up on transmitter power, that's a noob mistake to think more watts will get you a lot more range.

Or, if you are a ham, use the local 70 centimeter band repeaters to increase your range. That's what they are there for.

 

[prcguy]

Transmit from 250 miles up. Big range, no multi path, lots of contacts.

 

[chapi]

Thanks, how about a directional antenna? Big effect?

 

[K4EET]

It almost sounds like you are designing a point-to-point communications system in the ham bands since this is the Amateur Radio subforum. If you let us know what you really want to do, we can probably help you a lot better.

 

[mmckenna]

Thanks, how about a directional antenna? Big effect?

A properly spec'd directional antenna can increase ERP quite a bit and focus most of your RF in one direction. That can help range.

However, remember, UHF is mostly line of sight and the curvature of the earth becomes the big challenge. You can blast all the power you want, but once the earth starts to curve away, you're just blasting power into space.

Remember TWO way radio. If you want this to work in both directions, both ends need to be set up similarly.

Providing more details about what you are attempting to do, what your license covers, what your skill level is, and what your budget is like can help us give you much better answers.

 

[chapi]

Thanks, this thread is very helpful but I’m afraid it’s not so easy to explain what is it that I’m trying to do. I’ll try anyway..

I’m using a tdoa direction finder but with one of the antennas connected to a rotating fan’s blade. A laser beam is fed to a photodetector but is cut by the fan’s blade and chopped by it.

The resulting radio audio output is fed to an oscilloscope and shown as combination of the Tdoa output in yellow from channel 1 of the scope and in blue from the laser from channel 2, see attached.

I am measuring the results from different distances on a straight line which is achieved by sending a laser ray from side to side and positioning the transmitter on different points along the laser’s ray.

I’m trying to measure minute differences and to see if they are proportional to the transmitter’s distance from the receiver.

According to my knowledge, it is impossible to tell the distance of a radio source without knowing its power, and without using other means like triangulation.

Am I right on that point?

 

[mmckenna]

TDOA from multiple sites and triangulation are what gets commonly used.

TDOA is used by some systems to locate transmitters pretty quickly and accurately. Triangulation isn't quite as good as you'd be dealing with antenna beamwidths.

I've done triangulation for tracking interference, and it's a pain.

You're right, you can't use power levels, just too many variables, especially if the source is unknown.

If you want to get the best receiving range, get your antenna up high and in the clear. Higher gain antennas, like a Yagi, will give you more received signal to play with, overcome feed line losses, and a narrower beamwidth.

 

[mmckenna]

There was a PhD that used to hang out on this site. Quite a brilliant lady with a lot of real world experience, a lot of knowledge, great communications skills, and a great sense of humor.
Unfortunately she's no longer on the site, or I'm sure she would have been a big help.

 

[RFI-EMI-GUY]

Thanks, this thread is very helpful but I’m afraid it’s not so easy to explain what is it that I’m trying to do. I’ll try anyway..

I’m using a tdoa direction finder but with one of the antennas connected to a rotating fan’s blade. A laser beam is fed to a photodetector but is cut by the fan’s blade and chopped by it.

The resulting radio audio output is fed to an oscilloscope and shown as combination of the Tdoa output in yellow from channel 1 of the scope and in blue from the laser from channel 2, see attached.

I am measuring the results from different distances on a straight line which is achieved by sending a laser ray from side to side and positioning the transmitter on different points along the laser’s ray.

I’m trying to measure minute differences and to see if they are proportional to the transmitter’s distance from the receiver.

According to my knowledge, it is impossible to tell the distance of a radio source without knowing its power, and without using other means like triangulation.

Am I right on that point?

You are describing almost exactly a doppler direction finder. Doppler uses 4 antennas that are sequenced by a PIN switch at a sub audible rate to synthesize a doppler shift between antennas and thus derive an angle of arrival from the source. See the manual below for basic theory;

Using doppler direction finders requires two or more observers or one observer to drive to different locations in real time and determine a compass direction to the source.

A TDOA direction finder uses two or more receiving stations to observe the signal in real time and determine time of flight from the source to the receivers and from that derive the distance from observer to location of the source.

The above are both triangulation techniques.

You cannot accurately determine distance based on signal strength received. If you are very close to the source, it may help pinpoint the source by signal level and using a directional antenna. I have done this in a very hilly terrain and it was very difficult. The signal fluctuated greatly. Not impossible, but thankfully the illegal transmitter was continuously transmitting and we had plenty of time.

http://www.dopsys.com/doppler-files/manuals/DDF400x.pdf

Very curious the results of your testing.

 

[RFI-EMI-GUY]

I noticed noaa’s satellite can reach a range of 1000 km with a 5w radio, and wonder how can I maximize the range of my 5w radio on earth, without tackling too much multi path.

Should I use it in an open area? Try to transmit from a high point to a lower one? Avoid power lines?

Thanks.

Is this what you are referencing?

Emergency position-indicating radiobeacon - Wikipedia

en.wikipedia.org