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Old Man Mike

1.2 Km with 10 mw Power

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I'm indeed pretty sure you get significantly more than 1mW radiated power, from anything "behind" the antenna connector. I've tested TXs numerous times with a dummy load on the antenna connector that's suposed to eat out everything, yet you can still get several tens of meters range.

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Hi Mike I am aware of this, back in the distant past I did some tests with a low noise pre-amp on 2.4ghz and found that I had more range with 3m of co-ax between the pre-amp and reciever than without it (the posts are on here somewhere). I was just looking to verify your results by putting the attenuator on the RX as I dont suppose you are going to fly out 32km any time soon???

I'll put the 30 dB on the RX if you wish and will post the video. How about you do the recommended test with the 50 ohm dummy on your 15 mw with 26 dB attenuator and tell us if you receive a video signal at 200 meters?

A couple of years back there were lots of claims made by Thomas S and others about theoretical ranges they could get based on lab tests and maths that have never come to anything.

I think Thomas proved the math was correct with this post of a video picture from 51 Km using 18 dB antenna & 500mw at 2.4 Ghz:

http://www.rcgroups.com/forums/showpost.php?p=10526535&postcount=11

My independant 32 Km calculation seems to be remarkably close to the results scaled from his system:

His 2.4 Ghz frequency compared to my 1.28 Ghz frequency is 6 dB worse

His 18 dBi beam gain antenna is 12 dB better than my 6 dBi omni antenna

His 500 mw TX is 3 dB worse than my 1 Watt TX

Net is that his system is 3 dB better than my system so I should have 25% less range:

51 Km * 0.75 = 38 Km

I had calculated 32 Km Range based on the 1 Km per 1 mw test results so it would seem quite reasonable to expect that performance.

What is it about the math that you do not believe? I've used the same calculations to build systems that bounced RF signals off the moon and receive them back here on earth. That worked just as predicted and was a lot more difficult then a simple FPV system.

I'm indeed pretty sure you get significantly more than 1mW radiated power, from anything "behind" the antenna connector. I've tested TXs numerous times with a dummy load on the antenna connector that's suposed to eat out everything, yet you can still get several tens of meters range.

I would certainly expect you to have a range of at least 50 meters with just a dummy load on your transmitter. That only requires about 0.01 mW of radiated power from leakage "behind" the antenna connector. Give it a try at 500 or 1000 meters.

I measured my leakage at 0.1 mW of power so the only signal being received at 1 Km was from the antenna radiated 1 mW.

OMM

Edited by Old Man Mike

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I'll put the 30 dB on the RX if you wish and will post the video. How about you do the recommended test with the 50 ohm dummy on your 15 mw with 26 dB attenuator and tell us if you receive a video signal at 200 meters?

Well if your happy to try it with the attenuator on the RX it would help to confirm your results for me but if you think there is no point fine. I dont have much time for playing with radio these days Im sad to say so dont hold your breath for my test but I will add it to my list of things to do ;)

I think Thomas proved the math was correct with this post of a video picture from 51 Km using 18 dB antenna & 500mw at 2.4 Ghz:

I may be wrong but I dont think Thomas had a flyable video signal, just some short clearish clips?

What is it about the math that you do not believe? I've used the same calculations to build systems that bounced RF signals off the moon and receive them back here on earth. That worked just as predicted and was a lot more difficult then a simple FPV system

I have know a guy that did EME on 2m and although not easy I think getting good video from a moving and twisting model plane is harder. The bit I find hard to believe is that with very modest gain on your system and omni performance you could get 32km.

I will admit I have no experiance on 1.2Ghz so maybe that is where my dought comes from but it far outstrips what most users are getting. What is the range that can be expected on 1.2Ghz with standard dipoles on both ends?

Terry

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...I have know a guy that did EME on 2m and although not easy I think getting good video from a moving and twisting model plane is harder. The bit I find hard to believe is that with very modest gain on your system and omni performance you could get 32km.

I will admit I have no experiance on 1.2Ghz so maybe that is where my dought comes from but it far outstrips what most users are getting. What is the range that can be expected on 1.2Ghz with standard dipoles on both ends?

Terry

Believe me, EME is much harder to get results that match the calculations. Here's video from a plane 12 Km away recorded with my omni system:

8mileFPVplay.jpg

I would say that is a fair amount of "moving and twisting". Except for a brief instant during the flip there is at least 6 dB of margin.

The plane was running half the power I use on the quadcopter and an antenna that is 2 dB poorer. Since I don't do any flips, I think this

also supports my claim that 32 Km should be possible. Of course if you do not believe math then ....

I will admit that my triple diversity system is unique with the extra signal processing and low noise preamps

located at the antennas so the performance is better than average.

OMM

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Of course if you do not believe math then ....

Im not saying that I dont think it is possable you will get 32km (you do seem to have the best recieving system I have seen) just that I have seen what should be possable when looking at the math not always work when tested in real life. For me their is no substitute for the real thing. I know computer models and math are good but for me its not real until its done in real life.

Repeatability seems to be the hardest part of our hobby. At closer ranges not so much but when flying out over 2 miles or so both the video and rc link can be unpredictable. Your tall mast should keep repeatability good I guess as its always in the same place and can see out over most obstructions where as most of us fly from different sites.

That 12km video clip is very good and for me is more convincing than your 1mW test flight, how did you find the pilot? have you seen any other flights he has done?

My best so far is 3.5miles on 5.8ghz with 30% on my rssi so I should get 4miles ok but I wont claim it until I do it for real.

As someone who transformed their 2.4Ghz system for hopeless to good by adding a low noise preamp about 10 years ago I would be interested to know what you think the real performance increase is by the preamps on your system?

Do you think the noise figure is more important than the gain?

Terry

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...That 12km video clip is very good and for me is more convincing than your 1mW test flight, how did you find the pilot? have you seen any other flights he has done?

I happen to capture that video entirely by chance. After determining the location of the plane, I eventually made contact with the flyer. The details are contained in a few pages of this thread starting here:

http://www.rcgroups.com/forums/showthread.php?t=1147430&page=31

(this was recorded with my earlier CPOD antennas. The new stacked PinWheels measured about 2dB better than my year old stacked CPODs probably due to sunlight degrading the PCB material.)

My best so far is 3.5miles on 5.8ghz with 30% on my rssi so I should get 4miles ok but I wont claim it until I do it for real.

As someone who transformed their 2.4Ghz system for hopeless to good by adding a low noise preamp about 10 years ago I would be interested to know what you think the real performance increase is by the preamps on your system?

Do you think the noise figure is more important than the gain?

I did some specific real world tests for video signal quality improvement using low noise preamps. Here is a summary of that testing:

http://www.rcgroups.com/forums/showpost.php?p=14776896&postcount=114

The bottom line is that with my current preamps (less than 1 db NF) mounted at the antenna, I'm probably about 5 dB better than the typical FPV guy. You do want to be very careful with the gain. The sweet spot for the typical FPV receivers used on 1.28 Ghz is around 6 dB. Much higher than that can lead to RX overload which will negate the improvements made by the low noise. I have about 12 dB of loss in the RX line going up the tower so I use a low noise preamp with 18 dB of gain.

In addition to the low noise preamps, the triple redundancy and special processing is probably adding another few dBs.

OMM

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Well all said and done its amazing range with no tracker used, I only wish I could use 1.2Ghz. I dont have any test gear for 5.8ghz so can only use off the shelf aerials which limits what I can do.

Terry

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