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Old Dec 21, 2006, 10:33 AM
JettPilot's Avatar
Miami
Joined Apr 2005
10,105 Posts
Discussion
Wireless Video Power Levels ... How much power do you need ???

There seems to be a push by some people lately to shame others into running the "Lowest Power Possible" in their video system. I also get a lot of private messages inquiring about how much power they should run for different planes and missions. So here are some things you need to think about when selecting the power level of your Wireless Video Transmitter.

" You should run as low a power as possible to prevent harmful interference " - This comes from the old Ham regulations, and had its place there. At low frequencies below 30 MHZ even low power signals can travel many thousands of miles. There was a good chance that if you used a frequency, you would be heard in many countries and would prevent many others from using that same frequency. At 2.4 GHZ, signals do not travel for more than a few miles, so this old style thinking of using low power just does not apply here. Take the area you will be flying, and draw a radius of 1/2 mile around your 1000 mw TX, that is the area where you have a good chance of even being seen by most consumer wireless equipment. Any further than that, the signal is so weak that you need very sensitive receivers and directional antennas to even pick up the signal. At a couple miles, you need to have a very high gain antenna pointed directly at your model to even see the signal.

BOTTOM LINE - Most other 2.4 wireless users are sending signals from one end of their house to the other, they have a very good connection and it would take a very high power model plane flying very low over thier roof before it would ever interfere with thier signals. Beyond about 1/2 miles, people will need good equipment to even detect you signal. If you are flying in New York City, this may be something to think about, but for 99 % of us, its is a NON ISSUE. So dont let anyone make you feel "guilty" for using a high power TX in your video flying.

As far as performance is concerned, a 100 mw video transmitter will give you margional performance using the best equipment. This video was posted by DiveBomberDave using a 100 mw video TX and very sensitive BWAV RX and directional patch antenna.

http://video.google.com/videoplay?do...28225526&hl=en

The signal starts to get weak at very short distances, you can hear it first as static then when the level starts to get really low you finally see it in the video. Much of the static in the video is hidden with the compression of this video, but if you were to watch the origional high quaility video before compression, you would see the static develop in the video about the same time you start to hear it, much sooner than in the posted google video and you would not be happy with quality.

Using the same setup with my 1000 mw video transmitter, my video quality does not degrade and get that much static until my plane is several miles away. If you want nice video without dropouts, you need about 1000 mw of video power. If you like dropouts and static even when your plane is close in then use the 100 mw low power TX. Just dont let anyone "shame" you into using less power than you will be happy with, 2.4 just does not travel far enough to cause anyone any problems at any power level you decide to run.

JettPilot
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Old Dec 21, 2006, 10:58 AM
I AP'd myself again......
aviatordave's Avatar
Yawn....Iowa
Joined Mar 2005
2,500 Posts
Jett,

Whats your opinion on 900 mhz systems. I see them for sale, but not used very much.... pros? cons?

Dave
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Old Dec 21, 2006, 11:43 AM
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lvspark's Avatar
Walla Walla
Joined May 2002
2,639 Posts
I use the lower output transmitters for 4 reasons. Keep in mind I fly smaller electric planes. If I had a larger plane, my though process could change based upon aircraft size and payload abilities..
1. Lower Cost
2. Lower Current consumption
3. Less RF to mess with my RC Rx
4. Lower Weight
500mw works good for me up to a mile, never tried or need to go much further..
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Old Dec 21, 2006, 12:04 PM
JettPilot's Avatar
Miami
Joined Apr 2005
10,105 Posts
Quote:
Originally Posted by lvspark
500mw works good for me up to a mile, never tried or need to go much further..
500 mw is a very usable power level. Its not so much the number of milliwatts as how many times you are increasing the power or decreasing it.

Lets start with 1000 mw. That is the power I use on a standard .40 sized glow trainer. Weight is not a huge factor with a .40 sized plane so I can carry the bigger battery and slightly heavier TX on the plane with no problem. Close in you get great quality video with no static or dropouts. There is enough power to fly for several miles with some static, and mild signal loss if you are inclined to do so.

500 mw --- Is one half of my power level, you have reduced the power level to 50 % of my power level is but it still works good, and has the advantages you stated for very small aircraft. I would probably do the same thing on a slowstick sized plane or anything smaller than a slowstick.

100 mw --- Is only 1/10 th of my power level, you have reduced the power level by 90 % range and performance is severly impacted when you take the signal down that much. Your video will be poor quality, constant dropouts and lots of static.

50 mw --- Is only 1/20 th of my power level, you have taken the power down by a factor of 20, you are only left with 5 % of my power, this level will barely get you a good signal out of the landing pattern.


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Old Dec 21, 2006, 12:58 PM
Pull out early!
DiveBombDave's Avatar
Lexington, KY
Joined Jan 2005
1,956 Posts
Quote:
Originally Posted by JettPilot
" You should run as low a power as possible to prevent harmful interference " - This comes from the old Ham regulations, and had its place there.

JettPilot

Listen, Jett, I've never hacked on you about any of the threads you've posted. Never once in my low-power thread did I try to "shame" or "guilt" anyone - I was providing information for the "line of sight" short range APers out there, and was careful to qualify this. You obviously do not fit into this group. If you feel shame or guilt, I'm sorry for you. If you fly a 10lb plane several miles from yourself, you do not fit into this group. You act as if I accused you of stepping on 2.4ghz in houses down below - which would be an extrapolation of my recommendation to use as low of a power as possible.

As for your reference to the "old" Ham regulations, I'll have to look that up. I can't believe the "new" ones say "use all the power you want for 2.4, it's just fine." Thanks for letting me know how times change - I'll have to find this new FCC policy you speak of so that I'll be as caught up as you.

I updated my thread with a local sampling of video from the 100mw, so maybe you should check that out and tell me why it wouldn't work for the 95% of people in THIS forum who use the downlink for framing still shots. Do that and I'll listen. Flying FPV miles away and wanting to "use" or publish the video, YES you would need more power.



Dave
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Last edited by DiveBombDave; Dec 21, 2006 at 01:09 PM.
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Old Dec 21, 2006, 01:05 PM
RIP Ric
Andy W's Avatar
Marietta, GA
Joined Jun 1999
43,312 Posts
Thank you for the information, Jett..
..a
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