3000mW Video Transmitter

[mckaneorg]

Just wanted to see if anyone is using anything this high out there. I have the unit powered by a thunderpack 2100 11.1v. The video looks good but the box gets real hot. I have all kinds of little end transmitters and I know the 50mw systems even get hot. Is this just getting extremely hot due to the radiation?

Anyone have any experience with 3w? I would hate to start a fire in the sky! :) My Thunderpacks are not overheating or overamping. Thats the only good news!

-j

[Mr.RC-CAM]

Is this just getting extremely hot due to the radiation?
If it is like the usual wireless video Tx, the heat is from the internal Vreg.

[mckaneorg]

i figured as much. I just wanted to be safe. I'm going to wire the temp back to my telemetry so i can keep an eye on it. Thanks I appreciate the help.

[poynting]

How is this legal? Maybe you're running it as an amateur radio system under FCC Part 97? The ouput limits for Part 15 devices (most 2.5GHz video transmitters) are generally much lower than 3W. I see this one on the market that boasts 3W: http://www.eyespyvideo.com/lawenforcement/thx-24x3.htm but it's clearly marked for gov't or law enforcement use only. Not interested in starting a flame war, just curious.

As far as the heat, as Mr. RC-CAM pointed out, it's probably partly due to the internal linear voltage regulator dropping your 11V input to 5V or less. If you want to minimize wasted power, run it at the lowest spec'd voltage. Otherwise, all of the excess power will be dissipated as heat.

If this is the case and you want to make your transmitter last longer, and you only have 11V to input, you can place a small-value high-wattage resistor on the input voltage line. This resistor will get really hot, but the transmitter won't get as hot and this technique should increase it's lifespan somewhat. You'll have to know the minimum input voltage to calculate this resistor's nominal value. Once you know this, the equation is (11.1V - MinInputVoltage(in Volts)) / Input Current (in Amps). This will give you a resistance value in ohms. Make sure the resistor is high enough wattage to dissipate the power you're putting into it.

Example for a 7V minimum input voltage and a 2-amp input current: (11.1V - 7.0V) / 2A = ~2ohms. The power dissipated by this will be Isquared * R, or (2A*2A) * 2ohms = 8W. For these fictional numbers, you'd need a 2ohm, 8W+ resistor.

Also, even really good power amplifiers are generally only about 30% efficient. So for a 3W output unit you're dissipating at least 6W of heat for a 9W input. In reality, your efficiency is probably even less than that, meaning more heat will be dissipated.

[mckaneorg]

That is the exact unit I have. I will try modifing the power supply thanks for your help.

[mckaneorg]

One other thing I thought I would mention since it falls under the same train of thought. I was doing some research that talked about RF safety. The FCC basically says that when discussing the biological effects of RF Absorption you must clearly specify the difference between Non-Ion and Ion based radiation. As we all know Microwave stays below the Ionization level. However that does not mean all levels are safe. You wouldn't stick your head in a microwave would you? But yet that is Non-Ion form of Radiation.

From my research I have found that you need to be careful with even 50mw tranmitters in close range. They can cause biological damage to your body and some areas are more sensitive than others. The eyes being the most sensitive.

I was just curious if anyone had any precautions they used and if they were willing to share.

[JettPilot]

I run a 5 Watt video transmitter, and had the 3 Watt but I like the 5 watt better. The heat is mostly generated by the output transistor, not the regulator. In smaller output models, the regulator accounts for a greater part of the heat, in larger models, the output transistor puts out far more heat than the regulator. My 5 watt transmitters are regulated to 9 volts, not 5 volts like the little bitty ones, which I assume you 3 watt is. You are dealing with a far different animal there than the little ones most people use You will probably start to have problems below 10 volts...

Getting that TX to hot will shorten its life, depending on how enclosed it is. It takes a while to heat up, so use airflow from the airstream and it will cool it very well if you dont run extended periods on the ground... Do not enclose that transmitter in padding without airflow, it will overheat it very badly. Also dont get close to the antenna, especially you face... If you put your finger right next to the antenna, you can feel radiated heat, not good ! The good news is that power dissapates very quickly with distance, and a couple feet fromthe antenna and you will be fine.

The other good news is that The current draw if the 3 watt is just around 1.5 amps, so that is not even an issue for a LIPO or any pack, most motors draw over 10 times that ... You will just need a pack big enough not to run down to quickly, but you will not over heat a big LIPO pack at just 1.5 amps...

JettPilot

[mckaneorg]

I have it in a heli and I had to pad it up with foam rubber due to vibration. What does your setup look like? Perhaps I could figure a way to put it on my system.

[reedchristiansen]

The 3 watt transmitter looks like an interesting replacement for the 500 mw blackwidow system we are running. A few questions for those with experience with these higher power systems:

1. Are you haveing problems keeping the 2.4 Ghz from interfering with GPS reception?

2. What kind of ranges are you getting using a directional antennia on the ground and an omni in the air. (We use 12 dbi on the ground and 1/4 wave dipole with 500 mw are are getting 2km reliably - almost no snow). What can I expect with 3 watts on the same setup.

Thanks,
Reed

[JettPilot]

I put the 5 watt transmitter far away from the GPS and it has been rock solid. My video transmitter is out on the wingtip to keep it away from the GPS ( 7 Feet from the GPS ) and it is about 3.5 feet from the RC reciever. The GPS is rock solid..... Never any problem. The RC reciever is a different story. It does reduce the RC Link range to just over a mile using a standard RC transmitter with a normal antenna. One receiver I tried was knocked out almost entirely by the video and was going into failsafe in the pattern !!!

The video range is miles and miles, eggactly how far I have not had a chance to check yet... But it will go much farther than your RC transmitter will. I had to use a directional antenna on the RC transmitter and I still was not getting any snow on the video at 3 miles. ( For video antennas I use omni
on the plane and directional on the ground unit... )

The transmitter can and should be wrapped in foam. Just make sure you have some really good airflow through the little vents in the case of the unit, front and back so air goes through at a good rate. My transmitter is not even warm to touch when I come back from a flight, although I have to be careful on the ground as it will overheat easily. I turn it on after engine start and just before takeoff. Its the first thing to get turned off after the engine is killed.

JettPilot

[reedchristiansen]

Sounds good. Thanks for the info.

What video transmitter are you using to get 5 w.?

Reed

[poynting]

@Reed:

Theoretically, range approximately doubles with every 6dB of transmit power gain. 3W is almost 8dB of gain over 500mW, so you should get more than double the range you're seeing now. In actual practice, this can vary widely depending on the resonance and efficiency of your antennas as well as situational and atmospheric conditions. I would think you can do better than 2k with that setup, but as busy as the 2.4GHz spectrum is these days, its not too suprising.