MadMike-Heli

Hello everyone, I'm looking for some valuable input into a problem that has been bothering myself and my business partner these past few days. Currently there are two standards that we have at our disposal. 900MHz and 2.4 GHz wireless video downlinks. I've been told two completely different things from two different companies. One states that 900 MHz is a better system since a high gain antenna which will be used is non directional - mount it and forget about it, as oppose to 2.4 GHz where the antenna is parabolic and needs to be pointed at the aircraft.

You may ask, why do we need to do this? Well we are research UAV development for out of sight useage in remote wilderness areas. We're currently working with Transport Canada so this is completely approved by the govt. We are ensuring safety at every level. We are just researching the video aspect of a downlink now.

So I guess what I'm asking is , everyone seems to use 2.4 GHz. Is 900 MHz better in any aspects? or 2.4 GHz is better, why and why not? It seems if for anything else the 900MHz high gain Yagi antenna would be a lot less fuss than the parabolic Yagi high gain.

I'm interested in feedback, all is welcome except flames and bashing....

Thanks

Mike

mklarich

Mike, 2 big things. How far do you want to go and how big is the airplane/heli that is going to be carrying the payload.

Matt klarich

MadMike-Heli

First of all thanks for the reply, secondly , like anyone in designing a prototype UAV you would love to go as far as possible but realistically with the type of transmsitters and receivers that are commercially available I'm thinking 1.5-3km's tops - basically 1-3 miles distance max. I'm using an FM Futaba 9CH radio system so I'm assuming it can go that far, I haven't done the research as of yet, but I'll be conducting some maybe this weekend, just by taking the tx and getting in my truck and driving for awhile, with a friend at my house, just to check the max distance of the system....

So, would you recommend a 900MHz or a 2.4 GHz system. Is one more limited in distance than the other, is taht what your getting at? I'd love to hear as much as you have to say about the topic.

Thanks once again,

MadMike-Heli

Fubar-One

My Feedback: (1)

I have used both systems and my results were:
The 2.4ghz system (200mw) seemed to have a better signal with less dropouts using the stock omni antenna than the 900mhz system.
The results with the 2.4ghz system improved with the use of a circular polarized patch antenna.
The absolute best results we got were with the 900mhz system and a 4' (aprox) yagi antenna.
My father held the yagi aimed at the plane while I flew it.

mklarich

I have been using Blackwidow A/V 600mW transmitter and a special receiver of mine. For a test I did standard omni antennas, I took off and had someone record from approximately 2 miles away. I had little to no dropouts and the video was fairly clean.

Keep in mind, this was on stock little 2db omni 2.4ghz antennas. With a slightly larger antenna I could have gone much farther with no dish pointing.

The receiver will be available through blackwidow in the next couple months, enuf said.

Matt Klarich

kd7ost

Mike,

I think you have a tall order. I want to follow your results closely. I am currently flying a fixed wing aircraft with a GPS guidance system and altitude lock, roll control etc. The systems are enabled through PCM action. Either I engage them with spare channels or they engage at the loss of signal from the transmitter. I'm using the Futaba 8UAP PCM Radio. Manufacturers build these radio's to put out ~750mw of rf. (There's only one way to know you have flown out of range.) With the stock 1/4 wave antenna on both ends I get just a little over 1 mile range. The receive antenna is mounted horizontal though and I hold the transmitter antenna vertical. You can likely get a little more range in a helicopter if you mount your antenna full length and vertical. Can you put it in a plastic antenna holder and mount it straight down? I can't do that in my aircraft. I am currently building a home brew 1/4 wave di-pole antena to see if I get better range with that. It will be mounted horizontal to match the rx antenna and about 20 feet in the air. (I can't find a 72 MHz yagi in the whole world). I still have the issue of the rx antenna being hit off the null though as the plane turns towards and away from me. A vertical mount would help, but at the end of the day I seriously doubt you could get much more than 1.2 reliable miles out of a stock radio. Your bigger concern is what happens when you do drop the signal? Mine just comes back to me and is cheaper and easier to set up in a plane than in a Helicopter. Are you employing any on board stabilization or automation systems?

I fly 900 MHz just because I have it on hand. It is my intention to purchase a 2.4 GHz setup in the future from someone like Black Widow AV. They have a 1 watt system I'm dying to range test. I can program my plane to fly autonomously so will just set up a Video link and have the plane fly out 10 or 20 miles and back. Then I just have to watch the Video to see where the drop out occurs. I live in the Idaho High desert though so would likely get much better range than you if your dealing with a wooded environment. 900 MHz is better at going through or around objects up to a point. (Trees) 2.4 GHz uses smaller antenna's and can get you great range but needs pretty good line of site. Outside of that, these other guys are the video experts. Another reason for me to use 2.4 GHz is because of the desire to fly Radio modems for tracking. Right now I track my plane when I'm flying autonomously using Ham Radio and APRS in the 2 meter band. There are small radio modems that can connect to your GPS and send location information back to a lap top. These Radio Modems operate at 900 MHz. I plan to swap my Ham tracking with this system. I want my Video frequency away from 900 MHz so I can downlink both signals with little to no cross talk.

Dan