START HERE |
|
Register | FAQ | PM | Events | Groups | Blogs | Calendar | Mark Forums Read |
Unregistered
|
FPV and Real time Video Discussions of receiving video in realtime from the aircraft |
|
LinkBack | Thread Tools | Display Modes |
01-11-2010, 08:28 PM | #1 (permalink) |
Registered Users
Join Date: Apr 2009
|
250mW or 500mW ?
Salut,
I want to buy a AVS 5.8 ghz on Future Hobbies shop. It came in 250 and 500 mW version. I'm sure that "500" is better than "250" but don't known if i will get, in range and video quality, the difference of 150 bucks between them. It's my first kit and i don't want to regret so... Which one should i choose? Thanks and have good fly! http://www.futurehobbies.com/index.p...mart&Itemid=53 http://www.futurehobbies.com/index.p...mart&Itemid=53
__________________
With a lot of repairs parts you can kill gravity |
Sponsored Links | |||
Advertisement |
|
01-12-2010, 11:47 AM | #2 (permalink) |
Registered Users
Join Date: Sep 2008
|
The difference is transmit power. More power equals greater range, and might equate to better video depending on a lot of other factors like how electrically "noisy" the heli is and what other sources of interference exist in the area where you intend to fly.
Unfortunately, I can't think of any way for you to make a quantitative choice. You can definitely say that if you have issues at 250mw, 500mw will probably work better, but it's impossible to say if 250mw will have issues or even if 500mw will eliminate issues seen at 250mw - you've just got to try it and see...
__________________
Fly in the street hangar includes: T-Rex 450SEV2, 250SE (MD500), Blade 400, SR & mSR & 120SR & mCPx & mCX & CX2, Walkera 4G6S & SeaCobra Parkzone Sukhoi (& XP), Centurion, Mustang (Micro and BL versions), µBeast, Mosquito
|
01-12-2010, 04:12 PM | #3 (permalink) |
Registered Users
Join Date: Nov 2008
|
Just get what you can afford.
__________________
-Smoky Download my Heli Setup Tracking Sheet: For Excel 2007+ http://www.eagleraceteam.com/Heli Configuration Tracker_Excel 2007.xlsx For older Excel http://www.eagleraceteam.com/Heli Configuration Tracker_Old Excel.xls |
01-12-2010, 06:21 PM | #4 (permalink) |
Registered Users
Thread Starter
Join Date: Apr 2009
|
Best for the bucks or bigger is better...
Thanks Rocketsled, usefull and if you want to known what i thinking about
the 500 mW just ask me in a few weeks. Smorkytyrz your answer is so usefull too.I known now that you use 5.8ghz kit. Can you tell me more about it? The range and quality of the video...and if you use a "patch antenna". Thanks again and sorry for my english
__________________
With a lot of repairs parts you can kill gravity |
01-12-2010, 07:23 PM | #5 (permalink) |
Registered Users
Join Date: Nov 2008
|
I dont go out too far, but 500mw will give u good range in most places. 5.8 will be more disturbed by ground clutter i think than 1.3 or 900mhz. But in my area 5.8 is a lesser used frequency since our phones jumped to DECT so quickly.
Video quality is great with the iftron stuff. All comes down to the camera quality.
__________________
-Smoky Download my Heli Setup Tracking Sheet: For Excel 2007+ http://www.eagleraceteam.com/Heli Configuration Tracker_Excel 2007.xlsx For older Excel http://www.eagleraceteam.com/Heli Configuration Tracker_Old Excel.xls |
01-12-2010, 09:46 PM | #6 (permalink) |
Registered Users
Join Date: Sep 2008
|
For the sake of comparison, a cell phone radiates with about 750-1000mW at about 1GHz, and if I remember can have a maximum unobstructed range of 20 miles or more. The frequency we're talking about here is higher, but 500mW should still ought to be sufficient for at least a few miles, especially if the transmitter is up in the air.
__________________
Fly in the street hangar includes: T-Rex 450SEV2, 250SE (MD500), Blade 400, SR & mSR & 120SR & mCPx & mCX & CX2, Walkera 4G6S & SeaCobra Parkzone Sukhoi (& XP), Centurion, Mustang (Micro and BL versions), µBeast, Mosquito
|
01-13-2010, 01:43 AM | #7 (permalink) | |
Registered Users
|
Quote:
Just an example: A system using a 10mW 5.8GHz transmitter and basic receiver will loose signal if you fly behind a tree some distance away. A 10mW 900MHz system performs flawlesly even if there was two or three trees... In theory the lower the frequenct, the better it will penetrate throug obstacles. Another example: A boyracer boom box car banging loud eurodance music some kilometers away. All you hear is the low bass beat because all the high frequencies get absorbed or scattered along the way. |
|
01-13-2010, 11:43 AM | #8 (permalink) |
Registered Users
Join Date: Sep 2008
|
Yep, I know. That's why I included a proviso about the frequencies being different and also why I gave my "estimate" a 10:1 attenuation factor for the 6x higher frequency and said "unobstructed".
Probably an exact calculation for radiated power and distance vs. frequency someplace, but I'm too lazy to go and dig it out of my ARRL books. I'd argue that the exact number isn't too important in this discussion. With the TX in the heli, up in the air and mostly unobstructed, 500mw ought to be good for a fair distance. What's the radiated power of a 2.4GHz RC Tx? I think it's in the same range as what we're talking about here, and 2.4G is close enough to 5.8G to be comparable. A 2.4G Tx is good for a longer distance than you will be able to see the model, no?
__________________
Fly in the street hangar includes: T-Rex 450SEV2, 250SE (MD500), Blade 400, SR & mSR & 120SR & mCPx & mCX & CX2, Walkera 4G6S & SeaCobra Parkzone Sukhoi (& XP), Centurion, Mustang (Micro and BL versions), µBeast, Mosquito
|
01-13-2010, 12:33 PM | #9 (permalink) |
Registered Users
Thread Starter
Join Date: Apr 2009
|
Thanks you all,
Tnrquill now i'm afraid...but thanks for the info. 900mhz past through obstacles and 5.8 don't? I'm not gonna be able to turn arround a house or a three or....name it! Do i have to go for 900?
__________________
With a lot of repairs parts you can kill gravity |
01-14-2010, 12:38 AM | #10 (permalink) | |
Registered Users
|
Quote:
Squarely Deadly: I have no personal experience on exact differencies between 900MHz and 5.8GHz, I have only flown with 5.8GHz video link. But a friend of mine did some comparison way back and was able to fly below treeline with 900MHz as the 5.8GHz setup dropped as soon as he dipped between the tree tops. |
|
01-14-2010, 12:06 PM | #11 (permalink) |
Registered Users
Join Date: Sep 2008
|
Yep. I went back and did a quick skim through some of my ARRL books. The frequency doesn't matter much if at all in Line of Sight (LoS) transmission. It's all about radiated power and antenna gain. When you are trying to transmit through objects, though, frequency is a huge factor. The higher the frequency the more attenuation.
The advantages of higher frequencies are primarily twofold. First, higher frequencies tend to be a little less crowded, though this is only a "transitory" advantage, since as new channels open up manufacturers rush to fill them. Second, you can achieve higher gain with smaller antennas at higher frequencies. This second factor is the one that's most pertinent if you're power-limited. The total effective LoS transmission range is a function of the gain of the entire "system", which consists of the Tx, Tx Antenna, Rx Antenna, and Rx. Greater range can be achieved with lower transmit power using a higher gain antenna configuration. But antenna gain is a function of the wavelength of the frequency being used, and lower frequencies with their longer wavelengths need larger antennas to achieve the same gain. At 900MHz a full wave antenna is 1 foot long. At 5.8GHz a full wave antenna is only 2.25" long. That all being said, without a doubt, 900MHz will transmit quite a bit better through and around obstacles than 5.8GHz. If you're worried about being able to receive video through trees or from behind buildings, the lower frequency is unquestionably better!
__________________
Fly in the street hangar includes: T-Rex 450SEV2, 250SE (MD500), Blade 400, SR & mSR & 120SR & mCPx & mCX & CX2, Walkera 4G6S & SeaCobra Parkzone Sukhoi (& XP), Centurion, Mustang (Micro and BL versions), µBeast, Mosquito
|
Thread Tools | |
Display Modes | |
|
|