Dec 18, 2009, 01:37 AM It just keeps getting better! Eureka, CA Joined Oct 2002 1,540 Posts Nice work! Lots of useful info and to the point.
 Dec 18, 2009, 01:48 AM Registered User Lijnden, the Netherlands Joined Oct 2007 38 Posts Great article IBCrazy, I am a bit confused maybe you can help me a little. In the article you tell about the old formula to calculate wave length in meters being 2.98 * freq in Mhz. Usingn your 910 Mhz example resulting in a wave length of 2711,8 meters. This seems a little long wavelength since you calculated a little bit further that the quarter wave would be 7.87 centimeters or 0,0787 meters. even when I take the 0.95 % in the equation I can't understand the big difference because 4 * 0,0787 is not equal to 2711,8. Where do I go wrong.
 Dec 18, 2009, 04:34 AM Registered User Romania, Dolj, Craiova Joined Sep 2007 17,163 Posts Excellent, all you need to make it perfect is to add some more bits about polarization Last edited by renatoa; Dec 18, 2009 at 05:30 AM.
 Dec 18, 2009, 06:14 AM AP-stick Montreal Joined Nov 2005 1,635 Posts subscribe! thanks is it possible that different type of antenna have a direct link with video TX power comsuption ?. i have a problem: my video TX (900mghz 500mW) become really really hot (untouchable), and pull between 600mA and 1 amp instead of 300mA as advertise...with the original antenna (i`w waiting my 2dbi dipole). I will built one of your model (dipole probably ?) to get more performance and save weight... !
 Dec 18, 2009, 06:59 AM Questionable judgement Charles Town, WV Joined Jan 2008 3,074 Posts Awesome post! I've been wanting to make my own tx antenna.
Dec 18, 2009, 08:10 AM
Iranair
Joined Aug 2007
585 Posts
Quote:
 Originally Posted by IBCrazy Building your own antennas for FPV use This is a basic guide on how to build and calibrate your own antennas for use in FPV. I will not be going into extreme detail as there are hundreds of papers on the designs of these antennas. However I will explain their construction, and most importantly, how to connect them and how to test them without specialized equipment. I will be covering 3 basic antenna types: The basic half wave dipole Half wave whip Inverted Vee I will discuss the limitations, design considerations, and best applications for each of these antennas. For those who wish to build a patch antenna, Mr. RC Cam has an excellent how to on his website titled The GP Patch antenna. I will refrain from reposting it here. -Alex
Hi IBCrazy

It seems that you are the one to ask this from. I Have a sheety Fpv system that i bout long time ago. It is and was very cheap, but it doesnt work really. I am not very good at this, but there should be someone or a site or somethig that i could turn this to a nice hobby working time.

What i want to know is. If i make a better antenna for it. would it improve the range? or what can i do with it?
I have thought of many things. Like jumping up and down on it and then see if it improves anything?
I havent done it yet but if you say so i promess i will........
here is a picture of it.

Images

 Dec 18, 2009, 08:51 AM Registered User Romania, Dolj, Craiova Joined Sep 2007 17,163 Posts The problem with your system it's the overall low quality, that can't be improved much only by changing antenna. First the receiver... I see in the picture the damned tuning knob, that is a sure sign of low sensitivity receivers that are very difficult to keep in tune, because they drft badly with both power voltage and temperature. Also, I suspect the transmitter too, if it is hidden in the camera case, picture is too small to see clear. If I guessed, then that transmitter has 10mW in the most optimistic case, but I expect to have even 2-3mW, so a range of under 100feet.
 Dec 18, 2009, 10:09 AM FPV Pilot United States, MT, Missoula Joined Mar 2006 1,264 Posts Very nice work IBcrazy. Good info your sharing .
Dec 18, 2009, 10:27 AM
Engineer for Christ
Amherst, VA
Joined Jun 2006
11,030 Posts
Quote:
 Originally Posted by RENATOA The problem with your system it's the overall low quality, that can't be improved much only by changing antenna. First the receiver... I see in the picture the damned tuning knob, that is a sure sign of low sensitivity receivers that are very difficult to keep in tune, because they drft badly with both power voltage and temperature. Also, I suspect the transmitter too, if it is hidden in the camera case, picture is too small to see clear. If I guessed, then that transmitter has 10mW in the most optimistic case, but I expect to have even 2-3mW, so a range of under 100feet.
Right on. You'll need to test with the RSSI pin extensively after this thing warms up some. Tune the knob to the highest RSSI (You'll have to back off about 20 feet before taking the reading). Once set, glue it in place. Use a voltage regulator to make sure the voltage is constant on the RX.

-Alex
Dec 18, 2009, 10:42 AM
Engineer for Christ
Amherst, VA
Joined Jun 2006
11,030 Posts
Quote:
 Originally Posted by jarconman Great article IBCrazy, I am a bit confused maybe you can help me a little. In the article you tell about the old formula to calculate wave length in meters being 2.98 * freq in Mhz. Usingn your 910 Mhz example resulting in a wave length of 2711,8 meters. This seems a little long wavelength since you calculated a little bit further that the quarter wave would be 7.87 centimeters or 0,0787 meters. even when I take the 0.95 % in the equation I can't understand the big difference because 4 * 0,0787 is not equal to 2711,8. Where do I go wrong.
That is the length of your antenna active component. It is 1/4 of your wavelength. At 910 MHz with a 95% propagation factor, your wavelength is 31.43 cm. 2,970,000 * .95 *100 / 910 MHz = 31.43 cm
Dec 18, 2009, 01:34 PM
Engineer for Christ
Amherst, VA
Joined Jun 2006
11,030 Posts
Quote:
 Originally Posted by ggtronic is it possible that different type of antenna have a direct link with video TX power comsuption ?. i have a problem: my video TX (900mghz 500mW) become really really hot (untouchable), and pull between 600mA and 1 amp instead of 300mA as advertise...with the original antenna (i`w waiting my 2dbi dipole).
Matching the antenna will have a direct impact on the heat generated by the transmitter, but not the power consumed. Poorly matched antennas direct the would be transmit energy back at the transmitter causing it to heat up.

Do yourself a favor and take apart the junk whip antenna on your TX by unscrewing the plastic holder. Solder on a piece of solid copper wire 6-3/16" long to the end of it and replace the cap to help support it. I'll bet you TX runs much cooler and your range doubles.

-Alex
Dec 18, 2009, 03:51 PM
AP-stick
Montreal
Joined Nov 2005
1,635 Posts
Quote:
 Originally Posted by IBCrazy Poorly matched antennas direct the would be transmit energy back at the transmitter causing it to heat up.-Alex
humm thats good news!

but the transmitter claim 300mA, and it sometime pull 1000mA !
it start to have an impact on flight duration !

anybody else have ever mesure theire 900mghz 500mW transmitter
power comsuption (i'v seen amp go near zero on most FPV video,
wich mean video TX need near nothing... )

thanks Alex
Dec 19, 2009, 12:17 AM
five by five
Panama City Bch, FL
Joined Jan 2009
2,074 Posts
Quote:
 Originally Posted by ggtronic humm thats good news! but the transmitter claim 300mA, and it sometime pull 1000mA ! it start to have an impact on flight duration ! anybody else have ever mesure theire 900mghz 500mW transmitter power comsuption (i'v seen amp go near zero on most FPV video, wich mean video TX need near nothing... ) thanks Alex
my 900mhz 500mw tx, camera, and a small fan pulls around 0.5a. i think im using a 1a fuse on my fpv gear.

like alex said, a tuned antenna is first and foremost. i don't know how it affects power consumption, but it certainly affects power output! when i was tuning my stock junk antenna power output varied from 400mw to 700mw.
 Dec 19, 2009, 02:58 AM Houba ! Houba !! United Kingdom, England, Milton Keynes Joined Sep 2003 6,613 Posts Thanks IBcrazy you have made so many points so much clearer. I'm off to get some bits for that dipole aerial
 Dec 19, 2009, 05:12 AM Registered User Joined Sep 2009 25 Posts IBCrazy, there is an interesting dipole antenna design on rc-cam.com you might like to include in your list. The benefit of it is that the transmitter is not forced to be at the centre of the antenna, and also that some length of feedline is possible (but note the comments about results varying with feedline). I haven't tried it yet myself unfortunately. Thanks for your article!