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- เผยแพร่เมื่อ 20 พ.ค. 2024
- This design (hack) is flawed as Rob has kindly pointed out below. I came to the same conclusion when tuning this antenna. Turns out that the optimum length for the best RSSI is well below a quarter wavelength, but as the design is bad I will build something else for the TX.
Marc builds a half wave whip antenna to improve on the poor ones that came with his openlrs (long range 433MHz) system. - วิทยาศาสตร์และเทคโนโลยี
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Great stuff! Building a smaller and better tricopter using your tips! Greetings from Lithuania!
Can't wait for a benchmark :)
I wonder how that velocity factory changes w time and region (ie environment), anyone have data on this?
First, 1/2 wave will not work. You need 1/4 wave and use similar thing like Velocity Factor, but I call it "shortening factor". It is rather complex diagram... I should to upload it somewhere. It depends of thickness of the "hot" wire and wavelength, you get no more than 98% of calculated length of the 1/4 wave antenna. The thicker the conductor the higher the shortening factor, for example 96% and so on... I tried to convert diagram into mathematic function, but I faild because of my poor mathematic skill. So, diagram will be much better.
I don't know why you put the speed of light at 298. In vacuum it's 299 792 458 and in air 299 700 000 m/s (cutting a few insignificant digits from the value for air since it varies slightly with temperature). In both cases, 300 x 10^6 would be a better approximation.
Interesting video anyway since I need to learn a little about antennas.
When you tune the antenna, you end up cutting past the optimal length, so do you make two antennas and sacrifice one for testing?
My fault I forgot to mention matching the impedance of the antenna (about 300 ohms for a dipole) to the line 50 or 75 ohms. It would need a balun transformer.
On the other hand if you use a folded dipole the antenna impedance would be lower and much closer to 50 ohms, I still have plenty of 144Mhz antennas here that I built when I was working Mir. A successful antenna I still use for high gain is a design called a Jpole.
Maybe you could look that up to try.
continued
which means some light tech work might be required to make them fit. Since it is a ratio being measured calibration is not such an issue but sensitivity could be - 1.3 milliwatts might not get you a reading.
To do serious work with VHF/UHF antennas, most Radio Amateurs tend to use a Voltage Standing Wave Ratio (VSWR) meter. I have been out of the business for a few years but they used to be fairly common and relatively cheap. Since they measure the ratio between Forward (transmitter) power and power reflected by a mismatched antenna, the standing wave, they are not particularly frequency sensitive. An item intended for the 470MHz amateur band should do. However, the connectors tended to be BNC or N
Very good my Friend!...Good Job!...Congratulation!...
Try a 1/4 wave with a counterpoise (Rat Tail) which can be argued to be a dirty dipole. I'm told you might also achieve directional if the counterpoise is perpendicular. For RC, this may be a win win. It will also be a more balanced antenna. End fed half wave is likely 140ohms. With antennas this small, you may also want to use metric as well.
1/4 wave = C / Mhz / 4 * vF or 300000/433/4*.95 which equals 164.5mm for a 1/4 wave.
Some people don't calc the velocity as it will only add 5-8mm (depending on material) or so and they will trim regardless.
Hey buddy, what was ya end length after tuning ? Does the wire thickness change anything ?
Hi Rob. Thanks for pointing out my errors, I still have a lot to learn when it comes to RF and this is something that I put together after reading up on various bits on rcgroups etc.
I discovered today that something was very wrong when I started tuning the antenna. The best RSSI length turns out to be somewhat less than a 1/4 wavelength, and as you say the design is flawed so a proper design should do better. Fortunately I did the tuning with the modules set at their minimum output of 1.3mW.
I realize Im pretty off topic but do anyone know a good place to watch new movies online ?
@Lukas Marlon flixportal
@Arturo Reign Thank you, I signed up and it seems like a nice service :D Appreciate it!!
@Lukas Marlon You are welcome :)
Thanks, I missed this comment. Found the article, looks very similar to the clover leaf and skew planar antennas.
Thanks. I've been looking for a design for an End Fed Half Wave Antenna for ages but couldn't remember what it was called ;)
Another quick note Marc. There is a Ham band not far from 433 Mhz at 470Mhz. Amateurs refer to this band as "70cm" so some searching for 70cm antennas will yeild plenty of food for thought.
Marc as a former amateur radio operator I have to say this design breaks all the rules on correctly feeding an antenna. May I suggest you search for "end fed halfwave antennas"
Things you need to consider.
What is the correct characteristic impedance for the TX. Usually it is 50ohm for typical communication TX's but who knows what the little module you have is rated at. For efficient transfer of RF energy the radio and antenna impedances must match.
Some of the more constructive comments I have seen. Good material, I am still trying to learn ER9X, is that a 6 pos switch I saw in the Aux 2 Pot position of your Tx? I have just ordered one with hopes of having my Arducopter Flight modes sorted. One thing for sure, this matter of antenna theory is not something to be taken lightly no? I imagine you have made logarithmic strides. I am looking to make a fixed mast for my long range FPV but will exhaust the range of my FrSky module that has just been installed. You are missing one hellacious winter - 95% of N.A. under snow!
I'm thinking of a few more antenna vids, by the moxon vid I had learnt a lot more.
I did an article on that switch. www.rchacker.com/projects/turnigy-9x/six-position-switch-modification-for-use-with-ardupilot
No winter here on the equator :). Cheers.
RCHacker Hi.
Have you revisited this idea of end-fed dipole since this video? Theoretically it should work when properly matched, but I dont know if there is a simple way to match it. On 5/8 wavelenght whip you just need few turns nearby the connector, maybe I try the 5/8 for my LRS.
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In reality it is difficult to come up with a good antenna design for a RC TX given the portability issues when mounted to the TX. Given you are trying to optimise performance for FPV and I note you like to sit stationary while doing so, perhaps a more conventional mast mounted antenna coax fed from the TX would be superior for you. This opens up numerous designs like a proper 1/2 wave dipole,J pole etc
Whip antennas need ground plate to outer (shield) wire,
they don't work well without it.
Just a small note, m=meter mm=millimeter.
In your video m is actually mm.
equality the first thing I thought within the first min of this vid.
I find them cheap (swr meters) when they are for CB frequency range. Otherwise i find them to be expensive.
Rather 32.6 cm, as f=433.9 MHz :)
I do have a 1/2 way dipole antenna mounted on my plane.. and it actually works much better.. I use an Armilec NB18 LRS and for some reason it seems next to impossible to have a 100% RSSI, I think that the owner of the company did that on purpose for motives that I'm not willing to share on an open forum...
Migueldeservantes can you tell me I like secrets
I'm a broadcast engineer in NSW, licensced amateur radio operator, and used to teach amateur radio classes 20 years ago. Since I started flying models I was horrified by some of the antenna designs in the RC community which aren't correctly matched or are simply set up wrong (including one or two of the IB Crazy ones). I have access to test equipment and I've made a few designs of my own that work very well, I'm hoping to get something up online when I have time.
I've learnt a lot since this video. nec models?, email them to me if you like.
Have you made an antenna vid yet I'd love to see it
josh smith I have just spent a few weeks going through a nightmare moving house. Then the VSWR bridge on the spectrum analyser I was using failed. Everything has settled down now so I hope to get back into this soon. I have been concentrating on getting my amateur antennas up and glassblowing lately but now summer is here I'll get back into flying again soon!
A normal mode helical is a normal mode helical, it is NOT a dipole.
Ha, after watching the whole video I realised you were feeding it an the end!!
Not done.
Bingo. If you go the mast mounted route I suggested Circular polarised too !!!
qslDOTnet/nwlarn/sat/70ParaLindy.pdf
Thanks Dad. Yep I'm definitely learning here.
Funny how all the old fart amateur radio experts come out of the wood work.
You haven't got a network analyser lying around in your shack do you?
Has anyone tried to float a few GPIO pins soldered to different points on the antenna then write a simple script to ground each pin one at a time and automatically pick the one w highest gain. I would loop through this every few seconds (shouldn't take more than a few milliseconds to get the RSSI).
Thats an interesting idea, sort of like a phased antenna array.
RCHacker Since I've got you on the phone I need some advice...I'm planning a large tricopter build (goal: lift 150lbs for 10 minutes) to address many problems w big problems multirotors crafts that I notice namely they use too many motors meaning poor power to weight ratio and too little pitch meaning the blades just slice through the air. A triangle is one of the strongest geometries but most tricopters use a star like pattern from the center, like this >- where I want to do this:
Andy Payne I'm a big fan of smaller, faster spinning props and motors to reduce vibration. The KK2 can be adapted to just about any configuration in the field with its custom mixer. Other than that I think you are looking at modifying multiwii code.
Andy Payne There is also OpenPilot and TauLabs which is the most complex and powerful, however I have no experience with it.
Marc Griffith I looked at the cpp code and it looks promising, thanks for that. I don't understand why a faster prop would be less prone to vibration, can you explain? Also I don't understand why all the dimensions get distorted when people think bigger (props become plan props, motors because relatively tiny high kv motors) practically I can see why because those are common parts and large bldc motors are just starting to become more popular. Ie look at this guy building a 20 kw bldc: watch?v=TKjZgAvZAwM.
two MM,s one M is for meters
hot glue and then heat shrink to strengthen
Not that your method didn't work
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simply end feeding a half wave like this will result in an extremely high impedance and could potentially damage the module with near full reflected power.
RSSI is not a reliable indicator of RF performance as it tells you nothing about the impedance match and hence energy transfer. The RSSI is also highly influenced by radiation pattern. Indeed the whole concept of gain is based on deliberately modifying the pattern to your advantage.
I have been trying to find out how to measure the impedance of the feed line and antenna. I have not been able to find a way to measure it. Can please you tell me and anyone else curious how to do it?
I see them around hamfest used for $15 to $ 30,I use a MFJ-817C
And use 468 divided by the frequency in MHz and 234 to get one side of the wave
234+433.000=0.5404157x12"=6.4849884" or 16.471870536cm
and use a small pice of RG8 mini 50 ohm coax
hamuniversecom/easydipole.html