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As you may have read from my previous blogs - I’m experimenting with an autonomous pilot system that is able to guide several vehicles in a coordinated fashion. Each vehicle is outfitted with a transmitter that sends telemetry information back to the main computer, and the main computer sends back guiding commands.

The telemetry is based on 3DR serial link radios (915 mHZ version). I did however find that the normal dipole antenna was heavy and was often “in the way” of propellers, airflow and just a general nuisance.

I discovered that Molex was producing an antenna for the same frequency band, that was quite different from the normal dipole and decided to try it out.

The antenna weighs less than 1 gram and has a self adhesive side which make it perfect for mounting it directly on to the fuselage or the wing - a short wire then connects to the radio through a cmx connector.

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The advantage is that you can easily place the antenna somewhere on the body or wing and because of the light weight, it will not upset the balance of the plane nor create any drag.

 

Testing it out

I decided to mount the antenna on the wing of my trusted Z-84 also known as UTV-3 - It has become the workhorse of many experiments and has the most flying hours.

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I flew in increasing distance and height and monitored the signal strength and telemetry errors.

This is by no means a thorough scientific test and comparison to the standard dipole antenna, but I experienced very little error (<1%) and I flew as high and far as the law allows.

I definitely will use this kind of antenna on my next builds because of their low weight and ease to stick on the fuselage or wing.

 

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Comments

  • @Jake + Adam

    What you want is a simple "This is better than the other" but I'm not able to give you that for at least two reasons.

    1. I do not use APM, the telemetry protocol I use is designed for swarms or very fast telemetry transmission, with several hundred full transmission every second. The protocol relies on being fast and if you loose one telemetry packet, you'll be sure to get a fresh 1/100 of a second later, so it don't matter. So no RSSI support.

    2. Comparing two antennas with different radiation patterns and gains is very difficult - plotting strength over distance is not going to cut it - in some scenarios one antenna will be better than the other and vice versa. There are so many ways to place and orient both antennas. This picture shows just how much is put into testing antenna design and performance if you want to get credible numbers.

    I did not invent the idea of using this type of antenna for this purpose nor do I secretly own a large antenna manufacturing plant. I haven't seen others write about this here so I thought I'd write a short post about it (not mentioning a review in any way), and maybe inspire some to spend the $4,99 on one of these and try it out. I think some did and they'll probably have some fun doing it and a remark or two from others who haven't seen this kind of antenna before. And maybe they can give you a description of their experience using this antenna.

    The rest is probably better of with the stock antenna anyways :-)

  • @Jesper

    If you can't get telemetry data, copy the .bin file off the sd card, in mission planner on the home page, go to the data flash logs tab, hit px4.bin to .log, then hit review a log and view the logs you've collected, you'll see the option to view RSSI on the right.

    I assume you posted the info to help others out, and this info will help others, unless they spend the money on the antenna and get a worse performance.  You say the performance is the same, but it would be great to quantify it.  

  • Didn't mean to neg you as much as that probably came across.  But it's frustrating to sort through all the spam out there when both sellers and people reviewing things always seem to fail at doing proper range tests.

    How many feet/meters of P3/4/5 signal do you get with the STOCK 2dBi antenna? (everyone has one for comparison!)

    How many feet/meters of P3/4/5 signal do you get with the antenna you are trying to review?

  • @Jake - judging from the thumbs up on this post, some did find it informative.

    What I simply concluded was that if you want to try out a different antenna design that is more aerodynamic, lighter and easier to integrate onto your airframe then give this type of antenna a try - I also concluded that I did not see any degradation to the signal compared to the standard dipole while flying within the allowed range - suggesting that it's safe to try out.

    I'd like to do a RSSI analysis, but I'm using a very low level binary telemetry protocol which is optimised for performance, so no RSSI info. 

    Alas I have no earnings on Molex selling these antennas.

  • Why even post if you're not going to test this in comparison to something?  Otherwise it's just advertising/spam.

  • If you have a pusher like your plane you could place it on the nose so its far away from everything else.

    Could you please do a test Jasper and plot the RSSI against distance for both antenna's?

    Thanks,

  • @Bertrand - No interference - it was a concern when I mounted it, but no problems there - cheap Turnigy servos seems to work great :-)

    @Justin - Yeah - they are really cheap and of good quality

  • This is great!  I found them at digikey for $4.50 USD!
    http://www.digikey.com/product-search/en?KeyWords=1052620003

    http://www.digikey.com/product-search/en?KeyWords=1052620003
  • the first pic just looked like a tail, i thought it was a serious integrated antenna design. it turned out to be a typical micro stripe.  

  • I use those one, no need to soldering.

    http://store.rfdesign.com.au/rfdflex1-900mhz-flexible-pcb-antenna-3...

    Your antenna seem to be near the elevon servo and cable. Is there any interference between the two?

    RFDFLEX1 900MHz Flexible PCB Antenna (300mm RPSMA)
    RFDesign designs and manufactures the Antennas, RF Electronics and the RFD900 radio modem
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