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Thread: THE ULTIMATE 5.8GHz VIDEO LINK (AND SIMPLER OPTIONS) EXPLAINED

  1. #1

    THE ULTIMATE 5.8GHz VIDEO LINK (AND SIMPLER OPTIONS) EXPLAINED

    Two years ago I posted a thread explaining a concept that improved the video link quality and eliminated video dropouts:
    http://fpvlab.com/forums/showthread....FPV-Video-Link

    In fact, that thread was indirectly responsible of the birth of Circular-Wireless…

    Since then, our hobby has grown incredibly, the technology we use has evolved, and 5.8GHz has become the most popular frequency band for the video transmission.

    My personal explanation for this fact is that most people still uses 2.4GHz for RC, which automatically discards this band for video, and if the available choices are 1.2-1.3GHz or 5.8GHz, 5.8GHz wins in video signal quality and antenna size.

    On the other hand, 5.8GHz has some disadvantages. Range is much shorter than 1.2 or 2.4GHz, it gets obstructed by almost everything, and it suffers a lot from multipath interferences.

    Multipath in particular makes almost mandatory the use of Circular Polarization antennas, as they naturally reject multipath.

    So, I thought it was the right time to introduce the redundant video link concept I have been successfully using in some of my 5.8GHz rigs, and summarize the different options we have got if we prefer something simpler (and cheaper…).

  2. #2

    RADIATION PATTERNS

    So, let’s start with a quick reminder about radiation patterns, and more specifically from the two circularly polarized antennas I am using.

    The Skew Planar Wheel antenna is an omnidirectional antenna, which doesn’t mean it radiates in ALL directions. Its radiation pattern has a doughnut shape. It radiates in the 360 degrees around its axis (and this is why it is called omnidirectional), but has a deep radiation null along its axis, which means that it won’t transmit if we aim the transmitter antenna axis towards the receiver, or if we aim the receiver antenna axis towards the transmitter.



    Using a 600mW transmitter, and a pair of SPW in the transmitter and receiver, we can expect to reach 1.5Km range with good video signal.

    The axial mode helical is a directive antenna, which means it needs to be aimed towards the transmitter. Its radiation pattern has a cone shape, more or less wide depending on the number of turns of the helical (more turns equals more gain, but narrower cone).



    Using a 600mW transmitter with a SPW, and one 7-8 turns helical in the receiver, you can expect to achieve 5Km with crystal clear video.
    Last edited by sircana; 26th May 2013 at 07:20 PM. Reason: format

  3. #3
    Let’s start now with the different setups we could use to build a 5.8GHz video link.

    For each setup I have included a bill of materials with market prices. I have excluded the camera and video goggles from this setup list, as they are common elements to all of them. The details include only the elements directly related with the video link. I know there are cheaper options out there, but I have used ImmersionRC, Servocity and our antennas as a reference, with prices taken from a popular FPV webshop.

    SINGLE VIDEO TRANSMITTER, GOGGLES RECEIVER WITH SPW

    This is the simpler setup, taking profit of the fact that the Fatshark Dominator goggles has got a modular video receiver.



    The main advantage of this setup is its portability. Just grab your plane, quad or whatever, your RC transmitter and your goggles, and you’re done. No tripod, no cables, nothing. Just switch on and fly.

    The disadvantage is the limited range (1.5Km), and the fact that using a SPW in the receiver means that you can fly into its radiation nulls (above your head if the antenna is installed vertical).

    BILL OF MATERIALS. TOTAL COST $193.96

    Video Transmitter 600mW $69.99
    http://www.readymaderc.com/store/ind...roducts_id=266

    SPW antenna $44.99
    http://www.readymaderc.com/store/ind...oducts_id=1027

    Goggles receiver $33.99
    http://www.readymaderc.com/store/ind...roducts_id=524

    SPW antenna $44.99
    http://www.readymaderc.com/store/ind...oducts_id=1027

    If we don’t use goggles with integrated receiver, we can always use an external receiver, which could bring some advantages if we install it as high as possible (with the goggles integrated receiver we could block the RF signal with our head in some positions):

    Last edited by sircana; 26th May 2013 at 07:40 PM.

  4. #4

    SINGLE VIDEO TRANSMITTER, EXTERNAL SINGLE RECEIVER WITH HELICAL

    If we are looking for longer ranges, we can use a directive antenna on the receiver. Using an HELIAXIAL58 or equivalent antenna, we can expect at least 5Km range with good video quality.



    This is the simpler setup for long range, but the directive antenna needs to be aimed towards the aircraft. If our flight plan is known in advance, it is just a matter of pointing the antenna towards our flying area, remembering that the radiation cone will cover +/- 25° approximately. The issue is that it is quite easy to fly out of this radiation cone, losing video. Keeping the orientation (and the calm…) makes quite easy to manually aim the antenna, or fly back inside the radiation cone. Seasoned pilots can even install the Helical directly onto the goggles, and use their head as an “antenna tracking system”.

    BILL OF MATERIALS. TOTAL COST $261.96

    Video Transmitter 600mW $69.99
    http://www.readymaderc.com/store/ind...roducts_id=266

    SPW antenna $44.99
    http://www.readymaderc.com/store/ind...oducts_id=1027

    Video Receiver Uno5800 $61.99
    http://www.readymaderc.com/store/ind...roducts_id=877

    Helical antenna $84.99
    http://www.readymaderc.com/store/ind...oducts_id=1026
    Last edited by sircana; 26th May 2013 at 07:21 PM.

  5. #5

    SINGLE VIDEO TRANSMITTER, DIVERSITY RECEIVER WITH SPW AND HELICAL

    This is one of the most used setups, as it is still quite simple and affordable. The idea is using a diversity receiver, which is composed by two independent receivers, and a diversity system that continuously selects the best signal from both receivers.



    Using an Helical on one of the receivers gives the same range as the previous setup, but using a SPW on the second receiver provides a backup when flying out of the Helical beam at short/mid range.

    Even being one of the most popular setups, most of the people do not place the antennas in the optimal way.

    This is the most common way of installing the antennas on a diversity receiver:



    Which means that we will receive signal in the region resulting from the combination of both antennas radiation patterns:



    With this position, we will still lose signal when flying overhead. It is way more practical to aim the antennas this way:



    As shown in the diagram below, the Helical covers perfectly the top null of the SPW, we can fly overhead perfectly, and if the antenna is aimed with a small elevation, the down null of the antenna is pointing to the ground.





    BILL OF MATERIALS. TOTAL COST $484.95

    Video Transmitter 600mW $69.99
    http://www.readymaderc.com/store/ind...roducts_id=266

    SPW antenna $44.99
    http://www.readymaderc.com/store/ind...oducts_id=1027

    Diversity receiver Duo5800v3 $239.99
    http://www.readymaderc.com/store/ind...roducts_id=265

    SPW antenna $44.99
    http://www.readymaderc.com/store/ind...oducts_id=1027

    Helical antenna $84.99
    http://www.readymaderc.com/store/ind...oducts_id=1026
    Last edited by sircana; 26th May 2013 at 07:21 PM.

  6. #6

    SINGLE VIDEO TRANSMITTER, SINGLE RECEIVER WITH HELICAL AND ANTENNA TRACKING

    Personally, I love antenna trackers…

    Every single time a make a demonstration to someone, they are amazed about the quality of the image in the goggles, and the ability to fly everywhere, but they are always even more impressed by the antenna following the plane as it flies. I like technology, and the antenna tracker has an incredible WOW factor.



    Now seriously, without any doubt is the best possible receiver setup, as effectively we are painting the whole sky with the beam of the antenna we are using, giving a total coverage, at the maximum range of the antenna used. With an helical, this means we can fly everywhere in a 5Km radius sphere:



    But there are some inconvenient (apart of the cost…):

    - You need to properly build and setup it. Getting the antenna moving arbitrary when flying at long range is not funny at all…
    - It is not plug-and-fly. You need to wait for the GPS satellite acquisition, set home, and then set the system orientation, which will take some minutes to complete.
    - It is totally against the KISS principle.

    But, when properly setup, the results are simply amazing.

    BILL OF MATERIALS. TOTAL COST $648.82

    Video Transmitter 600mW $69.99
    http://www.readymaderc.com/store/ind...roducts_id=266

    SPW antenna $44.99
    http://www.readymaderc.com/store/ind...oducts_id=1027

    EzOSD $161.99
    http://www.readymaderc.com/store/ind...oducts_id=1186

    Video Receiver Uno5800 $61.99
    http://www.readymaderc.com/store/ind...roducts_id=877

    Helical antenna $84.99
    http://www.readymaderc.com/store/ind...oducts_id=1026

    EzAntenna Tracker $99.99
    http://www.readymaderc.com/store/ind...products_id=54

    Pan system including servo (3:1) $119.98
    http://www.servocity.com/html/spg785a_top_mount.html
    Tilt Servo HS-985MG $59.99
    http://www.servocity.com/html/hs-985...er_torque.html
    Tilt system $24.99
    http://www.servocity.com/html/ddt500...rive_tilt.html

    UBEC $4.42
    http://www.hobbyking.com/hobbyking/s...turnigy%20ubec

    LC filter $15.49
    http://www.readymaderc.com/store/ind...roducts_id=533
    Last edited by sircana; 26th May 2013 at 07:21 PM.

  7. #7

    REDUNDANT VIDEO SYSTEM

    All these setups use a single video transmitter with a SPW antenna. We have been discussing about the way to improve reception, but there are a couple of big issues related with the transmission.

    First one is signal blocking. Our planes have got many conductive elements that totally obstruct 5.8GHz signals. This means that our theoretic 360º radiation patterns will have several “holes” on it. For example, a typical wing with the video transmitter in one wing, and the motor, battery and camera in the center:



    On the other hand, the SPW has got radiation nulls along its axis, which means that when the transmitter antenna will be pointing towards the receiver (our position) we will lose signal:



    What I developed two years ago was the use of a redundant video link. The concept is using two different transmitters, transmitting in two different channels, and two receivers tuned to these two channels and connected to a diversity system.

    This has two advantages. If we install the two transmitters for example in both wings (or in two opposite arms of a quadcopter), when one of them is being blocked by some element, the other has a clear line of sight:



    The other advantage is that if we install the two SPW antennas 90º apart (for example, each one tilted 45º in opposite directions), when the null of one antenna is pointing to the receiver, the other is radiating at its maximum:



    The only issue is that we need two receivers tuned in different channels, plus a diversity system to select the best signal at any moment.

    Unfortunately, the Duo5800 v2 did not allow selecting different channels in both receivers, which means that we need to do a simple internal modification, which I explained here:
    http://fpvlab.com/forums/showthread....l=1#post138246

    Another option would be to use single receivers, and an external diversity system (Oracle, for example).

    With the Duo5800 v3 this has been solved, and with a special firmware it will be possible to select different channels from the pushbutton. The only issue is that the hardware is ready for this, but the firmware hasn’t been released yet (sorry about the pressure, Anthony…), and I had to do a similar hardware mod in order to be able to select different channels. If IRC do not release this firmware version, I will post full details about the hardware mod.

    There is a small issue about using two transmitters on the plane. Depending on the channel separation, we could slightly interfere with each other. To reduce this, it is better to transmit with Right Hand Circular Polarization on one of the transmitters (and receive also with an RHCP antenna in the corresponding receiver) and Left Hand Circular Polarization on the other transmitters (and receive with a LHCP antenna on the second transmitter).

    I’ve been using this system for long time, and you get almost rid of the unpleasant video glitches and dropouts, especially when performing acrobatics at mid and long range.
    Last edited by sircana; 26th May 2013 at 07:51 PM.

  8. #8

    DUAL VIDEO TRANSMITTER, DIVERSITY RECEIVER WITH HELICALS AND ANTENNA TRACKING

    So, finally this is the Ultimate Video System setup:



    Another of the advantages of using this redundant video system is that you don’t need to worry too much about signal blocking due to elements on the plane. This allows (for example) to embed the antennas in the wing foam:



    The BOM becomes quite impressive, but at the end of the day, the Ground Station is common to several planes (you could use this one with a single video transmitter plane too), never gets lost or crashed, and has a big influence in the final video link quality.


    BILL OF MATERIALS. TOTAL COST $1126.78

    2x Video Transmitter 600mW $139.98
    http://www.readymaderc.com/store/ind...roducts_id=266

    2xSPW antenna $89.98
    http://www.readymaderc.com/store/ind...oducts_id=1027

    EzOSD $161.99
    http://www.readymaderc.com/store/ind...oducts_id=1186

    Diversity receiver Duo5800v3 $239.99
    http://www.readymaderc.com/store/ind...roducts_id=265

    2xHelical antenna $169.98
    http://www.readymaderc.com/store/ind...oducts_id=1026

    EzAntenna Tracker $99.99
    http://www.readymaderc.com/store/ind...products_id=54

    Pan system including servo (3:1) $119.98
    http://www.servocity.com/html/spg785a_top_mount.html
    Tilt Servo HS-985MG $59.99
    http://www.servocity.com/html/hs-985...er_torque.html
    Tilt system $24.99
    http://www.servocity.com/html/ddt500...rive_tilt.html

    UBEC $4.42
    http://www.hobbyking.com/hobbyking/s...turnigy%20ubec

    LC filter $15.49
    http://www.readymaderc.com/store/ind...roducts_id=533


    The below video is a comparison between the ground signal from a single receiver, and from the redundant video system. I recorded it adding on top of the redundant video system a single receiver with another helical, and recording both at the same time:



    The left half shows the single receiver (Uno5800), and the right half the redundant system. As both signals were recorded simultaneously but with different DVRs, I haven’t been able to synchronize them better:

    Last edited by sircana; 26th May 2013 at 07:22 PM.

  9. #9
    PRODUCT INTRODUCTION

    Obviously all the setups explained are perfectly valid for any antennas, but at Circular Wireless we have developed an antenna kit suited for the Redundant Video System.

    There are two versions, with “normal” antennas, and with embedded antennas.

    The first version includes two SPW with angled SMA male (fixed, no adaptor, as it is supposed to be installed at 45°, attached to a “flat” transmitter), one RHCP, another LHCP. It includes also two Helicals, with SMA male (no adaptors again, as it is supposed to attach directly to the Duo5800), one RHCP, the other LHCP. To avoid misunderstandings, the antennas are clearly identified (Red LHCP, Green RHCP):



    The second version is designed for embedding the antennas in the foam. The antennas use a straight SMA male, and are permanently bent at 45°:



    You can find these two sets at www.circular-wireless.com.

    Considering is a quite special product, and that we expect very few pilots will demand such a professional system, these sets will be built on demand, so please expect 3-4 weeks lead-time.
    Last edited by sircana; 26th May 2013 at 07:43 PM.

  10. #10
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    Great information, thank you a ton!

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