Anyone have a 100% reliable 5.8Ghz video downlink ?

[ZAxis]

We have an important project coming up and our video downlink is being problematical. It is impossible to maintain the link 100% of the time.
The performance of the whole package, Mini ccd camera/Mondo Stinger 500mW Tx/Yellow Jacket Passport diversity Rx / one rubber duck-one patch antenna / Liliput 7" field monitor, has been perfect off the Hexa (MK electronics). We had it transmit a link from a moving cable car over 2Km from the bottom to over the top of a Scottish mountain. Fly it on the Hexa and it starts dropping out almost immediately. It doesn't seem related to the transmission distance but possibly to the weather conditions. Flying in heavy mist recently saw a really high dropout rate, however nice sunny days don't mean no dropping out.
The Tx is strapped to one leg of the Hexa and has its aerial pointing straight down. We've tried the aerial horizontal, hung from the bottom of the leg and repeated it using a 100mW Tx. At the Rx we've had 2 rubber duck aerials, both vertical, both horizontal, one each direction, one rubber duck + patch.
Is our experience typical or we doing something wrong ?

andy

 

[AIRCONROB]

Andy, have you tried some of these, I can't remember what they are called but i saw them on the webb when my mate told me about them as he flys alot of FPV, I looked into them and knocked up a jig out of balsa, cant remember what guage wire it was our of a mig welder but they work mint.
View attachment 2785View attachment 2786View attachment 2787

 

[kloner]

heres what hes talking about. i haven't played with it enough to have an answer for ya

http://www.readymaderc.com/store/index.php?main_page=index&cPath=11_45_49

 

[ZAxis]

Rob...
It would be a good experiment to try them. Do you still have the jig ?

andy

 

[Macsgrafs]

You really need to join www.fpvlab.com & put the question there, trust me someone will have the answer for you, you can even PM direct the guy that makes these aerials "IBCrazy" is his name, great guy as well.

Ross

 

[AIRCONROB]

Rob...
It would be a good experiment to try them. Do you still have the jig ?

andy

Andy, the way I look at it, it's not rocket science, with the wright guage wire and connectors from Maplin a simple jig just to hold cloves in place to solder together for experimenting I don't justify paying $59 where it cost me less than £5 and i got a good result. Yes i still have the jig in the garage it must be over a year scince i made the last ones, but i am thinking of knocking up a propper jig for them.

http://www.youtube.com/watch?v=submrMo5QWs

 

[kloner]

Thanks for that youtube link, i'm gonna order up the supplies and give it a go, need a few so any savings will help

 

[Bartman]

We have an important project coming up and our video downlink is being problematical. It is impossible to maintain the link 100% of the time.
The performance of the whole package, Mini ccd camera/Mondo Stinger 500mW Tx/Yellow Jacket Passport diversity Rx / one rubber duck-one patch antenna / Liliput 7" field monitor, has been perfect off the Hexa (MK electronics). We had it transmit a link from a moving cable car over 2Km from the bottom to over the top of a Scottish mountain. Fly it on the Hexa and it starts dropping out almost immediately. It doesn't seem related to the transmission distance but possibly to the weather conditions. Flying in heavy mist recently saw a really high dropout rate, however nice sunny days don't mean no dropping out.
The Tx is strapped to one leg of the Hexa and has its aerial pointing straight down. We've tried the aerial horizontal, hung from the bottom of the leg and repeated it using a 100mW Tx. At the Rx we've had 2 rubber duck aerials, both vertical, both horizontal, one each direction, one rubber duck + patch.
Is our experience typical or we doing something wrong ?

andy

andy
my wireless video went from 50% to 95% just by ditching the rubber duck antennae and using the Blue Beam cloverleaf antennae from IBCrazy I'm using the same Tx and Rx that you are.
aim the Tx one down and the Rx one Up and you'll have virtually fuzz free video all the time. I still get the occasional period when my video goes to hell but it's way more good than bad.
good luck,
bart

 

[RCNut]

The 'rubber duck' antennas are dipoles which work best when the RX and TX antennas are both orientated in the same polarity (i.e both vertical or horizontal) and in line with each other. The Dipole signal projects outwards horizontally like a donut and the receiving antenna also receives within the same donut area so the two donuts must overlap to transfer the signal. The more gain the rubber duck has, the more squashed is the donut resulting in increased horizontal range but decreased vertical performance. This makes the angle of orientation of each antenna very critical and if the angle of one dipole to the other changes due to banked turns or flying too high the signal decreases significantly causing dropouts. Also, when flying near obstacles, reflected signals can also change the polarity and cause interference.


The answer is to use circular polarized antennas as mentioned by airconrob. Their circular polarization means you don't need to worry about the angle between the RX and TX antennas when climbing or during banked turns. They are also less affected by reflections when flying among obstacles. The 3 element and 4 element versions are the recommended ones. Use the 3 element on your transmitter and the 4 element on your receiver (the 4 element has better immunity to reflected signals). If you decide to make your own, make sure both antennas have the same circular rotation. Most of those available commercially are right hand circular polarized (RHCP) so I suggest sticking to that type, but it doesnt really matter if they are RH or LH as long as theyre both the same.


For increased directional range you can also add a circular polarized gain antenna at the receiver, pointing in the direction you're flying. I''ve just bought a RHCP 8db patch antenna from readymaderc just for that purpose but I haven't had a chance to test it yet. I'll be using the new patch antenna with the 4 element IBCrazy antenna along with a diversity box to get the best available signal at all times.


For me, I made my own versions of the 3 and 4 element IBCrazy antennas and they are like chalk and cheese compared to the supplied dipoles. I now get no dropouts at altitude or during banked turns. Im using a 200 mw transmitter at 5.8 GHz and although I dont go out beyond about 700 meters at the moment. I couldn't get even 100 meters reliably during normal flight with the original dipoles.


Lastly - as you've noted, heavy mist or rain will attenuate the signal at 5.8 GHz. Also flying behind large obstacles is not recommended as 5.8 is typically line of sight.

 

[Bartman]

The 'rubber duck' antennas are dipoles which work best when the RX and TX antennas are both orientated in the same polarity (i.e both vertical or horizontal) and in line with each other. The Dipole signal projects outwards horizontally like a donut and the receiving antenna also receives within the same donut area so the two donuts must overlap to transfer the signal. The more gain the rubber duck has, the more squashed is the donut resulting in increased horizontal range but decreased vertical performance. This makes the angle of orientation of each antenna very critical and if the angle of one dipole to the other changes due to banked turns or flying too high the signal decreases significantly causing dropouts. Also, when flying near obstacles, reflected signals can also change the polarity and cause interference.


The answer is to use circular polarized antennas as mentioned by airconrob. Their circular polarization means you don't need to worry about the angle between the RX and TX antennas when climbing or during banked turns. They are also less affected by reflections when flying among obstacles. The 3 element and 4 element versions are the recommended ones. Use the 3 element on your transmitter and the 4 element on your receiver (the 4 element has better immunity to reflected signals). If you decide to make your own, make sure both antennas have the same circular rotation. Most of those available commercially are right hand circular polarized (RHCP) so I suggest sticking to that type, but it doesnt really matter if they are RH or LH as long as theyre both the same.


For increased directional range you can also add a circular polarized gain antenna at the receiver, pointing in the direction you're flying. I''ve just bought a RHCP 8db patch antenna from readymaderc just for that purpose but I haven't had a chance to test it yet. I'll be using the new patch antenna with the 4 element IBCrazy antenna along with a diversity box to get the best available signal at all times.


For me, I made my own versions of the 3 and 4 element IBCrazy antennas and they are like chalk and cheese compared to the supplied dipoles. I now get no dropouts at altitude or during banked turns. Im using a 200 mw transmitter at 5.8 GHz and although I dont go out beyond about 700 meters at the moment. I couldn't get even 100 meters reliably during normal flight with the original dipoles.


Lastly - as you've noted, heavy mist or rain will attenuate the signal at 5.8 GHz. Also flying behind large obstacles is not recommended as 5.8 is typically line of sight.

RCNut


thanks for the more thorough answer. you're saying to have the Tx antenna pointed down and the Rx antenna pointed towards the transmitter?

 

[Vortex]

RCNut, I hope you can answer this for me.

I have just built an antenna tracker and have a 5.8G 14db patch antenna mounted to it and have it coupled up to an Immersion dual receiver. What would be the best antenna to use for the second (backup) socket.......Would a clover leaf be a good choice and would the std Immersion TX whip be worth using on the 600Mw TX or do you suggest something else.

Thanks,

Lance

 

[RCNut]

RCNut


thanks for the more thorough answer. you're saying to have the Tx antenna pointed down and the Rx antenna pointed towards the transmitter?

Hi Bartman


For dipoles, its probably better to keep the TX antenna vertical but angle the side of the receiving antenna towards the model to account for an altitude component.


It shouldn't matter if the antenna is mounted above or below the model as long as its visible from the ground. As far as general performance goes, the radiation pattern should be the same whether the antenna is pointing up or down.


Because of my flamewheel's short legs I've mounted my cloverleaf antenna on a mast on the top. If you use Yuri's leg extensions (mine arrived yesterday) then you could probably mount the antenna underneath (keeping it clear of the carbon fibre legs).


If someone still want to use a dipole antenna for receiving you can improve performance by using a V antenna at the transmitter. The V antenna is just a bent dipole but the bend distorts the radiation pattern slightly to give a more downwards-pointing signal. Its still not as reliable as a circular polarized antenna but its more reliable than two regular dipoles.

 

[RCNut]

RCNut, I hope you can answer this for me.

I have just built an antenna tracker and have a 5.8G 14db patch antenna mounted to it and have it coupled up to an Immersion dual receiver. What would be the best antenna to use for the second (backup) socket.......Would a clover leaf be a good choice and would the std Immersion TX whip be worth using on the 600Mw TX or do you suggest something else.

Thanks,

Lance

Hi Vortex.


Your 14dB patch antenna is pretty high gain so its likely to be vertically polarized. I'm therefore guessing you're using a vertical dipole (rubber duck) on your model. With that sort of gain you're going to need a tracker because the beam width will be quite narrow.


It should be OK to use a circular polarized antenna like the cloverleaf for a second antenna on your system. Circular polarized antennas can pick up both horizontal and vertical signals quite well, although not quite as well as a dedicated vertically or horizontally polarized antenna. For example, if the incoming signal is vertical, a vertical dipole will usually give you a slightly better signal than the cloverleaf. However if the signal changes polarization to horizontal (because the model banked or the signal reflected off nearby objects) the cloverleaf should do much better than the vertical dipole in that situation giving you less dropouts than the dipole.

 

[Vortex]

Hi Vortex.


Your 14dB patch antenna is pretty high gain so its likely to be vertically polarized. I'm therefore guessing you're using a vertical dipole (rubber duck) on your model. With that sort of gain you're going to need a tracker because the beam width will be quite narrow.


It should be OK to use a circular polarized antenna like the cloverleaf for a second antenna on your system. Circular polarized antennas can pick up both horizontal and vertical signals quite well, although not quite as well as a dedicated vertically or horizontally polarized antenna. For example, if the incoming signal is vertical, a vertical dipole will usually give you a slightly better signal than the cloverleaf. However if the signal changes polarization to horizontal (because the model banked or the signal reflected off nearby objects) the cloverleaf should do much better than the vertical dipole in that situation giving you less dropouts than the dipole.

Hi RCNut,

Thanks for the reply.

Yes I was planning to use the std vertical whip aerial which is supplied with the TX but will replace it with something better if you think it's a good idea.

Thanks again for the quick reply.

Regards,

Lance

 

[Macsgrafs]

Lance, the vertical rubber ducks that come with all these units suck!!! They are roughly cut to some where near where they need to be & slung on. I find a centre fed dipole on the transmitter gives me great results & is easy to make.

Ross

 

[RCNut]

Lance, the vertical rubber ducks that come with all these units suck!!! They are roughly cut to some where near where they need to be & slung on. I find a centre fed dipole on the transmitter gives me great results & is easy to make.

Ross

Thats often the case. The V antenna is a bent centre-fed dipole that gives a slightly better air-to-ground radiation pattern that a straight dipole. The construction is described by IBCrazy on RCGroups.

http://www.rcgroups.com/forums/showthread.php?t=1159968

 

[ZAxis]

I seem to have sparked off quite a discussion here !
Thanks for everyone's input. I reckon I'll go the IBcrazy way and make/buy a pair of cloverleaves.

andy

 

[Vortex]

Thanks Ross.....I thought it probably was fairly ordinary......Now I know!!

New antennas coming

 

[ZAxis]

A quick extra question ..
I'm using a diversity Rx so what is the best mix of aerials if I have a cloverleaf on the Tx?
Circular polarized patch (Vitenna -8dB) + circular cloverleaf or 2x circular cloverleaf ?

andy

 

[RCNut]

Hi Andy

The idea of the diversity box is to select the strongest signal from one of two antennas so there isnt much point in using two cloverleaf antennas at the receiver as they're both going to receive the same signal levels.

Use the circular patch antenna and a 4 element cloverleaf (skew-planar) antenna at the receiver. The patch will give you long range reception in the direction you point it and the cloverleaf will give you good 360 degree coverage closer in. The diversity box will choose whichever signal is the strongest. Mount the cloverleaf antenna a little above the patch antenna so one doesnt create a shadow for the other. The patch usually has a horizontal beam width of around 60 -70 degrees depending on the gain so try to aim it into the centre of the area youre flying into and raise the elevation by tilting it backwards about 15 - 20 degrees to account for the altitude you intend to fly.