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Aerial Photography and Video > Wireless Video Links Setup Help and Advice Please

FlightPower
Veteran
Location: Herts UK

Hi,

I'm struggling. I have tried two kinds of 100mW 2.4GHz downlinks in standard patch and dipole TX + Mag-Mount RX configuration. I would estimate 50% of the time I'm getting drop-outs/static/white noise no matter what I try. I have done a search of RR and found very little information on this - so hopefully this topic will end up as a valuable resource for many people intested in this subject.

From what I understand, the 100mW links I got ( HAR01 and AAR14 ) are high quality so I guess I'm doing something wrong with my setup. Monte at WVC has offered every assistance but he's 1000s of miles away making every tweak a 2-week round trip by air mail, and in the final analysis I need the knowledge to understand what I'm doing with my total setup so I can take charge of putting it right instead of relying on Monte and UPS.

I'm not really keen to just up the raw power of my TX especially because I understand there may be legal issues as well as battey consumption and possibly extra RF reflections that could make matters worse if I go that route (plus 100mW is rated by WVC to 1 1/2 miles and that's more than 3 times what I need, surely I should be able to get 300metres with no difficulty). So I'm keen to hear from anyone who's getting excellent results from their downlink who could kindly show and tell what they are using and how they set it up. I'd be particularly interested to hear from anyone using WVC 100mW equipment successfully and show me (please) how they set it up to save me starting from scratch.

To define a little better what I need: non 3D flight, carbon high-lift blades (can't do without them), moving heli through a slow pattern for video or positioning heli for stills shot, never more than .5KM from the operator. If I play back 5 minutes of video from the downlink, a few minor glitches is OK by me, but not lots of white noise.

Is anybody using a downlink that comes close to performing like this, please jump in?

Thank you,

Julian.

05-27-2003 Over year old.

mr.rc-cam
Heliman
Location: USA

Quote
I'm not really keen to just up the raw power of my TX especially because I understand there may be legal issues as well as battery consumption and possibly extra RF reflections that could make matters worse if I go that route...

Well, you are already operating a system that requires a amateur radio license, so going with higher RF power is not an legal obstacle. Your ham license allows up to 50W at 2400-2450 Mhz. But, your other points are very valid and RF power higher than 100mW is really not necessary for 0.5 km range.

Quote
Is anybody using a downlink that comes close to performing like this, please jump in?

Yes, several of us are. Mine are all sort of home built (they were not ready-to-use products), so I cannot offer you a one stop shopping solution. But, I can say that a decent 100mW system should be able to fully satisfy your application. All I use is 50mW and 100mW and I get very good performance (at least 0.5km in a urban setting).

This fellow is using 100mW with a Yagi on the Rx and gets incredible range (just take a look at his "Moviestar video 5.5mb" AVI): http://home.online.no/~la9ex/

Quote
To define a little better what I need: non 3D flight, carbon high-lift blades (can't do without them), moving heli through a slow pattern for video or positioning heli for stills shot, never more than .5KM from the operator.

With that sort of requirements the carbon blades are not expected to be a threat to the signal. Our tests with wood, fiberglass, and carbon showed that they all worked well (at least for us).

Quote
If I play back 5 minutes of video from the downlink, a few minor glitches is OK by me, but not lots of white noise.

That should be possible with 100mW at 0.5km. For example, with my lower power 50mW system that is based on the Lawmate Tx, I get nearly perfect (almost glitch free) video. The Tx has a very inefficient factory installed helical stub on it and I use the RC-CAM Goof Proof Patch antenna on the Rx. In my urban setting (local park) the homebrew GP Patch antenna radically reduced the video glitches (multipath interference) when compared to my PCB based commercial patch aerials.

It is tough to say why you are having so much trouble. I cannot comment on the your specific equipment because I am not a user of it. But, because you are having the same problem with two systems, I suspect that you might be suffering from environmental issues. For example, competition from other ISM devices can cause grief. Nearby buildings, wire fences, cars, and such can introduce multipathing problems too.

If you have not done so lately, drive out to a very open field that is far away from everything, including wire mesh (e.g., cyclone) fences. Perform some simple range tests and compare them to what you usually get. This will set the base level of what your current equipment and its specific installation will provide. If it is inadequate at short range then something is wrong with the installation or equipment. A solution at this point would require hands-on RF trouble shooting, so I cannot help much.

Lastly, I would like to say that UHF & microwave RF is a very unforgiving medium. Everything matters, right down to how tight the RF connectors are and the position of the antennas (and so much more). This is the reason that I roll my eyes whenever I hear someone claim that their R/C video systems are plug-n-play. Yes, sometimes it is, but sometimes it isn't.

RC-CAM

05-27-2003 Over year old.

HOMEPAGE

MPA
Elite Veteran
Location: Australia

Hi Mr

I spent time messing with antenna chasing a clean picture and it ended up being the vibration on the AV box.
I hung it from one rubber band alone and took it up and the pic was clear.
It was isolated befreo but seem it wasnt enough.

Once I got that out of the way I tried a varation of antenna.
1/4 wave with ground plane (see rc-cam guy) worked best.
Rx I use a dual quad made from thick bronze welding rod.

My gear is all low power std off the shelf AV link

Cheers

05-27-2003 Over year old.

HOMEPAGE

mr.rc-cam
Heliman
Location: USA

Quote
I spent time messing with antenna chasing a clean picture and it ended up being the vibration on the AV box.

This is a common problem on some wireless video Tx's. The typical symptom is horizontal lines that change in intensity with engine or rotor RPM. It is the PCB or components wiggling around (at a microscopic level). Given our UHF/Microwave RF frequencies, minor movement will impact the RF circuitry in a huge way.

Second on the list for varying horizontal lines is an overdriven audio microphone on the Tx. Loud engine noise or intense vibrations will affect the audio sub-carrier on designs that do not use a audio limiter. In some cases the mic needs to be removed if damping attempts fail.

But these do not appear to be happening in this case. The symptoms are "drop-outs/static/white noise" which indicates multipathing and weak signals.

Quote
I tried a variation of antenna.1/4 wave with ground plane (see rc-cam guy) worked best.

Good point. The fellow behind the la9ex link I gave is also using a 1/4 wave ground plane on the Tx. This will earn you +3dB of gain, which is the same as doubling RF power. Yb2normal has the basic details here: http://www.geocities.com/xcamflyer/antenna2.html

RC-CAM

05-27-2003 Over year old.

HOMEPAGE

FlightPower
Veteran
Location: Herts UK

Thank you Mr RC-Cam for a most thoughtful and analytical response-really appreciated.

Briefly regards HAM licensing, I'm in the UK, I promise to check out the local rules and get myself compliant as soon as I know which equipment I am trying to license - right now I'm not generating any UHF/microwave output if you get my drift. We have two "license free" bands in the UK that I'm aware of 2.4GHz and 1394MHz (I don't know the power output criteria for license free 2.4 here but you can have 100mW of 1394 for free) - the latter is something of a broadcast cameraman's secret i.e. I can go and buy a ridiculously priced 1394MHz unit from http://www.optexint.com that will carry 700+ lines of PAL - but of course even that unit is not designed for moving flying platforms.

Back on topic, may I beg one more favour of you please, could you post or point me to a picture of your heli setup showing locations of anteannae and other pertainent equipment so I can get an idea of what I'm aiming for. Thank you. Also, do you think I stand a chance by 1/4 wave + goof-patching my WVC link or would it be best to start over?

Re la9ex 5.5 meg moviestar avi - yep, that's the ticket, that's the stuff of my wildest downlink dreams! I'm guessing the long winters up there make for some great time for clear thought, that's the second Norwegian project I've seen that is so 100% perfect (the last one that had me in awe was a perfect RC hovecraft).

MPA, Dave, I take it you are getting good downlink performance, would you be able to share what the guts of this system is?

Thanks

Julian

05-27-2003 Over year old.

mr.rc-cam
Heliman
Location: USA

This page shows how I mounted my X10 transmitter that was hacked for 50mW operation. http://www.rc-cam.com/rc-cam4b.htm#rc-cam4_top

It worked well for up to about 600 feet. My 100mW system, which is not X10 based, installs about the same. I do not fly heli's anymore since I have caught the electric park flyer bug. I find it to be much more relaxing.

This page shows how I mounted my 50mW Lawmate on a model plane:
http://www.rc-cam.com/campod.htm
(I have since moved the Video gear to the cockpit to allow for ROG takeoffs.)

Quote
Also, do you think I stand a chance by goof-patching my WVC link or would it be best to start over?

Your system appears to have an integrated PCB patch, so the RC-CAM GP Patch success will be much lower than usual. It is designed for goof proof improvements on those systems that have an SMA connector and do not need a feedline.

As far as the UK Spectrum rules go, I had those in mind when I replied. I believe you are limited to 10mW EIRP on 2400-2500Mhz. Within that range, I hear that there is a narrow sub-spectrum that allows several mW's of data, but that is not what you are doing. There are also some ETSI and CE requirements, both of which I have no idea if the WVC gear is fully compliant with. I think you should just assume you need a ham license, especially if you make changes to a fully approved system.

RC-CAM

05-28-2003 Over year old.

HOMEPAGE

MPA
Elite Veteran
Location: Australia

rc-cam

I was looking for the horizontal lines but it seems the frequency was a bit high (?) Im not sure but the lines (i was expecting after reading you most informative forum) where just overall interference in my case..
my AV unit is on the tail boom near the tail rotor, perhaps that was the diff.

My audio is not used and is capped with resistors (soldered inside RCA plugs and plugged in) on the audio inputs at the AV unit to pull them down. -

I made a little radome for the y2b antenna to protect the legs and the square container holds the legs all at the same angle firmly
It got mangled a few times over it life but serves well.

Julian

my system is just an off the shelf 4 channel AV sender, power is to FCC regs.
Runs off 10NiMh's with a tap off the pack to run mini camera 5v, no reg in the circuit anymore it sucks loads of power..

I pulled the receiver antenna off and replaced it with a "dual quad" type antenna.

The Tx antenna is the y2b antenna at RC-CAM site with little legs on it inside the yellow plastic thing at the rear of my heli..
It has the least amount of multipathing problem to any other Tx antenna Ive made up.
Handy to be able to select alternative channels to make up for any antenna shortages, it indicates which end of the frequencies is more favourable to the antenna after I make it up which has helped with ensuing ones Ive made. (after mangling them in the car)

The Tx box hangs on 3 rubber bands which is a little bit dodgy but fixes vibration probs in the vid.

It is pretty close to how others are doing it at rc-cam forum less the amplifiers, Im considering getting a reciever amp as the range is not quite as good as Id like but that more the dual-quad that has a fair spread of the signal but not the best for distance so I figure, short of running a yagi helmet on my camera man (I dont know if I can get that past him), I might try an Rx booster which is legal.

The other thing is Ive been tunning the Rx sitting on the ground which is again not the best and I have intended to grab a sliding tent pole and fit a bracket to it to sit to Rx and antenna on up off the ground.

My Rx antenna feed line is very short and it is mounted on the Rx box as one unit not a seperate antenna with cable to it.

Cheers

05-28-2003 Over year old.

HOMEPAGE

d_wheel
Veteran
Location: Deep in the heart of Texas.

Hello again,

I can't believe that I didn't take any pictures of the setup. Probably because it was a temporary affair just to check things out. Here's a link to a picture of the Zagi cam:

http://dwheel.com/zagicam2_4ghz.jpg

These are the same components used on the heli setup. To give you an idea of what it looked like, here is a picture of my canopy with the items "photoshoped" in:

http://dwheel.com/rapcanopy.jpg

The battery is a 560 mah 3 cell LiPoly unit going through a 3 amp, 5 volt regulator. The wiring is just twisted together and tie-wrapped to the inside of the canopy.

I hope this helps.

Later;

D.W.

05-28-2003 Over year old.

FlightPower

Veteran - Location: Herts UK -

playing catchup

Hi guys,

Here it is, 30.0 mm all round by caliper and hot-melt glue encased to keep it straight. FYI, the radiating element on the dipole this replaces measured at 35.76mm - I've heard of the 2.4GHz frequency refered to a 3cm waves, I don't know for sure but I wonder if I got a Friday night unit that wasn't tuned quite right?? - I hope it was something so simple.

It would be contary to the laws of Murphy for this to fix the deal in one hit but I like the look of it. Fingers crossed for field test tomorrow, you never know, sometimes miracles do happen.

Thanks for all your help.

Julian

05-28-2003 Over year old.

mr.rc-cam
Heliman
Location: USA

Quote
...hot-melt glue encased to keep it straight.

If the hot melt glue is found to get soft when microwaved in the oven for a few minutes then it will not be a good choice. This is a sign that it aborbs the RF, which will result in signal attenuation. Also, its affect on the driven element's dielectric constant will impact the antenna design, even if microwave transparent. In other words, the 30mm length would no longer be resonant.

My thoughts are that you should remove the glue trickery and find an alternate way to keep it sturdy. Best to just leave it bare. With microwave RF, everything matters.

RC-CAM

05-28-2003 Over year old.

HOMEPAGE

FlightPower

Veteran - Location: Herts UK -

Better?

(I microwaved a gluestick full-on for 3 minutes, it wasn't cold but I'd judge it was ambient to the platter & air temp rather than cooked).

I just hit the above with a hot-air gun leaving just enough hot-melt to keep the 0.7mm radient element sturdy - hope that's OK.

Regards 35.76mm do you think that could cause a de-tuned effect?

Thanks,

Julian

05-28-2003 Over year old.

mr.rc-cam
Heliman
Location: USA

Quote
Regards 35.6mm above do you think that could cause a de-tuned effect?

The length of a radiator is dependant on a number of factors. The materials used and deliberate attempts to control impedance will affect the length. So, I cannot really say (but it does sound a bit long). It would be interesting to see what your old antenna looked like up close.

If you had a RF field strength meter, like the cheap ones used to test microwave ovens, you could start with a driven element that was a bit long (perhaps 35mm). Then slowly trim its length, 0.05mm at a time, until the power reading starts to fall.

If you can, remove more glue.

RC-CAM

05-28-2003 Over year old.

HOMEPAGE

MPA
Elite Veteran
Location: Australia

Here is my cover

Couldnt find a right angle so I drilled a T internally down to junction insde to make an elbow and capped it.

It holds the legs in place, mine are at 45 deg.

I had one at 30mm legs and tip that got mangled.
This one I measured the dipole antenna it had on it out of the box and noticed it had 28mm length so I made this one 28mm for tip and legs and it seems to work OK although I havent checked other channels to see if it is best closer to centre of the channels it has..

Cheers

05-28-2003 Over year old.

HOMEPAGE

FlightPower

Veteran - Location: Herts UK -

Quote
It would be interesting to see what your old antenna looked like up close.

like this: Brass ground element 3.84D x 24.2L soldered to shield. radient element protruding 35.76mm finished off with a heatshrink cap.
(I microwaved this too and it didn't shrink more). I should also mention that I cut the feedline down by 260mm leaving me with exactly 150mm ouside the case, also I have another one of these TX units, the radiator is 34.51mm on this one. Perhaps instead of turnstiling it straight away I will try chopping it down little by little and range testing to see what happens.

Julian

05-28-2003 Over year old.

FlightPower
Veteran
Location: Herts UK

Thanks d_wheel,

That raptor canopy image speaks volumes - nice and practical, exactly what I'd hope was possible.

Cheers,

Julian

05-28-2003 Over year old.

mr.rc-cam
Heliman
Location: USA

Quote
... radient element protruding 35.76mm finished off with a heatshrink cap.

That looks long to me too. A miniature coax based collinear design (like what you have) would normally be about 28-32mm long at 2450Mhz.

RC-CAM

05-28-2003 Over year old.

HOMEPAGE

d_wheel
Veteran
Location: Deep in the heart of Texas.

"That raptor canopy image speaks volumes - nice and practical, exactly what I'd hope was possible"

Thanks Julian,

The only problem was engine vibration. The entire video looks like double vision. No lines like have been described, just obvious high frequency vibration of the camera. As soon as the final part comes in, I am going to convert one of my Raptors to electric and try it again. Videos from electric airplanes are VERY smooth and I am hoping for similar results from the RaptorE.

Later;

D.W.

05-28-2003 Over year old.

MCSalot
Heliman
Location: Murrieta, CA

For What it is Worth

Transmitters and receivers on 2.4GHz is touchy enough to tune and adjust with expensive test equipment, it is understandable that you would effect the performance of the equipment when you modify the receiver antenna as well as the transmitter antenna. Unless you have the test equipment and the education in Microwave RF systems it is not recommend you modify the equipment.

Would you modify the RF circuit of your JR, Futaba, Hitec, or Airtronics radio with out having the proper test equipment or education in RF electronics to make sure it is correctly tuned? I do not think so.

MCSalot

05-28-2003 Over year old.

yb2normal
Senior Heliman
Location: Broomfield, CO

I have a slightly more updated version of the groundplane antenna now.

Take a look at the link below, first row, third column, titled "groundplane antenna, Version 3"

http://www.yb2normal.com/flightindex.html

PAL-rotor, you are definitely asking for trouble with the hot melt on that antenna. You don't really need the extra support, the antenna is designed to give a bit when handled or landed on

A small drop of glue at the base of the antenna will help prevent chafing of the driven element by the pcb board, but that's all I would recommend.

Good luck!
Bill

05-28-2003 Over year old.

HOMEPAGE

FlightPower
Veteran
Location: Herts UK

Update: Instant success

A HUGE thankyou to mr.rc-cam and yb2

The turnstile antenna is a huge success I now have completely practical glitch-free range out to 300m+ in every direction around my mag mount, I'm sure a directional RX antenna would increase range dramatically if that was required.

To check out the before and after videos go to:

http://www.btinternet.com/~autography/index9.html

Thank you, you guys rock!

Julian.

05-28-2003 Over year old.

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Aerial Photography and Video > Wireless Video Links Setup Help and Advice Please

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