Ben Diss

My Feedback: (23)

I'm building a system with a Panasonic CX-171. I want to use it in a 16 cell electric high wing airplane to take shots of the flight line at big events. I'm building a pan/tilt mount for and plan to mount it under the airplane. I'm shopping around for a transmitter/receiver system. I don't plan on going very high or far away with this system, but I want absolutely perfectly clean video with no aberations. I've looked at both Tinywireless and Blackwidow sites and can't decide what to get.

1. What frequency should I be looking at? Some flying fields are flat with little obstructions, while some are in a valley surrounded by hills.

2. How much power do I need?

Any and all thoughts are appreciated.

-Ben

Ben Diss

My Feedback: (23)

I guess another thing to consider is 900, 1.2Ghz or 2.4Ghz. Any comments?

-Ben

PlaneKrazee

My Feedback: (14)

Ben,

Start by listing exactly how far you will fly away from the receiver and whether or not you will doing aerobatics. What is the maximun payload for the video setup? Are you willing to purchase or make different antennas? Are you willing to purchase a receiver antenna amplifier?

900mhz equipment has only one legal channel, 910mhz in the less expensive ($100.00-300.00 range) equipment. It will transmit farther per mw than the higher frequencies, it will transmit the best thru the aircraft, the picture on mine and others I've seen is good, but there is a great deal of equipment near this frequency that could cause interference problems.

1.2ghz equipment, you will need to verify the frequencies it transmits on, should be between 1240-1300mhz. It will transmit twice as far as 2.4ghz of the same power. This equipment will provide good airplane penetration, range, and will not be affected by moisture in the air. The equipment I have seen in this range that is supposed to transmit on legal frequencies seems to overstate the power, a lot.

2.4ghz equipment is the most widely available equipment at this time. It will require over three times the power to transmit the same distance as 900mhz equipment providing that both systems have been optimized. It will provide a clean signal in a straight line to the antenna, it will be affected by moisture in the air, it will not penetrate the aircraft very well. More and more equipment is coming out on this band but inerference should be low do to the low transmittion range.

So to transmit the same distance as 900mhz you need at least 3X the power with 2.4ghz. Most commercial video equipment does not transmit over 700mw of power.

More power is a safety issue. Do not hang around the transmitter antenna with the power on. There are very powerful transmitters being sold in the USA from China that have not been tested by the FCC. I would not recommend these to anyone except someone who has a ham license and has experience with RF radiation. You can't see the radiation, but you may feel microwave radiation, you gunna cook sucka!

People used to freak out about microwave ovens. You will get more radiation from a 1 watt 900-2400mhz transmitter three feet from you on any of these frequencies in one minute than if you sat in front of a microwave oven your whole life!

There are many variables to all this equipment. Power requirements for the same mw output could be double with some equipment.

Most of the equipment that is being sold is having the power output exaggerated by 50-200%. I have not seen a company in China that is advertizing 1500mw, 3000mw, or 5000mw. On the Chinese websites they are listed as 1000mw, 2000mw,and 4000mw.

At this time there is no standards on any of thjis equipment. You need to educate yourself the best you can, talk to some hams and get your license, buy some equipment and check the measured frequency and output. Then check to see how it works in the plane. Move wiring, shielding, antennas around, make dc/dc switching regulators and add rf filters until it all works. Make different types of antennas and try them out.

You are entering into the twilight zone.

Someday there will be a truely RTF system that will work great in most installations, the closest I have seen is the Supercircuits $400.00 system, or for up close slow flying (300ft max) the blackwidow spidermite. I bought my 900mhz 1 watt tx/rx from Microcameras but have not been able to fully evaluate it yet. It seems to work well.

Ben Diss

My Feedback: (23)

Brian- Thanks for the GREAT writeup. That should be placed in a FAQ somewhere. Excellent summary.

It sounds like I should stick to 900mhz. I'd love to keep everything 5V. Do you know of any 900mhz systems that run on 5V?

-Ben

Ben Diss

My Feedback: (23)

I just realized that I didn't answer your questions.

1. I doubt that I would ever be more than 1000' feet away. Maybe if I try to capture some aerotow sequences I could exceed that, but I doubt it.

2. No aerobatics ... maybe. It would be pretty neat to put a system on a DLG and watch the extreme launches, but that's a distant second in priority to flight line fly-bys.

3. This will be places in a good sized airplane, so if I keep everything under a pound I'll be happy. I think I can do it for a lot less than that.

4. I'm willing to purchase whatever it takes takes to make this happen. I'm willing to do some building as I'm handy with a solder iron, but not a trained EE.

-Ben

PlaneKrazee

My Feedback: (14)

Ben,

Unfortunately all the 900mhz equipment I have found requires 12v.

At this time I would buy from either Black widow, Microcameras or Supercircuits. I do not have any affiliation with any of these people although I have communicated with all three.
Tiny Wireless needs to verify the power output of all their equipment in my opinion and so do the other companies on their higher powered equipment.

The 2.4ghz equipment has the best selection of ready made antennas, to see a few here is a good place to start: http://www.hyperlinktech.com/web/hg908p.php this page shows a 900mhz ready made antenna for $50.00, to the left is other links for 2.4ghz.

They also sell amplified patch receiver antennas with 30db of gain for about $150.00. This is the way to go for distance and still be able to fly around!

At a 1000' from the receiver you will probably need a 500mw-1000mw at 2.4ghz with the supplied antennas, a directional amplified receiver antenna (30dB Amplified Receive Antenna 2.4 GHz HyperGain® Model: HG2414PLNA) and a vertical on the transmitter would give much more range (I would guess at least two thousand feet) and supply very clean video. You will need to aim the receiver antenna if you fly in close but if you fly out a several hundred feet all should go well.

I think that if you are going to fly close-in (25-1000') a 500mw to 1000mw 900 or 2400mhz transmitter will be fine. Use a turnstile receiver antenna and set it up so you get a wide beam with only about 3db of gain. This will let you do close-in flybys with no dropouts. When you want to fly farther out switch to a patch antenna with more gain. For aerobatics I am going with a turnstile transmitter antenna. It is two crossed dipole antennas phased at 90 degrees to make a circular polarized, spherical, omni directional antenna. There are no polar dropouts with this type of antenna. It cuts the transmitted output by 3db (cuts the transmitted distance in half) because it is transmitting in all directions vs. a dipole that transmits in one direction or plane.

I believe the best system for myself at this time to be a Microcameras 1000mw 900mhz transmitter with a homemade circular polarized turnstile transmitter antenna (this will allow aerobatics with the least drop outs), a HyperGain® Model: HG908PLNA amplified receiver antenna for distance work, a turnstile with ground plane for an adjustable beam receiver antenna for very close in work, Texas instruments PT5541 12v dc/dc 4.8v-9.0v to 12v volt booster to power transmitter and KT&C camera. With the amplified receiver antennas I think a 500mw transmitter is plenty, we will soon see. That's if it will stop snowing and warm up.

Make sure you range check your r/c gear with this equipment and if you have the ablity to shut off the video transmitter in flight with failsafe do it!

Mr. RC CAM and RC Bugman have the most experience with video equipment and will hopefully correct any mistakes I have written.

As soon as my Turnstile antennas are fully tested I will give the dimensions and approximate radiation patterns.

Fubar-One

My Feedback: (1)

VERY interested in your turnstile antenna.
My results with 900mhz have been pretty disappointing so far. Part of the problem might be that the tx antenna is not extended in a straight line but is bent 90 degrees at the hinge point due to how I installed the tx into the plane. This I will change. Those guys are definitely using a yagi antenna to get the results they show in their video! I have also checked into both patch antennas and a 24" dipole antenna made by Hypergain. Unfortunately they have a $100 minimum order policy and I am a bit hesitant to buy one of each just to make up the minimum order.
BlackwidowAV sells a 2.4ghz patch antenna which I purchased along with his 200mw 5v system which I hope to test out tomorrow.

PlaneKrazee

My Feedback: (14)

Fubar-One,

Which Supercircuits system did you get? I have a friend that has it and has had very good results with it. He did not fly more than 1000 feet away from what I can tell on his video. he is using the stock antennas.

Did you see the amplified 900mhz patch Hypergain sells?

It has the range of a yagi but the beamwidth of a Patch 75X65.

I think it will be a good match for the Turnstile.

I am using 1/4" rings of 3/4" cpvc pipe with holes drilled at 90 degree angles to hold the 3/32" brass tube elements of the turnstile. The center conductor of the coax is easier to solder inside the tube than outside giving the proper phase length easier.

I am going to make one out of 1/16th inch brass tube as well to see what affect it will have on tuning. It would be tough to make one of these for 2.4ghz as Cyber-flyer discovered. The phasing coax is a bit unruley and the lengths are very critical at higher the frequency. A 1/32" mistake at 1.2ghz is a 1/64" mistake at 2.4ghz.

HoboDog

My Feedback: (1)

I bought the patch antenna from Blackwidow. 8db gain I believe. Does anyone know the front end pattern for this antenna. Beam width? Cone of maximum reception? I don't know how to ask this. How accurately does it have to be pointed? Polar curve?

Doug

IA-Flyer

Skypilot_one,
Where did you find the information to build the turnstyle? I saw links to pictures and a discussion site on it at Cyber-Flyers site but couldn’t find the directions. Did a Google and came up blank.

TIA!
Jim

yb2normal

The 8dbi patch has about a 65 degree 'cone' of coverage. The cone is defined by the antennas ability to provide a signal above -3dbi


Ben,
I think the 600mw 2.4ghz tx/rx set, coupled with the 8dbi patch antenna, will satisfy your needs. Since the transmitter operates at the same voltage as your camera, you can simplify your power regulation circuit. The circular polarized patch on the rx will satisfy most of the same requirements that a turnstile on the tx would, and it would allow you to fly with the 'stock' antenna in the air.

For the limited range you are talking about I'd normally suggest the 200mw transmitter, but it sounds like most of your flying will be done on a plane that can easily carry the 600mw unit, and this unit will give you more flexibility in the long run.

To keep things in perspective, the 600mw unit can be built into a flyable system that easily comes in under 3 ounces. The one I'm designing for a 'ready-to-fly' 600mw system tips the scale at 2.5 ounces, minus the batteries of course, and I am expecting over 1/2 mile of range. I'm a big fan of li-poly cells, and with a 1020mah 2 cell pack I expect to get just under 2 hours of run-time on a charge.


Regards,
Bill

PlaneKrazee

My Feedback: (14)

IA-Flyer.

Information for turnstile antennas is in book Reflections2, ARRL handbook and ARRL antenna books. There is also some information on the web. Look for crossed dipole and turnstile antennas.

You need to calculate the length of the antenna elements based on frequency, the length of the phasing lines based on frequency and the velocity factor of the phasing cable. Then you need to set up the antenna and check performance trimming until no further gain is detected. Give me some time and I'll get the dimensions posted. What frequency are you looking for?

Bill,

The 5v systems are much better for smaller planes do to the weight savings of the batteries and power switchers. Your videos are always so good! I never see any flare or color shift/magenta problems in your videos. Are they edited out or does the Panasonic CX 121 maintain the color that well? What would happen if the lenes gets a eye full of direct sun for a milli second?

How well will the 600mw 2.4ghz system work if the transmitting antenna is blanketed by the structure of the aircraft, say 1/8" and 1/4" balsa and monokote, we will leave out other equipment, at 1500 feet?

I think some field testing with structures similar to our aircraft would shed a great deal of light on the subject. The tests could be performed with the equipment mounted on 20' 2" PVC poles with the receiver stationary and the transmitter capable of being moved to simulate flight. The pole could be rotated and the transmitter could be mounted on the side of the pole with a wheel, this way all antenna angles could be checked and there would be no reflections that would interfere with the transmissions. This 20' height would support 2.4ghz transmission for over 1.2miles and a very good test would be possible.

I would like to compare the 900mhz-2.4ghz equipment in this way to help determine how much power at each frequency is required to transmit not only the distance but to penetrate simple structures.


I have heard good reports of equipment on 2.4ghz, I am confused as to why people would not have good results on the lower frequencies with the same or even less power.

Quote fron Hamtv.com:

Line of sight distance can be predicted given power,
antenna gain, coax loss, receiver noise figure and
bandwidth. Non line of sight cannot - you just have to
try it to see what you get. 426.25 or 434 MHz is
suggested for R/C and simplex because the 900 MHz
band goes half the DX as 400, and 1200 goes 1/3 Also
the higher the frequency, especially with ground R/C
vehicles, the more chance of mulipath problems.

If you increase your radiated power or receiver
antenna gain by 6 dB (4 times) you double the distance
for the same picture. On 426.25 MHz, the snow free P5
line of sight DX dipole to dipole, aligned in their
maximum radiation lobe to each other for 100 milliwatts
is about 1/4 mile and goes to 1 mile if a OAL 5L-70cm
beam is used at the receive end. With 1.5 watts it is 1
mile and 4 miles respectively.

So from this we see that 100mw at 2.4ghz will transmit about 1/6 as far as 70cm or about 220' with stock dipole antennas. This is based on a AM signal. A FM signal is 30 to 60% more efficient than AM so with the same bandwidth the signal would travel about 300'. 400mw would travel about 600', 800mw about 1200'. With a 8db antenna -2db for losses you could fly about 1800' out.

yb2normal, does this sound about right?

Fubar-One

My Feedback: (1)

Brian,
I have the AVX900S9-V Supercircuits system which went for $349 plus shipping. The camera kicks butt but the video system seemed quite a bit too prone to signal dropouts. Nothing like the results they show in their video! Possibly one reason is that I have the tx antenna folded at a 90 degree angle where it exits the fuse. I will re-mount the tx so the antenna is straight down or up depending on what a PITA it is to mount. I am using the stock "whip" antennas both on the tx and rx. I have seen the HyperGain patch antenna and would have purchased one but they have a $100 minimum order. Maybe buy that one and the small yagi they sell. I got decent signal results at distance (never did find the range limit) but when flying near or over the rx, the signal went to crap.

Yukondog,
I flew today using the BlackwidowAV 200mw 5v system (insert Tim Allen grunt here!) for the first time and recorded video using the stock whip and the patch antenna. Patch antenna wins hands down! I set it up at one corner of the field aimed at the opposite corner and tilted back at possibly a 45degree angle. Mounted it on a camera tripod. The ONLY time I had signal dropout was when the plane was sitting on the ground and I was walking towards it which put me right in the LOS. The camera and tx are strapped to the top of a US 60 and I put that sucker thru every gyration I could come up with, rolls, loops, snap rolls, tumbles, you name it. Not one signal dropout. Near as I can tell the patch antenna is not picky at all.
I am tickled pink.[sm=lol.gif]

I will be posting video later with this disclaimer: The video itself is not that great. This is due to my installation of the system and not due to the system itself. The plane is powered by a .91FS Magnum and the prop may be less than balanced due to pebble collisions. Also, I didnt put enough foam around the camera and the engine at full throttle shook the camera like a rat. I also hard mounted the tx to the balsa case I built and picked up some lines that were determined to be caused by the tx also being shaken like a rat.
In a nutshell, the video problems are all caused by vibration. When the engine ran outta fuel, the picture cleared up remarkably!
As far as the system itself: I couldnt be happier!
BlackwidowAV? [sm=thumbup.gif][sm=thumbup.gif][sm=thumbup.gif]

PlaneKrazee

My Feedback: (14)

Fubar-One, Glad to hear of your sucess!

I have a friend with the same SS system as you and had very good results with it., The AVX900S7-V system is supposed to be superior according to RC Bugman.

yb2normal

The color rendering of the CX161 and KX121 are very good. The main advantage of these cameras is that they are CCD cameras. The magenta tinge you talk about is something you'll see a lot on CMOS based cameras.

I have driven 800' from a 200mw 2.4ghz video transmitter, using stock whip antennas, with perfect video. Don't get trapped in analysis paralysis. Consider real life equipment in real life applications.

One trick that I picked up is to seal the edges of the tuna can with muffler tape. This provides a solid electrical and mechanical connection between the transmitter case and lid. GOOP down all your wires, voltage regulators, etc, so nothing has a chance to vibrate.

PlaneKrazee

My Feedback: (14)

That Is good!

PlaneKrazee

My Feedback: (14)

Dan,

You were getting dipole dropout with the 900mhz system. With a patch or turnstile receiver antenna it should work very well. Your 900mhz system produced very good, clear, long distance results?

IA-Flyer

Thanks Skypilot_one,
2.4Ghz (2.435 center) but 900 would be interesting to see for the dimensions. I'll do some searching for crossed dipole, I just looked for (turnstyle), not sure where I was it with the "y" but it stuck. Lots of google hits on turnstile, I'll check it out.
I had hoped to try the 360x360 MP bullet antenna but 5oz is just to heavy for me. Don’t do much work unless you were going to do it anyway, I can do some research now that I know where to look.
Thanks again
Jim

For anyone interested in frequency / power / antenna / range calculations.
This is the calculator I’ve been using for a few years.
http://www.ydi.com/calculation/som.php

To convert milliWatts to dBm you can use this calculator.
http://www.ydi.com/calculation/watts-dbm.php

The “calculations� link on the left side of the page has several other useful utilities, you can use the downtilt calculator to find the best receiver antenna angle for a given distance and altitude in a backwards sort of way.

PlaneKrazee

My Feedback: (14)

AI Flyer, Your welcome.

Below are the calculations for my 910mhz turnstile.

299.7924563/f mhz=wavelength in meters 299.79245/910=.3294422 meter
or
11802.85261/f mhz=wavelength in inches

wavelength/4=1/4wavelength .3294422/4=.0823605 meter

1/4wave driven element length=82.3605mm, need four.

1/4wavelength x velocity factor of coax= phase and matching line lengths .0823605x.69=.0568287 meter or 56.8287mm

Velocity factors of some coax: http://www.nr6ca.org/vf.html

Velocity factor of Beldon 83264 RG179 75 ohm coax is .69

This is a good starting point, the antenna will probably need to be trimmed to resonance.

The phase line and matching line coax lengths are critical.

Go to the P.C. Electroics website and then to the rocket ATV notes.
http://www.hamtv.com/pdf.files/Rocket.pdf

There is a 426.25mhz turnstile antenna at the bottom of the page.

PlaneKrazee

My Feedback: (14)

Bill,

After hearing Fubar-one's report you have the best legal equipment that performs well and has several antenna options readily available at the best prices from one source.

Fubar-One

My Feedback: (1)

Yeah, pretty much. I never seemed to reach the range limit and it actually worked better far out than close up. After the success I had today with the BlackwidowAV system using a patch antenna, I will look into one for the 900mhz setup. Possibly that amplified Hypergain one.
C'mon tax refund!

yb2normal

Thanks skypilot, I appreciate the kind words.

For anyone interested in putting together a turnstile at 2.4ghz, take a look at the work done by www.cyber-flyer.com for some good details, just click on the "video, telemetry, navigation" link on the left side, then scroll down 4 or 5 pictures to see how he built his.

Building a 2.4ghz turnstile using phasing line is apparently a bit tricky since the lengths are so short. Cyberflyer struggled with signal uniformity on his turnstile until he replaced the phasing line with the hybrid quadrature.

I've noticed this too and I have a theory about it. I think that when the tx is in close, the receiver has to damp down it's sensitivity (via AGC) to avoid being swamped. This means that null spots in the transmitter antenna pattern are more obvious because the receiver gets caught with it's pants down. When you fly a bit farther out, the receiver maintains a higher gain, and the null spots become less obvious. That's my theory anyway. IA-flyer made a similar comment with his old setup (correct me if I'm wrong IA-flyer), saying that it didn't really get "on step" until the plane got a bit farther away.

Regards,
Bill

HoboDog

My Feedback: (1)

Just my 2 cents worth. I threw away my Hong Kong stuff. I have a half hour of BlackWidow video now. CX161, 600mw 2.4 ghz, 8db patch antenna, LiPo powered, on a SoarStar. Bullet Proof! I love this setup. It comes with great online RCU support from Bill and others.
Now I want to see how it looks when the sun comes out. Maybe today. If it does I might get brave enough to try to post a sample.
No, I don't work for BlackWidow.
Thanks to all for the help,
Doug
KB7VNE

PlaneKrazee

My Feedback: (14)

Dan,

I will buy a patch with you, this would meet the minimum order. Let me know. Seems like the amplified unit would be overkill unless we could fly over a mile out.
Using the horizontal patch with the turnstile aerial would work well. Won't have to worry about the two turnstiles going into deep null from RHCP to LHCP during inverted manuevers.

I would like to someone build a monokote covered balsa shield around a 2.4ghz transmitter and antenna to see what affect it has on signal propagation for a given power output. I am still hung up on this.

PlaneKrazee

My Feedback: (14)

Website for quadrature hybrid parts.

http://www.merrimacind.com/multimix/QHD_2H_23G.pdf

Cyberflyer noted it is vibration sensitive.