How can improve radio range?

[Alexandre Cruz]

Hi,

I am flying FPV and I would like to improve Futaba´s original range.
I would like to improve it to 10km or more. Is it possibe? What should I do?

[alexcmag]

I am sure some people will give better suggestions, but just for start:

1) Let the transmitter and receiver to a good technician for fine adjust. Transmitter power can increase from 200mW when unadjusted to over 700mW and receiver gain can be increased with fine-tunning;
2) Use a higher gain aerial, maybe a directional one;
3) Install aerial high over the ground (limit in our country is 20m above ground level);
4) Use a high quality receiver with high sensitivity and smart decoder;
5) Include an automated "back-to-home" feature.

What is FPV?

I found "Federação Paulista de Volleyball", "Ford Performance Vehycles", ...

[Miami Mike]

"First person view (http://www.acronyms.ws/af-query.asp?Acronym=fpv&Find=find&string=exact)". It's a gamer's term. He means that he'll be looking through a camera mounted in the model.

[vintage1]

The most useful thing is to put a bigger piece of wire on the receiver, as an aerial.

Plus tuning up the transmitter, and even adjusting it for more power.

Also, a ground station with an antenna strung up high above ground will improve the efficiency of the transmitting aerial.,

BUT if you stay within legal limits for transmitted power, none of this will help if there are other modelers and transmitters around. Its all very well having a sensitive receiver, but 'the wider you open the window, the more the dirt flies in'..

You will find that background noise from many sources, not the least of which will be the models own circuitry, will limit the range.

If in the USA consider getting a ham band rig.

[Miami Mike]

If in the USA consider getting a ham band rig.That won't help range, at least not to any degree that I've noticed. The legal limits are 750 milliwatts for the regular 72 Mhz r/c frequencies and one watt for the 50 Mhz amateur band. In practice, radios like my JR XP8103 have the same output power with a 72 Mhz rf module as with a 50 Mhz module.

[vintage1]

Oh? I thought they had more...5W or so.

The ham band, though, is less cluttered than the 72Mhz one.

I am also wondering just how the OP is going to receive his visual data from the plane..legally.

Its likely that the feedback from the plane will give out before the radio control does.

[alexcmag]

"First person view (http://www.acronyms.ws/af-query.asp?Acronym=fpv&Find=find&string=exact)". It's a gamer's term. He means that he'll be looking through a camera mounted in the model.

Thanks, I stopped PC gaming several years ago.

That time I was working on a company that does maintenance on arcade games, pinball and simulators. Of course when the technician fixed a Twin SEGA Rally or similar, with 56" screen, force-feedback steering wheel (really force-feedback, not that most PC wheels have), gear, and so on we had to test it for sure :P, most times all day running :P

The PC games become so boring... When PC's get powerfull enough for it I was too old...

[alexcmag]

That won't help range, at least not to any degree that I've noticed. The legal limits are 750 milliwatts for the regular 72 Mhz r/c frequencies and one watt for the 50 Mhz amateur band. In practice, radios like my JR XP8103 have the same output power with a 72 Mhz rf module as with a 50 Mhz module.

In our country the legal limit is the same for 72Mhz and 50Mhz, and 50Mhz band is allowed only for certified HAM radio operators, but I found some choices...

For 26Mhz and 27Mhz the legal limit is 4W and for 27.255Mhz the legal limit is 25 watts.

This will need a station license and a better modulation (PPM is not a good idea), but we can provide a FSK modem and software encoding/decoding with CRC.

On remote control applications (all bands) the law says the antenna is not allowed to have a gain greater then half-wave dipole and can't be over 18m height.

Here is the legal document about it, in portuguese: http://www.anatel.gov.br/Tools/frame.asp?link=/biblioteca/resolucao/2004/res_365_2004.pdf

[alexcmag]

Xará,

Some guidelines to follow are on http://www.rcgroups.com/forums/showthread.php?t=378861

They used standard JR radio with antenna mounted on a tripod. You can use the antenna mounted high over the ground.

They have a "back to home" feature, we will provide this.

They used the audio channel of 2.4Ghz downlink to send data, a good idea. I think there is a good idea to send GPS position, altitude, speed, heading and battery voltage, so it will be easier to get back if you get lost.

Using a smart decoder on receiver you can get signal error level too, so you will know if the airplane is almost out of radio range.

[rcBluebird]

Keep your TX antenna vertical, and try to keep your RX pointing straight up or down for the same polarity. Otherwise, you may loose up to 3dB of signal power if antennas are in different polairty.

[Miami Mike]

Otherwise, you may loose (meaning lose) up to 3dB of signal power if antennas are in different polairty.The standard figure for cross-polarity loss is 30 db.

[rcBluebird]

Quote:
Originally Posted by rcBluebird
Otherwise, you may loose (meaning lose) up to 3dB of signal power if antennas are in different polairty.

The standard figure for cross-polarity loss is 30 db.
Mike,

You are right, my typo -30dB polarity isolation. Thanks for checking.

[vintage1]

The standard figure for cross-polarity loss is 30 db.

Hmm. Comments on using an omni directional array? like three wires perpendicular and connected in the middle to the receiver?

[dalbert02]

I am currently on the HAM band (50Mhz) and have experimented with different antennas.

J-Pole http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=7573
MFJ 6M whip http://www.mfjenterprises.com/products.php?prodid=MFJ-1728B
MFJ 6M telescopic whip http://www.mfjenterprises.com/products.php?prodid=MFJ-1806T
Par Electronics Omni Angle http://www.parelectronics.com/omnis.htm

I would also like to try a dipole called a buddi-pole http://www.buddipole.com/

Using an On Screen Display video overlay from RC-CAM, I can see the RSSI recieved signal strenth. Different antennas work better in different situations i.e. high over head or low and far out. If nothing else, going to the 6m wavelength gives you more options for antenna experimenting as commercial 72Mhz are not very common. I have come to the conclusion that playing with antennas has more to offer then trying to increase yout Tx output from 750mW or whatever to 1W.

-dave

[Miami Mike]

Hmm. Comments on using an omni directional array? like three wires perpendicular and connected in the middle to the receiver?You mean like an X, Y, and Z axis? I don't think that would work. The radiation pattern would be a complicated mess of reinforcements and nulls, and would be anything but omnidirectional.

[vintage1]

You mean like an X, Y, and Z axis? I don't think that would work. The radiation pattern would be a complicated mess of reinforcements and nulls, and would be anything but omnidirectional.

I am not so sure actually.

[Pinecone]

No real omni directional antennas. There are nulls in some direction.

A basic 1/4 wave ground plane antenna is easy to make and surprisingly effective. You basically have a 1/4 wave vertical element and 4 or so ground plane elements, bent down about 45 degrees below horizontal. The vertical element attaches to the Tx output, the ground plane elements are connected to the Tx case. From Tx case to antenna piece of coax would be best, with the output tothe center conductor, the ground to the outer.

I have made these for 2m ham and hit a repeater over 50 miles away with a couple of watts. Repeater is up at something like 800 feet, but my end was 4 feet off the ground.

[alexcmag]

No real omni directional antennas. There are nulls in some direction.

A basic 1/4 wave ground plane antenna is easy to make and surprisingly effective. You basically have a 1/4 wave vertical element and 4 or so ground plane elements, bent down about 45 degrees below horizontal. The vertical element attaches to the Tx output, the ground plane elements are connected to the Tx case. From Tx case to antenna piece of coax would be best, with the output tothe center conductor, the ground to the outer.

I have made these for 2m ham and hit a repeater over 50 miles away with a couple of watts. Repeater is up at something like 800 feet, but my end was 4 feet off the ground.

Pinecone,

I liked your idea, I readed on a topic about a 48hs electric glider flight and the guys used a coax cable with antenna mounted on a tripod and worked at a great distance, but I would like to know more details.

The transmitter output has usually a small wire connected to the antenna.

Can I simply connect one end of a RF cable (75ohms) to the PCB with shild grounded to the battery, and the other and to the antenna, or must make something to match impedance?

Thanks in advance.

[treehog]

In the computer world they are getting ranges of of 20 miles 30kilometres with 2.4ghz wifi ising direction antenna often made from empty can of beans

i would be inclined to think a RC unit like specrtrum DX7 with 2.4ghz on directional antenna and coupled with extra reciever cables done as in this link

http://www.rcgroups.com/forums/showthread.php?t=657685

from gliders could get you a lot futher than the 2 miles achieved from some users with no extra additions

and spectrum would give you 2 channels

Also a lot of the good futaba RC units with modules i soppose will bring out a 2.4ghz module and that could save some money

With futaba I think also two channels are sent to plane
but in channel hopping spread spectrum as apposed to fixxed spectrum like JR spectrum sets

i suspect a bit of directional with 2.4ghz and ten miles no rproblem even with 90% frame loss rates the 10% will be easly 10 times the frame rate from 100% of 72mghz signal sent

unless it rains a lot as 2.4ghz is sensitive to water


Ralf

[alexcmag]

Ralf,

I think my friend Alexandre Cruz will use a 2.4Ghz for video down link, so he will not be able to use 2.4Ghz remote controls. But it is very good to know the directional antennas can reach 20 miles on a WiFi link.

I found several publications on directional 2.4Ghz antennas, but none with some information on possible range. Maybe they avoid complaints about range, so I didn't know this is so good.

I have an electronics magazine explaining how to make a good one and all the math involved.

A possible automatic approach is to use a pair of standard-servos on ground station to aim the receiver antenna to the airplane based on GPS information coming from the onboard GPS, this will solve the downlink range issue.

Thanks,

Alexandre

[Pinecone]

Pinecone,

I liked your idea, I readed on a topic about a 48hs electric glider flight and the guys used a coax cable with antenna mounted on a tripod and worked at a great distance, but I would like to know more details.

The transmitter output has usually a small wire connected to the antenna.

Can I simply connect one end of a RF cable (75ohms) to the PCB with shild grounded to the battery, and the other and to the antenna, or must make something to match impedance?

Thanks in advance.

a) Most Tx circuits I know of are balanced for 50 ohm coax.

b) Not sure where I would hook the ground of the coax. I would need to open up the RF unit and take a look.

[Pinecone]

If you wanted serious range, and it was legal and you could live with non-omni operation, a basic yagi can give you some serious range at minimal power.

And if you need more, you can go phased array. :) I run a pair of 11 element yais phased on 2m and 440MHz. :)

[alexcmag]

a) Most Tx circuits I know of are balanced for 50 ohm coax.

b) Not sure where I would hook the ground of the coax. I would need to open up the RF unit and take a look.

a) Good, we will try 50 ohm coax so.

b) What is the best approach? The nearest ground from antenna? The nearest ground from output transistor? Sorry for so many questions, I just want to understand the concepts and avoid mistakes.

[alexcmag]

If you wanted serious range, and it was legal and you could live with non-omni operation, a basic yagi can give you some serious range at minimal power.

And if you need more, you can go phased array. :) I run a pair of 11 element yais phased on 2m and 440MHz. :)

Non-omni would not a big trouble since we will have GPS coordinates from the airplane and it will have a "back to home" feature, but it is not legal to use more gain then a half-wave dipole (2.14dBi) and must be polarized vertically.

I found some information that 1/4 wave ground plane gain is around 1.73 dBi (below legal limit).

I did some research of 1/4 wave ground plane antennas and got some useful information, there is a link (sorry, it is in portuguese) where the author says his FSR 100mW FSR radio that has a small range with original antenna but can talk over 8Km with a fixed ground plane ( http://www.hamtronix.com.br/faqs_talkabout5620.html )

Dalbert and Mike wrote about keeping the RX antenna vertical. If course it is not possible with a 1m antenna, but is possible with smaller antennas.

This is easy to fit a 10" antenna vertical on any RC airplane, difficult to fit a 20" antenna and almost impossible to fit a 40" vertical antenna (except on very large models).

In all my park flyers I use a vertical mounted base-loaded antenna (4" wire, 1.5uH inductor, 6" wire) on receiver and works fine, even on my waterplanes where the 1m horizontal mounted antenna fails even with dual-conversion receiver at a 100ft range.

Here is the question, is a 1/8 wave antenna (-7.7dB gain compared to a 1/4 wave according to Mr RC-CAM experiments on http://www.rc-cam.com/ant_exp.htm) with correct polarization better or worst then a 1/4 wave antenna with wrong polarization?

Is a 10" base loaded antenna better ow worst then a 1/4 wave antenna or 1/8 wave antenna?

Sorry for so many questions...

[Pinecone]

A proper base loaded antenna with a good ground plane will work almost as well as a full sized 1/4 wave antenna.

You might want to check out some of the ham radio books on antenna design, the ARRL Handbook and the volumes of the Antenna Compendium.

[alexcmag]

A proper base loaded antenna with a good ground plane will work almost as well as a full sized 1/4 wave antenna.

You might want to check out some of the ham radio books on antenna design, the ARRL Handbook and the volumes of the Antenna Compendium.

Thanks, I will read more on antenna design and make some tests with ground-plane antenna with 50ohms on transmitter and base-load vertical antenna with ground-plane on receiver.

I will follow the Mr. RC-CAM's approach to measure gain on airplane, to use a R4P receiver and log its signal level information from the IC.

[dalbert02]

Your transmitter antenna needs a 'ground'. But 'ground' does not simply mean a metal rod in the earth. When an electrical wave leaves your antenna, it needs a way back to complete the circuit. Usually this 'way' back is through the earth. The earth is very lossy, it has high resistance or impeadance to rF. Hence, you often see vertical ground plane antennas with metal rods at the base of the antenna pointed in circular pattern. The ARRL says something about over 100 wires at least 1/4 wavelength long laying on top of the earth at the base of the antenna to create an ideal 'ground'. Obviously this is not practical in a mobile application, but it is good to know. The ARRL Handbook and ARRL Antenna book are both very good at explaining this concept (far better then I). IF I were you, do a search on QRP, that is known as low power communication in the HAM world.
-dave

EDIT
Read these:
http://www.bencher.com/pdfs/00361ZZV.pdf
http://www.bencher.com/pdfs/00803ZZV.pdf

[Miami Mike]

When an electrical wave leaves your antenna, it needs a way back to complete the circuit.You need to brush up a bit on this part. If it was true then we couldn't communicate with astronauts or space probes, could we? ;)

In fact, our satellite dishes wouldn't work!

[dalbert02]

Does not the dish's feed point itself create the counterpoise or ground plane since the feed is usually a dipole? Possibly only relevant to verticals? Teach me, I am new at this. :)
-dave

[Miami Mike]

I'm just pointing out that when an electrical wave leaves your antenna, it's gone. It might even keep going through space until it reaches some alien version of SETI, but it certainly doesn't need a way back to complete the circuit.

[dalbert02]

Ok, I understand what you are saying, but I *think* that all antennas need some type of ground or counterpoise. Even out in space or wherever, it is like having just one side of a battery or one side of an electrical outlet if you don't have a counterpoise, you can't complete the circuit. I could be wrong, I'll admit I am guessing, but please point to where I can learn more if I am incorrect. :)
Thanks,
-dave

Parabolic Dish Antennas: One of the most common antenna types used for space applications is the parabola because it can be used over a variety of frequencies by only changing the feed system. The feed then is usually only a dipole in front of a small reflector to focus the energy into the dish. The largest structure of the dish acts as nothing more than a reflector to focus energy on the feed.

[dalbert02]

A microwave ground plane antenna.
http://www.yb2normal.com/antenna1.html
-dave

[dalbert02]

Radiation patterns, gain, and frequency limits of different types of antennas:
http://www.tscm.com/radiapat.pdf
-dave

[vintage1]

Ok, I understand what you are saying, but I *think* that all antennas need some type of ground or counterpoise.



Yes, But it can be the other half of te antenna - i.e. a dipole.

A radio wave carries its own 'ground' with it..

Earthing a transmitter by holding it is good, as the antenna is designed as a monopole whip.

Those need an infinite ground plane to work properly..


Even out in space or wherever, it is like having just one side of a battery or one side of an electrical outlet if you don't have a counterpoise, you can't complete the circuit. I could be wrong, I'll admit I am guessing, but please point to where I can learn more if I am incorrect. :)

No need. plenty of AC circuits complete without a direct connection. Capacitors and transformers will show no DC connection. 'free space' is. to electromagnetic waves, a huge collection of such things.

[dalbert02]

Yes, But it can be the other half of te antenna - i.e. a dipole.
Does not the dish's feed point itself create the counterpoise or ground plane since the feed is usually a dipole?

Precisely!

Capacitors and transformers will show no DC connection.
True, but an rF connection exists. Using an MFJ antenna tuner, I can see changes in the resistive part of load impedance, and the reactive part of load impedance simply by changing the position of the antenna.

-dave

[deh6]

Hmm. Comments on using an omni directional array? like three wires perpendicular and connected in the middle to the receiver? Not having read this thread, by coincidence, a friend and I were talking about this at breakfast. As a near-retirement project he went back for a 2nd MSEE, this time in electromagnetic fields. Besides having a good grasp of the theory/math, he has been a ham for years so knows the practical aspects.

From our discussion this morning, Miami Mike is probably correct that there would be nulls, etc., IF the three dipoles were fed in phase. However, if they each were fed at 120 degrees to each other, would it produce a wave that is circular in all directions? Or, is there are there a one (or three) pairs of nulls? A prof at Univ So. FL refers to this omni-directional problem as "combing the hair on a coconut," in that topologically there is always a "hole." This friend was going to look at the math, so at the moment we have no conclusion. This hobby seems to have a way of turning up interesting problems.

Putting some numbers to the problem of getting 10 km range--

If 1 mile is the range for satisfactory operation of the receiver/transmitter, then 10 km requires a range increase of rouighly 8 times. A range increase of 8 times requires 64 times power/gain. Increasing the power from 200 mw to 1 watt (assuming the 200 mw is the current power output), would give 5x times increase, which is close to 7db, leaving 11 db required for improvements in the antenna. Building a 11 db transmitting antenna for frequencies in the 50-72 MHz range is possible, but it would be a monster and hardly practical.

The easiest place to improve range appears to be the receiver (such as adding a pre-amp), but as one post mentions, it may pick up stuff not wanted, such as a transmitter in a neighboring field, intermodulation problems from other strong transmitters, etc. Some sort of code, or transmitter identification, scheme only prevents the plane from responding to another transmitter, but in meantime one loses control. My thinking has been that for long distances the real-time control gets dicey and instead one needs to feed commands, and in the absence of commands a "fly-home" mode using the gps kicks in.

[vintage1]

One can certainly build FAR more sensitive receivers than are currently sold..teh issue is of course making them selective enough.

I think the absolute limit would be something like 20nV..thats roughly where the noise is over a 4Khz wide channel. My guess is that few, if any of our sets are better than 50uV..so there is about 60dB more gain available in theory.

In practice you would have to suppress everything, and go at least dual conversion, with probably an RF amplifier and dual stage delayed AGC as well.

Even the best communication receiver rarely go much below a uV sensitivity..there is so much trash out there anyway, its unlikely that you would pick out the signal anyway.

[Pinecone]

Look at a the Cushcraft antenna site. There is acommon repeater antenna that is 4 folded dipoles, arrayed around the support pole that are phased to give a higher gain, omni directional line of sight pattern.

[Acetronics]

Hi,

I am flying FPV and I would like to improve Futaba´s original range.
I would like to improve it to 10km or more. Is it possibe? What should I do?

Hi, Alexander

one solution is to run faster ... :D

Alain

[Alexandre Cruz]

Yeap.. looks simpler :D
Me, a friend and AlexMag are working hard in this issues, GPS to fly home is mandatory if you want to fly without seing your plane.
I've found a 5 and 10W transmiter for the camera (20 and 40 miles range) but almost nothing related to the radio control.
Also, I've heard JR. radio work at 1W is it true? If so, things can get simpler...

[Acetronics]

Some years ago ...

I knew some 3 W(HF) R/C HF Heads kits ... but halas, production has been stopped 6 years ago.

I do not have their scheme nor ...

Alain