Long range, low bitrate, small data transceiver unit for telemetry data

I suppose he could have his receiver up a tethered balloon too to increase line of sight.

Reply to
Mark Harriss
Loading thread data ...

Dear "Tauno Voipio"

Thank you for this formula and the information.

After your posting I've found the following link regarding equation of "d =

1.23 * sqrt(altitude)"
formatting link

Leo Patrick

Reply to
Leo Patrick

Huh??? An altitude of about 700 meters ought to put it above the horizon over flat ground or water.

If the limit really is 7 grams, this looks very difficult---especially if that has to include the power supply.

Mark Borgerson

Reply to
Mark Borgerson

Just in case someone might be more interested in technical details than in the mud slinging contest, here are some details.

Troposcatter links have been used for decades in areas with no infrastructure to carry telephone circuits prior to Inmarsat satellite phones.

For instance between the North Sea oil rigs and main land England/Scotland. On the land side huge fixed reflectors were erected, but still quite high transmitter (kilowatts) power was required. There was even a fear that the high field strength at the oil rig might create some sparks and ignite the oil/gas vapour floating around.

The idea with a troposcatter link is that both stations should see the same air mass in the lower troposphere (1-2 km) and when the transmitted signal hits that air volume, it will scatter somewhat and part of it will scatter towards the receiving station.

This is a similar situation as the afterglow after sunset, when the western sky (on both hemispheres) is still bright, while the sun is below the horizon. The sky is brightest around the area where the sun just set, i.e. the scattering is strongest in directions close to the ray direction.

The situation in troposcatter is similar, the larger the scatter angle, the weaker the signal will be. The longer the troposcatter link, the higher the commonly visible air volume must be (and thus the air is less thick) and also the scattering angle becomes large, thus hugely increasing the attenuation.

For a 100 km line of sight path (e.g. between two balloons), the path loss will be about 120 dB. A 100 mW (+20 dBm) transmitter and a receiver with -120 dBm sensitivity should be easily be able to communicate with a 20 dB margin. However, on a license free band, all devices that are within the radio horizon of the receiver would appear as interference, most likely interrupting the communication.

However, if we want to build a ground to ground troposcatter link at

100 km, in addition to the 120 dB free space loss, you would have to add about 50 dB (100000 times more power) for the troposcatter losses at this distance for maybe 50 % of the time. Thus, a few wats with a small yagi at both ends should do the trick.

However, the troposcatter link is notorious for fading, so if you need a higher reliability, the transmitter power needs to be increased. To get from 50 to 90% reliability of the time, the transmitter power would have to be increased 10 times (10 dB). Also stepping up to 99% would add an other 10 dB as would going to 99.9 %. Even the Perks dish with a huge transmitter would not be able to provide 100 % reliability, since maybe during an hour each year the signal would simply escape into space due to the air refractive index.

All the previous calculations have assumed that there is a free view to the horizon. However, if there are some local mountains, you would have to beam your signal higher to get above the mountains and hit a common air volume above them. The higher in the air the scattering volume is, the larger deflection is required and the losses will increase.

As a rule of thumb, for every degree you have to increase the antenna elevation to get past the mountain, the troposcatter attenuation will increase by 10 dB, i.e. the transmitter power should be increased 10 times.

VHF/UHF/microwave communication is certainly possible behind the horizon, but to get a reliable link, you might end up at power levels that are hazardous to your health.

------------- One other interesting observation of wireless products advertised by various vendors is that in order to get the distances claimed, the station would have to be in orbiting satellites, preferably on the far side of the Moon :-), to avoid the noise and interference from other stations in the same frequency band.

Paul

Reply to
Paul Keinanen

"Mark Borgerson" Phil Allison

** I have already answered this point - twice.

Curvature of the earth is not the issue - but the local terrain is.

Imagine that from the ground receiver's position, there is a hill 50 metres higher, sited 1 km away.

How high is your horizon out at 100 km now ?

........... Phil

Reply to
Phil Allison

Paul,

Thank you for your very informative posting. I've read with greath appriciation. Regards,

Leo Patrick

Reply to
Leo Patrick

"Leo Patrick"

** Is there the slightest chance YOU are going to explain what your requirements are in sufficient detail ??

Or are you just another stinking troll ??

BTW Get a bloody spell checker !!

.......... Phil

Reply to
Phil Allison

Assuming first that the earth is flat, the horizon at 10 km would be

500 m above ground and at 100 km 5 km above ground.

Since the earth is a sphere, we have to add the horizon for a perfect sphere at 100 km and we end up somewhere between 500-700 m depending on some assumptions as previously calculated in this thread, thus the required altitude would be about 5,6 km, which is not in the stratosphere not even on the poles, even if we notice that the earth is an ellipsoid and not a perfect sphere.

Those calculations apply for a visual contact. However, the Fresnel zones around the direct line of sight path becomes larger at lower frequencies. At exactly the optical horizon the lower parts of the Fresnel zones are cut off. Assuming the hill is sharp, the knife edge diffraction model can be applied, which yields 6 dB extra attenuation. At angles above the optical horizon, the losses are smaller, dropping more rapidly at higher frequencies, as the Fresnel zones are smaller.

Paul

Reply to
Paul Keinanen

"Paul Keinanen" "Phil Allison"

** Which is a HELL of a lot more than 700m - f*****ad.
** The phrase used was " ... free line of sight ".

(snip rest of this tedious wanker's s**te )

.............. Phil

Reply to
Phil Allison

*** Humphhh!!!????!!!!

That showed him, eh, toaster-boy. He won't want to try fooling with us again!!!!!!!!!!????????????!!!!!!!!!!!!!

** Don't know why he bothered in the first place...

..............Phil

Reply to
Phil Allison

Do you normally correspond with any customers that you may have in this manner? Other people are responding reasonably to the OP's requests for information and you did indeed respond in the same vein originally. Just because you disagree with other peoples replies there is no need to descend into personal abuse: a cogent and coherent response would be much better. Several of the people that you have insulted have made, and continue to make, many useful contributions to this group on a number of subjects. Your response merely demeans you not them.

Andrew

Reply to
Andrew Jackson

"Andrew Jackson" >>

** Oh lordy lordy - now we have a self appointed member of the manners police butting his pointy nose in.
** Who made YOU into a one man judge, jury and executioner ??

Or maybe you just puff yourself up like a toad whenever the mood takes you - right ???

** Complaints should always be quite specific and contain no unjustified assumptions.

Or else they are no more than mindless abuse posturing as comment.

Which is what your post is.

** Add yourself to the list, please.

You get my pompous, ignorant ass award.

............ Phil

Reply to
Phil Allison

** Well, you would, but it's mine, all mine, and I'll never, ever, give it up! So there!!!!!!!!!!! [Autistics are like that.]

................ Phil

Reply to
Phil Allison

Leo,

What is your application? I have launched weather balloons a couple of times for the purpose of photographing the curvature of the earth at very high altitude. I used a mobile phone on one and radio beacon on another. A future launch will occur in a month or so with a similar setup.

You can read about my failures and successes here:

formatting link

My email address is at the bottom of the balloon launch 2 page if you wish to contact me. There are some issues that have to be overcome. Some of which you may know and others you may not. Here are a few:

  1. Modern GPS units only report to 18km altitude. Balloons can go over 30km alt
  2. Mobile phones don't work above a couple of hundred metres. If you want to use one, its purpose will be limited to letting you know where the payload is only after it has landed on the ground assuming it lands in a mobile phone coverage area.
  3. Air currents can be strong. My last balloon ended up almost in NSW. I launched it only 10km north of melbourne CBD. Its flight time was only around 3 hrs.
  4. Flight time can be calculated rather accurately. Its a function of the balloon size, and how much gas you put into it. So at least you will know when your balloon will pop and descend.

There are of course many more issues including air safety etc etc.... With regard to your specific question of data transfer, there are a number of options. On my last balloon I had a 1mW beacon courtesy of the local beacon finding club. It weighed about 15 grams excluding battery. It was powered by a D size lithium cell. This would have lasted at least 2 weeks continuous TX and contributed to most of the % of weight of the payload. It worked very well. Anything at that altitude will work very well for hundreds of km.

For a bit of nostalgia, I will be choosing the hellschreiber (google) technique to transmit data back to the tracking vehicle next time but of course there are much more complex systems you can go for. The Tiny Trak may be just what you are after if you are after a cheap and easy more or less off the shelf approach.

Regards, Phil

Reply to
Heywood Jablome

Sounds like a cool experiment, there used to be a CAA regulation ages ago about banning photos within a certain angle of vertical, I'm not sure what the reason was but it may pay to check if it still exists.

Regards Mark Harriss

Reply to
Mark Harriss

Methylphenidate or clonidine could help here but in definitive nothing can be achieved if the person is not willing to cooperate.

It is said also that behavioural therapy can alleviate these problems.

This is really tragic for parents and for the persons who suffer from that syndrome so this is a bad joke hopefuly.

Reply to
Lanarcam

In a similar vein to hat Phil (not Allison) wrote, from the few high-altitude balloon things I've seen on the net, it seems more common to rely on data-logging based on the idea that you can locate the balloon when it returns to earth.

Reply to
Poxy

A few suggestions:

- Contact your aviation authorities early in the project. You might get some useful hints.

- Contact your telecom authorities early in the project. You might get good suggestions of what kind of systems to use and what _not_ to use. If this is a one off launch, you might even get dedicated frequencies for the launch with generous power limits etc.

- I would suggest keeping the command and telemetry circuits separate, i.e. keeping both unidirectional at the protocol level, i.e. no ACKs transmitted back at the protocol level.

If the telemetry is constantly transmitted, try to grab as much as possible, but do not expect 100 % capture.

The telemetry could be sent on a license free band (check your local telecommunication authority if this is acceptable for airborne systems) and use a steerable high gain receiving antenna to recover the telemetry. There is no limitation on the receive only antenna gain that can be used and thus it is easy to attenuate any local noise source from similar equipment in the same band.

Use some telemetry inputs to monitor the command receiver outputs.

When you want to command the balloon, blindly and repeatedly send commands to the balloon and monitor the telemetry for the command receiver outputs. When the command receiver output has changed, you can stop sending that command.

If the balloon is going to ascend to say 10 km, the radio horizon will be about 400 km away and practically any station within that 500000 square kilometers (larger than most European countries) will be in LOS path. If you are using some shared frequency bands, be prepared to compete with all other transmitters within that frequency range. Thus, I would _strongly_ suggest that you get a dedicated command frequency for your balloon.

Regarding the problem of a hill 50 m high at 1 km distance as someone pointed out, I actually live 1 km from a sandy ridge created by the Ice Age, which is 50 m higher than my balcony and 70 m above a nearby lake. It is one of the steepest hills within a few hundred kilometers. While I agree that it is hard to get any signals from that direction, I am also very happy, since by climbing that hill, I can make VHF/UHF contacts from 100-300 km with 2-5 W transmitter power and a 10 dB yagi antenna.

If one would be fortunate enough to have such a hill close by, I would strongly suggest moving the balloon telemetry station on such hill.

Paul

Reply to
Paul Keinanen

I cant for the life of me figure out why this rule would be there. I would ignore it anyway. It's a free country.

Reply to
Heywood Jablome

It is common in the aviation regulations in many countries.

Probably the reason is to prevent unauthorized map creation.

--
Tauno Voipio (commercial pilot & instructor)
tauno voipio (at) iki fi
 Click to see the full signature
Reply to
Tauno Voipio

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.