RF module hunting

[Ian.M]

That looks like its a form for a calculation of the theoretical line of sight range.  It takes no account of attenuation due to ambient atmospheric conditions, multi-path effects and 2.4GHz band background noise.  The actual range achievable may be as low as 10% of that.  To get anything close to the theoretical range you'd have to be operating in a remote valley with no line of sight to any habitation, communications masts etc.

[hendorog]

Thanks Ian!

How accurate would you guys say this is?

Their miles to km conversion is the wrong way around.

For a real world datapoint - 100mW at 2.4GHz is the same power and frequency as a typical RC model transmitter, I have an oddball brand (WFLY) which has worked out to 3km or so with the rubber ducky antenna it came with. Others have issues at much shorter ranges though so YMMV.

Pushing that out to over 21 kms with a high gain rx antenna seems highly optimistic for the reasons Ian said.

[uncle_bob]

Hi

Ok, there is no big need for a lot of calculations at 2.4 GHz. Everybody runs WiFi in that band. The antennas and power level are roughly what you will be running. We have empirical data !!!

Fire up your router/ grab your computer run a test. Can you get a mile from your router and talk to it? Nope. So much for 10% of the calculated 12 miles. Can you get a few hundred feet? Yes, you probably can. That's maybe 1% of those apparently magic numbers.

There is no magic in this. I have line of sight to the router all the way to the way back yard. That's as much line of sight as your drone would have. I have no confidence of being sure to hold the connection at 500'.

Same band / same crowding / same problem. No 12 mile range with a simple antenna.

Bob

[aaronhance]

This was based on a high gain antenna (24dBi) with 18dBd power before the antenna. So I assume it will get better range than a pcb antenna with 20mW~ of power.

[uncle_bob]

This was based on a high gain antenna (24dBi) with 18dBd power before the antenna. So I assume it will get better range than a pcb antenna with 20mW~ of power.

Hi

Still not something that is going to be very practical with a drone (at least without a fancy auto tracking system on the antenna).

Bob

[tggzzz]

This was based on a high gain antenna (24dBi) with 18dBd power before the antenna. So I assume it will get better range than a pcb antenna with 20mW~ of power.

I don't know what you mean by "dBd"; I've never seen that before.

Apart from that, if that antenna is at the transmitter, the range will stay exactly the same. (Exception: if you transmit illegally, are prepared to stomp over other radio users, and are therefore willing to accept a criminal conviction).

Do you understand the significance of the "E" in EIRP, and the difference between EIRP and IRP?

[PA0PBZ]

I don't know what you mean by "dBd"; I've never seen that before.

dBd is gain over a dipole, same use as dBi, but I think he tried to type dBm.

[aaronhance]

I did mean dBm yes, sorry .  As for auto tracking, I've already said in this post I'm doing that. I've also said that I will be using the high gain antenna for rx not tx. Thanks!

[uncle_bob]

I did mean dBm yes, sorry .  As for auto tracking, I've already said in this post I'm doing that. I've also said that I will be using the high gain antenna for rx not tx. Thanks!

Hi

There is a slight difference between dBd and dBi but they are indeed the same idea

If you are trying to fly the drone, and steer a high gain antenna at the same time, you overload quickly. To much to watch, to few hands, not enough time. If the telemetry or video matters, any miss-steer is likely to be an issue. If you put your control stuff on the same channel, a drop out could be quite exciting. (Indeed I've seen this done several times). The choice is to either have somebody who does nothing but point the antenna *and* another who controls the drone, *or* you use an auto tracker. Gain and directivity are directly related, high gain means good pointing accuracy. Either the person or the machine need to do a pretty good job.

Bob

[tggzzz]

Gain and directivity are directly related, high gain means good pointing accuracy.

Just so.

The OP shouldn't forget to add in the effects of turbulence, which - especially at low altitude - can be considerable. That will help determine the necessary control loop bandwidth and hence maximum latency.

Failure to do that may result in something that works only in ideal conditions.

[tggzzz]

I did mean dBm yes, sorry .  As for auto tracking, I've already said in this post I'm doing that. I've also said that I will be using the high gain antenna for rx not tx. Thanks!

OK. Your phraseology

a high gain antenna (24dBi) with 18dBd power before the antenna.

made me think otherwise.

[aaronhance]

Ah yes, 18dBm on the transmitter

[Ian.M]

I don't think turbulence will be a significant issue other than to the UAV's attitude control system.   

Although theoretically one could put a tracker and high gain directional TX antennae on the UAV, the prime spot to do so (underside center) is usually reserved for a camera mounted in pan&tilt gimbals.   If its mounted topside, it wont be able to get enough down-angle unless its on a fairly long boom which will cause aerodynamic issues.  Also there is the all-up 7Kg upper weight limit for licence free operation to contend with, and the extra mass of a UAV mounted tracking antennae will directly cut into payload and flight time.  Although this does not absolutely rule out a tracking antennae on the UAV, it makes it extremely difficult to do so unless its a neutrally buoyant blimp, which has the sheer volume to make non-interfering gimballed camera and antennae mounts possible.

Therefore, when the only tracking antennae system is for RX at the base station, all one has to consider is if turbulence can take the UAV out of the antenna's primary lobe faster than the tracker can slew the antenna.   I already pointed out that close-in tracking would be limited by the antenna slew rate, so suggested an additional receiver with an omnidirectional antenna so the tracker doesn't have to follow accurately while the UAV is moving rapidly close-in. 

A good quality semi-portable parabolic dish antenna (i.e under 1.2m diameter) may have a 3db beamwidth of as little as 6 degrees.  At 50m range, that's a little over 5m.  Assuming the tracker tries to keep the UAV in the center third of the beam, it can tolerate a rapid displacement of up to 1.75m before it reaches the 3db beam edge.

Basically, if the turbulence is that bad, the craft wont be controllable anyway, its just too gusty to fly.

The devil now will be in the details.  I suspect it will need to be man-portable and its got to be reasonably easy to set up and anchor then align relative to true north.  For that bit, probably the easiest method would be to put the UAV into a position holding hover at a range of a couple of hundred meters then manually control the tracker to acquire the UAV, and use the GPS bearing to auto-align to.

[aaronhance]

 This is a fixed wing(think airplane), but the idea of having a tracking antenna on the UAV, hmm, interesting! I'm defiantly going to look into the points you made! Thanks agian Ian!

[Ian.M]

There is absolutely nothing to be gained by a tracking TX antenna unless the transmitter is licensed, due to the EIRP limits on license-free transmitters being so small that it is easily possible to reach them with an omni-directional antennae.

[aaronhance]

Thanks! If I get an amateur license from ofcom, can I still use higher power transmissions from ground, even if I can't on the uav itself?

[uncle_bob]

Thanks! If I get an amateur license from ofcom, can I still use higher power transmissions from ground, even if I can't on the uav itself?

Hi

That is a per country sort of thing. In general the answer is no. One reason is that by running high power in the middle of the WiFi band you pretty much wipe out all the other users.

Bob

[Ian.M]

No, as its a communications licence and all transmissions must be directed to another amateur, which your UAV certainly is not.

[PA0PBZ]

No, as its a communications licence and all transmissions must be directed to another amateur, which your UAV certainly is not.

I've never seen that restriction. 

My understanding is that it is a license to experiment with radio waves.

[djacobow]

I don't know what you mean by "dBd"; I've never seen that before.

dBd is gain over a dipole, same use as dBi, but I think he tried to type dBm.

In fact, dBi = dBd + 2.15.

That's because a dipole has 2.15dB gain over an isotropic radiator.

[uncle_bob]

No, as its a communications licence and all transmissions must be directed to another amateur, which your UAV certainly is not.

I've never seen that restriction. 

My understanding is that it is a license to experiment with radio waves.

Hi

Exactly how the regulation is worded and what frequencies are impacted in which ways varies from country to country.

Bob

[janoc]

No, as its a communications licence and all transmissions must be directed to another amateur, which your UAV certainly is not.

I've never seen that restriction. 

My understanding is that it is a license to experiment with radio waves.

Depends. In Slovakia where I am from it is still illegal for HAMs to use packet radio nodes that are connected to the internet, for example - even if it is only for a HAM to HAM connection. The reasoning goes that as it is going over non-HAM network, devices on that network will control the transmitter (indirectly by sending data packets) and as they (or rather their operators) are not licensed, it is illegal, period. So even stuff like Echolink is out.

Our licensing authority is seriously backwards and hyper conservative, they were among the last countries in the world to drop the requirement for Morse if you wanted to have HF privileges. And even now the basic N class license is severely restricted on HF, basically allowing you to use only the Morse parts of the bands, sans anything remotely usable for DX-ing (aka - "you didn't want to learn Morse? OK, we cannot drag our feet anymore because CEPT, so here you are. But screw you, no SSB for you, buster!").

Running video over a HAM band would be likely a no-no as well, because it isn't an approved mode, as would be operating an unattended station (a drone). Unattended operation (repeaters, packet nodes, etc) requires a special permit.

My guess is that it is the heritage of the communism where owning a radio transmitter (even a CB station!) required that you (and all your relatives!) were considered "reliable" by the communist party, were vetted by the secret police  and it was a privilege of a few, certainly not a right like today where you pass an exam and get your ticket automatically. Unfortunately a lot of the "cadres" of that era are still sitting in the same offices.

In contrast to that, in Denmark where I lived before I have got an all-band/all-mode HF license up to 100W power with no questions asked, it was enough to show my Slovak ticket. In France where I am now it is likely similar.

So to correct your understanding - it is a license to operate an amateur radio service station using approved frequencies, modes and power levels, not to experiment with radio waves. Or at least it isn't the universal understanding of it. The experimentation certainly can fit into it, but the legal frameworks could be very restrictive, depending on country.

And anyway, HAM license doesn't cover operation of commercial equipment in the ISM bands. I didn't check how much overlap is there between normal 2.4GHz wifi band and HAM allocation there - there it could be potentially possible, but one has to carefully check the local rules about interference and modes allowed.

[djacobow]

No, as its a communications licence and all transmissions must be directed to another amateur, which your UAV certainly is not.

I think a lot of people see that (in the US) the amateur radio license forbids _broadcasting_, and they take that to mean that all ham activity has to be amateur to amateur.

That's not a correct inference. For one, the FCC defines broadcasting quite clearly:

Title 47 Subpart A 97.3(a)(10): Broadcasting. Transmissions intended for reception by the general public, either direct or relayed
(http://www.ecfr.gov/cgi-bin/text-idx?SID=eb4ca1e28d7c18f69299fa1ca8a33a25&mc=true&node=pt47.5.97&rgn=div5#se47.5.97_13)


It is the intention that makes it broadcasting, not the activity.

Furthermore, amateurs are allowed to use their radios for RC activities. That's described here:

"
§97.215   Telecommand of model craft.
An amateur station transmitting signals to control a model craft may be operated as follows:
(a) The station identification procedure is not required for transmissions directed only to the model craft, provided that a label indicating the station call sign and the station licensee's name and address is affixed to the station transmitter.
(b) The control signals are not considered codes or ciphers intended to obscure the meaning of the communication.
(c) The transmitter power must not exceed 1 W.
"
(http://www.ecfr.gov/cgi-bin/text-idx?SID=eb4ca1e28d7c18f69299fa1ca8a33a25&mc=true&node=pt47.5.97&rgn=div5#se47.5.97_1215)


As another poster commented, experimentation is actually part of the very purpose of the amateur radio service and is expressly ALLOWED. 91.1(b):
 [a list of the purposes for the amateur service...] (b) Continuation and extension of the amateur's proven ability to contribute to the advancement of the radio art.


However, one thing that is expressly forbidden is encryption. That limits the amateur band from being useful for most personal communications or control of things that are "important."

-- dave j
WE6EE

[aaronhance]

Coming from ofcom "Amateur radio is a unique hobby in that it allows you to develop and experiment with radio equipment;"

Looks like I might need an intermediate amateur license to send data packets in the uk, I'll need to do some more research.

[uncle_bob]

Coming from ofcom "Amateur radio is a unique hobby in that it allows you to develop and experiment with radio equipment;"

Looks like I might need an intermediate amateur license to send data packets in the uk, I'll need to do some more research.

Hi

Ummm .... errrrr .... That's the 24 GHz band not the 2.4


Bob (the guy who makes posting errors about once every 4 minutes ...)