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Radio Beacons - Multiple Questions Within

David3D

Newbie
Joined
Oct 8, 2020
Messages
3
Location
Auckland, New Zealand
Hey guys,

Brand new to the forum and the colosal deep dive that radio communication has taken me on. With that in mind, my questions or understanding may seem stupid or downright ignorant of rules and regulations at best, or the laws of physics at worst, so my apologies in advance.

I'm designing a tracker designed to use GPS, GSM and the SigFox/IOT network to keep expensive equipment locatable in the event of said equipment being stolen. Could I buy an off the shelf product? Probably. Would that be nearly as fun? Probably not. Anyway, I want to implement a radio transmitter capable of transmitting a pulse to a directional or omni-directional antenna in the event I have to turn the recovery of the equipment in to a fox hunt if it goes missing. The questions I have are regarding power output, antenna types/gain and optimal performance for certain situations.

In my case a battery operated device which would otherwise be dormant is awoken with a text message and the beacon starts transmitting. But I'm anticipating the likes of garages, shipping containers and the like getting in the way. Shipping containers are of particular concern.

Question one: "What would be the optimal frequency to consider if I wanted the beacon to penetrate solid objects to ensure a strong signal in urban environments?"

From what I understand, the lower the frequency the better penetrative power it has due to it's longer wave. I'm not against licensing a particular part of the spectrum to get the best range capabilites and penatritive properties possible. It would be nice if that could be avoided, but needs must.

Question two: "At what point does a beacon's power become too powerful and the correct size antenna/gain become more important for my particular usecase?"

If my limited research has taught me anything, it's that I can make the beacon so powerful, it's almost impossible to narrow down exaclty where it is, because directional antenna don't work nearly as well when close to the source. Is this true?

Question three: "Is the ISM band too (high frequency wise) to be able to transmit effectively over long distances?"

I know this question is so dependant on so many variables that it's almost impossible to answer. But I guess what I'm asking is if anything in the ISM band is remotely useful for my usecase.

Question four: "What specifically is the difference between say a $160 - $300 Marshall transmitter beacon and a $5.00 ebay special when both communicate on the 433MHz band at 500mw?"

There are YouTube videos of people using LoRA modules to communicate 2 or more kilometers away. This is more than enough range in terms of what I'm looking for, but they are using their equipment line of sight. I'm certainly not doing that. So would that make this technology irrelivent for me specifically? Or would I just need an order of magnitude more power to get the same range.

Question five: "Would implementing multiple beacons that transmit at different frequencies be the solution to my problem?"

Would transmitting at variable power limits across different areas of the spectrum be a catch all to make sure the device can be contactable in a broader range of scenarios?

Sorry if any of these questions come off a bit silly. I'm trying to get a better understanding of the ISM band, what constitutes high power or not enough in the kind of scenarios not a lot of people utilise the band for. Maybe I'm asking too much of the technology, I don't know.

I was thinking, should I get a rough idea as to where the tracker was via the mobile network, but no GPS location, a drone with a suitable antenna array attached to the bottom would be my best way to achieve a better line of sight. But those rules and regulations are for a different forum, haha.

Very much looking forward to the discussion.

Cheers!
David
 

AK9R

Lead Wiki Manager
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Jul 18, 2004
Messages
6,427
Location
Central Indiana
Is this device going to operate in the amateur radio bands?

Do you have an amateur radio license? Will the device identify with your amateur radio callsign?
 

David3D

Newbie
Joined
Oct 8, 2020
Messages
3
Location
Auckland, New Zealand
Is this device going to operate in the amateur radio bands?

Do you have an amateur radio license? Will the device identify with your amateur radio callsign?
Thanks for your reply. I don't currently have a license or a callsign. The beacon won't transmit any usable data of any kind except an audible tone. Possibly multiple tones at different power levels to determine distance. I'd rather not need a license for the device to operate. But if a HAM radio license allows me to tap in to other frequencies and licencing my own part of the spectrum makes the device more effective, I'll do it.

This is the part of the spectrum licensed to everyone in New Zealand.

I'm not sure if it's worth mentioning that this device won't be transmitting all the time. It will only transmit if I know it can get within resonable range of it and confirm it's location.

I hope this all makes sense.
 

popnokick

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Premium Subscriber
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Mar 21, 2004
Messages
2,074
Location
Northeast PA
The OP's questions lead directly into a commercial RFID application. The OP should seek a consultation with a competent RFID integrator. Not relevant to Amateur Radio.
 

mmckenna

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Joined
Jul 27, 2005
Messages
13,530
Location
SNCZCA01DS0
Question one: "What would be the optimal frequency to consider if I wanted the beacon to penetrate solid objects to ensure a strong signal in urban environments?"

From what I understand, the lower the frequency the better penetrative power it has due to it's longer wave. I'm not against licensing a particular part of the spectrum to get the best range capabilites and penatritive properties possible. It would be nice if that could be avoided, but needs must.
In urban environments, higher frequencies will penetrate buildings/concrete/etc. better. This is one of the reasons why cellular phones use higher frequencies, building penetration is better than lower frequencies.

As for licensing, I'm not familiar with the rules in New Zealand, you'd need to research those carefully and I'd recommend talking directly to the agency in your country that sets those rules.

Question two:
"At what point does a beacon's power become too powerful and the correct size antenna/gain become more important for my particular usecase?"

If my limited research has taught me anything, it's that I can make the beacon so powerful, it's almost impossible to narrow down exaclty where it is, because directional antenna don't work nearly as well when close to the source. Is this true?
Yeah, too much power and the signal will bounce around and make it very difficult to narrow down. You also need to consider your power source. If you want this to be small and manageable, power levels and battery size will need to be carefully balanced carefully.

On that note...
A common misconception of the newcomer to radio is that range/performance is -entirely- about transmitter power output. There are many more variables involved.
Using lower power levels allows smaller/lighter power sources. If you want this to be reliable and beacon out frequently enough to use a directional antenna, you'll need to keep power levels low. I've chased rouge transmitters before for work, and it's an exhausting process. You need it to transmit long enough to sweep a full 360º with your directional antenna, and do it frequently enough to be able to get reliable/repeatable fixes from many different locations.

Lower power levels can be countered by using more efficient antennas. I'd rather have low power and a high gain antenna than high power and a low gain antenna. In your application, a directional antenna for the person searching for the beacon will be an easier approach.

Question three:
"Is the ISM band too (high frequency wise) to be able to transmit effectively over long distances?"

I know this question is so dependant on so many variables that it's almost impossible to answer. But I guess what I'm asking is if anything in the ISM band is remotely useful for my usecase.
Again, you need to balance antenna size, power levels, battery size, etc. to make this work. Also, licensing will be a limiting factor. Not familiar with New Zealand rules, but likely you are going to be very limited where you can run a device like this legally.
Here in the USA, I'd probably look at the 900MHz ISM band. 900MHz would give you some appropriate spectrum to use, reasonable power levels, good building penetration, and manageable antenna size.


Question four:
"What specifically is the difference between say a $160 - $300 Marshall transmitter beacon and a $5.00 ebay special when both communicate on the 433MHz band at 500mw?"

There are YouTube videos of people using LoRA modules to communicate 2 or more kilometers away. This is more than enough range in terms of what I'm looking for, but they are using their equipment line of sight. I'm certainly not doing that. So would that make this technology irrelivent for me specifically? Or would I just need an order of magnitude more power to get the same range.
There's a lot of cheap crap coming out of China. You'd need to look at the —full— specifications for all of them. It's easy to build a cheap transmitter with little/no filtering that will transmit on a frequency. It's harder and more costly to make one that is reliable, stays on frequency, transmits cleanly, is reliable. In other words, you get what you pay for.
Also, before you buy 433MHz stuff, make sure that's legal for your intended uses in your country. Just because something is sold on e-Bay doesn't necessarily mean it is legal to use in your country. Lots of unknowing consumers are falling for that here in the USA...

Question five:
"Would implementing multiple beacons that transmit at different frequencies be the solution to my problem?"

Would transmitting at variable power limits across different areas of the spectrum be a catch all to make sure the device can be contactable in a broader range of scenarios?
Depends on exactly what the problem is. You need to figure out what your goal is. Making a locating beacon that works everywhere, every time, in every application is going to be difficult.
Range vs. Building penetration. Lower frequencies will travel farther, higher frequencies will penetrate buildings better. You could try multiple frequencies, but then you have to have multiple efficient antennas on EACH end. You have to power both radios for long enough time to work effectively. You also need to stay within the rules of the country.
There are usually only a few frequencies or bands you can use without lots of licensing/approvals, etc. You'll have to figure that out in your own country, and those rules will differ from country to country, so if this is a product you intend to market outside New Zealand, you are really going to have your hands full making it legal.

In some applications, you also need to monitor before transmitting. Preventing interference may be a requirement you will need to overcome. Unless you have dedicated spectrum for this, simply blasting out a signal isn't going to sit well with the powers that be. Causing harmful interference to other users/systems will not go over well.

Sorry if any of these questions come off a bit silly. I'm trying to get a better understanding of the ISM band, what constitutes high power or not enough in the kind of scenarios not a lot of people utilise the band for. Maybe I'm asking too much of the technology, I don't know.

I was thinking, should I get a rough idea as to where the tracker was via the mobile network, but no GPS location, a drone with a suitable antenna array attached to the bottom would be my best way to achieve a better line of sight. But those rules and regulations are for a different forum, haha.

Very much looking forward to the discussion.

Cheers!
David
It's all about the antennas. Line of sight will be important.

You'll really need to research the rules in New Zealand. Unless you get someone from there to comment, most of us will be applying knowledge from other countries that may or may not apply. Sifting through the comments and deciphering which country they are from and if the same rules apply will be difficult. Many will read these questions and answer it from various points of view that may or may not apply. I've seen a few projects started by well meaning individuals that were going to "revolutionize" the industry with their do-all radio, only to find out they didn't do their regulatory home work first. A lot of money/time/effort gets wasted.

Good luck!
 

David3D

Newbie
Joined
Oct 8, 2020
Messages
3
Location
Auckland, New Zealand
Thanks for the replies everyone!

Your first step might be to determine what frequencies in your country you can get licensed to use for your proposed system.
Bill
Definitely. But I've not yet settled on what frequency would be most effective at building/ground penetration. I think this is one of the sources of greatest confusion for me. But I've got a much better understanding now.

The OP's questions lead directly into a commercial RFID application. The OP should seek a consultation with a competent RFID integrator. Not relevant to Amateur Radio.
Not commercial. And while not technically "amature radio" in the intended sense of the words, I'm still very amature at radio. If there is a better catagory this thread could be discussed in, let me know and I'll ask a moderator to move it.

In urban environments, higher frequencies will penetrate buildings/concrete/etc. better. This is one of the reasons why cellular phones use higher frequencies, building penetration is better than lower frequencies.
This makes a lot more sense. I think for some reason I had it backwards and that the KHz band would be better at the likes of ground penetration rather than distance and the high frequency bands were for range (because mobile phones used them) but my understanding was exactly the opposite to the truth, so this clears a few things up for me.

Yeah, too much power and the signal will bounce around and make it very difficult to narrow down. You also need to consider your power source. If you want this to be small and manageable, power levels and battery size will need to be carefully balanced carefully.
I've not yet decided on a power source, but it would be battery powered. I've not yet got so far as to deciding what battery chemistry or voltage would be required to keep the beacon going at any particular power level, because I havn't settled on what part of the spectrum I'm using and felt that maybe how much power I used depended on that. Maybe I'm wrong.

Lower power levels can be countered by using more efficient antennas. I'd rather have low power and a high gain antenna than high power and a low gain antenna. In your application, a directional antenna for the person searching for the beacon will be an easier approach.
This is exactly what I needed to know. I think what I might do is assemble a bunch of different radio beacons in the general use band and test different antenna.

900MHz would give you some appropriate spectrum to use, reasonable power levels, good building penetration, and manageable antenna size.
Thank you! I'll take this in to consideration. I've been focusing on 433MHz area because that is what everyone seems to be using, but you've given me a much more educated starting point.

There's a lot of cheap crap coming out of China. You'd need to look at the —full— specifications for all of them. It's easy to build a cheap transmitter with little/no filtering that will transmit on a frequency. It's harder and more costly to make one that is reliable, stays on frequency, transmits cleanly, is reliable. In other words, you get what you pay for.

It's all about the antennas. Line of sight will be important.
I didn't even consider the fact that a signal being transmitted can shift frequencies with wear and tear. This is something I'll have to take in to consideration. If antenna play a larger role in this equation, then maybe I'm misplacing my attention. I think a lot of this is going to come down to trial and error.

Also, before you buy 433MHz stuff, make sure that's legal for your intended uses in your country. Just because something is sold on e-Bay doesn't necessarily mean it is legal to use in your country. Lots of unknowing consumers are falling for that here in the USA...
I've put a focus on making sure I stay within the bounds of the appropriate legislation. I'm not at all oppossed to my country's licencing fees for my own slice of the spectrum. And I'm more than happy to get qualified if that's a prerequisite for transmitting. I just wanted to get a better feel for the best part of that spectrum to use first and sort the rules out later. You've given me a much better basepoint than I had before.

Thank you for your detailed response, I really appreciate it!

At the end of the day, the radio beacon in this case is simply the ambulance at the bottom of the cliff. An alternative way to manually locate what all other networks failed to do. I've got some more homework to do thanks to everyones insight (mmckenna's especially) and I'll let everyone in on how it goes at a later date. I may even have more questions!

Cheers,
David
 
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