459MHz UHF legal Tx and Rx - Arduino based programability.

[thundead]

Hey ollyb,

Not sure about any EIRP rules in the UK, but if you want to use the openLRS for long range you need to get a booster (meaning you'll lose the bidirectional link) as the stock range is not so good (ground test aprox 500m).

Hi All

Just been reading this thread with interest as I'm planning on getting into FPV (and possibly autopiloting). Seems there are a multitude of options for TX and RX (not thinking about video freqs at the moment), but 459 seems to have great range and is two way too.

I'm seeing a lot of talk about patch antennas, so was wondering if the EIRP rule applies to the 459MHz freq. For those that don't know, the EIRP (Equivalent Isotropic Radiated Power i think) is the power needed to produce the strength of signal that you've got using a patch antenna (for example) but by using an omni.

For example, if you've got 100mw tx and an 8db patch, to get the strength of signal the patch produces but by using an omni, you'd need 160mw tx. (number picked out of the air, but you get the idea.

In the UK, wifi frequencies, for example, are limited to 10mw EIRP, which basically means sticking a yagi on a 10mw tx makes it illegal.

Does the same rule apply to the 459MHz band. It would be bad to go to all this effort to remain legal if sticking a patch on it makes it illegal!

[Devonian]

We are allowed 100mW ERP (Effective Radiated Power) on 459MHz.

In reality, this means that the actual antenna is only allowed to radiate 100mW.
So, if the antenna has zero gain and is right on the Tx, with no cable or connector losses, the Tx should be at 100mW output power.

If however, in the extreme, you intend to run a 50 metre coax cable from the Tx to that same antenna and the cable loss is 10dB, you are allowed to increase the power of the Tx to account for that loss so that the antenna still radiates 100mW.

Same goes for an antenna with 10dB gain, when mounted right at the Tx with no losses, you must reduce the Tx power to account for the antenna 10dB  gain.

HTH

Nigel.

[ollyb]

Thanks for the quick replies.

Just to clarify, does this mean the traditional TX control has a greater range than receiveing telemetry back?

Same goes for an antenna with 10dB gain, when mounted right at the Tx with no losses, you must reduce the Tx power to account for the antenna 10dB  gain.

This is the bit that I suspect is getting ignored for the most part. In effect, to stay within the law, you'd get no extra range by using more directional antennas.

[Devonian]

Just to clarify, does this mean the traditional TX control has a greater range than receiveing telemetry back?

I'm not sure I fully understand your question.
Presuming the Tx and Rx have equal output power and antennas, then theoretically, telemetry should be equal to the full range of the equipment.

Same goes for an antenna with 10dB gain, when mounted right at the Tx with no losses, you must reduce the Tx power to account for the antenna 10dB  gain.

This is the bit that I suspect is getting ignored for the most part. In effect, to stay within the law, you'd get no extra range by using more directional antennas.

Correct

Nigel.

[ollyb]

Just to clarify, does this mean the traditional TX control has a greater range than receiveing telemetry back?

I'm not sure I fully understand your question.
Presuming the Tx and Rx have equal output power and antennas, then theoretically, telemetry should be equal to the full range of the equipment.

That's what I thought. But Thundead above said you lose the bidirectional link at about 500m. Given that the ranges discussed in this thread have been a lot longer than that, I thought he was talking specifically about the bidirectional nature of the link, ie getting the telemetry back drops off at 500m, implying normal tx goes further.

[thundead]

I was referring to ground range. Bidirectinal link should work as good as the rc link as long as you got matched antennas on both your tx and rx. Also i was saying you lose the bidirectional link if using a booster :)

[papa_lazerous]

For me the bi-directional link isnt worth having.  And I have it turned off, if flying FPV its safe to assume you will have a OSD displaying information including RSSI so why have the Tx making a noise if you lose a few data packets as the RSSI indicator on your screen will report exactly the same. 

The name OpenLRS is somewhat misleading, it is not a long range system and stock out of the box has less range than I get with my Dx7 and a HobbyKing 6ch Orange Rx without satellite.  With some nifty firmware thats getting better each revision and the employement of a booster which ofcourse wouldnt be legal to use then you have a long range system!  So its only long range if you up the power output, which to be fair is exactly what all the other UHF systems do to get long range.  The real benefit of this system is you are on a UK legal frequency so Ofcom wont be on your case, and it free's up other frequency's like 2.4GHz to broadcast your video signal on.

[thundead]

Darn... haven't been getting emails about new posts.

well to keep it short S**T just got real :D 10ch hopping like the wind through Aberdeen's finest granite buildings = >500m ground range. fw will be released in a couple of days :D

Here is a peak preview of what;s to come:


btw, I'm seriously thinking of not releasing any source code for this as I already spent way to much of my free time developing a proper fw and didn't get any help from anyone else in the community regarding code etc. and everyone seems to be keeping their stuff to themselves anyway. (excepting all who contribuited to the infamous pringles and redbull fund - Huge thanks to you all once again)

Nigel I personally believe we will get better range on a static channel, partially because of how the RF module is not hopping so well. Mihai is working on something at the moment to give us a better hop without too much trade off as far as range goes but I guess we will have to wait for him to give more details as and when.

Adding diversity to an existing board would be too much work, but you can have diversity with 2 receivers at present that's what I run in my skywalker,


Sent from my iPhone using Tapatalk

[papa_lazerous]

Mihai the sneak preview looks sweet, a nice way of configuring things. I'm used to editing the config.h file now but definitely a nice touch. It's wrong that others aren't sharing as we could all benefit from people sharing. As it is the source code has remained static for months now.  I think I'm good on the beer and Pringles fund right now ;). Serious note, if you get the hopping working without the RF module dropping out randomly like it does at present I'll happily donate enough pringles to make you sick of them :)


Sent from my iPhone using Tapatalk

[thundead]

Hopping already sorted mate :) it nicely jumps over "x" bad channels and resyncs with the tx :P

Mihai the sneak preview looks sweet, a nice way of configuring things. I'm used to editing the config.h file now but definitely a nice touch. It's wrong that others aren't sharing as we could all benefit from people sharing. As it is the source code has remained static for months now.  I think I'm good on the beer and Pringles fund right now ;). Serious note, if you get the hopping working without the RF module dropping out randomly like it does at present I'll happily donate enough pringles to make you sick of them :)


Sent from my iPhone using Tapatalk

[papa_lazerous]

Well as far as I can see it affordable legal UHF just became a whole step more viable. Thumbs up mate :)


Sent from my iPhone using Tapatalk

[thundead]

did I mentioned its got in-flight fs and very very reliable rssi as well ? :D

Well as far as I can see it affordable legal UHF just became a whole step more viable. Thumbs up mate :)


Sent from my iPhone using Tapatalk

[papa_lazerous]

Oh I need good RSSI, it's no use when it's going up and down all the time as you can't tell when you are getting low signal. Which was the problem before


Sent from my iPhone using Tapatalk

[SouthPawPaul]

I'd loved to have helped with the firmware, but I've so often got my head buried in Delphi/Java/C++ at work that trying to get my head around yet another language after a full days work is often not the most appealing thought.  :dazed:

Nice job though. Well done.
You seem to be putting way more effort into it than anyone else in the OpenLRS community (even the sellers!).  :clap: :ohyeah: :respekt:

[simondale]

Hi Thundead,

I've been enjoying using my OpenLRS but haven't touched/ thought about the firmware since I first flashed it with, I think, the first 459MHz version.  I simply haven't  had any problems with it so I haven't touched it. 

I don't do anything particularly clever with it, not even RSSI, but it is bi-directional (I know because it beeps when I turn the Rx off)!

Should I upgrade to a newer firmware now?  What would I gain if I upgrade?  Is there proper FHSS in your latest version?  That would be great!

All the best

Simon