The product page for the 3DR radios is full of bogus specs!  Could you please post the REAL specs?

For example, the page claims "Receiver sensitivity to -121 dBm".  That is the spec for the SiLabs chip radio.  HopeRF lists the specs for their radio module as significantly less sensitive, and obviously you can't obtain the spec of the module when used within another product, like the 3DR radio.


Also, what's with the range claims?  I see you've changed it at least once, but why not make a realistic range claim.  These radios should do around 8 km.  So why only say one or a few?  Have you really not properly tested them over a few km?


Also saying "with Si1000 8051 micro-controller and Si4432 radio module" sounds like the product page writer may not have a good grasp of the hardware.  It has one Si 1000 radio chip in it.  I guess you can argue that statement is sort of true, but it certainly could cause someone to misunderstand and think it has two chips on board.


Don't take this as a rip.  I just see a lot of radio retailers out there that either flat out lie about the specs or have such a poor understanding of the technology that they mistakenly put wrong specs.  I don't think DIYdrones is either of these, so I thought I'd offer some constructive criticism to help you guys get going.


I also kind of feel responsible since I recommended using these chips in a radio design in several posts last Sept..  So if you need any help, just ask.

Views: 41362

Reply to This

Replies to This Discussion

Jake,

I can assure you that I do try to make the docs as accurate as possible. Yes, I have really done range testing, but as I explain in the docs, range varies depending on a lot of factors. I say "a few kilometers" because that is about as precise as you can get with a radio. The radio doesn't suddenly stop working at X kilometers and what absolute range you get varies a lot between tests.

Secondly, the receive sensitivity numbers are not just based on the Si docs, they are based on real lab tests. We found that the chip does actually exceed the spec sensitivity. The sensitivity also varies a lot with air data rate. The highest sensitivity is at very low data rates. The radio can be configured for 2 kbps if you like, in which case you will get a great receive sensitivity result, but you will also not be able to send much data.

At some future time we hope to publish lab results to make it easier for people working on compliance.

Also, what's with the range claims?  I see you've changed it at least once, but why not make a realistic range claim.  These radios should do around 8 km.  So why only say one or a few?  Have you really not properly tested them over a few km?

yes, I've really properly tested them. With the supplied antennas you can get some packets through at 8km, but not many. The packet loss at that range is usually quite high, mostly dependent on what the local noise floor is. In practice I expect people will need high gain antennas to achieve 8km with these radios without amplification.

Cheers, Tridge


any data on the range for the 433Mhz  ?

Any description of proper antennas made of a piece RG179  ?  - the provided antennas are too bulky and heavy - I'd like to make my own.

Hi Gabriel,

Most of my testing has been done on the 900MHz radios. In theory the 433 radios will provide more range for the same power level as the path loss for 433MHz is lower than for 915MHz, but in practice the key to the range of the 433 radios is the noise floor. I will shortly be posting some information about a problem with noise from the USB bus on some computers for the 433 MHz radios (based on my recent testing) which can limit the range a lot when on some laptops as ground stations. That is a problem we are trying to address at the moment.

Cheers, Tridge

Andke,

The simplest solution is to use a simple wire antenna. Just cut a 1/4 wave wire antenna and solder it onto the middle of the 3 antenna pads. A wire antenna works nicely for a small UAV.

If you want to get fancier then do a google search on antenna design. There are heaps of pages out there on all sorts of designs for 433 and 900 MHz radios.

Cheers, Tridge

Hi Veikko,

There is a single documentation page. What we have here is a discussion forum, which is meant to allow us to discuss the radios, come up with new ideas etc.

Regarding lab test results, I hope to be able to post some results soon. They will not be 'official' results in any sense - they are done by a diydrones member who works at an RF test lab.

Cheers, Tridge

ok my HAM friend says 433Mhz and everyone else is saying 900MHz...

ok my HAM friend says 433Mhz and everyone else is saying 900MHz...

both are right :-)

If you have a low noise environment then 433MHz will go abut twice the distance of 900MHz for the same power level. This is because the "path loss" at 433 MHz is about 6dB better than the path loss at 900MHz, and 6dB approximately doubles your range.

What really matters though is what your noise floor is at each frequency, and what power you are allowed to transmit at. The 433 ISM band is quite narrow, and may contain a lot of noise from other transmitters. So it may be quite noisy. If it is 6dB more noisy then you've lost your path loss advantage.

Then there is the power you can transmit at. Here in Australia I can transmit up to 1W EIRP between 915 and 928MHz under the LIPD rules as long as I'm using 20 channels of frequency hopping. At 433MHz I'm limited to 25mW, which is 16dB lower. So for me the 915 band will give longer range, if I have a radio/antenna setup that can put out 1W. That's why I use the 915 radios.

Cheers, Tridge

I haven't priced it, sorry

I know range testing is a real PITA and subject to countless factors, making it questionable to claim much.  But an open field range test is very useful to know the potential.  I'd like to see a maximum range achieved spec such as 10% packet loss @ X baud @ Y distance.

The xbees make some outrageous claims and I'd hate for anyone to get confused and think they're a better radio based on false range claims.  The xbee pro in the store claims, "Up to 6 miles (10 km) RF LOS with high gain antennas".  Now the SiLabs radio has twice the transmit power and greater receive sensitivity, which equals a MUCH higher link budget and thus MUCH longer range.

So I would clarify this to people by either greatly reducing the xbee claimed range or doing the range testing on the SiLabs radio to be able to make an equivalent or better claim.

.

OTOH I would also revise the receive sensitivity claims on the SiLabs radio.  Claiming -121dBm is misleading!  The chip claims -121dBm, the HopeRF module used claims -117dBm, so you need to claim LESS than this.  BEST case I would claim -116 dBm to account for losses from the module to antenna, especially since it leaves the ground plane and runs through that unshielded 90 degree solder joint.

Regardless of what your testing shows, anyone with common sense will realize that the entire radio can't achieve what the module does with NO losses, just as the module can't obtain what the chip does with NO losses.  So you could certainly mention that the chip sensitivity is -121, or the module spec is -117, but you should not claim over -116 for the entire unit.  I think even that is a pretty bold claim, but reasonable and within at least the realm of possibility.


-Jake

The radio guide claims 7.4km x 4 range with the Spireen amplifier.

http://code.google.com/p/ardupilot-mega/wiki/3DRadio

Does that mean I can almost double that range with a set of higher gain antennas with a patch antenna on ground station and omni in air and achieve around 30 miles??

Hi Steve,

Possibly, yes, but I haven't tried that, and radio range is something that can be hard to predict. A lot of it depends on your local noise floor. Also its a good idea to leave some dB up your sleeve as fade margin. A reasonable rule of thumb is to keep at least 5dB 'spare'.

Using an amplifier at both ends (so you have an EIRP of 1W at both ends) is probably the best bet for really long range. I suspect that as long as you have clear line of sight that 30 miles is achievable. If you try it, please let me know!

You also need to make sure you are within whatever UAV/aircraft rules apply in your country too.

Cheers, Tridge

Reply to Discussion

RSS

© 2019   Created by Chris Anderson.   Powered by

Badges  |  Report an Issue  |  Terms of Service