7 replies to this topic

[Edouard]

ok, not a fully successful test, but nevertheless, I was able to get a sync between the modems, with a 11km LoS path. The GCS and the UAV did not manage to transmit a full UAVObject - or maybe they did once or twice - but the UAVTalk protocol managed to detect the link, i.e. it got a handshake regularly. The modems were on 100mW with a 128kbit rate, I will try again with a much lower bitrate to see whether this makes a difference. The antennas were simple rubber duck 868MHz antennas.

[Gary Mortimer]

Hang on a minute are we not using 400 Mhz?? That is very impressive for miss matched whip antennas?

Clicks on Wiki to look for frequency....

Just checked, did'nt realise they did 433 868 or 915MHz

http://wiki.openpilo...Pilot PipXtreme

I think if I were trying long range I would opt for 433, which frequency is the optimal one for power out??

Try some dipoles to try and increase the range Ed, even some beams if you can find them although it can be like pointing a pencil at a moving target I have found with other modems.

[Pip]

Excellent Ed!

Gary Mortimer, on 19 February 2011 - 07:31 PM, said:

I think if I were trying long range I would opt for 433, which frequency is the optimal one for power out??

You get upto 100mW on all bands.

Easier to use the higher bands I guess if your going to use beams or such like due to the antennas being somewhat smaller, but are a bit more affected by trees and buildings.

[Edouard]

Gary Mortimer, on 19 February 2011 - 07:31 PM, said:

Hang on a minute are we not using 400 Mhz?? That is very impressive for miss matched whip antennas?

Clicks on Wiki to look for frequency....

Just checked, did'nt realise they did 433 868 or 915MHz

  The RF22 radio chip in the modem can do all bands, but of course you need matching circuits around it. Actually, this is a big source of confusion all over the Internet: when you use RFM22 modules (i.e. the RF22 chip already mounted on a small module with all necessary ancillary circuits) , you have to buy those matched for one specific frequency, though many online shops do not mention this, and you can't really know in advance which frequency you're going to get! My modems are on 868MHz, for example. Though it is probably a good thing if you use a 446MHz talkie next to your modem for communicating during range tests

[peabody124]

Yeah for example I got some modules for Sparkfun and they were 433.

For the record we'll probably only sell 433 Mhz or ones without a chip to minimize what we have to stock.  At least at first.

[dankers]

Because of the limited resources of the project we are going to start with the 434Mhz versions. During testing we created all three versions of the modem to validate the design, there is 434Mhz, 868Mhz and 915Mhz all out there and working. Because these radios have been design from day one to live happily with FPV gear, GPSs  and RC there are a bunch of different filters required at the difference frequencies and we simply don't have th resources to create and then stock all three types. This is not your normal xbee type modem, it is far more advanced than that of course.  

With the 868Mhz version we also have to be careful of exceeding the maximum allowed transmit time allowed for that frequency in Europe as well, short flight we are fine with but longer flight will exceed the allowed duty cycle. 434Mhz is a sure thing and will be released soon, the other frequencies might be handled by us creating a partially assembled board that lacks the filters and the module, the end user will need then add the correct parts for the frequency.

Gotta say, Pip you are amazing! I know the massive amount of effort you have put in to this modem, I have seen the huge amount of care that was put in to planning and routing every single trace on the PCB, quality RF PCB design is hard and takes years of experience to get right. Of course you also wrote the firmware as well!

Seeing a 11km connection out of 868mhz, with small rubber duck antenna and close to water is fantastic, even though it was LOS, it was also a land to land test with all the Fresnel zone implications of that as well. The goal of the devices is 8km LOS with 433Mhz  version, we should do that easily.

[peabody124]

P.s. awesome result!

[Gary Mortimer]

As ever all very cool, well done Pip! I will be back in the UK soon and up for some airborne range checks with some 433 units!