Not at all, even with 2.4 ghz they are
a luxury but when you start using frequencies like 900mhz for
telemetry and 1280 for video they are needed.
Also sometimes they are needed to reduce interference of the 900-1.3ghz video tx (not modem) with the GPS.
This also means that GPS units with antenna band pass filters are better for smaller UAVs.
Your biggest friend is spatial separation of the antennas and using different polarization for the video, telemetry and/or GPS.
In bigger UAVs with video rf power > 10w they use an rf switch (or two video tx units) and two 180-240 degree radiation antennas each mounted on the wing tip and activated according to the position of the UAV in respect to the home station thus avoiding radiating directly the UAV's fuselage.
Btw i found this and i am tempted to try it with a normal 2w bidirectional amplifier:
http://www.aliexpress.com/item/2-4Ghz-Digital-wireless-one-transmitter-with-one-receiver-for-Bus-autotruck-agricultural-vehicle-etc/704072104.html
From the specs i see that i can tolerate the 100ms latency (provided that the specs correspond to reality) since we are not actually doing any fpv flying and it's size looks very small.
If anyone has used it or something similar let us know...
I am also using this for experimenting but not at full power, 5w are more than enough and cooling is easy when mounted near the propeller:
http://www.ebay.com/itm/25W-Spectrian-Linear-RF-Amplifier-Board-2-3-2-35-GHz-18dBg-12V-/221316227454?pt=US_Ham_Radio_Amplifiers&hash=item338779a17e
Chris
On 11/15/2013 08:44 AM, alonso acuña wrote:
Also sometimes they are needed to reduce interference of the 900-1.3ghz video tx (not modem) with the GPS.
This also means that GPS units with antenna band pass filters are better for smaller UAVs.
Your biggest friend is spatial separation of the antennas and using different polarization for the video, telemetry and/or GPS.
In bigger UAVs with video rf power > 10w they use an rf switch (or two video tx units) and two 180-240 degree radiation antennas each mounted on the wing tip and activated according to the position of the UAV in respect to the home station thus avoiding radiating directly the UAV's fuselage.
Btw i found this and i am tempted to try it with a normal 2w bidirectional amplifier:
http://www.aliexpress.com/item/2-4Ghz-Digital-wireless-one-transmitter-with-one-receiver-for-Bus-autotruck-agricultural-vehicle-etc/704072104.html
From the specs i see that i can tolerate the 100ms latency (provided that the specs correspond to reality) since we are not actually doing any fpv flying and it's size looks very small.
If anyone has used it or something similar let us know...
I am also using this for experimenting but not at full power, 5w are more than enough and cooling is easy when mounted near the propeller:
http://www.ebay.com/itm/25W-Spectrian-Linear-RF-Amplifier-Board-2-3-2-35-GHz-18dBg-12V-/221316227454?pt=US_Ham_Radio_Amplifiers&hash=item338779a17e
Chris
On 11/15/2013 08:44 AM, alonso acuña wrote:
Hello. Regarding the filters. Do you think they are needed when using 900mhz for telemetry and 5.8Ghz for analog video?
On Wed, Nov 13, 2013 at 3:13 AM, Chris <address@hidden> wrote:
I forgot to mention that you will need a 900 Mhz low pass filter on the 9xtend modem and/or a 900-1000 / 2000 Mhz high pass filter on the tx transmitter to reduce interference between the various receivers.
You can also use a 2.4 ghz wifi video server and a wifi amplifier for better integration since it is possible to have telemetry also through wifi but i doubt that it will make it for long range based on a US airforce range experiment i have read plus it will be power hungry and heavy.
Beware this road needs a lot of development and experimentation so i wouldn't choose it for immediate use, i have seen it at work but i didn't like it.
Even today the analog video transmitter is the best choice for long range video transmittion.
Chris
On 11/13/2013 02:08 AM, GalapagosUAV wrote:
Hello Chris,
Thanks for your responses. One more question: Could you recommend me something to use as an adjacent communications system (to use besides the 9Xtends for telemetry) for video streaming over long distances?
Regards,Jorge
Sent from my iPad1) Yes i do this all the time, i have lost track of how many of them i have used.
2) Absolutely not, video through a serial modem is out of the question.
3) i am not sure the 5v ftdi cable i use supplies 5v directly from the PC's usb port so if the usb port can supply 700+ma it can power it directly but for 3.3v the ftdi cable probably has a regulator inside it and i am not sure if it can provide 500ma needed for the max 0.5W RF output (when using 3.3v)
Serial Signalling can be either 5 or 3.3v since both the modem and the LPC cpu are 5v tolerant.
4) i don't know as i have never used a 9xtend USB modem.
Chris
On 11/12/2013 07:31 PM, Jorge Pantoja wrote:
JorgeHello Stephen and Chris,Thank you very much for your help. I went through the information you sent me and the integration of the 9Xtend radios seems pretty straight forward. Although, I have a couple of more questions before I go ahead and get them:
1) So, you basically recommend me to get 2 9Xtend OEM for both, ground and air? The one in the ground station can be connected through the FTDI board to the computer and the one in the air directly on the Xbee ports as explained in the wiki.2) Can I use the Digi 9Xtend Modems to also send video through them?
3) Can I connect the 9Xtend modem in the ground station directly to the FTDI 3.3V power supply and get it to work? I know that this will decrease my transmitted power (and also range) but I don't want to make a BEC only to supply 5V to the ground modem for the initial testings.
4) Can I use a 9Xtend USB on the ground and and 9Xtend OEM on the air? If so, how should I connect the the 9Xtend USB to my computer and how should I configure it? Will I have any advantages/disadvantages using this configuration?
Best Regards,
On Mon, Nov 11, 2013 at 6:11 PM, Stephen Dwyer <address@hidden> wrote:
Hello,
Be sure to check out http://paparazzi.enac.fr/wiki/Modems#Digi_9XTend for configuration details.
In the past I have used the Digi development kit that includes a couple of modems and a couple of development type boards. These are useful for programming. They also have RSSI and status lights useful as part of the ground station, but are RS232 only, so you then need an RS232 to usb adapter. A good alternative is just an FTDI adapter like Chris says. You will probably want to get the right 2mm x 10mm headers. Sparkfun sells a nice breakout board too (https://www.sparkfun.com/products/9596) to convert to 0.1" header sizes or direct soldering. Samtec will send you free samples of the right sized header, just take a look around on their site.
The only major downfall of the development kit is it has one modem with the RP-SMA connector and one with the MMCX connector. I would definitely recommend against the MMCX connector, or if you use it, use it on the ground side in an enclosure where you never wiggle the connector. We have had multiple failures due to these connectors + vibration + multiple insertion cycles.
Also be sure to mount the antennas away from anything else on your aircraft. At 1W output, you can make servos jitter pretty easily if the servo line runs near the antenna.
And as mentioned by Chris, run them with transparent telemetry, at least for now, you will might need to tweak the api interface, though it is very similar.
Hopefully that helps a bit.
Thanks,-Stephen Dwyer
On Mon, Nov 11, 2013 at 3:08 PM, Chris <address@hidden> wrote:
Hi.
I always use two 9Xtend OEM modems but the ground modem also has a usb to ttl serial (FTDI)
converter plus a 5v power supply (a normal BEC used for rc airplanes powered from 12v or a 2S lipo pack) capable of at least 1A.
The 9xtend modem needs 5v for the full rated power of 1w, if you only need 0.5W 3.3v will suffice.
Connect it to the Yappa as you would connect the Xbee modem but power it from a 5v power supply,
the Yappa's power 5v regulator should do just fine.
Since you use the transparent mode you only need to set up the baudrate correctly.
9xtend oem modems can only use 9600 or 115200 bps for over the air communication.
Set them using the digi setup program at 9600 bps over the air and 115200 over the cable (modem to autopilot or pc) and also i suggest to use the polling mode, set one as the master and the other as a slave by giving them different adresses (read the 9xtend oem manual and in particular the polling mode)
For the antennas use a minimum of 8db gain patch antenna for the ground station or even better a 12-14 db yagi which is much better.
Search for 900 MHZ GSM antennas and you will find plenty.
For the airborne use a dipole antenna or a ready made for 900 Mhz like this one (900 mhz wheel antenna): http://www.wa5vjb.com/prices.html
Be carefull the wheel antenna has horizontal polarization which will give you the best range available
plus the lowest drag when correctly mounted on the airplane.
The ground station antenna can be setup with either polarization but the wheel antenna only works with horizontal polarization.
You can also buy your antennas from here, for the airborne antenna:
http://www.readymaderc.com/store/index.php?main_page=product_info&cPath=11_45_47&products_id=16
and for the ground station antenna:
readymaderc.com/store/index.php?main_page=product_info&cPath=11_45_47&products_id=296
I have used them and the small dipole antenna is a very good airborne antenna.
Finally buy some thin and long but shielded usb cable extension and use it for the 9xtend signals and power to the pc or to the autopilot, you will get much lower RFI with this kind of cable.
I hope i helped somewhat.
Chris
On 11/11/2013 11:27 PM, Jorge Pantoja wrote:
Dear all,I am looking for a way to extend the communications range I currently have by getting the Digi 9XTend modems shown in the wiki. However, before getting them I would like to know some things:1) Just to make sure, the 9XTend USB Modem (http://www.digi.com/products/wireless-modems-peripherals/wireless-range-extenders-peripherals/xtend) is for the ground segment and the 9XTend OEM Modem (http://www.digi.com/products/wireless-wired-embedded-solutions/zigbee-rf-modules/point-multipoint-rfmodules/xtend-module) is for the airborne equipment?2) I am using a YAPA2 autopilot board, how should I connect the 9XTend OEM modem to it? Can anyone help me describing a connections diagram?3) How should I configure my airframe file to use the 9XTend modems? I am currently using Xbees and my configuration is the following:<section name="MISC"><define name="XBEE_INIT" value=""ATPL2\rATRN5\rATTT80\r""/>...</section><firmware name="fixedwing">...<subsystem name="telemetry" type="transparent">
<configure name="MODEM_BAUD" value="B57600"/>
</subsystem>
</firmware>4) How can I achieve the range shown in the Paparazzi wiki (Up to 64km line-of-sight)? What combination of antennas should I use? I plan to use the 900 MHz band.5) Is there any additional equipment you recommend me to purchase like antennas or cables to facilitate the integration process? or do you have any other suggestions?Best Regards,
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