900 mhz data antenna location for the S800?

[srbell]

You'd think it would be simple, but... DJI recommends pointing down, but it will be in the cameras field of view when panning. Pointing up, it's pretty close to the GPS mast as shown in the photo. Any thoughts? BTW, the GPS mast is temporally off while I make a quick release keyed mount for it.


View attachment 8980

 

[ChrisViperM]

I would just leave it where it is a t the moment and try it out. It's easier to mount the GPS a little bit further away. I have mine mounted where the red cables are visible on your picture and the GPS right on the front of the craft. Due to damn snowfall I couldn't try it out yet, but if ther is a problem with this configuration I will try and mount the 900 mhz on the landing gear. Another option would be a high quality shielded antenna extention cable and just route the antenna somewhere else....if it is a good quality cable you should not notice any decrease in performance.


Chris

 

[PeterLester]

Since you are both installing the 900 Mhz datalink, where did you find the spare canbus port?
Seems I have to install the iOSD to get the spare port since the WKM doesn't have enough by itself to support LK900.

According the the HAM radio course, your best range is achieved with the antenna polarization is on the same plane, i.e., both antennas vertical.
Inverting one is just fine. But the ground station antenna has to be pointed up for maximum distance radiation.

 

[srbell]

Since you are both installing the 900 Mhz datalink, where did you find the spare canbus port?
Seems I have to install the iOSD to get the spare port since the WKM doesn't have enough by itself to support LK900.

According the the HAM radio course, your best range is achieved with the antenna polarization is on the same plane, i.e., both antennas vertical.
Inverting one is just fine. But the ground station antenna has to be pointed up for maximum distance radiation.

Ive got the OSD as well, so there's enough ports for the Zenmuse and data link. Kinda liked where I have it located, but I don't want to interfere with the GPS and compass. Not sure if I want to be the beta tester on that lol.

 

[Tahoe Ed]

Mine is pointed down but I don't have retracts so it is not a problem for me at this time. Maybe later.

 

[PeterLester]

Key benefit of pointing the LK900 Mhz antenna down versus up are:
1) No signal path attenuation from MR airframe metal and CF components.
2) Less chance of the antenna repositioning in flight to get clipped by on of the MR props (assuming prop diameters could be that large relative to antenna location.

GPS signals are coming in at Gigahertz frequencies shown on table at right)....
therefore the risk of rfi from the downlink is likely minimal at 910 Mhz +- bandwidth (just under 1 Gigahertz)
Remember that the datalink duty cycle at the MR end is relatively quiet overall since the data is sent in quick bursts. A
nd when in receiving mode there can be no issues at all with GPS interference.

Band	Frequency	Description
L1	1575.42 MHz	Coarse-acquisition (C/A) and encrypted precision P(Y) codes, plus the L1 civilian (L1C) and military (M) codes on future Block III satellites.
L2	1227.60 MHz	P(Y) code, plus the L2C and military codes on the Block IIR-M and newer satellites.
L3	1381.05 MHz	Used for nuclear detonation (NUDET) detection.
L4	1379.913 MHz	Being studied for additional ionospheric correction.[SUP][citation needed][/SUP]
L5	1176.45

 

[srbell]

Thanks for the clarification on GPS frequencies. 1.5 to 1.1GHz is a fair ways from .9, should be ok. As for attenuation, I should be ok as I hate flying directly above myself lol! I'll take it up as it is and watch the signal strength. Of course my TX radio antenna will be mounted below the frame. Thanks for the input. Seems to be a number of us from western Canada eh?

 

[PeterLester]

By far the best decision one can make for a reliable long range data link is to locate the GCS baseas high as possible and the antenna as high as possible above that! The MR antenna location is far less critical.
Good to here there are others into GCS as well on this side of the border as tech support issues ramp up fast when you add all the bells and whistles and datalinked thru to Google Earth will do that!

Do you have an amateur radio license to use 900 Mhz radios above 1/2 watt?

 

[srbell]

VA7AKX

Got that when my son decided he needed a TeleMetrum GPS tracker/flight computer for his new rocket. It operates on the 70cm band giving real time telemetry and 3d google earth flight path along with manual override for deployment. Pretty much the only way to get these things back.
View attachment 9069

It's over 9' tall and can use either an AP or hybrid "M" class motor. All I can say is, it all started with a little Estes Mad Max lol.

 

[PeterLester]

SRBell,
Interesting.... as we are both into High Power Rocketry as well. I have plans to turn one of my Multirotors into an aerial remote control launch pad but for a small b or c motor.
Currently flying a carbon fiber Mongoose 98 knock off and hoping to achieve L4 certification with at this summer. It uses a BigRedBee 70cm GPS which I may also be testing on my Multi rotor for range etc.

 

[srbell]

A Mongoose 98 is a pretty smokin' hot rocket, nice. This is just a Hyperloc 1600...all cardboard, ply and fiberglass. Saw you other post on the ground station, that's a good heads up on the software install.

 

[PeterLester]

You can easily relocate your GPS puck and mast to the opposite side of the center plate. Then make the appropriate position adjustments to the controller config using WKM assistant software. Every centimeter counts.

 

[PeterLester]

SRBell....if interested...... see my additional comments on the GCS antennas etc. at the following location:
http://www.multirotorforums.com/sho...-Station-experts&p=88635&viewfull=1#post88635

 

[thinwing]

Anyone having connection problems with lmk 900 data links...most of the time I get no permission message at the end of the handshake.Position of aircraft on map always comes thru though.I am using a 9 ft extension cable to get lmk 900 unit up on a tripod away from the laptop.Got it to connect once today after numerous trys...my airborne unit is mounted aft on an aux battery tray pointed straight down...regards kp couch k6zk extra class

 

[gtranquilla]

The IEEE indicate USB was developed for PC peripherals and the limitation on cable distance to be 15 feet for the firewire variant of USB and possibly less for standard USB.
Additional attenuation of the signal and loss of voltage will also occur on the longer cables. And there is only 5 volts available to begin with.
Also it is only marginally feasible to power a radio transmitter using 5 volts and only 500 to 900 milliamps (hence the redundant USB plug on one end of the cable - but I discovered mine was wired incorrectly as it caused a USB short!

It is far better to select an antenna c/w a length of RG58 50 ohm impedance coax antenna cable. By selecting an antenna for the 900 Mhz band with a dB gain of 4 to 11, you not only regain antenna coax cable dB loss but also significantly increase your radio range if you choose an 11 dB antenna. Keep in mind that some countries allow use of FHSS 900Mhz band unlicensed but restrict the wattage of the transmitter to 1/2 watt in an effort to limit the range. Using a high gain antenna does not increase the watts but does increase your range significantly which can cause problems with others depending on the amount of FHSS traffic in the transmit range. FHSS is supposed to enable many operators to use the band. But the truth is a heavily congested radio band will still cause problems even when using FHSS. To discourage operators from extending their radio range, the new inverted sma connectors are designed to not accept conventional coax cables and antennas but there is an easy way around that. Here is a 900 Mhz antenna that I use.
http://www.mroelectronics.com/mro/product.php?id_product=4295

Anyone having connection problems with lmk 900 data links...most of the time I get no permission message at the end of the handshake.Position of aircraft on map always comes thru though.I am using a 9 ft extension cable to get lmk 900 unit up on a tripod away from the laptop.Got it to connect once today after numerous trys...my airborne unit is mounted aft on an aux battery tray pointed straight down...regards kp couch k6zk extra class

 

[thinwing]

Thanks for reply...in an attempt to boost voltage..I have a 5 volt "dumb" usb charger up on the tripod with the supplied USB pigtail plugged into that.That should eliminate voltage drop over 10 cable run as it is up by the transmitter.Your suggustion of data signal drop out over the extended run has merit..I will test that out by moving lmk 900 unit off the tripod and just use the supplied usp cable.Remember rg58 is really lossy at high frequencys...something in the Belkin 9000 series double shielded cable would be better.One issue is that our flying site is close to a cell phone tower and comments by another operator was that 900 mhz didnt work too well there..maybe I should have been closer...linear amps in the 3 to 5 watt range are expensive...and of course require amatuer license..more later after testing...a high gain yagi would be best but would require an antenna tracker though..kp couch

 

[FerdinandK]

Why don´t you extend the antenna wire? I have the 2,4Ghz module and my range is beyond the range of my copter.

best regards

Ferdinand

 

[gtranquilla]

Europe uses 900 Mhz cell phone frequencies extensively (called GMS or GSM) but North America has moved away from 900 Mhz for cell phone communication.
Regardless of the frequencies cell phone towers use, the high wattage transmitters will stamp all over lower wattage radios that are tooooo close by due to harmonics and spurious emissions etc.
Other users of 900 Mhz include the Armed Forces, Oil and Gas Industries, Pipeline industries, Turnpike toll booth and monitoring sites etc.

From my investigation the Belkin 9000 seems to be an audiophile audio cable or USB signal cable! We were talking about a coax cable to extend the antenna away from the radio transceiver.
For that you require a system matched radio coax which is 50 ohms impedance for this radio and antenna..... hence RG58 or RG59 radio system standards. Best to complete HAM radio course before one goes there!!

Thanks for reply...in an attempt to boost voltage..I have a 5 volt "dumb" usb charger up on the tripod with the supplied USB pigtail plugged into that.That should eliminate voltage drop over 10 cable run as it is up by the transmitter.Your suggustion of data signal drop out over the extended run has merit..I will test that out by moving lmk 900 unit off the tripod and just use the supplied usp cable.Remember rg58 is really lossy at high frequencys...something in the Belkin 9000 series double shielded cable would be better.One issue is that our flying site is close to a cell phone tower and comments by another operator was that 900 mhz didnt work too well there..maybe I should have been closer...linear amps in the 3 to 5 watt range are expensive...and of course require amatuer license..more later after testing...a high gain yagi would be best but would require an antenna tracker though..kp couch

 

[thinwing]

gtranquilla..try Beldin 300 series..50 ohm compatible/double shielded..half the loss of rg 58...I domt know where i got the belkin 9000 from..a faulty memory maybe...anyway Last year I strung 500 ft total while moderizing my shack....thanks for advice to complete ham radio course...I can always learn more ...due you know of any class higher than amateur extra???73 gtranquilla , look me up QRZ.com K6ZK

 

[gtranquilla]

thinwing - thanks... Excellent info on the Beldin coax..... I have Basic + but the next level up for Canada would be Advanced, if I recall correctly...... I am not going to get in to morse code and don't need to go there with present requirements...... having too much fun with MRs etc.