UAV Control TX Blinding VIdeo RX

[dknguyen]

Suppose I have a handheld UAV radio groundstation and on it is a 500mW-1W 900MHz two-way data link running off an omnidirectional for flight data and control purposes. On the same groundstation there is also I also have a 5.8GHz video receiver.

Now...I'm pretty sure the 900MHz antenna could blind the 5.8GHz antenna during a data transmission to the UAV with them being placed so closely together. Would I be correct in thinking that using a directional antenna rather than an omni-directional antenna for the 5.8GHz video link would go a long way in ensuring a minimal amount of 900MHz RF energy being transmitted by the datalink would feedback into the video link (as long as the 5.8Ghz directional antenna did not have the 900MHz omni-directional antenna in it's FOV).

And I suppose a tricky potential problem is also on the UAV itself which needs to transmit 5.8Ghz video and transmit 900Mhz data while also receiving 900MHz data from the groundstation. I'm concerned about the 5.8Ghz video transmitter interferring with the 900MHz data reception. Directional antennas are a no-no since I have no room (or patience!) for onboard antenna trackers. But the situtation is not as severe as the ground station I suppose because the video link transmission is 250mW.

 

[mneary]

Are you worried about the shadow cast by one antenna, or the RF overloading the input?

 

[dknguyen]

Are you worried about the shadow cast by one antenna, or the RF overloading the input?

Overloading the input of the 5.8GHz antenna used for the video RX link with the emissions of the 500mW 900MHz TX data antenna.

WIth the opposite onboard the UAV- overloading the 900MHz data RX antenna with the emissions of the 250mW 900MHz TX video antenna.

 

[mneary]

HAM repeaters (not to mention cell phones) handle this all the time. It's standard practice for TX and RX to share an antenna in full duplex.

 

[JimB]

The ability to operate transmitters and receivers at the same site depends on several factors.

The frequency separation
The filtering on the input circuits of the receiver
The linearity of the RF amplifier and mixer in the receiver
The screening of the receiver and transmitter circuits
The phase noise spectrum of the transmitter.

How these factors apply in your situation:

Frequency separation, 900Mhz and 5.8Ghz are widely separated and not harmonically related. This is good.
Filtering, Linearity, Screening, and Phase Noise are completely unknown at the moment.
My only suggestion would be to set it up and see what happens, my best guess is that it will work fine if you just separate the 900Mhz and 5.8Ghz antennas as much as possible in your situation.

You also infer full duplex operation on 900Mhz, this will certainly be problematic.
To do this you will need a wide as possible frequency separation between transmit and receive.
As mentioned by mneary, it is quite common practice in amateur radio repeater operations to operate transmit and receive simultaneously on a single antenna at both VHF and UHF frequencies.
However the frequency separation is of the order of 0.4% and the filtering requirements for the diplexer and transmitters and receivers is severe.
Do you really need simultaneous transmit and receive at 900Mhz, or is rapid changeover half duplex good enough?

JimB

 

[dknguyen]

The 900MHz is half duplex. It does both transmit and receive, but the Maxstream/Digi module takes care of the switching between the two on it's own. They built it, I'm going to assume they've taken care of those issues.

 

[JimB]

OK if the 900Mhz is half duplex, there should be no problem.
I suggest that you just keep the 900Mhz and 5.8Ghz antennas separated as far as possible, and ensure that the "low frequency" wiring within the equipment is well screened just to help things along.

JimB

 

[Nigel Goodwin]

The frequency difference is so great that there should be no problems with any decently designed equipment.

As mentioned, radio amateur relays do this using the same aerial with only a 600Khz split at 145MHz - but it uses VERY specialised equipment to do it.

We used to have commercial radios in the vans, with a 10MHz split (76.0625MHz and 86.0625MHz), at the base station separate aerials were used, with vertical seperation between them - even so, using 'talk through mode' (van to van) reduced range noticeably.