openrcforums

I am asking some inputs to build a wireless relay for 2.4 GHz radio transmission.
The idea is to control the model inside building/car/obstructed area but pipe the radio signal to a relay outside the obstructed area within a short distance to fly the model.
The idea is to use a XJT(or any module that has matching cppm rx) in the radio Tx and a cppm capable rx. ON the cppm capable rx, the cppm will be wired to another DJT/XJT module ppm input pin then control the flying model. The cppm rx and DJT/XJT will be powered by a 3S lipo and BEC. The whole thing can be on top a pole or high in the sky with a balloon. I figure this will get maximum range. Some times, even flying in my club flying field, we have roof covered area for model preparation/repair that does not have sun or rain with seats and tables, it would be more enjoyable to fly sitting under the roof.
Do you think this can work?
This can also be applied to fpv 5.8GHz tx/rx, if the idea works.

If so, the module in the relay setup can be a DJT/DHT to have 16 ch or has to be another XJT to get 16ch?

Hi kaos,
Sounds like something that could be none, but am not sure how to do it.
To do it wireless, maybe the 9Xtreme with blue-tooth, but there maybe a problem with there being too much delay.

What about having your XJT outside on a pole and you run cables (4 wires from 9x Pins 1, 3, 4, and telemetry 5) from 9x radio inside the house to your XJT outside.
That could work!

I have another idea that is different and may sound a little wild.
There are diversity receivers that are use with 5.8 GHz FPV video signal, which you can have two different antennas and the antenna that receives the stronger RSSI signal is then used.

1) I was thinking to help with the XJT 2.4 GHz signal to be more reliable with its signal connection to its model receiver X8R, have between the XJT and two different transmitting antennas, a diversity circuit that would be
reading the returning RSSI telemetry data and would then switch to the antenna with the strongest RSSI signal.

2) This idea maybe crazier.
Using two XJT modules each with a different kind of transmitting antenna to a single X8R receiver.
The XJT module with the strongest RSSI signal would then be transmitting the 2,4 GHz signal.
Or have the both XJT transmitters working together (same signal hopping) each with a different kind of antenna.

Having the transmitting antennas higher from the ground, will help to maintain model connection between 9x radio and model receiver.

Bob B.

It's illegal most places not to have direct visual contact with the model.

Daedalus66 wrote:It's illegal most places not to have direct visual contact with the model.

Maybe, But it could be discriminating against a Poor Minority of Bedridden Blind Persons
with there Seeing-Eye-Dogs outside. They have a right to fly too!

Bob B.

Hi Daedalus66,
What do you think about these two ideas ?

bob195558 wrote: 1) I was thinking to help with the XJT 2.4 GHz signal to be more reliable with its signal connection to its model receiver X8R, have between the XJT and two different transmitting antennas, a diversity circuit that would be
reading the returning RSSI telemetry data and would then switch to the antenna with the strongest RSSI signal.

2) This idea maybe crazier.
Using two XJT modules each with a different kind of transmitting antenna to a single X8R receiver.
The XJT module with the strongest RSSI signal would then be transmitting the 2,4 GHz signal.
Or have the both XJT transmitters working together (same signal hopping) each with a different kind of antenna.

Bob B.

I think a better idea is the way Spektrum do it with their dual transmitting antenna setup alternating orientations. You don't need feedback via RSSI, just an assurance that however the transmitter is aligned and located there will be a strong signal. After that it's up to receiver antenna diversity to get a decent signal.

bob195558 wrote: What about having your XJT outside on a pole and you run cables (4 wires from 9x Pins 1, 3, 4, and telemetry 5) from 9x radio inside the house to your XJT outside.
That could work!

I have another idea that is different and may sound a little wild.

Your ideas are irrelevant in this case, the goal is to transmit from within a location where transmission can't be expected to go far enough out to a model due to obstruction. Diversity won't magically help.

The setup he describes is quite common, although usually used with LRS transmitters instead of a 2nd standard 2.4 link. Nothing unusual, wired or wireless. Wireless can add quite a bit of lag, a few LRS systems can take SBUS in so you gain quite a bit by using that between the receiver and the TX. Wired use PPM between radio and module, PXX is too high frequency to properly survive long cable runs.

kilrah:
so wired ppm should work if the the distance is within reason (say < 20 some ft).
while wireless may have significant lag? but using a SBUS can decrease the lag?
did not know sBus has higher transmission rate.

I've successfully used PPM with an LRS over about 20m cable if I remember well.

SBUS can reduce the lag, but the 2nd transmitter module must obviously support it as an input and that isn't common.

if as I described using the cppm as input on the 2nd Tx on one ch, and receive at the 2nd rx in one ch by cppm then use a cppm converter to multichannel ppm, could that work? or the 2n tx has to be able to receive cppm AND trsansmit cppm?
I know there is something funny about this wireless relay thing.

Bob1955558:
yes, I know 5.8 Ghz video can be done easily since it is only one ch. the question here is ppm multichannel.
thx for the thoughts though.

Daedalus66:
Thx for the 'legal' advice. I think I am asking a technical question for the sake of electronic knowledge. I will consult a real lawyer for legal issue when there is a need. Believe me, I have many lawyer's phone numbers in my cell phone I can call 24/7. Especially if I am detained in midway house.

kaos wrote:if as I described using the cppm as input on the 2nd Tx on one ch, and receive at the 2nd rx in one ch by cppm then use a cppm converter to multichannel ppm, could that work? or the 2n tx has to be able to receive cppm AND trsansmit cppm?

Huh?

Kilrah, everybody knows that most TXs and receivers can receive multi CPPM signals on different channels. I can't believe you don't know such a thing
Sorry I forgot that I am the dumb person that doesn't know anything about anything..

Here is a new product, Quanum Diversity FPV Receiver: (https://www.youtube.com/watch?v=PCl4YeT-Lsk). Quanum Overlord 5.8GHz 40CH 6 Antenna Diversity Receiver w/Raceband: (https://hobbyking.com/en_us/quanum-over ... eband.html).

Bob B.

The easiest way to do this in my opinion would be to use the trainer port of the TX and therefore wired PPM to a a TX module. As someone mentioned, most LRS add-ons like DragonLink or EzUHF do exactly this, but the "wired PPM" cable length is typically inches rather than feet. I've seen someone use a 15 foot trainer cable to an EzUHF module that was mounted on a ground station. But I bet you could go 50 feet with it (you should test of course). If you run into range issues on wired PPM link. You could probably eek out a bit more range with a thicker gauge cable.

Going with an RX->TX solution back to back would work too, but it feels like you're introducing more complexity, things that can break, and latency.