Can I extend these antenna cables?

[Alex_Baker]

Hello, I am looking for some input from somebody with some RF knowledge.


I am planning on using this FrSky receiver for a large RC boat. From experience I know that water is good a attenuating the signal from the transmitter so I would like to put the antennas as high as possible above the water. The ideal solution is if I could put the antennas up high, and the receiver unit in the hull where wiring would be much easier.

So, will it negatively impact the receiver's performance if I extend the coax connecting the board to the PCB antennas? I would like to extend them possibly up to 18 inches with an inline connector somewhere.

There is also a large brass framework on top of the boat, will this have any effects on the receiver?

Thanks!

[u666sa]

2.4 GHz?

I'm not sure about which connectors are most adequate in your application based on size, so you judge yourself. But they will most likely be either u.FL or IPEX. So idea is get cable like this of proper length for your application https://aliexpress.ru/item/1005001583427049.html
Then on your board you solder u.FL or IPEX connector, instead of soldering wires directly to the board.

It could look something like this.



Signal loss on 2.4 GHz is around 8 dB per 1 meter. 18 inches is 0,4572 meters, so 8 * 0,4572 = ~3.7 dB signal loss. But in your application that could be acceptable, since the other way around, signal loss could be greater.

Cheers.

[Alex_Baker]

Thanks u666sa!

The FrSky receiver actually has u.FL connectors on it already, just hidden inside the case.

I may just end up doing a comparison test after I order some cables. I plan on using SMA connectors in the middle. Basically the tradeoff I am faced with is extending the PWM wires from the receiver by 18 inches or extending the antennas 18 inches.

[u666sa]

I may just end up doing a comparison test after I order some cables.

SMA might be heavy for your application. There are a smaller connectors, MCX, QMA.

You need two tools.

1. TinySA Ultra for measuring output power and sensitivity.
2. LiteVNA 64 for fine tuning your antenna.
(both can be bought real or fake, so be careful)

Finally, be careful with chinese antennas, they are usually crap, but not always.

[Alex_Baker]

Thanks for the input u666sa.

By comparison I meant really crude comparison, like standing a set distance from the antennas and watching the signal strength telemetry on the transmitter, not scientific at all I know. Although using some "real" RF tools would be fun.

The weight of the SMA connectors wont be a problem, one end will be mounted down permanently. For context the boat I am putting this in is 4 feet long.

I am reusing the PCB antennas that come with the receiver, so my hope is that the only losses that I introduce myself is the extra cable.