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I've intend to install a RUT955 on our sailing boat and place the 4G antennas in the mast. The total cable lenght is 20 meters. What is the maximum RF-cable lenght when using external 4G antenna? What type of RF-cable is recomended (i.e LMR-200/300/400?)? Can the cable lenght be increased if a low loss cable is used?

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Hello, 

Recommended cable length should not exceed 10m, as the longer the cable, the greater the losses, which eventually reduce the gains of placing the antenna outside. It is though advisable to keep the cable shorter. For 4G connectivity, LMR - 200 seems a reasonable choice as other cables (300/400) are aimed at reducing losses at higher frequencies.

Also, there are third party solutions, with IP67 enclosure to keep the device next to antennas, eliminating the need for lossy coaxial cables. An example is in this link. However, it also requires a passive PoE injector to supply power to the device.

Best regards,

Žygimantas

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Hello,

If the limit is 10 m cable lenght with a LMR-200. At 900 MHz this cable type has a loss of 3.6 dB.

If I'll use instead a LMR-400 and a cable lenght of 20 meters, this will give a cable loss of 2.9 dB. So the loss is lower compared to the recomendation and should therefore work fine.

best regards

Fredrik
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Hello,

10 meters is only general guideline, but 3dB is already a loss of half the power the router transmits. However, comparing the cables, 20 meters of LMR 400 does have lower attenuation than 10 meters of LMR 200 at 900MHz and 20m length of LMR 400 performs even better than LMR 200 at 1800/1900MHz frequencies. It is more expensive, but calculations show that is should work. If possible, I would suggest to try to reduce the distance between the router and the antenna as much as possible. Another way to improve the connection quality is to use a high gain antenna. Usually, directional antennas have better are better at providing higher gain but might not be suitable for moving objects such as a boat.

It would be really interesting if you could comment back with the results from your testing with the specific cable.

Best regards,

Žygimantas
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Yes, I agree with you. Also when connecting two or more devices it likes losing signals