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Old 23-01-2012, 07:23   #1
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Satellite Phone Antenna Cable Spec ?

I need to extend the cable from my satellite phone to the antenna and I can't read the spec on the existing cable. What coax cable do I need for a 30' run?
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Old 23-01-2012, 07:32   #2
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Re: Satellite Phone antenna cable spec?

It will depend the make / model. Many satellite systems use 75 ohm coax but some use 50 ohm.
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Old 24-01-2012, 07:36   #3
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Re: Satellite Phone antenna cable spec?

I am ignorant about this. Would that be a RG-58U, 59U, 8X, 213 cable or something else?
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Old 24-01-2012, 08:20   #4
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Re: Satellite Phone antenna cable spec?

Lets get back to basics, coax cable has two main characteristics. In simple terms, one is the impedance of the cable and the other is the loss of the cable at the frequency in question.

The impedance of the cable should match the impedance of the equipment. Most radios require a 50 ohm cable. Most TV systems require 75 ohm cable. Satellite systems are a bit of a mixture, some require 50 and some require 75.

The loss is easier, the longer the cable, the greater the loss for a given cable. Note that the loss is also frequency dependent.

So in your setup where you want 30' ft of cable, I suggest a reasonably low loss cable (but not an extreme low loss). However I can't tell if you need 50 or 75 ohm cable without knowing either the make/model of the system or the type of existing cable.

Sometimes (but not always) the connectors can give one a hint as to the cable spec.

So what is the make/model of your satphone and do you know what connectors are being used?

For the record, RG 58 is 50 ohm coax while RG 59 is 75 ohm coax. Both are relatively high loss.
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Old 24-01-2012, 10:20   #5
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Re: Satellite Phone antenna cable spec?

For my Iridium satphone I have a stern-rail-mounted antenna, and perhaps 30 feet of LMR-240 coax, running to the navstation. This is a low-loss 50-Ohm cable. Here's a comparison to the commonly-used RG8X coax:

Attenuation -- 100 Meters, 1.5 GHz
LMR-240: 32.4 dB
RG8X: 29.2 dB

The length of cable I have is giving me about 3.2 dB of loss, plus any connector loss. It looks like the RG8X might be marginally better, but my LMR-240 came with the antenna. Both of these cables have a good braid/foil shield.

You do need to match your cable to the radio and antenna, and to the connectors you want to use. Cable loss becomes an issue with long runs.
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Old 25-01-2012, 06:44   #6
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Re: Satellite Phone Antenna Cable Spec ?

thanks everyone,
George
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