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Iridium Sat Phone Antenna
My wife and I are travelling around the world in our yacht. We are
currently in Thailand carrying out some repairs on the boat. We have an Iridium Sat Phone that allows us to communicate by voice and email via the uuplus.com service. The fixed masthead antenna seems to have developed a fault and we can find no info in Thailand or on the net about its circuit or test parameters. The antenna is a motorola model that has a spiral antenna some 4 inches tall with a small number of surface mount resistors all encased in a conical plastic housing. The resistance measured by a multimeter if 55 Ohms on the connector. Is the antenna active or passive. Thanking you in advance. Tony Rowlands S/V Ambrosia |
Hi Tony,
I'm 99% sure the antenna is passive, not active. Check the solder joints where the four helical wire antennae join onto the board at the bottom. I've had one experience with faulty connections (came loose due to excessive vibration) here. If a visual inspection of the antenna otherwise looks OK, check the coaxial cable, in particular the connector at the antenna end. Has any water got in here? Iridium antennas don't have much gain, and any additional losses in the coax cable and connectors really reduce the receive signal. Regards Vaughan Henderson |
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Me
Thanks for the advice. Looks like I will get a new one. I guess it is a good time seeing that the US$ has gone down against the Aust$. Do you have any recommendations as to an antenna supplier. Cruising is great but there is no time for play. Tony S/V Ambrosia |
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Vaughan Henderson wrote: (Tony Rowlands) wrote in message . com... Me Thanks for the advice. Looks like I will get a new one. I guess it is a good time seeing that the US$ has gone down against the Aust$. Do you have any recommendations as to an antenna supplier. Cruising is great but there is no time for play. Tony S/V Ambrosia Before you spend real money Tony, I'd suspect the fifth component. The smd devices marked 221 should be resistors, each with a value of 220 ohms. Four of those, effiectively connected in parallel, would give you the 55 ohms you are measuring on the multimeter. The fifth component (unmarked) is most likely a capacitor and would be more liable to be permanently damaged by the water. Difficult to test with a simple multimeter unless it also has a capacitance range(s). If you measure across it, it should read some very high value of resistance (greater than 10 M-ohm). I don't have any idea what it's value would be, but could be around 100pF (picofarads). If you are up to replacing smd components and can get one, (should cost less than 50cents) you could try replacing that. "Me" may well be right that the lacquer coating you applied has totally detuned the antenna, so all the above may be a waste of time. Regards Vaughan Henderson |
Vaughan Henderson wrote: (Tony Rowlands) wrote in message . com... Me Thanks for the advice. Looks like I will get a new one. I guess it is a good time seeing that the US$ has gone down against the Aust$. Do you have any recommendations as to an antenna supplier. Cruising is great but there is no time for play. Tony S/V Ambrosia Before you spend real money Tony, I'd suspect the fifth component. The smd devices marked 221 should be resistors, each with a value of 220 ohms. Four of those, effiectively connected in parallel, would give you the 55 ohms you are measuring on the multimeter. The fifth component (unmarked) is most likely a capacitor and would be more liable to be permanently damaged by the water. Difficult to test with a simple multimeter unless it also has a capacitance range(s). If you measure across it, it should read some very high value of resistance (greater than 10 M-ohm). I don't have any idea what it's value would be, but could be around 100pF (picofarads). If you are up to replacing smd components and can get one, (should cost less than 50cents) you could try replacing that. "Me" may well be right that the lacquer coating you applied has totally detuned the antenna, so all the above may be a waste of time. Regards Vaughan Henderson Vaughan Thanks for the advice. Antenna is now working after finding local technician who could test it. Apparently replaced the capacitor. Works great. Problem now is the length of the cable from antenna (on top of mizzen mast 12m up) to the phone. Overall run about 18m. Signal using RG58 is almost on existant. Using 6m Microwave cable and 4m RG58 get good signal. Love to have the antenna at the top of the mizzen. Would a total of 18m (with connection) made up of 6m Microwave cable and the remaining 10m of RG 213/U give me adequate signal. What is the option of a masthead amplifier.? I know there are heaps of questions but I am technical enough to be dangerous!!! Regards Tony S/V Ambrosia |
Don't forget that you are communicating with a satellite. Unless it is
near the horizon, getting the antenna higher isn't going to help much once it is up out of the spray. As you have found out, feed line losses can be huge at these frequencies. If the way your vessel layout allows it, you may get better performance with the antenna on a relatively short stern pole, or some similar arrangement that keeps it clear of the sails and close to the transmitter. A few generalities: Coaxial connectors can introduce as much loss as several feet of cable and there should be as few as possible. Reflections and standing waves can also result from the slight impedance mismatch in the connector. All else being equal, big fat heavy cable has lower losses than thin light cable, which is just the opposite of what you want way up high. The antenna is easier to fiddle with if it is easier to get at. I suppose that last one could be a plus or a minus. :-) Just my 2 cents, Steve wrote in message ups.com... Vaughan Henderson wrote: (Tony Rowlands) wrote in message . com... Me Thanks for the advice. Looks like I will get a new one. I guess it is a good time seeing that the US$ has gone down against the Aust$. Do you have any recommendations as to an antenna supplier. Cruising is great but there is no time for play. Tony S/V Ambrosia Before you spend real money Tony, I'd suspect the fifth component. The smd devices marked 221 should be resistors, each with a value of 220 ohms. Four of those, effiectively connected in parallel, would give you the 55 ohms you are measuring on the multimeter. The fifth component (unmarked) is most likely a capacitor and would be more liable to be permanently damaged by the water. Difficult to test with a simple multimeter unless it also has a capacitance range(s). If you measure across it, it should read some very high value of resistance (greater than 10 M-ohm). I don't have any idea what it's value would be, but could be around 100pF (picofarads). If you are up to replacing smd components and can get one, (should cost less than 50cents) you could try replacing that. "Me" may well be right that the lacquer coating you applied has totally detuned the antenna, so all the above may be a waste of time. Regards Vaughan Henderson Vaughan Thanks for the advice. Antenna is now working after finding local technician who could test it. Apparently replaced the capacitor. Works great. Problem now is the length of the cable from antenna (on top of mizzen mast 12m up) to the phone. Overall run about 18m. Signal using RG58 is almost on existant. Using 6m Microwave cable and 4m RG58 get good signal. Love to have the antenna at the top of the mizzen. Would a total of 18m (with connection) made up of 6m Microwave cable and the remaining 10m of RG 213/U give me adequate signal. What is the option of a masthead amplifier.? I know there are heaps of questions but I am technical enough to be dangerous!!! Regards Tony S/V Ambrosia |
Why do you want to put it on top of the mast? It won't be enough closer to
the satellites to make a difference. wrote in message ups.com... Vaughan Henderson wrote: (Tony Rowlands) wrote in message . com... Me Thanks for the advice. Looks like I will get a new one. I guess it is a good time seeing that the US$ has gone down against the Aust$. Do you have any recommendations as to an antenna supplier. Cruising is great but there is no time for play. Tony S/V Ambrosia Before you spend real money Tony, I'd suspect the fifth component. The smd devices marked 221 should be resistors, each with a value of 220 ohms. Four of those, effiectively connected in parallel, would give you the 55 ohms you are measuring on the multimeter. The fifth component (unmarked) is most likely a capacitor and would be more liable to be permanently damaged by the water. Difficult to test with a simple multimeter unless it also has a capacitance range(s). If you measure across it, it should read some very high value of resistance (greater than 10 M-ohm). I don't have any idea what it's value would be, but could be around 100pF (picofarads). If you are up to replacing smd components and can get one, (should cost less than 50cents) you could try replacing that. "Me" may well be right that the lacquer coating you applied has totally detuned the antenna, so all the above may be a waste of time. Regards Vaughan Henderson Vaughan Thanks for the advice. Antenna is now working after finding local technician who could test it. Apparently replaced the capacitor. Works great. Problem now is the length of the cable from antenna (on top of mizzen mast 12m up) to the phone. Overall run about 18m. Signal using RG58 is almost on existant. Using 6m Microwave cable and 4m RG58 get good signal. Love to have the antenna at the top of the mizzen. Would a total of 18m (with connection) made up of 6m Microwave cable and the remaining 10m of RG 213/U give me adequate signal. What is the option of a masthead amplifier.? I know there are heaps of questions but I am technical enough to be dangerous!!! Regards Tony S/V Ambrosia |
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