RG 223U for Iridium Go?

[Neziak]

I’ve just received my Iridium Go with marine kit. The antenna cable that comes with the kit is quite thick and inflexible. I have a spare length of RG 223U. Is this cable compatible with the Go? If so I will buy some crimp on connects for it.

[billknny]

The cable that ships with the IridiumGo external antenna is a very low loss cable, hence its annoying physical characteristics.

Using other cable will decrease single strengths to the receiver. Will that be a problem? It depends. Can you tolerate the occasional drop connection? How good a view of the sky for the antenna? Will your cable run be shorter? Sources of interference?

I am afraid there is no simple answer... Do not toss out the Iridium cable until you are fully happy with an alternative install.

[AllenRbrts]

The standard cable is lhr 240 for short runs and lhr 400 for long runs. Nether cable is very flexible because it has double shielding. A quick check indicates lhr 240 vs rg 233 has about 3x less loss per meter at 1.5 GHz so if you run is short probably okay, otherwise you will need a cable with less attenuation at iridium frequencies.

[Discovery 15797]

Originally Posted by Neziak

I’ve just received my Iridium Go with marine kit. The antenna cable that comes with the kit is quite thick and inflexible. I have a spare length of RG 223U. Is this cable compatible with the Go? If so I will buy some crimp on connects for it.

The cable is LMR 400. It has a solid core conductor which makes it very stiff and restricts its bend radius.

A much better cable is LMR 400 UF (ultra-flex). The specs between LMR 400 and LMR 400 UF are virtually identical, but the ultra-flex is easier to work with, and has a tighter bend radius.

At ham frequencies the difference between LMR 240 UF and LMR 400 UF is minimal in short runs.

However, Iridium frequency is between 1616 and 1626.5 MHz. At that frequency LMR 240 UF has almost twice the attenuation (db/100ft) as compared to the LMR 400 UF. The Iridium transmission output power is 2 watts. I personally would not install a cable that will impede the output.

BTW...the RG223 cable appears to have an even higher attenuation at Iridium frequencies as compared to the LMR240UF, so I would not suggest using it.

[Andrew MacKenzie]

Three times less loss is NOT POSSIBLE. Maximum loss of anything is 100% i.e ONE TIME. Does the writer mean 1/3 less or 2/3 less? Andrew

[AllenRbrts]

Hummm... If lmr 240 is .3db per meter at 1.5 GHz and rg233 is .9db / meter seems to me the loss (attenuation) is 3x more in the rg233 cable. I wasn't referring to percent loss, but if I had it seems that 1% loss of signal is 3x less than 3% loss in the same length.

The OP could use a short piece of his rg233 (less than 5meters) and it would have the same loss as a 15 meter (max recommended lmr 240) run.

Originally Posted by Andrew MacKenzie

Three times less loss is NOT POSSIBLE. Maximum loss of anything is 100% i.e ONE TIME. Does the writer mean 1/3 less or 2/3 less? Andrew

[Brian.D]

Most systems work off of Signal to Noise ratios. If the hub detects the transmitter is not transmitting enough power to satisfy minimum SNR then it will ask the device to increase power. Between .3dB/m and .9dB/m there should be sufficient power available to increase SNR.

Since RF cable is not THAT expensive one can make a test using different cables to see which one works the best. Not sure if there is a way to determine your signal strength at the far end, except maybe your unit seems to be transmitting more than it should. Use the LMR240 (if that is what the unit came with) as a base metric for comparison.

When you ask for compatibility, you are probably referring to impedance and not attenuation. So to answer your original question of compatibility, that should be yes. Are there any markings on the original cable? Or maybe a manufacture like Times Microwave, or Belden, or Amphenol or some other manufacture.

[Mike Banks]

If the two cables have the same transmission characteristic impedance, and they will connect with a properly designed connector of similar impedance, then there should only be the extra attenuation loss (which may be significant) in using the more flexible inferior cable.

[Discovery 15797]

Originally Posted by Brian.D

Most systems work off of Signal to Noise ratios. If the hub detects the transmitter is not transmitting enough power to satisfy minimum SNR then it will ask the device to increase power. Between .3dB/m and .9dB/m there should be sufficient power available to increase SNR.

Since RF cable is not THAT expensive one can make a test using different cables to see which one works the best. Not sure if there is a way to determine your signal strength at the far end, except maybe your unit seems to be transmitting more than it should. Use the LMR240 (if that is what the unit came with) as a base metric for comparison.

When you ask for compatibility, you are probably referring to impedance and not attenuation. So to answer your original question of compatibility, that should be yes. Are there any markings on the original cable? Or maybe a manufacture like Times Microwave, or Belden, or Amphenol or some other manufacture.

I value Brian's insights, and maybe I am missing his point, but SNR ratios are important for signal reception and the receivers' ability to isolate the signal from the noise. Coax has very little impact on SNR (unless the shield is compromised). (Also, the Shannon-Hartley theorem doesn't apply in this case.)

IMHO, at about $1 per foot for LMR cable, and without expensive signal generators and signal analyzers the "see which one works best approach" is not a feasible or realistic approach.

The 50 ohm impedance of the coax cables discussed in this thread all match the Iridium Go transceiver rf in/out impedance. (Impedance is a fancy way of saying resistance.) There are other factors affecting impedance such as bends in the cable and poorly installed connectors, but essentially you can use any 50 ohm cable. HOWEVER...there is a big and very important difference in coax cables. Please note that cable manufacturers use attenuation to compare and evaluate how effective a specific length of cable will be in receiving and transmitting a signal at a given frequency.

[Brian.D]

That is correct about SNR. The actual term used on satellites is C/No but most people do not know that term. So SNR is about the same. The difference is Signal vs. Carrier.

Anyway, the signal over the noise is reported on both ends. If the hub cannot hear the remote very well, it will issue a command to increase output power. If the power has not reached saturation, then the remote will boost its output. Of course there is only so much power available.

With that in mind, if the OP uses a cable that is 1dB/m worst that the cable offered by the vendor then the output power of the remote may, operative word there, may have to increase by 1dB to compensate. That is if the cable length is 1 meter.

Unfortunately the OP did not give that information on total length needed so we are left to best guessing.

[Neziak]

The supplied cable is 12m LMR400. The RG223U can be cut down to 7m. I feel comfortable crimping the connectors on the 223. Less so on the 400 so unlikely to cut it down from 12m.

[AllenRbrts]

I think you will lose about 6db (75%) using 223. I would recommend buying the correct length of lmr 240 to minimize loss or find a way to shorten the run. The antenna just needs a clear view of the sky.

Originally Posted by Neziak

The supplied cable is 12m LMR400. The RG223U can be cut down to 7m. I feel comfortable crimping the connectors on the 223. Less so on the 400 so unlikely to cut it down from 12m.

[Neziak]

Thanks for all the comments. Given that the antenna housing is made of fibreglass I assume that the radio waves find fibreglass invisible. I could shorten the run by installing the antenna below deck under the thinnest bit of fibreglass. How much degradation would there be for solid glass about 5mm thick. It would have a clear view of the sky above. Is this recommended?

[Brian.D]

You can use it below decks as long as the deck and any material (such as headliner) is free of any moisture. But you will see degraded service as your signal must go through multiple layers. And... it must be a really clear day with very minimal cloud cover. If it is raining or heavy cloud cover, you should put the antenna outside.

If you look at commercial airplanes you will notice small aerodynamic domes on the upper fuselage. Those are either Ku- or Ka-Band Fresnel beam antennas. They are in thick fiberglass housings that have to withstand the stress of 600MPH airflow. So thin fiberglass that is moisture free should be OK at IG frequencies.

With that said, it is recommended that your antenna be located free and clear of any "shadowing" items like the mast or wet sails. Moisture absorbs RF radiation in the frequency band used by Iridium Go. Since IG uses L-Band, it is not as susceptible to rain fade as Ku- and Ka-Bands.

Again, since you already have cable, try running a test below decks and see what the results are. Try both on a nice clear day and one that is producing a torrential downpour. Maybe even with snow on the coach roof.

[Discovery 15797]

In addition to what Brian suggested, I read about folks who did not get the external 'marine antenna' with their Iridium. Some indicated the built in antenna worked fine below decks, some indicated it didn't work at all, and everything between.

I tested mine without the external antenna below decks and had sporadic results. In the middle of the ocean I don't want sporadic results. And coverage is not uniform around the planet, so depending on your intended cruising area I suspect you want to optimize the system as much as possible. As Brian says...this system really likes a big open sky.

(The really odd thing about the unit is that the internal or built on antenna must be in the extended position for the thing to turn on, even with the external antenna connected....weird design. )