Clear Hub Express on Tugboat

[generalagony]

I work on a tugboat that moves from dock to dock in the Houston ship channel and have recently purchased a Clear Hub Express. I do get service in most areas of the ship channel but am interested in putting an antenna on top of the wheelhouse that I hope will improve overall reception and get a stronger signal at the docks where right now I have to move the modem around to pick up a signal. I have pretty much decided on the 2.3-2.7GHz High Gain Omni-Directional WiMax Antenna, since the boat is always in different orientations a directional antenna clearly is out of the question. Should this antenna accomplish what I am needing and would it be ok to use a Low Loss 200 cable since I will only be using a 10 ft run or do I really need the 400 cable I keep reading about? Any help is appreciated. Thank you.

[thuor]

Good question. LMR-400 has an attenuation of 6.9dB/100ft at 2.6GHz so a 20ft run causes a signal loss of about 1.4dB. LMR-200 cable on the other hand has an attenuation of 17.2dB/100ft so a 20ft run causes a loss of 3.4dB. Recall dB is a logarithmic scale so this is a significant difference. Also note that a 3dB loss is actually a loss of 50% of the power.

That said it really depends on how strong your signal is to begin with and how much "room" you have to spare (or more accurately "what your link budget is"). Because this 2.5-2.7 GHz omni antenna has 12dBi of gain, even after 4dB of combined insertion losses and cable losses you still have a residual 8dBi gain which is much better than the typical 3dBi of the integrated printed antennas so an LMR200 cable may not be such a disaster. It is also much easier to work with.

[generalagony]

thank you for the reply. I may go ahead and just spend the extra money for the 400 but could you explain what you mean by it being easier to work with than 200?

[generalagony]

thank you for the reply. Could you explain what you mean by 400 being harder to work with than 200?? I have no experience with either

[thuor]

The 400-series cable is thicker so stiffer and harder to maneuver around (remember you should not make abrupt 90degree angles with coaxial cable). Outer diameter is ~0.405 in vs ~0.195 in for 200-series.

[generalagony]

finally got my antenna hooked up. Everything went great for setup but my RSSI and CINR have not changed and do not change when I switch back to the internal antenna. I have read a couple small threads that mention that the modem antenna selection switch doesn't work properly but there are no details on possible fixes. Are you aware of any steps I can take to troubleshoot this issue or to make sure the antenna is working? I of course release you or your site from any and all liability on suggestions given.

[generalagony]

another question. I had to take the plug end off the cable to fit the cable through a drilled hole on my boat. I put the plug back on and it was snug. Did I ruin the connection by doing this and what is the proper way to put the plug end back on the cable properly? Thank you

[thuor]

another question. I had to take the plug end off the cable to fit the cable through a drilled hole on my boat. I put the plug back on and it was snug. Did I ruin the connection by doing this and what is the proper way to put the plug end back on the cable properly?

You often would know once you start to use the modem. Especially if your performance degrades then it could be that the connector is now more lossy than before. Because of the high frequencies involved, the connector quality is very critical so as to minimize insertion loss or impedance mismatch losses. You typically have to use a special crimping tool such as: http://www.rfwel.com/shop/LMR400-Coa...rimp-Tool.html

[generalagony]

so soldering is not needed, correct? I have not noticed any improvement on my signal over using the internal antenna. I have the new antenna mounted on handrails on top of the boat with a full 360 degree view of the open sky whereas the modem itself is inside the wheelhouse, which is made of steel. Any suggestion?

[thuor]

No you normally do need to solder. Here is a nice video on how to crimp LMR400 cable using EZ connectors such as: http://www.rfwel.com/shop/EZ-Style-N...r-LMR-400.html that don't require soldering.

http://www.youtube.com/watch?v=aX5igLdgcdw

The best way to compare your results is to test how well the modem performs when you use it on the top of the boat without the antenna. If it works well then you would expect the same or better performance when the modem is now placed inside and hooked up to an external antenna.

If the performance of the modem at the top of the boat without the antenna is the same as when the modem is inside and antenna is attached it would suggest that your outside signal is too weak to be captured anyway. Remember the external antenna, being a passive device, is really just to overcome the RF shielding effect of enclosures and not really to amplify a weak signal (as you would get from an active amplifier/repeater).

Of course it could also mean that the crimping destroyed your performance in which case attaching the antenna could actually be worse than having the modem outside without the external antenna attached.