I currently have RG-8X coax in my mast and boat conduit.
At the base of the mast is a connector, allowing the mast to be removed.
Should I expect better performance if I replace the 50 feet of RG-8X coax in my mast with RG-8U, while leaving the boat conduit as 17 feet of RG-8X? Any side effects to mixing cable ?
http://en.wikipedia.org/wiki/Coaxial_cable
Wikipedia says they have similar electrical characteristics, but an installer told me thicker is better for longer runs. I suspect you will have more to worry about getting the connectors on. This is just about the only place on a boat where solder is a must.
Dan,
In short yes -- replacing a section of the cable with lower loss cable will still lower your loss in dB, as this loss accumulates per meter (yard, foot) of cable. All you need to is make sure the impedance of all parts in the 'chain' is 50 Ohms -- cables and connectors.
As to whether RG-8U is the best option I have my doubts. Why not go for RG-213, LMR400 or Ecoflex 10?
This last cable is the best marine coax: low loss (uses a PE-LLC dielectric with a gas content of more than 70%) but flexible (multi-stranded core). Ecoflex is a "hit" over here in Europe, but not very well known in the USA.
Thank you everyone !
Kees ... I understand LMR400 is no good for sailboats, something about the insulation soaking up water.
The diamater and weight of those other products is quite big, e.g. 10mm width and weights more, is the difference in performance worth it on a sailboat ?
Isn't RG-8U also 10 mm?
As to "difference in performance" that depends what you're going to do. If this is purely for VHF probably not, with this size. As the frequency you're using it goes up, it quickly gets interesting. For instance, if you use the mast antenna for your GSM then you're using it at 850-900 or even 1800-1900 MHz.
Look at this table: http://www.on4sh.be/ham/coax/ (note: there are many more, this is just an example I googled quickly.)
For your case (20m ie. 1/5th of 100m), loss with RG-58 at VHF freq. is 19 dB/100m so 19/5 = 3,75 dB i.e. not very much, half your power remains. But at 1296 MHz it's 65 / 5 = 13 dB, e.g. 1/16th of your power remains.
But with Ecoflex 10 your loss at these frequencies is 4,8 / 5 = 1 dB and 16,5 / 5 = 3,3 dB respectively.
Given the above I wouldn't bother for VHF but definitely go for the better cable if you're using a longer length or are using a higher frequency.
The best 50 Ohm coax for boats at the moment seems to be CELF400. Minimum water leakage and electrical loss. Maximum bending, small radius. You can verify the specifications of the different coax cable types including Ecoflex, Aircom and others at www.antennekabel.nl/celf400.htm (in The Netherlands). No I am not the supplier, but he told me that this is the cable they sell the most at this time. On the other hand, VHF is a pretty low frequency, below 2000MHZ. The differences in electric loss compared for frequencies above 2000 MHZ are much less. The graphs "Losses in DB for 100meter (cable length)" tell for themselves
Thank you for the advice to look at other options than the RG-8U. Although it was a tough install, I am very satisfied with the LMR400.
Hi all,
The LMR400 and CELF400 do have the disadvantage of their large diameter (over 10mm) . An option with almost the same performance and only 7.3mm diameter is the AIRCELL7 which also is much more flexible.
I myself exchanged 11 meters of the total of 14 meters RG58 with AIRCELL7 and gort an improvement of about 2.2>1.4 db SW.