coaxial cable, how to tell the difference between 50 and 75 ohm?

Ian_Edwards

Ian_Edwards

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I need a 10m lenght of 50ohm coaxial cable to do some testing. I have a box of old coaxial cable in the garage, it's probably a mixture of 50 and 75 ohm cable. Is there an easy way to tell the difference? Visually or using something like a vernier caliper?
 
If it's been mouldering in your garage with the ends not sealed, it's probably neither by now.
75ohm will have a thinner core and/or a lower dielectric constant. Foam dielectic or the ridged polythene with lots of air space is an indicator of 75ohm.
But anything decent will be printed with a type number such as RG-nn .
 
What are you using it for? For small runs the difference between 50 and 75 is negligible, certainly for receiving and testing.

For a boat installation get the proper stuff correctly terminated
 
You have both missed the point. I searched for 10 metres 50 ohm co-ax. That was the first search result.
We don't know what the OP is proposing to do. It may not be anything to do with boats.
My suggestion is that he can get what he needs very cheaply. There were probably many other result without terminations. The ends were not the issue.
 
I have little idea of what you are talking about but I suspect you've already been given the answer

So what’s different?
Physically, the main differences can be found in the center pins and dialectric insulators. 75-ohm BNC connectors feature Teflon as a dialectric, and surround the outer spring fingers with air. Its center pin maintains a consistent diameter in both the front and rear areas (this is important—read on to find out why). 50-ohm connectors, on the other hand, use Delrin to surround the spring fingers, and its center pin is larger in the crimp area. You’ll need different crimp tools for each type of center pin
» 50 Ohm vs 75 Ohm: BNC Connectors Explained - MilesTek Blog
 
It's just a temporary connection to try out an AIS antenna on the pushpit. If I get a reasonable range out of it in comparison to the mast head, which is fed via a splitter, then I'll but some good stuff and run it in properly.
The route is through a pipe under the cockpit. the pipe is around 150mm ID and is already full of cables. Getting another one through will be possible, but it's a lot of scrambling about rodding it through.
Thanks Coopec, I can see some the coaxial is full of air. The cable is dry the garage has background heating to stop my tools going rusty.
 
Ian_Edwards said:
It's just a temporary connection to try out an AIS antenna on the pushpit. If I get a reasonable range out of it in comparison to the mast head, which is fed via a splitter, then I'll but some good stuff and run it in properly.
The route is through a pipe under the cockpit. the pipe is around 150mm ID and is already full of cables. Getting another one through will be possible, but it's a lot of scrambling about rodding it through.
Thanks Coopec, I can see some the coaxial is full of air. The cable is dry the garage has background heating to stop my tools going rusty.
Click to expand...

Two things spring to mind regardless of the co-ax you use :

1. Pulpit mount will give very poor range ... I have my AIS Rx antenna on the pulpit and I can honestly say - its near useless there. VHF is line of sight and pulpit height is too low.
2. Putting the Co-Ax through a conduit with lots of other cables ? There's all sorts of conflicts come to mind ... interference from field around cables ... inductance ... etc.

When my mast comes down again - I am seriously thinking to mount my AIS Rx antenna up the mast maybe on a crosstree or maybe another bracket other side of mast head from existing VHF antenna.
 
Refueler said:
1. Pulpit mount will give very poor range ... I have my AIS Rx antenna on the pulpit and I can honestly say - its near useless there. VHF is line of sight and pulpit height is too low.
Click to expand...

But the antenna on the ships will be much higher, so a pulpit mount receiver will give more than adequate range.
 
My pushpit mounted AIS antenna connected to my NASA AIS "RADAR" receiver had a range of 20 nm when I first installed it (2004). As the cable deteriorates with age the range comes down. but it is still well over 8 nm. now. How much further does one need?
 
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