Cutting coaxial cable

Any discontinuity in a coax connected to a transmitter causes some of the transmitted power to reflect back. The bigger the discontinuity, the larger the impedance mismatch, the bigger the reflection. Why bother on something that could be safety critical when you can add 2 connectors and a barrel?
Alex_Blackwood said:
I wouldn't worry too much about the dia. as long as you can insulate the inner from the sheath and
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Nope, the cable impedance depends on the distance between inner and outer being correct. This is why cables have minimum bend radiuses too.
 
st599 said:
Why bother on something that could be safety critical when you can add 2 connectors and a barrel?
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Because the alternative is not having it at all.
Anyway, connection now made in the manner described by Refueler. Let's see how it works in the real world.
If I'm not happy with it, next time I see coax connectors I'll pick some up and do the job properly.
 
Alternatively replace the deck gland with an Index Marine split rubber deck gland. Retains the integrity of the made cable and plug and cable can be removed and fitted at will in the future.
 
Not sure what type of deck gland you have, but I assume the hole through deck under gland is large enough for connector to pass through. Just slit the rubber bung in the gland and put cable through slit into hole (assembling all the other bits in right order on cable first of course). Better/easier to get the right gland than compromise the cable.
 
st599 said:
Any discontinuity in a coax connected to a transmitter causes some of the transmitted power to reflect back. The bigger the discontinuity, the larger the impedance mismatch, the bigger the reflection. Why bother on something that could be safety critical when you can add 2 connectors and a barrel?

Nope, the cable impedance depends on the distance between inner and outer being correct. This is why cables have minimum bend radiuses too.
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Also depends on type of insulation air gaps and all sorts, so a bit of a coin toss all round :unsure:
 
RunAgroundHard said:
If you get an opportunity to buy and fit later, I recommend this style of cable port https://www.svb24.com/en/stainless-steel-deck-cable-lead-thru.html

I originally bought mine from Salty John (no longer trading). I use mine at the mast and the VHF plugs and other plugs easily fit through. Very effective at keeping water out, bone dry headlining under the deck hole, after many years.

OEM sales blurb Cableport - ELVABRO AB
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Fitted one of those (from Salty Jon too), excellent kit. Seen them fitted to a lot of Legends, so maybe standard fit for them.
 
I have used Refueler's method many times, going right back to the days of cb radios in the 80s. Always worked a treat.

My new to me boat had two joins in the coax to the vhf both made with block connectors...radio received ok, I never transmitted with it..
 
Update: system is up and running, I'm picking up a boat 6.5nm away, not sure if there's anything further out than that. Aerial is on the pushpit so I'm not expecting massive range anyway. It'll do for now.
 
Sea Change said:
Update: system is up and running, I'm picking up a boat 6.5nm away, not sure if there's anything further out than that. Aerial is on the pushpit so I'm not expecting massive range anyway. It'll do for now.
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Pushpit mount - many people talk about up to 10nm .... but that will also depend on any obstructions / seastate ......

I had my AIS first on the pushpit and I was not impressed - targets of 6 - 10nm ....... far enough to give me warning - but made me wonder if there were any I might miss.
Changing to masthead was a major improvement ..... the number of targets in that up to 10nm increased as well as getting the greater range.
 
Refueler said:
Pushpit mount - many people talk about up to 10nm .... but that will also depend on any obstructions / seastate ......

I had my AIS first on the pushpit and I was not impressed - targets of 6 - 10nm ....... far enough to give me warning - but made me wonder if there were any I might miss.
Changing to masthead was a major improvement ..... the number of targets in that up to 10nm increased as well as getting the greater range.
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On the old boat, we had a spare masthead aerial and in freak conditions I once picked up a boat over 300nm away. 80nm wasn't unusual.
I might eventually install a masthead aerial for the AIS, but I need a quick and easy solution for now. And I've not long finished installing the wind instrument so I feel like I've spent quite enough time up there already 😁
 
Just picked up a big cruise ship 17.5nm away. That's good enough for now.
By the way, the aerial is actually lashed to the wind gen pole, so I was a wee bit worried that it might have a blind spot, but it does seem to be working fine.
On to the next boat job... it never ends...
 
john_morris_uk said:
For another example. We have a Raymarine system. (AIS & Splitter) that uses the masthead antenna. Normal range is about 30 miles plus.
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That's the easiest way - to add a splitter so the VHF antenna serves both duties.

I have the Onwa Passive splitter and it works very nicely thank you ... targets are at good distance .. well over 20nm on average ...

You can of course go for Active splitter (12v powered to reduce losses in TX / RX of AIS) .... but then you pay a lot more .... and have to power it.

I have compared my Passive to an Active when moored next to each other .... both masthead ... both similar heights. He did have a few more targets than mine - but they were low power yachts AIS signals - most likely the older plain B class at 2W. The results though made me feel content with the performance of my Passive setup.
 
Sea Change said:
Just picked up a big cruise ship 17.5nm away. That's good enough for now.
By the way, the aerial is actually lashed to the wind gen pole, so I was a wee bit worried that it might have a blind spot, but it does seem to be working fine.
On to the next boat job... it never ends...
Click to expand...
Anything metallic within about 6m in the radiation plane will affect the radiated pattern. It'll no longer be omnidirectional
 
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