COAX

David2452 said:
RG58 is OK, RG59 is better but thicker.
Click to expand...

RG59 is the same diameter as RG58 but is 75 OHM and not suitable for VHF.

For the VHF frequencies you need 50 OHM, and the choices range from the small diameter, 5mm, and very 'lossy' RG58 up to RG213 which is a 9mm cable with good performance but is difficult to handle and a bit OTT for small boats. RG8X is the best compromise - a 7mm cable - and RG8U is an option although it is also a 9mm cable.
 
Aircell 7 is better and thinner than all the aforementioned imho.

Can be bought at Nevada

Oh and get the best connectors like these

He has them made for him but I don't think they are on the website.
 
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Aircell 7 is good low loss data cable. It has a couple of drawbacks - it isn't tinned and it has a very open cell foam dielectric. Tinned is good for corrosion resistance and soldering and the open cell foam is easily damaged if you step on the cable. Some say that these open cell dielectrics can wick up moisture, but I'd need convincing of that.
 
Salty John said:
RG59 is the same diameter as RG58 but is 75 OHM and not suitable for VHF.

For the VHF frequencies you need 50 OHM, and the choices range from the small diameter, 5mm, and very 'lossy' RG58 up to RG213 which is a 9mm cable with good performance but is difficult to handle and a bit OTT for small boats. RG8X is the best compromise - a 7mm cable - and RG8U is an option although it is also a 9mm cable.
Click to expand...


OOps, meant to type RG58U
 
For your information

AIRCELL 7 RG213/U RG58/U

Capacity pF/m 75 101 102
Velocity factor 0,83 0,66 0,66

attenuation dB/100 m
10 MHz 2,2 2,0 5,0
100 MHz 6,28 7,0 17,0
500 MHz 14,72 17,0 39,0
1000 MHz 21,52 22,5 54,6
3000 MHz 40,88 58.55 118
 
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Salty John said:
RG59 is the same diameter as RG58 but is 75 OHM and not suitable for VHF.

For the VHF frequencies you need 50 OHM, and the choices range from the small diameter, 5mm, and very 'lossy' RG58 up to RG213 which is a 9mm cable with good performance but is difficult to handle and a bit OTT for small boats. RG8X is the best compromise - a 7mm cable - and RG8U is an option although it is also a 9mm cable.
Click to expand...

It's nothing to do with the frequencies - it's a question of the requirements of the transmitter. Each transmitter (and receiver, though it is less critical to operation) has an output impedence - measured in ohms - which it expects to see matched by the attached cable and antenna. Almost all equipment is designed for 50 ohm and requires corresponding 50 ohm cable and an antenna that presents 50 ohms.

It is perfectly feasible to design a transmitter that expects 75 ohms, but 50 has just become the standard. Simple antenna designs also tend towards 50 ohms, so it all hangs together very easily.

If you don't match the impedence throughout the system, you get "standing waves" in the cable. These result in a loss of transmitted power and, if bad enough, can damage the transmitter. it does result in a small degradation in receiver sensitivity too, but this is not really noticeable unless the mismatch is very large.
 
I stand corrected for being sloppily over-simplistic. I should have said that leisure marine vhf radio equipment is designed for 50 ohm impedance. The point was, don't use telly cable!
 
Salty John said:
I stand corrected for being sloppily over-simplistic. I should have said that leisure marine vhf radio equipment is designed for 50 ohm impedance. The point was, don't use telly cable!
Click to expand...

And as Salty John says get the proper tinned cable - it won't corrode like the cheaper stuff. Another recommendation is not to use a deck connection at the mast base but make a connection inside the boat using a deck gland which accepts the plug diameter.
 
Coax

If the job is to connect an AIS receiver then the RG58 will be fine presumably for connecting a low mounted antenna. Buy tinned copper shield wire for long life.
The figures for various 50 ohm coax are interesting particularly the attenuation. At 17 decibels per 100 metres at 100 megahertz is quite alarming. Our marine VHF com is more like 160mhz so more attenuation. While we typically might have a cable run of 12 or 15 metres so the attenuation is far less than the 100 metre figure it still represents a huge loss of actual power. So we could easily lose half of the transmitted power using RG58. However losing half the power does not affect actual received signal very much. (It is all logarythmic) But still worth fitting the low loss cable for long runs. good luck olewill
 
maby said:
It's nothing to do with the frequencies - it's a question of the requirements of the transmitter. Each transmitter (and receiver, though it is less critical to operation) has an output impedence - measured in ohms - which it expects to see matched by the attached cable and antenna. Almost all equipment is designed for 50 ohm and requires corresponding 50 ohm cable and an antenna that presents 50 ohms.

It is perfectly feasible to design a transmitter that expects 75 ohms, but 50 has just become the standard. Simple antenna designs also tend towards 50 ohms, so it all hangs together very easily.

If you don't match the impedence throughout the system, you get "standing waves" in the cable. These result in a loss of transmitted power and, if bad enough, can damage the transmitter. it does result in a small degradation in receiver sensitivity too, but this is not really noticeable unless the mismatch is very large.
Click to expand...

50 ohm is a compromise between power transfer and noise addition. 75 ohm is the lowest noise addition. Therefore 75 ohn is used for receiving stations, 50 ohn for transmitting stations.
 
Don't judge characteristic impedance by the diameter of the cable. The impedance is determined by the relative diameters of the centre conductor and the shield and the dielectric constant of the plastic between. You can get big fat 50 ohm cable and very thin 50 ohm cable.
 
Thanks for all the replys.
The set up we have at present is the VHF radio aerial is not very long and is situated in the centre of the winded, I guess it's all one unit. I'm
I'm assuming that as this came as standard equipment when the boat was new it may not be very good, I may be wrong.
What I want to do is fit nice big aerial to the top of the mast and use the one in the middle of the windex for the ais.
I also have an emergency VHF aerial just in case of dismasting.
The aerial I intend to use is an SB 1 S 156-163 MHz.
The gain is stated as being 0dBd, 2.14 dBi with a band width of 9.3 Mhz at 158MHz and is 1060 mm long.
What are your thoughts on this new set up, I am after better VHF and ais range.
Thanks in advance.
 
dougg said:
Thanks for all the replys.
The set up we have at present is the VHF radio aerial is not very long and is situated in the centre of the winded, I guess it's all one unit. I'm
I'm assuming that as this came as standard equipment when the boat was new it may not be very good, I may be wrong.
What I want to do is fit nice big aerial to the top of the mast and use the one in the middle of the windex for the ais.
I also have an emergency VHF aerial just in case of dismasting.
The aerial I intend to use is an SB 1 S 156-163 MHz.
The gain is stated as being 0dBd, 2.14 dBi with a band width of 9.3 Mhz at 158MHz and is 1060 mm long.
What are your thoughts on this new set up, I am after better VHF and ais range.
Thanks in advance.
Click to expand...

0 dBd means it has the same gain as a bog standard dipole. Gain is traded for directionality, so the beam won't be very focussed, good on a rolling yacht.

You'll get quite an increase in range with the increase in height.
 
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