I'm going to replace the masthead antenna and cable. I always thought that the reception wasn't that great, and it recently got confirmed when I received a good reception on the hand-held VHF but the build in VHF with masthead antenna was sh!t.
Question: What should I use, double shielded or quad shielded coaxial?
My assumption is that the quad shielded would provide less interference, is that the case?
Also, is there a difference between a Shakespeare Coaxial and one from Bunnings?
Not all co-ax is created equal and you will find that the Green Shed stuff is all 75 ohm made for television whereas radios use 50ohm impedance. If you want to mitigate the problems for longer intervals use a co-ax that has tinned braid as a shield and some braids are very loosely woven and other are quite tight, go for the tight one. The attenuation should be as low as possible but the lower you go the more expensive it gets.
Check out RS Components, I use them and find them excellent to deal with plus they will do casual sales without needing an account.
au.rs-online.com/web/c/cables-wires/coaxial-cable/coaxial-cable/?searchTerm=coaxial+cable
Hiya Jev,
As Loose said, make sure its 50ohm, 75 ohm coax is a much cheaper and lower quality cable and impedance mismatch will screw you before you even get started. There are significant other differences too
-- Conductor type: Coax cable is matched to the desired frequency band. The higher the frequency the more the signal runs on the outside (or skin) of the centre copper conductor. Low freq runs through the guts, high freq moves to the outer edge. TV coax (75 ohm) uses a copper coated steel conductor as TV signals (45-860mhz for FTA and 950-2150mhz for cable) runs on the outside of the conductor, so they use a steel core for the conductor core because its cheaper. .
50 ohm coax cables is used for radio transmission (lower freqs, around 150mhz) so the conductor is changed to pure copper, much more expensive but miles better performance than a CCS (copper coated steel) conductor can do.
--Braids. 75 ohm coax can get away with aluminium foil/polyester wraps for the shield, rather than a copper braid. Quad shielded coax is an improvement on the usual double shield but was built for cable TV (Foxtel), so not relevant to VHF which requires a bare copper braid as well as the bare copper centre conductor. All 50 ohm coax will have a copper braid, not aluminium foil as the shield. Some may throw an additional aluminium foil over the braid as an EMI measure, but all 50ohm for VHF should be a 95% copper braid as the shield, not aluminium foil.
--Loss. Loss is king. Try and lose as little signal as possible if you want reliability. I never use RG58 past more than 15mtrs, and even then its starting to effect performance. My choice would be RG213 or CNT400 for a masthead run. RG8 is just as good, but not as easy to find in OZ.
--Connectors. Don't use BNC (6mm push twist) connectors on 1/2" coax, use proper N type or UHF 12mm connectors. Use a 6mm RG58 pigtail patch lead if you have to reduce it to BNC connector style, which I doubt as all radios have proper interfaces.
I've done a quick list of the 50ohm coaxes below, this is from memory so you should confirm numbers, but this will be about right.
If you are struggling to find a good supply, let me know, I still have some old contacts in the coax game.
The summary is that VHF (50ohm) demands a more superior (proper?) coax cable. TV (75ohm) is the opposite, cheap and nasty.
Cheers,
SB
Connectors are probably your biggest loss of signal. Keep them to an absolute minimum, or avoid them all together. It will make a very noticeable improvement.
That's some awesome information in regard to cable types and connectors, thanks guys! It certainly stopped me from getting some cheap coax cable from Bunnings.
CNT 400 looks like a good choice, will try to get my hands on some of that over the next few days.
While I'm at it, I'll also mount a 2nd VHF at the helm and a 2nd antenna on the davits for redundancy. I currently only have a VHF at the nav station, which is a pain most of the time, and end up using the handheld.
Select to expand quotejev7337 said..
That's some awesome information in regard to cable types and connectors, thanks guys! It certainly stopped me from getting some cheap coax cable from Bunnings.
CNT 400 looks like a good choice, will try to get my hands on some of that over the next few days.
While I'm at it, I'll also mount a 2nd VHF at the helm and a 2nd antenna on the davits for redundancy. I currently only have a VHF at the nav station, which is a pain most of the time, and end up using the handheld.
G'day Jev,
If the second antenna is intended for redundancy for the main radio as well as the backup radio, keep the cables separate, two antennas and coaxes hanging off one radio is not a good idea without proper active splitters.
When racing, the rules require a backup VHF antenna for offshore or overnight work, so Whitworths and everyone sell backup antenna and coax pigtails in a kit. This is what I used as redundancy, I just had a permanent mount on the pushpit, the rest stayed in the bag in the emergency locker.
Cheers,
SB
I will be keeping them separate and simple, each VHF connected to their own antenna. An additional separate cable to run from one cable end to the other VHF and vice versa, just as a back-up. I know it could be overkill given there will be 2 antennas and VHF, but it's just a spare cable.
I have a splitter connected to the masthead antenna, splits signal to VHF, AIS, and FM Radio. Seems to work ok.
Select to expand quotejev7337 said..
I will be keeping them separate and simple, each VHF connected to their own antenna. An additional separate cable to run from one cable end to the other VHF and vice versa, just as a back-up. I know it could be overkill given there will be 2 antennas and VHF, but it's just a spare cable.
I have a splitter connected to the masthead antenna, splits signal to VHF, AIS, and FM Radio. Seems to work ok.
Sounds perfect mate, all the best with it.
