Hi folks, dumb question time! It's been too long and I have gorgotten: The boat has some old and stiff RG-8X coax for the VHF. I have stacks of RG-58 and RG-58U left over from a flirtation with ham radio, many years ago, but the cable is in as new condition. Is it OK to mix and match? Can I splice in a new section og RG-58 to the existing RG-8X that comes out of the mast? Or will I run into impedance problems? Any insight is, as always, much appreciated. Good sailing, Chris s/v Nausicaa
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NO
Each type of coax is designed for a different impedance. All the marine VHFs I know of work off 50 ohms impedance. If you want to install an antenna balancer then you COULD get away with it but that probably defeats the intent if using stuff you have on hand. If you have a S/W meter then you could futz around with it but I'd recommend you take the antenna off the mast first and make the new configuration work that way before instaling it. It could be a lot of trips up the mast to "get it right" For the rest of the group, impedance is the combination of resistance, inductance, and impedance for an AC (read RF AC in this case) circut that is equilivant to a DC resistance. For AC circuts you want ALL the component impedances to match to get max output. Otherwise the circut will have a lot of "resistance" to the flow of power to the antenna. This resistance has a generaly negative effect on the transmitter, i.e. it burns it out do to the power being "traped" in the circut and since it can't get out via the antenna it goes back to the transmitter. In the above case the power would not even leave the transmitter due to the "resistance" being in the connecting cable. Let the sparks fly!!!!
Each type of coax is designed for a different impedance. All the marine VHFs I know of work off 50 ohms impedance. If you want to install an antenna balancer then you COULD get away with it but that probably defeats the intent if using stuff you have on hand. If you have a S/W meter then you could futz around with it but I'd recommend you take the antenna off the mast first and make the new configuration work that way before instaling it. It could be a lot of trips up the mast to "get it right" For the rest of the group, impedance is the combination of resistance, inductance, and impedance for an AC (read RF AC in this case) circut that is equilivant to a DC resistance. For AC circuts you want ALL the component impedances to match to get max output. Otherwise the circut will have a lot of "resistance" to the flow of power to the antenna. This resistance has a generaly negative effect on the transmitter, i.e. it burns it out do to the power being "traped" in the circut and since it can't get out via the antenna it goes back to the transmitter. In the above case the power would not even leave the transmitter due to the "resistance" being in the connecting cable. Let the sparks fly!!!!
they are equivalent
RG8x, 58 and 58u are all 50 ohm coax and are interchangeable. The only differences are in the velocity factor and outer insulation, neither of which are relevent for your purpose. You can connect them together; the only negative to doing so would be in the slight loss in the Pl259 connectors but a little solder will minimize that. Don (K1VSK)
RG8x, 58 and 58u are all 50 ohm coax and are interchangeable. The only differences are in the velocity factor and outer insulation, neither of which are relevent for your purpose. You can connect them together; the only negative to doing so would be in the slight loss in the Pl259 connectors but a little solder will minimize that. Don (K1VSK)
Depending on how old the existing coax is ...
why not run a new line all the way. Just one coupling inside the cabin is best to keep the moisture out. Nothing like seeing cu braid that great shade of green to think about coax connector sealant. Us ham guys would cut the line to just the right length ... multiples of electrical 1/2 waves. But for short range VHF commo ... probably doesn't really matter. X does seem to be better up in the VHF area and more expensive as I remember, but it is doubtful you would ever notice it. Just remember to stay away from that crap that doesn't use cu braid. Vic "Seven" WW 4 OK
why not run a new line all the way. Just one coupling inside the cabin is best to keep the moisture out. Nothing like seeing cu braid that great shade of green to think about coax connector sealant. Us ham guys would cut the line to just the right length ... multiples of electrical 1/2 waves. But for short range VHF commo ... probably doesn't really matter. X does seem to be better up in the VHF area and more expensive as I remember, but it is doubtful you would ever notice it. Just remember to stay away from that crap that doesn't use cu braid. Vic "Seven" WW 4 OK
Gentlemen...
...very many thanks for the input. I thought it would be OK, but just wasn't 100% sure. I've run the new cable from radio to mast base under the settees, all hidden, and through the deck near the mast base, through a watertight compression cable mount, and terminated in waterproof (?) connector. The cable exiting the mast base also has the other end of the connector, both gold plated brass with O ring seals. This allows lowering the mast for trailering. Again, thanks for the advice. Chris, s/v Nausicaa N2NOJ
...very many thanks for the input. I thought it would be OK, but just wasn't 100% sure. I've run the new cable from radio to mast base under the settees, all hidden, and through the deck near the mast base, through a watertight compression cable mount, and terminated in waterproof (?) connector. The cable exiting the mast base also has the other end of the connector, both gold plated brass with O ring seals. This allows lowering the mast for trailering. Again, thanks for the advice. Chris, s/v Nausicaa N2NOJ
I stand corrected
Don and Gord are correct, they both are 50 ohm. I had just finished my taxes and was out of my mind with numbers. Looking back I don't know what I was thinking in the first place. sorry for the confusion.
Don and Gord are correct, they both are 50 ohm. I had just finished my taxes and was out of my mind with numbers. Looking back I don't know what I was thinking in the first place. sorry for the confusion.
's'OK, Bill...
your heart was in the right place. I just couldn't remember if they were all the same impedance. Thanks for responding. Chris
your heart was in the right place. I just couldn't remember if they were all the same impedance. Thanks for responding. Chris
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