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antenna cable cobra 29
- Thread starter nappy
- Start date
the longer the run the better shielded coax you'll need so the sky's the limit.
the longer the run the more power will be radiated as heat and to reuduce that heat the better shielded coax will make sure more of your radios power makes it to the antenna.
nothing less than rg-8 will do you any good and considering the center conductor of the coax is a good idea also, the larger the center conductor the larger the path rf will have to travel on.
the longer the run the more power will be radiated as heat and to reuduce that heat the better shielded coax will make sure more of your radios power makes it to the antenna.
nothing less than rg-8 will do you any good and considering the center conductor of the coax is a good idea also, the larger the center conductor the larger the path rf will have to travel on.
Having thought about it, my conscience bothers me about that first post. So, here are some 'further' thoughts on the subject.
The 'key' in the question is the length of the run, the resistance/impedance characteristics of the coax, and the 'size'/quality of that coax. Of those three things, the impedance is probably the 'biggest' or most important part. The 'length' of the run second most important. And the quality of the coax the third most important. They are all important, some just less so than others, from a 'wasted power' point of view.
Here's my reasoning. If the characteristic impedance of the feed line isn't at least 'close' to that of the antenna and radio, you've introduced some losses/imbalances to start with. Not good, especially when it isn't necessary. Since most radio gear is aimed at 50 ohms impedance, why not use that impedance feed line? A 75 ohm impedance instead of a 50 ohm impedance will yield at least a 1.5:1 SWR (everything else being as it should be). Not so particularly bad, just not really necessary.
The length of the run will determine how much loss any particular feed line will detract from what reaches the antenna. The longer the run, the more potential loss. So, taking a look at the characteristics tables of different 'sizes' of coax will give you an idea of what you might loose, and is a pretty good idea. There's a 'catch' there, though, especially at HF. If the difference between feed lines is a fraction of a dB of loss, don't worry about it, you'll never know anyway. Until that loss gets up around 3 dB, it's just not very practical to worry about it (depending on the cost of the coax of course). Since very few of those 'tables' ever get to 50 foot increments, figure the next larger length (200 feet), to get into the 'ball-park' with your guesstimation of losses. (that word is intentional, by the way)
Different manufacturer's, different 'grades'/'sizes' of coax have different losses per 100 feet. That's sort of important to keep in mind, but don't waste good worry on it too much. There are a few practical aspects that you should take into consideration when you're picking a feed line. They include availability, cost, ease of use, and finding things that will work with it (right sized connectors/adapters for instance). While RG-58 isn't the 'best' for runs of about 100+ feet, it will certainly work, don't rule it out completely. Using "Andrews" hard line is also possible, but one or two of it's characteristics sort of rule it out for the average person (co$t, ease of use, connectors! and it's over rated at HF).
So I guess the 'best' answer is probably, use the coax you have on hand (if any), or the less expensive type stuff (good quality though, hows that for a "Say what?" kind'a thingy?). If the rest of your gear is supposed to be 50 ohms, use 50 ohms coax. And as to the length of the run, add a few feet cuz you need some 'wiggle room' to make it easy to connect stuff.
- 'Doc
(PS - I just happen to sell the absolute best coax around! Costs $75.00/foot, all connectors supplied. No brand name or characteristic impedances on the jacket (it's a secret!). How many feet you need??)
... think that'll fly?
The 'key' in the question is the length of the run, the resistance/impedance characteristics of the coax, and the 'size'/quality of that coax. Of those three things, the impedance is probably the 'biggest' or most important part. The 'length' of the run second most important. And the quality of the coax the third most important. They are all important, some just less so than others, from a 'wasted power' point of view.
Here's my reasoning. If the characteristic impedance of the feed line isn't at least 'close' to that of the antenna and radio, you've introduced some losses/imbalances to start with. Not good, especially when it isn't necessary. Since most radio gear is aimed at 50 ohms impedance, why not use that impedance feed line? A 75 ohm impedance instead of a 50 ohm impedance will yield at least a 1.5:1 SWR (everything else being as it should be). Not so particularly bad, just not really necessary.
The length of the run will determine how much loss any particular feed line will detract from what reaches the antenna. The longer the run, the more potential loss. So, taking a look at the characteristics tables of different 'sizes' of coax will give you an idea of what you might loose, and is a pretty good idea. There's a 'catch' there, though, especially at HF. If the difference between feed lines is a fraction of a dB of loss, don't worry about it, you'll never know anyway. Until that loss gets up around 3 dB, it's just not very practical to worry about it (depending on the cost of the coax of course). Since very few of those 'tables' ever get to 50 foot increments, figure the next larger length (200 feet), to get into the 'ball-park' with your guesstimation of losses. (that word is intentional, by the way)
Different manufacturer's, different 'grades'/'sizes' of coax have different losses per 100 feet. That's sort of important to keep in mind, but don't waste good worry on it too much. There are a few practical aspects that you should take into consideration when you're picking a feed line. They include availability, cost, ease of use, and finding things that will work with it (right sized connectors/adapters for instance). While RG-58 isn't the 'best' for runs of about 100+ feet, it will certainly work, don't rule it out completely. Using "Andrews" hard line is also possible, but one or two of it's characteristics sort of rule it out for the average person (co$t, ease of use, connectors! and it's over rated at HF).
So I guess the 'best' answer is probably, use the coax you have on hand (if any), or the less expensive type stuff (good quality though, hows that for a "Say what?" kind'a thingy?). If the rest of your gear is supposed to be 50 ohms, use 50 ohms coax. And as to the length of the run, add a few feet cuz you need some 'wiggle room' to make it easy to connect stuff.
- 'Doc
(PS - I just happen to sell the absolute best coax around! Costs $75.00/foot, all connectors supplied. No brand name or characteristic impedances on the jacket (it's a secret!). How many feet you need??)
... think that'll fly?
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@ ButtFuzz:Please advise me to what is a good replacement mic for my SR-497HPC... Answer: 497 is "wired like Cobra", so many choices available. That radio does not need a power mic, so purchase a stock "coffin style" mic with a decent cord, like the ones that Astatic uses. The Superstar DM-507 is my go-to. https://www.ebay.com/itm/3050474478...adANq91JSiEEnz8EGqPJRBloTgEyaVsBoCtoMQAvD_BwE $12.99 + .99 cent shipping.
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