coax and base setup

[ex-28]

hi all i currently am a cartake of a 3 story apaartment block , currentlly running my grant lt
i am in bottom floor my antron 99,is mounted on top of roof which is 40 feet off ground and then i have a pole off the chimny 6 feet up at the top of that is the a99 , i am running about 60 feet of rg8x coax so far had no interference or anythign , my grant lt is pushign out about 16 watts , i am going to be picking up a rci 2995 base unit in a few months and am worried about interfering with my other tennents, should i replace the rg8x with rg 213 cable so it would be better shielded ? i dont ahve the ground kit on the antennia and my swr's are 1.1 - 1.3 so i'm happy with that .


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[ex-28]

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[Foxhunter]

If you're worried about that sort of thing, and it might very well be justified, you'd probably want to look into getting a coax type that's double shielded.

As good as RG213 is, it's a single shield coax. People wanting to avoid interference often like to use something like Belden RG214 or Times Microwave LMR-400. Something along those lines will help reduce possible interference, provide maximum shield grounding and give you excellent low-loss signal transmission. By the way, welcome on the CBRT


Foxhunter 351 NJ

[ex-28]

ok ty verry much appreciate the welcome , will lookinto it , maybe see how things go with my rg8x before i run out and buy cable , it is going to be snow all over when i purchas the 2995 in a few months so just planning on spring time here just incase !

['Doc]

I think waiting to see if it's necessary is a pretty good idea. You know, most interference like you're worried about doesn't 'leak' out of the shield of the coax. Most of it tends to come from the antenna it's self, because it's close to susceptible electronic stuff, and from CMC on the outside of that coax. Why not do the simple stuff first? Those CMC on the outside of the coax, wind a choke in the feed line near the antenna first, see what happens. A trip to the roof is a lot cheaper than a new run of coax.
- 'Doc

[Foxhunter]

You're welcome and it's always good to see a new member. What Doc said is true in many cases. And it never really hurts to plan ahead on possible needs and scenarios. But the RCI 2995DX is rated around 150W or so, a big jump from just a stock radio. The radio isn't exactly the cleanest one on the market and heavily filtered, although some report no problems (and still others don't care).

Using "plain" single shield RG8, at (unfiltered) 200W PEP, I blare right over the cordless phone here. And true it's a good chance that it's radiates purely from the antenna. But using double shield coax would assure that, there'd be no doubt. And the double shield coax cables are usually premium grade types. There are many reasons for advocating the use of double shield, ask just about anyone. But it's only one of several areas to focus on. Many other things like output filtering, good grounding etc etc. And still there are no guarantees. But using the best possible grade coax you can (or can reasonably afford) is one of the "fundamental things" with radio. Pretty much that and a decent antenna system are primary.

So anyway in the end I wouldn't be surprised if the other tennents are going to be hearing you talking and probably guess at who it is. Not a definite but I'd plan on buying some various preventative measure/grade materials. Most rural country folk don't have to take the same steps and go to the same lengths to try and co-exist with others living right beside them. People living in more urbanized settings like your apartment complex and wanting to transmit will always have a few more steps to take to try and keep the neighbors happy. Not always but usually. I know what it's like to live with nearby residents as they're all around me here in NJ and it's probably good practice to lay low and keep your on-air converstations confined as much as possible. Sometimes things go great and other times you really tear up TV's PC's telephones baby monitors etc. You never know but few could argue to go down the list of steps to take to minimize RFI/TVI, including the use of quality double braid coaxial cable. Good luck!


Foxhunter 351 NJ

[721HACKSAW]

That 2995 is going to get into computer speakers and suround sound system speakers, especially with a power mic. Good luck.

[ex-28]

I think waiting to see if it's necessary is a pretty good idea. You know, most interference like you're worried about doesn't 'leak' out of the shield of the coax. Most of it tends to come from the antenna it's self, because it's close to susceptible electronic stuff, and from CMC on the outside of that coax. Why not do the simple stuff first? Those CMC on the outside of the coax, wind a choke in the feed line near the antenna first, see what happens. A trip to the roof is a lot cheaper than a new run of coax.
- 'Doc

are you talking about Choke Balun ?

[Hawk+1]

Yes, he would be refering to an air balun as they call it, for your rg8x you could use a pice of 2 inch pvc pipe and wrap about 18 feet of coax around it making sure the wraps are tight. Keep it as close to the antenna as you possably can. It acts like a for of resistor, adding resistance on the outer jacket of the coax and reduceing the rf feild that tends to travle along the outer parts of coax. Aslo getting the gpk for you a-99 would also be a good idea, since those antennas are also known to cause tvi/rfi, the gpk wouldnt be a bad idea. Might even get your swr down to 1.1-1 al across the band.


73's and welcome to the forum
From the Keystone were off the key

['Doc]

Yes, I an referring to a 'coaxial choke', since it'll never be a 'balun' in any sense of the word. Lot's of ways of making one. Coil the coax up like a rope, wrap it on a form, and who knows how else. Do that wrapping on a ferrous/iron pipe! Just increases the amount of inductance on the outside of the feed line, doesn't do anything to what's inside that feed line.
- 'Doc

[ex-28]

for that can u just use rg8x around the 2: pipe ? , does it matter how many times i go around ? , i will be running the rci 2995 on 10 11 and 12 meter.

['Doc]

First, none of this is very exact, closer to 'eye-ball' measurements rather than micrometer stuff. Don't get too tied up with how many turns there are in that coil, or what 'size' they are. The biggest worry about size is how tight do you do that wrapping. Different size coax have different 'bend' limits before doing any harm to that coax. As long as you don't go too far, any size will work. Got a 2 liter soda bottle, or the plastic thingy 50 or 100 count blank CDs come in, something that size? Ought'a work just dandy. How about the larger plastic bottle instant Folgers coffee comes in? If the mast you have your antenna on isn't too small of a diameter, it'd work too. That's figuring you are using RG-8X or something about that size. I have no idea what the 'bend radius's for the different size coax's are so use your own judgment. The number of turns in that coil is another one of those 'ball-park' thingys. For 10 - 20 meters, something like 4 - 10 turns usually is enough. Not sure, think it might need a little more? No big deal, add a couple or few more turns. You know you've gone too far when you end up with more than maybe a quarter or half the feed line length in that coil.
About that ferrous/iron pipe thingy. If you just happen to have some of that handy, and it's not ever going to be used somewhere, sure, why not. If you don't happen to have any, don't worry about it, it really isn't going to be a biggy. Just add a couple more turns to the coil, sort of.
!! OR !! If you just happen to have an old TV stashed away for parts, with a real-live picture tube in it. Strip the 'yoke' wrapped with 100 miles of copper wire off of it. At the bottom of all that wire there is a ferrite coil form. Odd shaped to fit the picture tube stem, that doesn't matter. It comes apart in two halfs, little metal clips holding it together. Wrap the coax on it or through it several times. Sort of ugly, but it works!
- 'Doc

[Hard Drive]

I was talking to an old-timer one day and he told me that he always run his coax cable thru a water hoes. Would that work the same way as a double shield coax?

[Hawk+1]

Here is a link to a few good home made Ugly Baluns(air choke) That we have been descussing. Even though it is not a true balun. And as far as the garden hose idea, Im not sure if that would help reduce any tvi. And as far as materials go to make the air choke out of, I think if you would use any metalic material it would defeat the perpose of the choke, metals are conductive(they will carry an electrical current), the idea of a choke is to create resistance, metals do not have the same resistance as plastic would( since plastics do not conduct electric) the rf on the coax would just travle through the metal like it was never their. Plastic will reduce the amount of rf since it is non-condutive. I hope this link is helpfull.
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73's from the Keystone

['Doc]

Hard Drive,
If he ran that feed line through a hose, and buried that hose, then yes it would certainly help. If he didn't bury that hose, just left it laying on the ground, in the air, whatever, then no, it isn't going to provide any shielding at all. Unless that hose was made from some conductive material! For some reason, I sort of doubt that.

And normally an insulator does only that, stops conduction. It is seldom, if ever, a 'shield' of any kind. The most common 'shields' at RF are metal, a conductor. A 'shield' on coax keeps the signal inside that shield, it doesn't flow on the outside of that shield, only on the inside. That's a hard thingy to get straight in your mind sometimes, but it's what's happening. That's the only good reason for there being coax to start with, and why it was invented. Plastics, rubber, whatever are 'shields' that keep you from touching something you shouldn't, they affect conduction. Metal is a shield because it can prevent radiation from 'touching' something it shouldn't. Nuthing ever turns out as simple as it seemed to start with, does it...
- 'Doc

[Foxhunter]

Although sometimes in real life it happens all too frequently, you really "shouldn't" have "radiating" coax cable to begin with, nor need to utitlize a coax choke. Anything that will work or get the job done I guess is best. It points to something amiss in the installation somewhere. It's a good bandaid fix though, but hopefully a good install where the RF is kept inside the shield is best. Many will prefer to take about 6-ft of coax and wrap it around a 5 or 6-inch diameter leftover/scrap piece of schedule 40 PVC pipe. Some will add a clamp-on split bead by the feedpoint, depends on what you want to do. Not trying to spend your money for you but still, getting a good quality length of coax with extra shielding is a great idea. Once again, and to be real, running any power level other than stock will greatly increase the chance of bleeding into the other apartment dweller's consumer electronics. It's a common challenge CBers and Hams alike face. Good luck!


Foxhunter 351 NJ

[Eagleman]

IF YOU HAVEN'T ALREADY, RUN YOU A GROUND WIRE #8 GAUGE FROM THE BOTTOM CLAMP OF THE A99 TO A GOOD GROUNDING LOCATION ON THE ROOF THERE, TRYING TO MAKE THE GROUND WIRE RUN THE SHORTEST LENGTH AS POSSIBLE. A GOOD GROUND WILL MAKE A BIG DIFFERENCE. SAME GOES WITH YOUR 2995 TOO, RUN A GROUND WIRE OFF OF ONE OF THE CHASSE SCREWS THAT HOLDS THE SIDE HANDLES ON TO A GOOD GROUNDING LOCATION THERE BY YOUR RADIO.... YOU SHOULDN'T HAVE ANY PROBLEMS THEN.... Dave