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jawharp

Internally Coiled RF Antenna Mast

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Hey guys,

So I've been toying around with this idea for a while, and I'm sure I'm not the first.  I'm surprised this doesn't exist yet.  Basically I want to see if it's possible to make an internally cabled antenna mast. 

The limiting factors I've thought of thus far are:

1. Minimum bend radius of shielded RF cable is very large, so the mast would have to be at least 4 inches in diameter

2. Coiled shielded RF cable does not exist from what I've seen

3. Coiling the shielded RF cable yourself via a heatgun would damage the center element or shielding if done improperly

I thought of building a straight cable internally cabled mast with a spool of cable at the bottom kind of like a fishing rod, but could not find a cost effective way to deal with the cable tangling as the reel spins.

I found one way to deal with it, but this slip ring is over a thousand dollars: http://www.naval-technology.com/contractors/rotary/spinner/

So the reel is out of the question which brings me back to internally coiled.  I have one major question about this:

Why not use thin, less shielded cable for the inside of the mast, like that found connecting the sma connectors in the back of an Audio Ltd. Quad box, and then shield the mast itself like a Faraday Cage?  BNC outs on the top of the mast would lead to 2 shielded jumpers to the antennas.  Two at the bottom to the receivers. 

This idea/project is not critical to my gear.  I'm just wondering at this point why no one's made one yet.

Also, the last alternative is an externally cabled pole, where the bigger coiled cable at the proper bend radius of like 4 inches sits outside the mast and stretches up and down around it.

Anyone ever try something like this?

joe

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You need to balance the cable loss with the length.  The thin cables you are refering too will probably have an incredibly high loss/distance rating. 

Edit: if these are similar to the cables used on the lectosonics multicoupler they are good for about 30cm max before experiencing unacceptable loss.

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Why not use thin, less shielded cable for the inside of the mast, like that found connecting the sma connectors in the back of an Audio Ltd. Quad box, and then shield the mast itself like a Faraday Cage?

Anyone ever try something like this?

joe

You have properly identified the factors mitigating against this idea and Michael has pointed out that the loss on the cable you choose is the biggest obstacle to success. I have been grappling with the same issue --- what to do with the cables from the antenna to the gear when the antenna mast is in its down position. In my case, I have 3 cables: 2 for the log periodic "shark fin" antennas and 1 for the 2.4ghz Zaxcom IFB-100 antenna. I have kept the cables relatively short, about 8 feet (which is the extent of the mast when fully raised) but that still produces a rather unwieldily mass of coiled cable when collapsed. Your idea is a good one, to mimic what we have with a fishpole with internal cable, but I don't think it can be implemented for the antenna mast.

-  Jeff Wexler

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Thanks for the responses guys.  Now I know why this is such a difficult/impossible thing.  Something Michael said raised another question for me:

I know that there is an acceptable level of RF that has to come through the cable, but how many dB of signal is acceptable?  I know the cable length that causes the loss would change per cable type, but is there a set amount of dB coming in that is considered acceptable across all RF equipment?  Or just as little loss as possible?

Thanks,

joe

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I know that there is an acceptable level of RF that has to come through the cable, but how many dB of signal is acceptable?  I know the cable length that causes the loss would change per cable type, but is there a set amount of dB coming in that is considered acceptable across all RF equipment?  Or just as little loss as possible?

joe

I think as little loss as possible is the goal. It is not easy to actually quantify or specify what is an acceptable signal level --- in the world of RF we find ourselves in, the highest signal level the antenna can provide to the receiver is what should be strived for. Any and all cables, adapters, etc. will cause some loss. This is why many people use their receivers with inferior whip antennas but move the receiver close to the transmitter --- this will almost always deliver better RF signal directly to the receiver. For those who use a centralized (on the cart) antenna system, every component including the length and type of cable needs to be considered. All of these signal level losses CAN be measured (if you have proper test equipment) and can be calculated, quantified and so forth. This is usually not necessary if certain base principles are applied: use of low loss cable, quality connectors fitted, no adapters or barrels in line, proper multicoupler designed for use with your particular wireless, etc.

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Thanks for the quick reply.  This whole idea is seeming like more trouble than it's worth.  One of those things that should just be kept as simple as possible.  Any method of doing this I think of sacrifices quality and adds more things to the signal chain that could go wrong.

As a last attempt at some sort of solution:  can you see any problems in regards to signal and reception if the excess cable were at the top of the mast?  Fed through the mast and out the top, coiled up.  This way the excess is up and out of the way of ratchets when the mast was down and not functioning, while close to the joints of the mast itself, which you would be by anyway if you were adjusting the arm.

Thanks for all your help,

joe

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As a last attempt at some sort of solution:  can you see any problems in regards to signal and reception if the excess cable were at the top of the mast?

joe

Unless there is active amplification involved, where the excess cable resides should have no bearing on signal loss.

-  Jeff Wexler

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As far as dealing with the mass of antennae cable, I've bundled the 6 separate cables and tied them every foot or so with cable ties and put it all inside 3/4 inch flex tubing. The nylon web-type, not the plastic version.

The whole mess is wrapped around the 12 foot (no interior cabling) K-Tec boom pole, which is secured to my cart. This slides elegantly when the pole is extended or collapsed. The flex tubing keeps the cables looking neat and avoids the cables from catching on the way up.

Why six cables? Two are for my Lectrosonic Venue racks, 1 for my Comtek 216 Whips, 1 for my IFB T-4 and 2 left over from my former 411a racks - but who knows what I'll get down the road. They are ready and waiting.

post-284-130815089191_thumb.jpg

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Thanks for the replies.  Richard, your flex tubing setup looks really nice and easy to work with.  I might just do something like that to solve my problem.

Thank you again,

joe

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On 9/24/2010 at 2:55 PM, jawharp said:

Thanks for the replies.  Richard, your flex tubing setup looks really nice and easy to work with.  I might just do something like that to solve my problem.

 

Thank you again,

 

joe


Thanks jawharp Joe, and Richard for sharing your antenna mast planning and setups. A nylon flex tubing snake of loomed antenna cables looks like a very clean and elegant solution, in lieu of the elusive internally cabled antenna mast... 

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