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Author Topic: Leaky Feeder Coax  (Read 1147 times)

Gian Luca Cavalliini

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Leaky Feeder Coax
« on: April 20, 2018, 03:39:57 am »

Hi all,
anybody ever used leaky feeder coax for IEM? I'd like to know more but can't find much about it. And I'd like to buy some but don't know enough about useful specs for this use (apart RF frequency range, obviously). Oh, also don't know where to buy...  ::)
Thanx in advance
GLuca
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Tim McCulloch

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Re: Leaky Feeder Coax
« Reply #1 on: April 20, 2018, 04:18:31 am »

Hi all,
anybody ever used leaky feeder coax for IEM? I'd like to know more but can't find much about it. And I'd like to buy some but don't know enough about useful specs for this use (apart RF frequency range, obviously). Oh, also don't know where to buy...  ::)
Thanx in advance
GLuca

Commscope has a product with controlled radiation called Radiax«.  I'm old enough to remember when that was an Andrew product...

https://www.commscope.com/catalog/cables/product.aspx?id=27
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Scott Holtzman

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Re: Leaky Feeder Coax
« Reply #2 on: April 20, 2018, 10:40:56 am »

Commscope has a product with controlled radiation called Radiax«.  I'm old enough to remember when that was an Andrew product...

https://www.commscope.com/catalog/cables/product.aspx?id=27

We used Radiax in hospitals for paging.  Celwave (they have a new name now too) makes a similar product.

All of these are solid jacked low density foam products in 1/2 and 7/8 sizes.
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Scott AKA "Skyking" Holtzman

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Jason Glass

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Re: Leaky Feeder Coax
« Reply #3 on: April 20, 2018, 05:18:21 pm »



We used Radiax in hospitals for paging.  Celwave (they have a new name now too) makes a similar product.

All of these are solid jacked low density foam products in 1/2 and 7/8 sizes.

Hi Scott,

For a long time, I've wanted to experiment with radiating coax and RAD coms, but can't find a US vendor for 3/8 or 1/4 variants by the foot. Plenty of 1/2 variants, but that's overkill for my application and I don't want to haul it around or coil it every gig.  Got any leads?

FWIW, leaky feeder on RAD is appealing to me because it seems feasible to diplex their VHF RX and UHF TX on a single feedline. And I already have appropriate diplexers.

Sent from my Nexus 5 using Tapatalk

Henry Cohen

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Re: Leaky Feeder Coax
« Reply #4 on: April 20, 2018, 09:18:01 pm »

Whereas signal attenuation through radiating (leaky) coax is comparable to standard coax of the same dimensions and general shield construction, the most significant factor with radiating coax is coupling loss.

If one considers a traditional UHF band antenna, the coupling loss - the transfer of energy from one medium (current in a physical conductor) to another (electromagnetic wave); in this case, the mathematical ERP value in dBm from the antenna to a point in space generally measured at one meter - will be about 20dB. In other words, whatever the effective radiated power level calculated at the antenna, one meter away will be about 20dB less.

Coupling loss with typical radiating coax tuned for UHF band will be about 78 to 82dB at one meter for 90% coverage (meaning that the radio system as fed by the radiating coax will provide 90% reliability as compared to an antenna at the same field strength). Coupling loss is such a significant factor that it is a standard specification provided by manufacturers of radiating coax. Given the tremendous coupling losses, radiating coax is generally used only in long narrow applications: hallways, transportation tunnels, train platforms, mine tunnels, catwalks and the like, where the portable radio device is never more than a defined distance from the coax. With modern engineering and manufacturing processes, radiating coax can be tuned rather tightly for a given frequency band(s) as well as a defined radiation pattern, both of which can reduce the coupling loss  by 3dB to 5dB.

Using radiating coax in non tunnel/hallway type locations usually does not work well unless a significant amount of TX power is provided, or very careful filtering and pre-amplification for RX, is utilized, and even then it will rarely be better than a proper antenna(s).

But in long hallway or pedestrian tunnel, radiating coax works great, given proper initial system RF gain structure. And yes, Jason, diplexing RAD outbounds and inbounds over the radiating coax works very well.
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Henry Cohen

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Scott Holtzman

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Re: Leaky Feeder Coax
« Reply #5 on: April 21, 2018, 05:13:09 am »

Henry,. 25 years ago we lit a hospital with a 75w uhf micor at the top of the elevator shaft and ran the radiax down the shaft with a dummy load at the bottom.  We then put 8 or ten rx chassis with a spectratac voter for the RX.  We also paged over the channel.  It worked very well.  Talk out was good.   I can't imagine it would work well for low power or receive applications.



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Scott AKA "Skyking" Holtzman

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ProSoundWeb Community

Re: Leaky Feeder Coax
┬ź Reply #5 on: April 21, 2018, 05:13:09 am ┬╗


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