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Author Topic: coax cable questions  (Read 646 times)
KD8DDW
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« on: April 14, 2006, 08:10:06 AM »

A comerical tower has come down in our naborhood and i got some coax. This coax is helax coax and i was wondering what frequencies you chold use it on. I would relly like to use it on hf is that possible.
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K5LXP
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« Reply #1 on: April 14, 2006, 08:52:48 AM »

It's way overkill for HF but it is certainly useable there.  Something to consider is the use of a combination of diplexers and triplexers and use one run of this coax for all your antennas from HF through UHF.

Mark K5LXP
Albuquerque, NM
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K6AER
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« Reply #2 on: April 14, 2006, 08:56:33 AM »

Heliax is going to work just fine for ham use. Losses at HF are very low and not much is saved by using heliax over good coax such as LMR-400. If your use is 10 meters or higher then heliax becomes a viable option to mitigate losses.

You need to know what the diameter is such as ½ inch, LDF-4 or 7/8, LDF-5. In general the larger the heliax the lower the loss. The larger coax connectors will cost more with ½ inch costing about $35 and 7/8” costing about $80. Very large coax connectors such as 1 5/8” will cost up to $200 each. Most commercial connectors will be for “N” type of connectors. Heliax will have a minimum radius bend and below that bend radius you can kink the heliax. Not all Heliax is the same. Of the corrugate type you can have a spiral or stacked dimple in design. There is also smooth wall heliax (trade name) like the Comscope which is becoming very popular for the connectorization and installation cost is much lower.
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WB2WIK
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« Reply #3 on: April 14, 2006, 09:04:19 AM »

Heliax is a trade name like Kleenex or Frigidaire.  It doesn't describe much of anything except who made it (Andrew).

What diameter is it?

And, what kind of HF antenna do you plan to use with it?

WB2WIK/6
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KD8DDW
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« Reply #4 on: April 14, 2006, 09:14:23 AM »

It is about 1 inch and i might put up a dipole or yagi.
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KB4EMF
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« Reply #5 on: April 14, 2006, 10:24:09 AM »

Well....  provided the coax is not damanged you could use it for any frequency of your choosing.  Just remember, the connectors are very expensive and the cables are very difficult to handle due to its diameter and stiffness.  Unless you have hundreds of feet to go, using such coax is a gross overkill for HF, although if you already have it, there's nothing wrong with using it.

Also, many heliax type cables have hollow dialectic.  (spiral)  That means if you get any water in it, it will come right out of the other side....

If it's in good condition, you might want to save it for VHF or UHF use later.  
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WB2WIK
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« Reply #6 on: April 14, 2006, 10:57:18 AM »

Heliax isn't made in "one inch" size, but it might be 7/8", which comes out to about one inch diameter when you include the vinyl jacket (coating).

You wouldn't use that to feed a dipole unless the center of the dipole was supported by a tower...because the Heliax would weigh a hundred times more than the dipole does, and pull it down to the ground.

For a yagi or any sort of rotary beam, you can use Heliax like this going from the station up the tower to the rotator, but you must stop it there and splice it to flexible line above the rotator.  7/8" Heliax cannot be repeatedly flexed and will not work going around a rotator.

WB2WIK/6
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KA0GKT
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« Reply #7 on: April 14, 2006, 01:46:23 PM »

Google the manufacturer and model number which ought to be printed somewhere on the jacket of the coaxial cable.

Corregated solid copper shielded cable comes in many flavors.  The lowest loss are air dielectric which must be pressurized with dry air, nitrogen or other gas in order to keep the cable dry, however flexible hard line is available with a foam dielectric as well.

One other thing to remember is that hardline is available in the 75-Ohm flavor as well.

While your heliax will be outstanding at HF, the cable's low loss charecteristics really shine at VHF and above.  You might consider using it for 50 MHz and upas opposed to the HF region unless you plan to use legal limit power into a moderately high vswr at high duty cycle.

73 DE KAØGKT/7

--Steve
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K5DVW
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« Reply #8 on: April 14, 2006, 05:08:16 PM »

Spell check on aisle 12!
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KC8VWM
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« Reply #9 on: April 14, 2006, 05:43:11 PM »

lol kd5vw
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