The AM Forum

Hello to all,

Anyone know of a supplier for large o.d. UV insulated round braided cable?

The desired o.d. is 1/2 inch round braid plus the UV insulated jacket.

This is for a home brew ladder line project.  I am trying to prevent from buying
coax cable and having to cut the center conductor ends off.

Thank you.

Chuck

 

Why not just solder the center conductors to the braid?

Hi Pete,

Yep, I have done that in the past, soldered
the coax center conductor to the braid.

however, if I am buying new cable I do 't want to pay for
extra copper, center conductor, when I don't need it. 

Chuck

If you do find it, I bet it won't be cheap. Coax stuff is far more common and probably would result in a cheaper price and achieve the same goal.

Exactly what I was going to tell him.  Commonly used cables are always cheaper than something that is rarely used, (with the same amount of copper).

Fred

Anyone else?

I agree with that, RG58CU or RG59 is far more cheaper than a big round cable of copper. An alternative what I use is thick isolated loudspeaker cable.
This is what I use for my antenna and feeders.

Martin

CATV, aka "cable tv" 75ohm coax is dirt cheap still.

If you run into an installer, you may get the ends of some rolls gratis...

I've seen rather large rolls of this "don't wanter" stuff at hamfests quite often.

Of course the center conductor is copper plated steel and will break if flexed too much, but for your
application, should be perfecto.

---------------

PD0RRT, Martin, you use it as-is, or split the wires and make up spreaders?
How much power do you run, IF you use it as-is??
What sort of impedance did you figure it to work out to??

                                          _-_-bear


PS. do you really need the equivalent of two RG-8 braids in parallel for OWL as far as power handling?? Or?

@WBear2GCR: I don't split the wire up, but use the two conductors in parallel.
This loudspeaker wire is an excellent antenna wire because it is so flexible and the isolation is transparent and this looks nice.
What I use is (two conductors of) 1,6mm diameter wire, this is similar to AWG14.
There are larger diameter loudspeaker wire's up to AWG11 (4mm diameter).
The power what I use is approximately 300Watt on 1,8MHz, the antenna is a shorted dipole made in resonance by the ATU.
The feeder is only 12 to 15 feet.

Another great stuff for antenna wire and feeders is Flex-weave, you can find this at Davis RF: http://www.davisrf.com/antenna-wire/flexweave.php (http://www.davisrf.com/antenna-wire/flexweave.php)

Martin

Looks to my eye that the "Flexweave" conductors are very similar to what is used in the high quality speaker wires... I guess this is ok for the legs of an antenna.

I have to admit that I have never heard of using speaker cable for OWL!
My suspicion is that the characteristic impedance is rather low compared to traditional OWL.
Also, my guess is that at 300w ur probably near or at the breakdown limit for the insulation and spacing.
Perhaps not so much of an issue where there is a good match on each end, but maybe not bulletproof
if a problem comes up on the antenna side of things?

Ah, but maybe ur talking about using it for only the antenna legs, in which case, no worries!
Except for maybe stretch.

I thought the OP wanted to use whatever he was looking to do was to use something for OWL, not
the legs of the antenna, but seems I am confused again!

                        _-_-

I think that I have expressed myself wrong. I use two loudspeaker wires for each leg of the feeder and antenna.
The spacing between the wires is about 8 inch.
So each wire have 2 conductors of AWG 14.

Ok!

Well that ought to be good for several kW at minimum!!  ;D


                 _-_-

Hi Guys,

I am looking for 1/2 inch o.d. copper braid (not including the outer jacket) because two 1/2 o.d. cables spaced 3 inches gives us approximately a 300 ohm open wire transmission line.

This is the goal.

Chuck

How do you want to keep support of the OD of a copper tube braid?

here is the braid itself:
Alphawire.com
    2174    Tinned Copper     Tubular     0.5          62     A-A-59569A
   94015    Tinned Copper     Tubular     0.5               
   96022    Silver Plated Copper     Tubular     0.5 


Just slip some 0.45 OD nylon tubing into it, and apply some protective insulation to it or slip it into another nylon tube. I assume it has to retain a tubular shape to be useful?

Or, slip the copper braid tube into an outer insulating tube and fill with great stuff white expanding foam which remains flexible and it'll keep it totally tubular..

If you just want to order it, these people can provide you what you want.
http://www.coonerwire.com/tubular-braided-wire/
or
http://www.erico.com/newsdetail.asp?newsid=56

I haven't looked at the equation in a long time, but are you sure about your numbers??  1/2" cable three inches apart doesn't seem correct for 300 ohms.  Maybe I'm wrong.

Fred

Hi Fred:

Here is the tool I used to calculate the 300 ohm impedance numbers.

http://www.smrcc.org.uk/tools/OpenWire.htm

I plugged in .250 inch radius spaced at 3 inches to arrive at approximately 298 ohms.

Chuck

Opcom,

Sir, yes the braid should be round with supportive dielectric
in the center and a protective jacket on the outside.

Chuck 

Why braid??
Why not wire?

Why such a large diameter?

Why not make the braid *flat*??

Then insulating it becomes relatively simple.
It still works as a conductor.

Etc...?

              _-_-

                 

The geometric mean impedance between 75 - 1200 ohms is 300 ohms.

The geometric mean impedance between 72 - 5000 ohms is 600 ohms.

A 300 ohm open wire feeder will have lower voltages than the 600 ohm feeder.  I can use smaller spaced air gaps with my air variable capacitors. 

I need a minimum 3 inch distance between the two conductors to help prevent snow and ice
build-up on the ladder line.  A 1/2 inch o.d. round conductor space 3 inches center to center achieves the goal of 300 ohms.

Because of skin effect I though it would be better to go with a tube or round braid rather than solid copper wire.  Most of the solid wire at 1/2 inch o.d. would not be used at RF HF frequencies.  

Flat would work but I don't know how to calculate for the 300 ohm impedance?  The above calculator is measured in round radius of conductor and not flat.

Hope this helps.

Chuck

1/2" solid copper would be expensive and very heavy for OWL.  Even something like RG-8 which is near a 1/2" would be very heavy.  Try to redesign what you're trying to do.  Maybe go up in impedance and use wider spaced caps.

I agree, solid cable or wire are to heavy.

I would like to stick with the 300 system and give it a try.

Chuck

The spacing does not need to be exact. Trying to be too fine is not terribly useful.

300ohms +/- 50ohms is nothing much, imo.

Iced up ladder line is plenty heavy. :D

Scaling the conductor size to the power likely to be seen is a good idea.
To me RG-59 CATV wire seems like what you want/need still... that braid is plenty
sufficient. Skin effect plays not much of a role at 3.5mhz or 7 mhz. imo.


                                 _-_-bear

Sorry, but which means OWL?

OWL is an abbreviated (short) expression for  "OPEN WIRE LINE"  as used for balanced transmission (feed) line, rather than coaxial cable   (unbalanced) for a wire  or, for that matter, any antenna...

GR-59 would require about a 1.5 (1.45) inch spacing to achieve
an approximate impedance of 300 ohms.  1.5 inches would not
work with snow and ice.  It would load up with snow real easy. 

In a weather mild area of the country this would be an good choice.

Chuck

Ok, then it seems I understand next to nothing about the relationship between wire gauge and spacing for OWL.

1/2" dia is much fatter than RG-59CATV coax, and 14ga is thinner... so which way does the spacing go with wire diameter?

I don't know where you live,  or the weather,  but here in central California I burned up #10 wire,  spaced 6 inches.   Snow and ice buildup......   It will cross at your spreaders.

Also flashed over the contacts in my Johnson matchbox (mini model.   If since upgraded to a manly tuna).

My weather wasn't normal up on the hill,  but I know it's a lot worse in other places (except the wind.   130 sustained was no laughing matter)....

--Shane
KD6VXI

Ya mon! Now that is impressive. Burning up #10 takes some powah!!

You must be one of those "Kalifornia Killowatts" that I used to read about!

Just thinking out loud, I'm not sure that standard insulation/jacket would stand up in those conditions?
I must say that I am extremely impressed by your arc welding in the air capabilities.  ;D

Curious, had the matchbox's setting changed to get a match when ur feeder was iced up on the day you burned it up? Do you have an RF ammeter in the legs? Does anyone do that?

Would a pair of big (like 200-300w) lightbulbs in series with each leg act as protection? The idea is that in series there would be not much vdrop - but I am a bit fuzzy on this idea.
 

                      _-_-