rf probe

[Jesse & Nicky]

I guess I am missing something here.  Why do the banana plugs have to be connected with rg 174 coax ??

If I have to use coax is there a "trick" to unraveling the braid ??
I cannot seem to get the tips of the banana plugs to accept solder.

As always, any help or advice would be greatly appreciated.

73 de Jesse w6jmm
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[michael taylor-3]

On 6/16/06, Jesse & Nicky <[hidden email]> wrote:
> I guess I am missing something here.  Why do the banana plugs have to be connected with rg 174 coax ??

The use of coax is AFAIK* to prevent the probe from picking up stray
RF energy from the powered up radio under test. The banana plugs are
used as the standard connectors to a DMM.

> If I have to use coax is there a "trick" to unraveling the braid ??
> I cannot seem to get the tips of the banana plugs to accept solder.

I used my wire cutter to make a parallel cut to the braid (parallel to
the length of the cable) to allow the braid to pulled to one side of
the insulation and then twist the braid into a "wire."

This might not be the best solution, but I filled the small hole in
the banana plug with solder, heated the solder, and let the braid (and
repeat for the wire inside the coax insulation) rest in the pool of
solder until it cools enough to hold it in place. Remember to put the
plastic covers inline before soldering.

> As always, any help or advice would be greatly appreciated.

I hope that make sense, and is useful to you.

*) AFAIK = As Far As I Know

-Michael Taylor, VE3TIX
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[ON4WIX]

Hi Jesse,

just read your post re the RF probe.
Your questions concerning the use of banana plugs are already answered so I'll have a go at the braid unraveling question.
I'm using a very small copper brush. It looks like a toothbrush but the brushes are made of copper wire.
After having cut away the outer sheath, I use the brush to "comb" the braid along the axis of the coax, combing from the sheath towards the end of the cable. It may take a few minutes of "combing" but this results in a set of perfectly aligned copper wires, no sign of interleaving or braid. Then it's really a piece of cake to separate them from the cable.

Hope this helps.

73 es gud DX

Glenn ON4WIX
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[Ron D'Eau Claire-2]

With smaller cables like RG174 (or even RG58) I sometimes do what Glenn,
ON4WIX does, using a brush or fine pointed tool to "unweave" the braid.

Most often I use another technique that does *not* require un-weaving the
braid. I cut the jacket back and then use a fine pointed tool to push the
strands of the braid apart to open a space where I want the center conductor
and braid to separate. This can be done without breaking any braid strands,
especially if you push the braid back from the cut end a bit to make it
expand slightly around the center conductor where you want to make the
opening, then push the strands aside with the pointed tool. Then, by bending
the braid and center conductor together, I make a loop in the center
conductor that I can tease out through the opening in the braid so I can get
my pointed tool through the loop and pull all of the center conductor from
that point to the cut end through the hole. Pulling the braid tight again, I
now have the braid and center conductors neatly separated. Finally I strip
off some insulation from the center conductor to expose enough to solder.

Ron


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[Matt Osborn]

I find that the shield is not particularly flexible and soon breaks
and unravels. With RG-174, just cut the shield back, leaving approx.
1/16" exposed beyond the outer wrapper. Wrap a flexible piece of
stranded hookup wire around the exposed shield and solder it to the
shield.   Cover the exposed shield/solder joint with some shrink
tubing and solder the other end of the hookup wire to wherever its
going.

Hookup wire survives flexing much better than the cable shield.



On Fri, 16 Jun 2006 10:43:09 -0700, "Jesse & Nicky"
<[hidden email]> wrote:

>I guess I am missing something here.  Why do the banana plugs have to be connected with rg 174 coax ??
>
>If I have to use coax is there a "trick" to unraveling the braid ??
>I cannot seem to get the tips of the banana plugs to accept solder.
>
>As always, any help or advice would be greatly appreciated.

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[Stuart Rohre]

Another classic way of using coax braid, is to push the braid back up the
central conductor, after removing the outer vinyl jacket.   Once you "bunch"
the braid, it spreads out and you can use a sharp pointed tool to make a
hole by spreading the crossed strands.  Using the pointed tool or a hook
tool, pull the insulated center conductor back thru this hole by folding a
"U" shape, and hooking the U to pull it thru the braid hole.  Now you have
the flat braid as one conductor lead, and it will not unravel past the point
it is penetrated by the central insulated wire.  Proceed to tin and then
solder the braid in into the cup of the banana plug; and tin, then solder,
the center wire into the other banana plug cup.

Stuart
K5KVH


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