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Re: Braided or Smooth Strap?
>Date: Fri, 15 Nov 1996 23:19:30 -0700
>From: Tesla List <tesla-at-poodle.pupman-dot-com>
>To: Tesla-list-subscribers-at-poodle.pupman-dot-com
>Subject: Braided or Smooth Strap?
>Reply-to: tesla-at-pupman-dot-com
>myfiles
>>From richard.quick-at-slug-dot-orgFri Nov 15 23:09:18 1996
>Date: Sat, 16 Nov 1996 03:42:00 GMT
>From: Richard Quick <richard.quick-at-slug-dot-org>
>To: tesla-at-poodle.pupman-dot-com
>Subject: Braided or Smooth Strap?
>Quoting Doug:
>> I'm nearing the completion of constructing my first coil
>> system, and have been assuming that I could use a large
>> diameter hose clamp (metal) to secure the ground strap braid to
>> the base of the secondary coil's tube.
>Quoting Malcolm:
> > , throw the braid away and use pipe, copper strap, v. thick
> > wire, *anything but*.
>Quoting Robert W. Stephens <rwstephens-at-ptbo.igs-dot-net>:
>> Wassamatta you don't like braid? I'm starting to use it a lot
>> now that I have some in stock. Picked up a beautiful roll of
>> 1.5 inch wide, tinned copper braid at the last hamfest. I like
>> it partly because you can squish it into a large crimp
>> connector at the end (I always solder after crimping as a
>> matter of good practice). Are you poo-pooing it because of
>> something you have been told, or do you have actual pulse
>> propogation test results in a research paper. If the latter
>> is true I'd love to get a copy of it.
>No, I agree with Malcolm on this, and we have both measured this
>effect: Braided strap has a markedly higher RF impedance than
>smooth strap (like strips of metal flashing). As Malcolm states,
>even a length of #14 solid copper wire has better RF qualities
>than a 1/2" wide braid strap.
>I have seen a braided groundstrap raise the dip of a coil on the
>scope, a measurable decrease in coil Q that can easily be
>reversed by swapping over to a smooth groundstrap.
>I still use braided groundstrap, because like you, I found a deal
>and stocked up (before I discovered how lousy it is for Tesla
>coiling); but I only use it on the 60 cycle side of my RF ground
>(pathing the transformer cores, cases, safety gap, etc., to the
>RF ground). The coil and all of the strike shielding is pathed
>with wide, smooth, flat, and cheap AL flashing to the RF ground.
>**********IMPORTED**POST*****************************************
>>From MALCOLM-at-directorate.wnp.ac.nzThu Nov 14 21:55:51 1996
>Date: Fri, 15 Nov 1996 08:30:11 +1200
>From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
>To: tesla-at-pupman-dot-com
>Subject: myfiles
>Hello all,
> My post on the braid was questioned (and reasonably so).
>Here is a post I sent to the list late last year that might help
>explain my stance on this one.
> ------- Forwarded Message Follows -------
>PERFORMANCE OF WIRE
> The following is a summary of a brief investigation into wire
>performance at low radio frequencies.
> Six wires of various types were tested. Copper strap was not
><SNIP>
>solid section wires performed well in small diameters. Departure from
>this was noted as significant for a thickness of 0.063mm (c.f. skin depth
>of 0.15mm at the test frequency).
> Personally, I'll never use braid again in an RF application!! Imagine
>how a few feet of this detracts from primary performance if it is included
>within the tank circuit.
>**********END**OF**IMPORTED**POST***************************************
>... If all else fails... Throw another megavolt across it!
>___ Blue Wave/QWK v2.12
Richard Quick and Malcolm,
Thank you both for your input on this subject. Malcolm, that test
data you re-posted for my benefit and that of others was most
interesting. Implications would appear that even the wire used to
wind the secondary should bear more consideration. In my two cases
to date of larger coils I have used #12 AWG THHN tinned copper stranded,
plastic insulated wire, PVC with a clear nylon outer sheath I think, and #18
AWG, PVC coated stranded tinned copper. Malcolm, your test results
indicate that silver covered, solid copper wire with Teflon or
Polyethylene outer sheath would be the best secondary wire for a
large coil system. Here I was proposing to possibly wind a large secondary
with RG-59, employing the outer shield as the conductor. Guess I'll
have to re-think that one!
The demonstrated effect that a lossy plastic covering over the wire
which is in intimate contact with the skin depth of copper doing the
work is interesting indeed, and this is seen on a piece of wire
stretched straight where the interturn capacitance effect of a coil
wound with the stuff does not apply.
I recently posted the details of the large primary tank coil which I
wound for my Coronatron vacuum tube oscillator employing the outer
double braid, silvered shield of RG-214 coax as the active conductor. I left the
PVC outer skin in place. I have had zero opportunity to gather any
accurate test data on it as yet, other than calming my concerns that it would
overheat at the 10-15 kilowatt levels proposed. Tests so far at 5 kW
RMS show that it can run for about 5 minutes continuously before it
gets dangerously warm for the plastic insulation. At 10 kilowatts
this time will be cut in half. This should therefore not be a
problem for a device that may only be operated up to a minute or so
at a time in laboratory work. I am very curious to see what the
difference may be if and when I replace this 30 turn tank coil with
3/8" copper refrigeration tubing (this is the largest diameter that
will fit in the coil form combs).
Have either of you considered 'why' bare coax outer braid is poor?
Is it because the individual wires which are woven together do not
'talk' to each other contact wise at RF and what we end up with is,
by the nature of the weave, a whole bunch of parallel conductors, ala
litz wire, but measurably longer than the actual length of the
finished cable. Such that a 10 foot section of coax in this series
resistance concept, actually represents a 15 foot or so length which
makes it measure poorer than a real 10 foot length of solid single
wire? Or is it merely that the plastic which insulates and accurately
positions the inner conductor conductor acts the same way as a
spoiler that a plastic outer sheath can have. This should not be so,
as the plastic employed inside the coax is the good stuff (polyethylene).
Very thought, and concern provoking gentlemen!
regards,
rwstephens