Pi * r squared is area of a circle. What you will need is 2 * pi * r, or pi
* diameter, which is circumference. However, this is accurate only for the
turns on one radius. You can get fairly close by counting the outer turns
across the reel, then estimate how many layers there are to the inner layer,
then adding all together. Calculate circumference using r measured from
center of layers to center (axle) of reel, and multiply by total number of
turns.
OR
Consult manufacturer's label (assuming it is still affixed)
OR
Simply unwind and measure with suitable tape measure.
If none of these methods are chosen, it may be that there is more on the
reel than is easy to handle. For example, I have a roll of Kevlar 12 gauge
rope that may be twisted with copper wire to make an exceptionally strong
suspended wire antenna. I am not about to unwind it to see how much there
is. I am just going to guess it is about 1000 feet based on the size
compared to a reel of similar size twine.
73, Keith NM5G
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Matt Patterson
Sent: Thursday, October 06, 2005 2:05 PM
To: Pat Barthelow; dolanmorrison@tiscali.co.uk; towertalk@contesting.com
Subject: Re: [TowerTalk] Cable on a reel using a formula?
Isn't the formula pi * radius(squared) * the number of turns what you need?
Been a long time since I did any geometry...
Matt
----- Original Message -----
From: "Pat Barthelow" <aa6eg@hotmail.com>
To: <dolanmorrison@tiscali.co.uk>; <towertalk@contesting.com>
Sent: Thursday, October 06, 2005 12:22 PM
Subject: Re: [TowerTalk] Cable on a reel using a formula?
>
>>How
>>to calculate the amount of cable on a reel using a formula?
>>Anybody know this formula.
>>GM0LZE
>
> I used to have an Allied Electronics reference guide from the 60s
> That had a formula for big audio inductors where the bobbin
> dimensions(diameter and spool length)
> the wire diameter were entered and it could calculate inductance,
> resistance....
>
> Hmmm...mebbe a better way...er two better ways...if the cable is newly
> manufactured, it often
> has foot or metre markers with numbers marked on the jacket every
> foot..look at both ends and subtract...but that would be too easy.. so
> probably not an option in your case...
> If Coax, and very long, take a good hi res ohmmeter, short one end, and
> measure the
> loop resistance and look up the factory loop resistance figures for that
> kind of cable..so
>
> Maybe some old solenoid design engineering formulas can be had to do the
> trick....
>
> Or, Get an MFJ 259B, and connectorize the free spool end, and use the
> legth
> function of the 259B to calculate the length to the end...
>
> 73, DX Pat AA6EG aa6eg@hotmail.com
>
>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
> Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with
> any questions and ask for Sherman, W2FLA.
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|