I often ask, why purchase when building is easy,quick, and saves
substantial cost.
This does not appear to be an item that would see wide use in industry.
OTOH, It takes little time to build one of these and they do not
necessarily need to be in a box. I prefer, out-in-the-open if possible
with this construction. It takes but a few minutes to wind two chokes
and put them in series. Then it becomes a question of what is your time
worth and do you need that much band width? In industry, the recharge
rate can be inordinately high. My time per hour as a project manager was
far higher than a tech. Still, depending on the corporation it may, or
may not be cheaper to buy or build. If I, as a tech, even with a high
recharge rate, have to consider the cost of ordering components Vs the
completed item.. I have to figure my time in the field Versus going
back to the stock room to get the parts,Vs planning ahead. Figuring the
cost of the item installed Vs built on site can be a complicated issue.
Having been both a tech in my early days and a project manager until
retirement after college, I was in a position where I had to evaluate
those cost differences. Quite often, where time was a consideration AND
we had techs with the skills, build on site was by far the cheapest when
it came to completing on time. There were other times where buying was
far cheaper.
As hams, we. are not normally in a position where those decisions are of
any importance whether I figure my time is valuable or not.
With chokes, I evaluate on-the-fly and build as I go. Ordering and
waiting for a simple to build item is seldom worth purchasing. As I
have an ample stock of parts, I can build, install, and use in the time
it takes to go back to the shop and order, so the decision is an easy
one to make as well as building for a quarter to a third the cost of
purchasing. For me the same is true of BCD decoders and remote switch
controllers.
OTOH since I lost the use of one hand, building is often not an option,
except for simple objects like chokes.
73
Roger (K8RI)
On 4/19/2016 Tuesday 1:27 PM, jimlux wrote:
On 4/19/16 10:06 AM, Jim Brown wrote:
There's something I don't understand here. In 2007, I published the
research upon which all of this is built, with measured data for a broad
range of chokes for the ham bands, and with full instructions for buying
the cores at very good prices, and a "cookbook" for the various ham
bands. Why in hell would you want to pay someone 3x the cost of doing it
yourself, when all you have to do to do it yourself is wind turns of
coax through ferrite cores?
Time's not necessarily free? For example, you can buy a spool of AWG
12 house wire and improvise all manner of insulators to make a dipole,
but sometimes it's nice to have all the stuff in a bag so you can hand
it to someone and say "put it up in the air", no soldering, no other
stuff.
We're often in a situation at work where we are short of people
resources and have money, so buying something that's already assembled
is expedient and "gets the job done".
So then, your incredibly useful report becomes something with which to
evaluate the design of a purchased widget.
AND -- l would not trust any published power ratings for ANY chokes
without understanding the common mode voltage that they will see in any
given installation. To do that, you've got to put them in an NEC model
that approximates YOUR installation. Simply putting one of these chokes
in a sealed enclosure greatly reduces its power handling because it
greatly reduces air flow around the choke.
Power ratings for amateur radio products are pretty non-standardized
and speculative in general.
73, Jim K9YC
On Tue,4/19/2016 3:30 AM, Jim Thomson wrote:
I just received a pair of CMC-230-5K common mode chokes...from
MyAntennas.com to experiment with.
They are configured as a line isolator, with silver-teflon SO-239s
on each side. They can also be configured as
a balun, with a pair of standoffs on the balanced ant side if you
like. Extremely well designed and built, better
than I expected.
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73
Roger (K8RI)
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