On 4/16/12 8:55 AM, Jim Brown wrote:
> On 4/16/2012 7:30 AM, Jim Lux wrote:
>> I think it's in a zone of "cost to build yourself, counting time" and
>> "buy retail" where it just doesn't pencil out.
> Jim, we're at cross purposes here.
> Somehow, you're missing the point that my primary beef with commercial
> products is not their cost, but simply that their designs are so bad
> that they are essentially useless. The technical basis for this
> statement is developed in considerable detail in several pieces that are
> on my website.
Oh.. I agree with you there.. my question is really directed at "why are
there no decent chokes available"... As you say, the design is
basically done (you've done it, lots of people have built and tested
So why are they not being offered for sale? (a lesser question is why
are ineffective things still being sold, but hey, that's the whole
> With almost no exceptions, there are virtually no technical specs on
> so-called "baluns" beyond power rating -- the only exception I've seen
> is for a few of Array Solutions' chokes, for which impedances at a few
> frequencies are published, but they're strings of beads, they aren't
> very good chokes. By contrast, the response curves of the W3NQN filters
> ARE published, and anyone who has built high performance filters knows
> that engineering that goes into building them makes them worth the cost.
yes.. and that's why I picked that kind of thing as an example.. to show
that it *can* be done, and that the sell price roughly corresponds with
the BOM cost (as best I can estimate it).
I think the material:sell price multiplier for a choke could be less.
The choke is a MUCH simpler device, and much more tolerant of
manufacturing variability. But a lot of the cost is really a "per item"
cost, and not really a percentage of the parts cost (that is, the cost
to put a filter or a choke in a box and ship it is basically the same).
> Except (possibly) for protection from freeze/thaw cyless, there is no
> good reason for a common mode choke consisting of winding multiple turns
> of coax through one or more cores to be in a box at all!
I was thinking about the brittle cores. I have lots of "bare" chokes
built to your recipe, and every once in a while I drop one on the
concrete, and it breaks.
Probably doesn't need to be a box.. some sort of cushioning sleeve would
probably work as well, or just putting it in a piece of PVC pipe.
There's also the whole "which gender connectors do you want?" question..
Someone wanting to sell it as a product could just decide and move
on..it doesn't change the pricing significantly.
> consists of running the coax through the core(s), and if there are
> multiple cores, lashing them together with ty-wraps. If they're on a
> wire dipole, or on coax coming from a vertical, you're done. If they're
> on a typical beam, the coax at both ends of the choke simply must be
> mechanically secured to the boom. The only reason for putting this kind
> of choke in a box is so that you can sell it to someone!
yes.. and you could probably sell bare chokes..
But the box cost is a tiny fraction of the ferrite cost. A buck or two
for the plastic box/tube/what-have-you vs the 30-40 for the toroids.
So why not put it in a box (tradeoff between power handling/dissipation
> The lower cost bifilar-wound chokes I've designed that DO require some
> sort of packaging, but I'm not at all convinced that they needs to be in
> a BOX. What IS needed is a means of adding SO239 connectors and strain
> relief so that they can be patched into an existing transmission line.
> My neighbor, W6GJB, who is much better with mechanical design than I am,
> worked up a nice method that uses PVC plumbing parts to hold the
PVC plumbing stuff is my goto material, as long as it's free hanging and
doesn't need good UV resistance (well, you can paint it). Rectangular
boxes (like the Cantex electrical boxes) are nice when you want to stick
it to something (VHB double sided foam tape is my preference.. lasts
forever, takes up small misalignments, etc. They use it to do stuff
like hold windows into skyscrapers.)
> I'm quite willing to pay good money for good products -- there are two
> K3s and two Ten Tec Titan amps on my operating desk in an SO2R setup,
> and both have W3NQN filters between K3 and power amp that were purchased
> from Array Solutions. Thanks to 40+ years employment in engineering,
> technical sales, and consulting, I have a pretty good grasp on the cost
> issues you've outlined, and I have no quarrel with them.
So how do we purge the useless dreck from the market?
Or is that a forlorn hope?
(tradition dies hard...)
TowerTalk mailing list