----- Original Message -----
From: "Michael Tope" <W4EF@dellroy.com>
To: "Jim Lux" <jimlux@earthlink.net>; "Rob Atkinson, K5UJ"
<k5uj@hotmail.com>; <towertalk@contesting.com>
Sent: Monday, February 21, 2005 9:50 AM
Subject: Re: [TowerTalk] RF Inquiry HI-Q Filter CF5KV
> Cable Xperts advertises that they will build custom coax jumpers
> to order. It wouldn't surprise me if you could arrange to send them
> the beads and let them do the assembly. Might be a good thing
> for a group buy.
That's half way to a solution. If you're buying toroids in real quantity,
they get a LOT cheaper (from reduced shipping costs, if nothing else). I was
just thinking that there are several suppliers of bead baluns in a PVC pipe.
Would it affect their sales materially if they were to tell you what
material and how many beads of what size? Probably not, and then you could
buy the product without worrying about what the performance might be.
I can understand that if there were some proprietary design that they didn't
want to have stolen, but I don't really think that's the case here. The NRE
for this kind of product is very, very low, and the fraction of time spent
figuring out what beads to use is correspondingly low (assuming they don't
just copy the design out of a handbook). Therefore, the only real
distinguishing feature between the various makes is the manufacturing cost
and quality, which is something that will be different for a competitor (not
necessarily better or worse, but just different). For instance, a mfr might
get a real good price on beads that another didn't. (perhaps due to large
quantity, or physical location, or just better shopping around), but
ultimately, the beads are a commodity item.
You bring up an interesting idea, though. Maybe CableXperts would be
willing to do all the steps, including procuring the ferrites. Sometimes,
all it takes is an indication from the market that a product is needed.
You can also just buy a pre-made RG-8X jumper
> and wrap several turns around an FT-240-77 core if you need a
> good common-mode choke for the lower HF bands (2 cores
> in series with 6 turns each will give about 1100 ohms common-
> mode impedance on 160 meters and 900 ohms on 80 meters).
> You can easily get 5 or 6 turns through the core even with PL-259's
> installed. Cost would be about $15.00 for the jumper and $10 for
> the 2 cores. If you need better suppression towards the middle of
> the HF range, you can substitute FT-240-43 cores in place of the
> -77 ones. The 43 cores will give an impedance peak around
> 12 MHz.
>
> 73 de Mike,
> W4EF.................................................................
>
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