Glad you rang in, Jim.
I haven't looked at anything other than lumped LC at this point. I
should look at the alternatives. I'd probably learn something.
In the meantime, thanks to other responses I located and purchased a
number of affordable NOS doorknob capacitors from eastern Europe which
ought to work just fine.
--
Art Greenberg
WA2LLN
art@artg.tv
On Mon, Aug 14, 2017, at 13:46, Jim Brown wrote:
> Interesting design problem. In addition to voltage breakdown, an
> important issue with capacitors for this application is ESR. The cheap
> stuff you found don't satisfy that. I did something like this on a 160
> Tee vertical, for which I needed series C in the range of 800 pF.
>
> I'm lucky enough to live an hour from one of the few remaining
> electronics surplus warehouses that used to be so plentiful in our major
> cities. http://www.halted.com/ I was able to browse the aisles and find
> a wide range of suitably rated capacitors, and bought a bunch to stock
> my junkbox. Without access to doc on their specs, I performed the simple
> test of putting them inline with the antenna feed, transmitting for a
> while at full power, then giving them the "touch" test to observe
> whether or not they were heating up. Enough passed that test that I was
> able to use various series/parallel combinations to get what I needed.
> Unfortunately, I doubt that the contests of these bins are listed
> online. :)
>
> Another suggestion. Have you considered designing a network using coax
> stubs? Or suitable lengths of coax as a capacitor? SimSmith is a great
> tool for doing that. Export the Z file from your antenna model to
> SimSmith and see what you come up with. I don't pretend to be an expert
> on voltage ratings of coax, but I do remember hearing that published
> voltage ratings are often for the outer jacket, not the dielectric.
> Perhaps voltage ratings could be inferred from power ratings. I'll bet
> that someone on the reflector knows more about this. :)
>
> SimSmith will compute dissipation in circuit elements, including coax,
> if loss data for the components are known and entered, and it includes
> data for lots of commonly used coax. Loss in coax below UHF is all I
> squared R from conductor resistance (center plus braid), and thanks to
> skin effect, loss is pretty low below 10 MHz.
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|