Wow, it is complicated ... no ones ever figured that out and give me an
answer? I should have known, ask 100 hams an opinion and you'll get 200
(at least) opinoins, non with a direct answer!
Guess I'll have to bake a few plastic boxes and find out for myself,
once I get back up home and can run some power!
tnx all, I love it!
73 de ns9i ... dwn here in the balmi 60 deg F
On 2/1/2011 9:11 PM, Kevin Normoyle wrote:
> On 2/1/2011 6:20 PM, DGB wrote:
>> .... and I repeat .... is it acceptable to enclose it in a
>> non-conductive enclosure, on a multiband antenna, say resonant on 160 or
>> 80, especially at high power (1500w)?
>>
>> 73 Dwight NS9I
> If you want to make some estimates:
>
> I used this paper before to make some rough guesses at thermal
> dissipation for enclosed electronics
> http://www.hoffmanonline.com/stream_document.aspx?rRID=233311&pRID=162534
> <http://www.hoffmanonline.com/stream_document.aspx?rRID=233311&pRID=162534>
>
>
> Assume you need to dissipate 30W or so. You can derate that by some
> duty cycle (assuming you listen sometimes? :)
> It's all about the total surface area of the box and it's material.
> Just because it's enclosed, doesn't mean it doesn't dissipate.
> Plus: a little breeze and you've got airflow on the surface.
>
> The biggest heat rise will actually be from the sun, I believe. (see
> evaluation of solar heat gain)
>
> Look at those charts and think about the black baluns you've seen.
> White is right!
>
> I was also going to comment on how I used 16 awg silver plated teflon
> for my bifilar windings so I could fit enough turns but still get
> substantial turn to turn spacing.
>
> Also, I've not seen enough agreement on the sources of stray
> capacitance..from what I read, the winding to core substantial
> capacitance...I wrapped my core with two layers of the yellow gas
> teflon tape (easier to handle than the thin white stuff). I've seen
> some stuff showing that tight winding of enamelled wire has more stray
> capacitance than insulated wire (which gets the wire up off the core).
> Thoughts?
>
> But then I figured I'd keep my mouth shut, because Jim will probably
> say parallel #12 THHN has lower impedance than my #16 parallel
> insulated. I suspect they're both about same though.
>
> -kevin
> ad6z
>
>
>
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