At 12:22 PM 11/3/2005, Rick Karlquist wrote:
> > A rotary joint shouldn't be a big deal for HF. We use a variety of N
> > connector rotary joints on the antenna range at JPL, and they are fairly
> > wide band. I would imagine you could find one surplus.
>
>You would need at least a coax and rotor cable to go through
>this joint. My long range plan is to have a stack, requiring
>multiple coax and rotor cables. This would be quite non
>trivial to build a rotary joint for. Not impossible, but a
>big project.
Depends on if you want it all on one big drum, in which case you DO need a
multi channel rotary joint. The control cables are no problem.. that's an
off the shelf unit, perhaps even from McMasterCarr. They're used in
rotating signs, for instance. The multi channel RF rotary joints are a bit
trickier, but they've been used in lots of military equipment, so surplus
is a very real possibility (the problem is that they would look weird, and
might have been junked as they didn't have any obvious mechanical
function). The multi channel ones I've seen basically use slip rings, the
dimensions of which form a 50 ohm line. For HF, you might even be able to
use the ones intended for 60 Hz power.
I have a 2 channel RJ on my desk here, but I have no idea what the innards
look like. It's a cylinder about 2" in diameter (excluding the mounting
flange) and 4" long with a pair of N connectors on each end.
A big mfr of RF rotary joints is Kevlin Microwave. They've been in business
a while, so their stuff might turn up surplus.
Another is Diamond antenna:
http://www.diamondantenna.com/images/rotary_joint_catalog.pdf
For an HF application, you probably aren't worried about a lot of the specs
that radar folks obssess about, like phase tracking between channels, etc.
However, if you have a single cable per drum, then you only need one rotary
joint per drum. You could do two cables, and have a joint on each end.
>Rick N6RK
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