On 5/13/10 14:55 , Mark S. Holden wrote:
D. Peter Maus wrote:
On 5/13/10 14:18 , Mark S. Holden wrote:
D. Peter Maus wrote:
On 5/13/10 13:39 , Mark S. Holden wrote:


And to include some closer to on topic content - has anyone here
experimented with using a slinky as a loading coil for a "portable"
vertical antenna? If so, any thoughts on if it's worthwhile?


That was discussed pretty much to death about a decade ago. And a
dozen or so members tried it. With, as you'd expect, mixed results.

As a quick-deploy horizontal, a slinky does pretty well in the field.
As a loading coil for a vertical, not so much. Largely because it
needs a form to keep the coil stable.



I was thinking I could put it over a section of pvc pipe.

Or I may just buy a screwdriver antenna. Can't count on having trees to
hang an antenna at a star party.

My AT-271 worked fine for RX, but now I'm doing the tx thing too.

Depending on power applied, within the slinky, you may have to deal
with volume of dissipation in the coil. It's not a copper conductor.
Nor is it uniformly round, which will make the areas of electric and
magnetic field density vary around the surface of the conductor. And
being a flat conductor will produce less effective skin conductivity
surface than the equivalent cylindrical surface area. This will make
capacitance distributed across the breadth of the coil a more
significant issue, and, dependent on frequency, this could be a
considerable tuning issue and SWL issue for the transmitter. An
antenna tuner will help with the match, but losses in the antenna will
continue to be losses, antenna tuner or not.

If losses are not a significant issue in your setup, then a slinky can
be an adequate loading device. If losses will matter, then there are
better solutions.




I have an antenna tuner, but it sounds like it would make sense to pick
up an antenna analyzer - on that basis I'll need to do more thinking.
Space is at a premium when I'm heading to star parties.



Then you'd want a broadband antenna. If you're VHF, a discone is
a good broadband, and compact, solution for RX & TX. If losses are
not an issue, an antenna tuner can match a VHF discone for HF use.