[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Helix feed details

Hi folks,

Ok, the pictures of the first turn's worth of a Helix feed, the words
that I read here, and the parts on my bench aren't quite matching

The N connectors that I can find locally have a considerable "bump"
on their back side, a little smaller in diameter than the front-
side barrel, and about 1+ mm high.  They are definitely not flat.

If I mount the N connector on a the end of my coffee can so that the
surface of the back of the connector is flush against the can, then
the bump sticks into the can far enough that the helix feed wire ends
up much farther away from the can than it's supposed to be.  I put it
all together this way, even if it's wrong, and I was barely able to
hear the beacon at apogee last weekend.  But, I expected better.  It
seems to perform about as well as the original dipole feed on the
original grill (which is now covered with a metal screen).

Should I bend the helix wire so that it follows the contour of
the bump down towards the can, and then angle it up slowly over
the first 1/2 turn?  Or, could I do something with the foil strip
that is soldered to the first 1/4 turn to compensate for the larger
distance?  (Easier, since the wire's rather stiff...)  Does this
even matter in practice?

The preamp is attached directly to the back of the can with a short
N-N adapter, then directly to the Drake.  It's not a great preamp,
(1+db noise, 10db gain), but it seems to help.  I want to get a
good baseline for what this setup can do before ordering a DEM unit.



Get your FREE download of MSN Explorer at http://explorer.msn.com

Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org