[amsat-bb] Building Helix, Have Questions

["Tom Smith" <cwdxer@xxxxxxxxxxxxxx>]

I am building a helix antenna to illuminate a 46 cm (18 inch) offset TVRO
dish ("Dish Network 500").  I am looking for a "sanity check" before I build
it.  It will be for AO-40 S2 receive only.  The plan is:

6 turns LHCP
Diameter: 3.98 cm (1.565 inch)
Turn spacing: 3.12 cm (1.227 in)
First quarter turn 0.64 cm (0.25 inch) above reflector
Reflector: 12.47 cm (4.91 inch) square
Wire: 6 AWG solid copper 0.41 cm (0.161 inch) dia

Questions:

Do I need to modify the dimensions to use plastic dowels to support?  I want
to use 2 dowels inside the coil, spaced 180 deg, to support the weight and
provide a guide for spacing.

Can I cover it with PVC pipe?  I want to protect the downconverter from
electrostatic discharge from inquiring fingers.

How important is it to tune it for 50 ohms if I only use it for receive,
with a commercial downconverter such as UEK-3000 or RX2400-144?  From what I
have read, keeping the first quarter turn near the reflector should move the
impedance closer to 50 ohms.  But I have no way to test it.

Thanks in advance!
Tom Smith KB6A
Anaheim, California, USA
cwdxer@concentric.net


----
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
Not an AMSAT member? Join now to support the amateur satellite program!
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org