[Lowfer] top hats

[lowfer@mailman.qth.net]

The top hat on my 160 meter vertical uses four 6 foot spokes. The tubing is 
6063-T832 3/8 inch tubing and the wind survival (without perimeter wires) is 
calculated to be 100 mph. I have perimeter wires but the wind survival still 
exceeds that of the self-supporting 38 foot aluminum mast (60 mph). I 
recommend the book Physical Design of Yagi Antennas by David B. Leeson, 
W6QHS. This will help with top hat design. Or, just design the spokes like a 
20 meter Uda-Yagi for top hats up to 5 meters radius. The capacitance of my 
top hat is 100 pF.

The vertical got it's first wind test last night. Scary to see it bending so 
far (estimated wind 35-40 mph) but nothing broke and it bends as calculated. 
Now to see about loading this thing on 1750 MHz. If I can build a coil light 
enough to go at the top that's where it will go. This would certainly be best 
electrically as it will double the radiation resistance. I can take a hit on 
the coil Q and still get ahead with top loading. With top loading the Rr will 
be 75 milliohms and the coil needs to be 8 mH. If the coil Q is 200 and my 
ground is 20 ohms, the radiation efficiency will be 0.1%. I might wind up 
with an ERP of 1 mW, if I'm lucky. 

I have not yet heard a signal on 1750 m but tonight I'm trying the ARGO 
software. I listened last night and logged dozens of NAV Beacons though. Can 
you guys recommend a frequency for my 1750 m beacon? I'm still working on the 
MEDFER beacon. Ran into a problem using copper tubing when I calculated the 
wind survival- and it's only 6 feet tall! And it was going to look so nice 
and coppery. 

   Dave WX7G


--- StripMime Report -- processed MIME parts ---
multipart/alternative
  text/plain (text body -- kept)
  text/html
The reason this message is shown is because the post was in HTML
or had an attachment. Attachments are not allowed.
Please post in Plain-Text only.---