[TowerTalk] 40M rotary dipole

[Dave Sublette]

I have spent the morning working on a 40M dipole made from leftover Telrex parts.  I took careful measurements of the lengths and diameters of tubing entered the dimensions into Antenna Model.   The 1.5:1 SWR bandwidth is  175 Khz and it centers nicely at 7075. The SWR rises only to 1.8:1 by the time you reach 7.3 Mhz.  I think it will work very well for me.  

Mechanically, the antenna is a bit more limber than I thought it would be.  I will have to add stays to hold the elements up.  I plan to use a double run of 3/16” dacron rope with small end insulators near the element.  I would imagine that when rain and ice arrive, those stays would affect the performance when wet.

The thing is really big!  I put up a rotary dipole for 80 meters once that was shortened to 125 feet with end capacity hats.  This antenna isn’t near what that one was.  The 80meter one was 125 pounds and this one will be only 27 pounds, not including the mount. But still, the 40M is a large antenna.

I’m now trying to decide whether to wind a balun or just coil a few coils of the feedline to keep RF off of the coax.  Do you have any preference?

thanks & 73,

Dave, K4TO

ps — my address system puts the name of an individual and then “via towertalk” and the list address.  I don’t know how it reads when you get it, but this is addressed to the list, not an individual.  I wish I could get to send just to the generic tower talk email address.