[TowerTalk] 40M rotary dipole

[Dave Sublette]

This thread has been very educational for me…. thanks to all who are contributing.  To my credit, I realized that the rf choke acts to isolate the dipole from the tower leg as I lay in bed last night.  Of course it is between the bonding point at the top of the tower and the connection to the dipole.  I’m old and slow and make lots of mistakes, but I get it … eventually.  

I am going to put the dipole up without RF choke first.  Later, I will add the choke.  I haven’t thought about how to go about measuring noise differences, but as I type this, it seems that my Softrock HF Ensemble II might be a very good way to measure and document differences in base noise between the two methods of connection.

Right now, I have all I can handle, finishing the dipole, planning how to put it up, finishing the job of erecting the tower (30 more feet and one guy ring to go).  In addition I am computer modeling (with some wonderful help from several sources) the Moxon 2 element 40M yagi, both electrically and mechanically.

There aren’t enough hours in the day for all the fun I am having!

73,

Dave, K4TO
> On Sep 21, 2017, at 3:12 AM, Jim Brown <jim at audiosystemsgroup.com> wrote:
> 
> On 9/20/2017 10:35 PM, Stan Stockton wrote:
>> I am curious.  The coax/tower (we'll call it Antenna 1) is isolated from Antenna 2 (the real antenna) with a choke.
>> 
>> Antenna 1 is still radiating the noise without, let's say, direct connection to Antenna 2.
>> 
>> So there is no propagation such that Antenna 2 picks up the noise radiated from Antenna 1, end of which is at most a few inches away?
> 
> Good question. The answer is, yes, and it's a question of degree. Let's assume that Ant 2 is a horizontal beam. This makes it cross-polarized with Ant 1, so there's much less coupling than if they were not cross-polarized. Also, the peaks of their radiation patterns are the direction of the other antenna. The result is that it's a LOT less coupling than direct via the common mode current.
> 
> Feedline chokes don't usually provide a LOT of noise reduction unless what you're starting with is a train wreck, but neither do Beverages. If you're trying to work the weak ones, 3-6 dB better signal to noise can make a big difference! As N6BT wrote in his self-published "Array of Light" book about antenna design, that level of improvement gives you another level of stations to work!
> 
> 73, Jim K9YC
> 
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