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@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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