The wood spacer is a good idea, maybe Jim can chime in on how much spacing is
needed. This is a real problem with double boom log periodics since both booms
are hot with RF, and running the coax along the lower boom is obviously
counterproductive. W8JI has some thoughts on this problem on his site, which I
followed with some success. I'm experimenting with different kinds of chokes
at the boom/mast junction and trying to find something that is mechanically
durable while maintaining the maximum choking impedance possible.
Chris
KF7P
On May 14, 2013, at 15:30 , Brian Alsop wrote:
I just taped the coax coil to a block of oak and tiewrapped/tapped the wood to
the boom.
Even worse than this is winding the coax turn on the boom. The boom ends up
being a shorted turn!
The way around all of this is to use a toroidal balun. More $$ but a much
easier and more robust mechanical solution. Electrically they are more
broadbanded and work well with multiband antennas.
73 de Brian/K3KO
On 5/14/2013 20:58, Chris wrote:
> Okay so how do you route the coax back to the mast from the driven element
> then? Dangle the coax below the mast? Add another choke at the mast? But
> wait! The mast is metal too! Just how much of a problem is this stray C,
> anyway?
>
> Chris
> KF7P
>
>
>
>
>
>
> On May 14, 2013, at 2:50 PM, Tom H Childers wrote:
>
>>
>>
>> One reason those folks, which has included me have done that, is
>> because most loaded Yagi-Uda antennas sold by CushCraft and others
>> recommend doing just that in the assembly instructions!
>>
>>
>>
>>
>> On Tue, 14 May 2013 20:28:54 +0100, "Ian White"
>> <gm3sek@ifwtech.co.uk> wrote:
>>
>> [snip]
>>>> How many times have you seen a coiled-coax choke taped
>>>> to a boom - think about that in terms of a high-Q parallel tuned circuit!
>>>>
>>> Not only that, but taping the choke to the boom is adding extra capacitance
>>> between one side of the driven element and the boom. In other words, taping
>>> the "choke balun" directly to the boom is making the antenna more
>>> UNbalanced! It's amazing to watch people doing this...
>>>
>>>
>>> 73 from Ian GM3SEK
>> [snip]
>> 73,
>> Tom
>> Amateur Radio Operator N5GE
>> ARRL Lifetime Member
>> QCWA Lifetime Member
>>
>> _______________________________________________
>>
>>
>>
>> _______________________________________________
>> TowerTalk mailing list
>> TowerTalk@contesting.com
>> http://lists.contesting.com/mailman/listinfo/towertalk
>>
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
>
> -----
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 2012.0.2241 / Virus Database: 3162/5823 - Release Date: 05/14/13
>
>
-----
No virus found in this message.
Checked by AVG - www.avg.com
Version: 2012.0.2241 / Virus Database: 3162/5823 - Release Date: 05/14/13
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|