TLW gives these loss figures for 250 feet (190' plus 60' up the tower)
of coax at 21 MHz (midpoint of James' tribander) with an SWR of 1.4:1.
RG-213 2.5 db
9913 1.4 db
LDF4-50A 0.7 db
I've seen LDF4-50A (1/2 inch Heliax) on eBay for around $1/ft less
shipping (and there's an outfit that regularly offers it for $1.25 with
free shipping). Connectors can be expensive but patch cables with
reusable N-connectors are not expensive ... neither are N-to-UHF adapters.
In my opinion, $100/db is tough to achieve anywhere else in the system
(other than maybe for a used linear amp).
73,
Dave AB7E
Jim Brown wrote:
> On Sun, 19 Aug 2007 14:49:31 -0400, James M. Daly wrote:
>
>
>> And on a side note; is there any significant advantage to using 9913 coax
>> over RG-213 at these lengths when operating at 10-20m frequencies?
>>
>
> The best answer to that is to plug some feedpoint impedances (or SWR) values
> across the bands into the TLW software that comes with the antenna book and
> let it crunch the numbers. I just did that for the 150 ft long feed to an
> 80/40 dipole and plugged the result into a spreadsheet to study it. The math
> told me that the difference between Belden RG6 with a steel center and 8213
> (RG11 all copper) was about 0.6 dB averaged over 80 and 40, taking SWR into
> account). LMR400 might have given me another tenth dB or so. The decision was
> made easy for me when I found a surplus spool of 8213 for about $.30/ft. :)
>
> 73,
>
> Jim K9YC
>
>
> _______________________________________________
>
>
>
> _______________________________________________
> 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
|