[CQ-Contest] CQ-Contest Digest, Vol 153, Issue 20

[Marvin Bloomquist]

Just a comment that may be obvious to most but 23 feet is not the 
correct length for all types of coax. It depends on the velocity factor 
- 23 feet is the length for Belden 8237 but, for example, if you use 
LMR400 it is 29.4 feet at 7.1 mHz. For Belden RG8x (Belden 9258) it is 
27.7 feet.  A nice little program to calculate these is TLW which comes 
with the ARRL Antenna Book. If you really want to be accurate or are not 
sure of the velocity factor of your coax use an antenna analyzer that 
measures impedance. You want to cut it so the reactive component of the 
open coax is zero at the frequency of interest.

Marv N5AW

On 9/10/2015 11:00 AM, cq-contest-request at contesting.com wrote:
> Ok.
>
> Now that you have put a 23' shorted stub on 40, put a 23' open
> stub on 20.  This will reject any 40 meter energy that shows up
> on your 20 meter feedline, and it will pass 20 just fine.
>
> Dave Hachadorian, K6LL
> Yuma, AZ

-- 
Marvin Bloomquist
Burnet, TX