Coax Calculator

According to dxengineering its ment for the 55zoom but i have seen vids with guys tuning (nulling/cutting)coax with an mfj259....
If i see one againg ill pass on a link..

 

Here's the formula:

Coax Length = 492 x VF/freq. If length is 14.7 feet, then cut coax to around14.8 1/2 inches. Take .7 x 12 = 8.4 inches.

So 492x.66 (66% VF for 58/u coax) equals 324.72, divided by 27.205 mhz (channel 20), equals 11.9ft long. That a why some tech's say 12 feet of coax is close enough.

I use RG213 coax with 66% Velocity Factor for my base antennas. So for a simple example, if the length for channel 20 was 12ft long, you would add another 12ft to get 1 wavelength, a total of 24ft. . Then keep adding 12ft to reach your antenna. Now you have to use every other 1/2 wavelength number. The problem is that if your 1/2 wavelength coax is 4ft short from reaching your antenna, you will have a lot of excess coax because you need to cut it at the next 1/2 wavelength. Also in this example, you would need to use a 1/2 wavelength 12ft jumper cable between the radio and swr meter, instead of the usual 3 ft jumper.

I just found this website that will explain it better.

RadioMods coax length page

 

Yeap..All the cab's metal skin helps

 

Found this one while surfin youtube..

 

Another about le

Another about length..

 

No im sayin that a mfj was used in the vid but useing the 35 would be able to do the same as mfj..You would have to use the screen that shows all the swr/resistances and resonance screen..
The 35 will not allow you to just calibrate the for the null of coax by useing an open/short/load....Not that i asked rig expert but according to the dx engineering site where i got my o/s/l its says for the 55 and up..