K8JRM wrote:
Hi Guys,


This is an age old question - what is the best way to get 450 Ohm ladder line
into my shack antenna tuning unit (ATU)? Here is my situation; I have two 4"
PVC tubes inserted into the exterior wall that allow the entrance of coaxial
cable into my shack. When I run the ladder line into the shack through one of
these ports, the multi-band wire antenna fed with the ladder line goes wild! I
can not get the antenna to tune with any of my ATUs.


I have received several suggestions on how I can overcome this problem. The
most promising one seems to be to use two short pieces of coax with center
conductor connected to either side of the ladder line. These pieces of coax, in
turn, would be fed through the PVC hole into the shack and the center
conductors connected to the ATU. The shield on the coax would float with no
connection to any thing. This solution sounds good; however, common sense
tells me that ladder feed line will still suffer because of its proximity to
other objects. Any thoughts on this solution?


Another possibility is using a piece of Plexiglas place under a metal framed
window pretty much as shown in the old hand books. My problem with this
solution is that the window is on the other side of the room from operating
table, the two coax entry ports and AC power.


Short of placing the tuner outside in the elements, is there a solution to my
problem? I would be interested in hear what has been tried!


Tom, K8JRM in OKC


Tom,

Sounds like your running the ladder line with some other conductors in
the PVC.

You never said how far the entry point was to the ATU, if its relatively
short less than 15' or so I would recommend you run a piece of coax from
the ATU through the PVC to a 1:1 balum located outside. there would be
some loss in the coax/balum but it would be low on 160-30M and some what
higher on 20-10 meters. I don not think you can quantify the amount of
loss but I don't think you will see it via RST reports. I have
successfully used this method over several years since I did not have
the 4" PVC that you luckily have for the coax and other conductors.

The above suggestion is made on the assumption that the ATU has a
unbalanced output for coax and is not a balanced only tuner.

With respect to the addition of two (2) pieces of coax as a feed through
on the inside of the home the shields are connected together and then
joined to the ground system in the shack. From the feed through point
then you can continue with the ladder line to the ATU.

I recommend the remote balum since it helps cut down on any coupling of
RF to other conductors in the PVC. Use a good current type balum since
the swr is likely to vary over the multiple band use. The length of
ladder line from the balum to the feed point of the antenna is some what
critical and there is lots of articles on the subject on the WEB, I
believe DX Engineering has some excellent white papers on this subject
for remote balums.

73 de
Ron W4LDE