Topband: K2AV Counterpoise

[Guy Olinger K2AV]

Hi Jim,

A lot of this is illustrated for you at k2av.com. Particularly for more
complicated situations. I suggest you read the opening page and "Taming the
Exasperating Inverted L" at the web site. You are always welcome to contact
me directly with further questions.

Assuming that you are not supporting the bend of your L from a tower:

Your old radials should not be connected to anything at the L/IsoT/FCP. You
do NOT want to put the FCP and radials in parallel. The FCP is deliberately
not resonant (5/16 wave), with the folds and size designed to sharply
reduce inducing lossy RF current in the dirt. Yes, not resonant, on
purpose. Putting the old radials and FCP in parallel will shunt the
counterpoise current to the coax shield and inevitable losses.

You can leave the radials in the ground but you do NOT want any RF energy
driven into them from the coax. (This is a complex issue if a tower
supports the L's bend - see the web page).

Connect the coax shield by itself to the the shack side of the isolation
transformer at the antenna. This also prevents noise from the house from
using coax shield to ground at the antenna as a common mode path to get
near the antenna. The isolation transformer is a brick wall common mode
current block with no metallic connection between primary and secondary. If
you ground the coax shield anywhere near the antenna, do so 20-30 feet away
from the feedpoint. Always ground the coax shield where it enters the house.

The antenna side of the isolation transformer should connect ONLY to the
FCP and the inverted L or possibly a series capacitor or inductor between
the transformer and the inverted L.

Again, supporting the L's bend from a tower is a special case, described on
the web page.

Tuning an inverted L, when folks get it right with an FCP, can produce a
surprising and EFFICIENT feed resistance (not impedance) of 20-35 ohms.
This can look like an awful SWR in the shack across a typical run of RG213
and convince you you've screwed it up, when in fact you've gotten it right
and other than matching it to 50 ohm coax, you're done.

See the section on k2av.com called "Taming the Exasperating Inverted L".
Well over half my correspondence on the FCP over the last five years
involves that in some way. Who knew? :>))

73 and good luck!  See you on 160.

Guy K2AV


On Wed, Oct 25, 2017 at 10:38 AM, James Denneny <57jndenneny at comcast.net>
wrote:

> I am constructing the K2AV FCP Counterpoise  for my TB inverted L
> antenna.  I live on a small lakeside lot.
>
> Should I disconnect the few ground radials when I install the FCP or leave
> them connected?  Would both together degrade performance?
>
> Jim K7EG
>
> Sent from Mail for Windows 10
>
> _________________
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