View Single Post
  #8   Report Post  
Old April 25th 12, 04:59 PM posted to rec.radio.amateur.antenna
Irv Finkleman Irv Finkleman is offline
external usenet poster
 
First recorded activity by RadioBanter: Jul 2006
Posts: 220
Default Indoor Counterpoise For Random Wire Antenna


"Sal" wrote in message ...

"Irv Finkleman" wrote in message
...

The real intent of my questioning is to provide
a counterpoise system whereas the tuner does
not just have an unbalance by simply feeding
the random wire, but a balance achieved
whereby the counterpoise connected to the
tuner acts as the other (missing) half of the
unbalanced system, thereby balancing it just
as the ground image does with a quarter wave
antenna. Does this make sense?


Yes and perhaps I have a workable idea to get there.

First, an assumption: Your long wire out the window frame has only a
short run to the tuner. That is, the tuner is on the same wall as the
window frame and is near the window. How'm I doing so far?


Bang on Sal -- the tuner is located about 18 inches from where the
wire comes through the window, but on the floor along the wall
with the window is the baseboard hot water heating unit so I can't
really run anything on the floor along that wall. Similarly, although I
understand your tape measure idea, there is a simpler solution
which I tested last night and worked perfectly.

I arrived at a solution through the following note from Bob, K5QWG
who wrote:

"I once had the little B&W vertical in a 3rd story apartment window. To
tune it, I used an SWR meter and simply unrolled my single
counterpoise wire across the rug until the swr was 1:1 for the band in
use. The counterpoise was on a wire spool. I never actually measured
the counterpoise length -- I simply found 40 meters meant the wire
went from the bedroom window to the kitchen."

I thought it made perfect sense and even downloaded the instruction
manual for the B&W AP-10 Windowsill Antenna which told me the
same thing as Bob wrote -- and it worked perfectly.

I too used a spool of wire connected to the ground post on the
MFJ-949E tuner, and unrolled it away from the tuner and antenna,
across the floor and through the room. At that point I tuned up on
frequency, adjusted the tuner for minimum SWR (nearly 1 to 1)
and that was that! It worked beautifully.

Your idea with the tape measures would have worked as well,
but would have been a little more expensive and possibly
unworkable due to the heater. Instead, I simply put a tape
marker on the counterpoise wire at the length where it worked
well on the band tested (80M). Now, when I want to operate
all I have to do is unroll the spool to the tape marker and
Presto! I can go on the air! Of course I have noted the tuner
settings, and will also add further tape markers on the
counterpoise wire for the different bands, and note the
tuner settings as well.

My next step may be to cut counterpoise wires for each
band of operation and permanently lay them along the
wall this negating the need to roll and unroll the spool
of wire each time.

With time there may be some minor changes. For instance
how far across the bands can I tune without any significant
change in SWR. I might also try putting a loading coil
in the counterpoise line at the tuner end so that I can fine
tune the counterpoise length electrically. I will build up
a little RF sniffer just to check for local stray rf but
that should no longer be a problem.

I could use the MFJ-1625 tuner which has a built in
switched coil to adjust the counterpoise, but it only has
a current meter, not an swr bridge. The MFJ-949E
tuner has swr metering. Therefore if the loading coil
for the counterpoise works, I can use the 949E and
sell (albeit at a small loss hopefully) the MFJ-1625
set complete to some ham who is able to operate
using the intended setup for the 1625. It is
an excellent system, but because of all the metal in
my building which negates indoor operation,
and the inability to put the whip out of the window
due to physical limitations existing in my suite,
I cannot use it. I had not considered the limittions
in my situation prior to buying the 1625 but it was
worth the try. I might even keep it (I may have
to if I can't sell it) for portable use when I go
fishing. It would be an excellent setup on a picnic
table or from a tent. Again, time will tell,

In any event, A BIG THANK You to all who helped in
this discussion -- I can now get on the air and as soon
as I have things tested and tidied up I hope to meet
you there.

Irv, VE6BP