David wrote:
On Sun, 1 Oct 2006 09:14:51 -0400, "Unrevealed Source"
wrote:
My outdoor longwire antenna works just about as well as I could imagine.
Very long wire, very high, attached to shielded 50ohm coax about 40 feet
from the house to avoid all the noise, and connected through a MLB. I get
amazing reception on all my radios.
So now I have a second "listening post" on another floor, and have decided
that I'll feed a high-impedance antenna to that spot. Some radios, mostly
my older ones, don't have a low-impedance input, just the normal
slotted-screw antenna wire hookup. This will give me an easy way to play
with these.
I might try a slinky outside, or maybe not. (Any real-world opinions on a
slinky vs. long wire?)
My real question is this: Can I use similar 50ohm shielded coax as my
feedline, to take advantage of the shielding and get the antenna away from
the house? I would of course not use the balun or even the connectors, just
connect the antenna to the center conductor, and strip away enough inside
the house to connect the center conductor directly to the radio. Will this
work? Is it a sound design?
Thanks,
Jeff
Use the ''balun'' to match the wire to the transmission line. Connect
the center conductor of the transmission line to the ANT screw on the
receiver, and the shield to GND. Ground the mess according to local
codes.
I solved my SWL antnenna noise problem by using 120 feet of 50 Ohm quad
shielded coax to a 30 foot vertical antenna in the back yard. I used a
Shortwave Antenna Longwire Transformer Balun - #LMZ-50 SWL Matcher,
which was made and sold by ERICKSON ENGINEERING. You must ground the
outside of the coax to the service ground. I also use a ground rod
with 6 gauge copper wire to the shack. My roof feed through
arrangement is shown at:
http://ph.groups.yahoo.com/group/Sho...os/browse/85e7
You should be able to get good results with just one of the baluns,
If you think you really want a High Z input to the radio, you could use
a second one of these transformers at the radio. The full description
of the balun is: ---------------
The purpose of this device is to match high impedance of the longwire
antenna to your low impedance receiver. Since a longwire antenna is
usually quite high in impedance (approx 400 to 700 ohms) you will have
considerable loss if you connect the wire directly to your low
impedance antenna terminals on your shortwave receiver. So by adding
this device at the end of your longwire you will increase your receive
signal strength a considerably amount on many frequencies across the HF
bands. By using coax for your feed you will also greatly reduce the
noises caused by TV's, computers, home lighting systems and other
electronics so that you can receive with much better clarity then with
a single wire through your window to the receiver. This device is also
shunt-fed so that static discharges are sent to the ground of the coax
rather than to your sensitive receiver front end. Some experimenting
with the length and height of your longwire may be needed to help your
reception even more. A length of 25 meters (approx 80ft) of wire is
recommended for best results, however if you have limited space to work
with a length of 30ft or more will give very good results This wire
does not have to be in a straight line to be effective as L or Z shapes
can work as well. The LMZ-50 is for use on radios with low-impedance
(50 ohm) antenna connection.
The LMZ-50 antenna match is designed for 50 ohm coax using PL-259
connectors on the coax. This is a special 10:1 Voltage Balun for
matching a longwire / random wire to 50 ohm coax down to your shortwave
receiver. The ground is carried down through the coax and then to the
radio. The radio receiver will then provide a ground to an outside
ground rod. An optional tuner / preselector can be placed between the
coax and the receiver.
Receive Frequency Range: 500KHz - 55MHz
THE LMZ-50 CAN BE USED ON LOW POWER TRANSMITTERS UP TO 10W (HF ONLY)
For information on WIRING and GROUNDING with the LMZ-50:
http://tinyurl.com/lnwcn
These impedance matching transformers are encased in a durable PVC
housing with heavy duty stainless steel connecting hardware for the
antenna terminal. This device is sealed from the elements and designed
for the weather. However it is always good practice to cover the
PL-259 connector with coax sealant tape to prevent water in your mating
connection.
------------
Noel N2FAV