TopBand: 160 Meter receiving loop (20k)
Greg Weinfurtner
weinfurtner@ouvaxa.cats.ohiou.edu
Wed, 18 Sep 1996 15:49:26 -0300
Here is the loop as I can draw it: It is SUPPOSED to be a square of course,
ASCII drawings won't let us draw a square on its corner. The construction
is not critical at all, including lengths of coax, within a 1' (.3M) or so,
because it is tuned with a variable capacitor. It is very forgiving of
sloppy construction...probably works better that way!
| <- see insert A
/ \
/ | \
/ | \
/ | \
/ | \
----------------- (Wooden cross arms)
\ | /
\ | /
\ | /
\ | /
\ /
* <---see insert B
| \
| \-------------------> Coax to receiver
|
|
|
1. Each of the four sides of the loop coax are about 5 feet (1.5M)long,
total length is 20 feet (6.1M).
2. The loop is made of any coax, RG/58, RG/59, etc. Mine is RG/59.
3. It is mounted on a wooden cross frame or any other non-conductor
as below: Each of the arms should be at least 4 feet long (1.2M)
|
*
|
|
|
|
|
___*_______________________*____
|
|
|
|
|
|
*
|
|
|
|
|
|
|
4. The "*" are the attachment points for the coax. They are
43" (109 cm) from the center crossover point of the wood. Just tape or tie
coax to these points. No connections are made here, just tie coax to the
wooden frame.
5. The bottom of the wooden cross is mounted in any convient way that will
allow you to turn the loop.
*****************INSERT A***********************
This is the TOP of the loop: Note that the shield is opened and cut away
for an inch (2.54cm) leaving the center conductor untouched. (Leave the
insulation on the center conductor for weather protection, I couldn't show
it with ASCII drawing) Then weather proof this with some caulk, tape, or
something.
_________ __________
/ | | \
/ -------- \
/ _______| |________ \
/ / \ \
/ / \ \
*****************INSERT B********************
Bottom of the Loop
\ \ / /
\ \ C1 _ / /
\ \ /| / /
\ \_______ | | ________/ /
\ | | /| | /
\ -------|/ |---|--- /
\_________| | | | |___________/
/ |
/ |
_______
_______ C2
|
|
|
___|___
| |
| |
| |
| |
Coax to receiver, any length.
NOTE****** ALL THE COAX'S SHIELDS ARE CONNECTED AT THIS JUNCTION. USE A
SMALL METAL BOX, CAN, ETC. TO WEATHER PROOF THE CAPS. LEAVE THE BOTTOM
OPEN SO IT IS EASY TO ADJUST THE CAPS.*************
6. C1 is about 600pf variable. I have a 560pf silver mica capacitor with a
200pf variable in parallel with it.
7. C2 is the minimum amount of capacitance that will allow a good signal to
the receiver without much attenuation. I have 330 pf silver mica in mine.
Experiment with this value.
***************************************
How to use the loop:
1. Mount as high as possible and clear of other objects as
possible. Keep as it as far away as possible from the vertical antenna,
sometimes they can re-radiate the noise they pick up. It can be nulled out
with the loop, but that doesn't allow you to null out other noise sources.
(Unless they are in the same direction.) I've mounted mine in the front
yard (Much to the shagrin of my long-suffering XYL...), only 50' from my
transmiting ant. with success.
2. With the coax from the loop hooked up to your receiver, tune
this capacitor for maximum received signal on your frequency of interest.
The setting will be broad enough to cover at least the bottom 100khz of
160, without readjustment.
3. The loop is bi-directional and can have very deep nulls (30 db
or more) Rotate the loop for minimum noise or to null out an interfering
signal. I have mine on an old TV antenna rotor about 10' off the ground, so
I can do it from the shack. You'll be amazed at the signals that pop up
when the noise dissapears!
4. Since the area of the loop is smaller than a full sized antenna,
it will not deliver as much signal to your receiver. With almost all
receivers this is not a problem, since most have more than adequate gain at
160 meters. There are some that may need a pre-amp, but I've found that
the preamps, even a solid state one, add to the noise on all the receivers
I have. (One is a 1960's tube type Lafayette KT-200 general coverage
receiver!) My homebrewed 160 meter rig doesn't need the preamp.
E-mail me back if you have any questions!
Good Luck and see you all on 160!
73 de
****************************************************************************
* Greg Weinfurtner AEE BSS *
* NN N SSSSSSS 8888888 OOOOOOO Electronic Design Splst *
* N N N S 8 8 O O Ohio University Athens *
* N N N SSSSSSS 8888888 O O GO BOBCATS! *
* N N N S 8 8 O O *
* N NN SSSSSSS 8888888 OOOOOOO *
* Can thou send forth lightnings *
* Amateur Radio that they may go and say unto *
* DXCC WAS EM89 thee, 'Here we are'? Job 38:35 *
* weinfurtner@ouvaxa.cats.ohiou.edu *
* http://ouvaxa.cats.ohiou.edu/~weinfurtner *
****************************************************************************
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