NDB and SWL Antenna

[weaksigs]

Yo Ho Ho!

A couple of you have inquired concerning the antenna I use for NDB listening. It is a 196 foot long randomly installed wire at an average height of 25 feet. The wire is terminated via a 9:1 Impedance transformer wound on a toroid core Type Ft-114-77 (the one I had on hand at the time of construction). I wound the transformer using 33 turns on the primary and 11 turns for the secondary. The random wire is connected to one side of the primary and the other side of the primary goes directly to a hard ground. The secondary has one side to this same ground and the other winding goes to a coaxial cable connector mounted to the enclosure. RG-58 coaxial cable is run from the connector to the radio. I had some excess cable so wound this into a common mode choke using a small piece of pvc pipe as the coil form. The radio thus uses the outside ground via the coaxial cable shield. This antenna and coupling transformer configuration produces good signals and less noise from 100 Khz up to and exceeding 20 Megahertz. Above that frequency good signals are received but I haven’t tried a direct comparison to another antenna for comparison. My ground system is four eight foot ground rods spaced between six feet and 12 feet in typical central Florida sand and a # 4 solid wire connection back to utility ground at the entrance panel. I’ve attached a quick picture of the random wire termination which is attached to the shack wall. It notes several of the components. This configuration, being connected to ground through the primary winding, also provides a path to drain off precipitation noise and potential buildups.

Antenna termination configuration

https://dl.dropbox.com/u/65026409/196%20foot%20random%20wire%20termination%20and%20matching.JPG

I use NDB beacon CLB (Carolina Beach, NC) as my general reference and baseline signal. This provides a good reference while trying other antenna configurations. CLB is about 460 miles from my location in a general NNE direction from central Florida. I’m not close to the beach so I do not benefit from any salt water signal enhancement.

Here is the signal from CLB as recorded January 30, 2013 at 1700 UTC (noon) on 216 Khz CW with a 100 hertz filter. During ID I was receiving about a -93 dbm signal whereas the noise level in between ID was just a little bit above -118 dbm. I was receiving on the CLB upper sideband during recording. This signal level produces loud audio from my Excalibur receiver as you will see from the attached.  The carrier level was considerably stronger than the sidebands as you can imagine.

CLB Carolina Beach, NC

 https://dl.dropbox.com/u/65026409/CLB%20217%20kHz%20at%20460%20Miles%20baseline%20signal.mp3

Nice to hear from you and let me know if anyone has a question.

PEACE!
weaksigs

[kmorgan]

Good good thank you I've been wondering what is used for LF reception that can be easily set up and this is the ticket. Nice post, description and image.

[ChuckRippel]

CLB is about 150 miles south of me.  Great recording and impressive reception for 460 miles at high noon.  Is CLB -> your QTH an all water path ?

Chuck Rippel
Chesapeake, VA

[weaksigs]

Sorry for taking soooo long to reply.
No, the path from here to CLB is not entirely over water.
My location is central Florida over complete sandy ground.
The path from CLB to here is over water to a degree as it slants down
to my location with a good start near waters edge.

I just checked CLB here once again and it is about the same strength.
Usually about this time of year the static levels drop to where it becomes
once again a good time to listen for NDB's.

Lets see what this season will bring!

Cheers!

weaksigs