K9FD Receiving Loop

  • K9FD Receiving Loop
    K9FD Receiving Loop

RECEIVING ANTENNAS

The K9FD Receiving Loop

The Answer To Suburban DXing On the Low Bands - by K9FD

Editor's note: Merv Schweigert, K9FD, has been working jusl about everything on
the 40, 80 and 160 meter band" this season. In this article he shares some of
his experiences with receiving antennas. lf you live on a typica! suburban lot
you might want to read this article carefully as you won't need forty acres to
use this antenna. A few months ago I lost access to my faim neighbor's corn
field that I used to utilize for Beverage antennas in the winter months. In the
past I would erect a few terminated Beverage antennas towards the east and south
to enhance my receiving capability on the low frequency bands. After losing this
superior receiving capability, I set out to find some kind of replacement system
that would again allow me to be viable on the low bands.

Early Receiving Antenna Trials - My first attempt at improved reception was a
low dipole for 160 meters. This antenna was installed at the 8' level. After
trying it for a few months, I abandoned it as copy was typically better on my
transmit antenna, an inverted L at 75'. The search for Q5 copy continued.

My next receiving antenna project was a 2 wire Beverage that is described in the
Beverage Antenna Handbook, written by Victor Misek, W1WCR. This antenna is 238'
long with the wires about 6' off the ground and utilizes a tuning network that
changes the phase angle to null the noise off the rear. This antenna worked
fairly well, to the south, but because of some power line noise to the north
that always seemed to surface as I was trying to make a DX contact this system
was also setaside.


        The third attempt at improving my receiving capability was to try a
receiving loop. My information said that the loop has a terrific null off of the
side and if shielded can be quite effective. The first receiving loop I tried
was made with RG-59 coax, as recommended and it did work rather well. You could
rotate the loop and null the noise down to zero and still hear signals. The
problem that I encountered with loop #l was that the signal strength was low and
a preamp would be required to correct this condition. When you run a kilowatt
in close proximity to a loop you can imagine what will happen to the preamp
unless switching considerations are taken. This switching concept is certainly
possible, but a more elegant solution with less complexity was tried.


        The next loop I constructed was similar to the RG-59 loop except that I
used 3/4" 75 ohm TV hardline in the construction. This cable has a much larger
center conductor. I am very much impressed with the results. The signal gain is
much better than the RG-59 loop and no preamp is required. This loop works well
on nulling powerline noise and can also help you null out the noise produced by
approaching thunder storms.


        Constructing the Loop - This receiving loop is constructed from a 20'
long length if 3/4" diameter 75 obm cable TV hardline. Form the length into a
circle and using a pipe cutter, cut through the shield at the top center of the
loop in two places about 1" apart. Then, using a hacksaw, careftilly split the
1" section from the hardline and peel it off. To strengthen this gap, place a 6"
long piece of (split) 1" PVC pipe over the gap and secure it to the cable using
a couple of hose clamps.


        You can house the trimmer capacitor in either a metal or plastic
enclosure. Use a grid dip meter to tune the loop for resonance on the band of
your choice. I used a 400 pf. fixed mica capacitor with a 400 pf trimmer in
parallel for the system at K9FD. Conclusion - In using this loop I sometimes see
some directive properties on DX signals. Some publications say that the loop is
omnidirectional to sky wave and only has directional properties to local noise.
I have no answer to this as it is not apparent on every DX signal. What I do
know is that the use of the 3/4" diameter 75 ohm cable TV hardline for
constructing the loop receiving antennamakes a huge difference.


        You will also find that the hardline loop will require less of a support
structure. When placing your loop in your yard try to locate it as far away from
your transmit antenna and other structures as much as possible.


        This antenna is not a substitute for an 80 acre Beverage farm, but if
you are on a small lot and are plagued by power line or other man made noise
this receiving loop will improve your receiving capability on the low frequency
bands. You won't work all of the DX, but you will get a much bigger share than
before.


THE LOW BAND MONITOR - NOVEMBER 1994