DX Engineering DXE-NOISELOOP-INS Series User manual

Receive Portable

Flag Antenna Kit

DXE-NOISELOOP

DXE-NOISELOOP-INS-Series Rev 0a



DX Engineering 2021

1200 Southeast Ave. - Tallmadge, OH 44278 USA

Phone: (800) 777-0703 ∙ Tech Support and International: (330) 572-3200

Fax: (330) 572-3279 ∙ E-mail: [email protected]

- 1 -

Introduction

The DX Engineering Receive Portable Flag Antenna kit is based on the design by Don Kirk,

WD8DSB. Don’s article on this antenna is published in the March, 2021 issue of QST Magazine.

The Portable Flag has become a real game changer in direction finding of RFI on MF and HF

frequencies, and you will also find it an invaluable tool when hunting RFI due to the following key

features.

Unidirectional (unlike a tuned loop)

Broadband (unlike a tuned loop)

Portable (easy to walk with while direction finding)

Don spent an enormous amount of time tracking down RFI (radio frequency interference), and

typically used tuned loops when tracking down MF (medium frequency) and HF (high frequency)

signals. Tuned loops work great, but they’re bi-directional and therefore the true direction of the

signal is unknown due to the 180 degree uncertainty of its bi-directional pattern. Don had been

considering a tuned loop along with a sense antenna to make his radio noise direction finding

system unidirectional but he felt there must be an easier system to implement. Hence the Receive

Portable Flag Antenna, a terminated loop was born.

Traditionally Flags are large and designed for stationary use,

whereas the idea for this was to design a Portable Flag. The

Portable Flag was designed to be the largest possible (to maximize

gain) that would fit inside a car and it’s still small enough to

maintain a cardioid pattern up through 30 MHz. The portable Flag

has an approximate dimension of 2 feet tall by 4 feet long which

you (or a helper) can easily walk with while tracking down a

signal. Unlike a tuned loop, the Portable Flag is a broadband

antenna with unidirectional properties, and it’s designed for

direction finding from 1.8 to 30 MHz as long as an appropriate

preamp is used. It’s even useful for direction finding down in the

AM broadcast band. The rear of the antenna produces a sharp null

when pointed at the signal of interest and the sharp null is often used for direction finding versus

using the broad peak which occurs when the front of the antenna is pointed at the signal of interest.

NOTE: This is a Receive Only antenna - do NOT attempt to transmit through this antenna.

Damage to the loop antenna and/or your transmitter may occur.

Optional Items - not included

A custom designed preamplifier / attenuator is available - DXE-NL-PRE-ATT-1.

Anti-Seize for stainless steel hardware: Jet-Lube SS-30 JTL-12555 or Permatex PTX-81343

- 2 -

Safety Considerations WARNING!

USING ANY ANTENNA NEAR POWER LINES IS DANGEROUS

Warning: Do not use the Receive Portable Flag Antenna near overhead power lines or other electric light or

power circuits, or where it can come into contact with such circuits. When using the antenna, take extreme

care not to come into contact with such circuits, because they may cause serious injury or death.

Parts List

QTY

Description

QTY

Description

13 ft

Antenna Wire, 14 ga, Black Relaxed PVC Insulation

PCB, Feed Point

Binocular Core, Mix 73, 0.3H x 0.4W x 0.6L

PCB, Resistor

Coax Cable, RG-58AU, BNC Male Connector Installed

P-Clamp, Stainless Steel, 0.3125”

DX Engineering Hardware - includes the following:

2 - Hex Nut - Stainless Steel, 1/4-20

2 - Flat Washer - Stainless Steel, 1/4”

2 - Split Washer - Stainless Steel, 1/4”

Resistor, 680 ohm, 1/4 w

Shrink Tube with Adhesive, 3/8” OD, 1.5” Length

Starboard Center, Black, Drilled, 6.5” x 8” x 1/4” thick

Tape, Double Sided, approx. 0.3” Wide x 0.5” Long

DX Engineering Saddle, 1-1/2”

Tube, Teflon, 13 AWG, .076” ID x 1.2” long

Element Clamp with stud, Stainless Steel, 1/2”

Tube, Wire Guide, 5/16” OD x 0.17” Long

Fiberglass Tube, 1/2” OD, .120” wall, 4 feet long

U-Bolt, Stainless Steel, 1/2”, 1/4-20 x 0.5 Thread Length

Fiberglass Tube, 1-1/2” OD, .120” wall, 4 feet long

U-Bolt, Stainless Steel, 1-1/2”, 1/4-20 x 0.5 Thread Length

Hex Nut, Nyloc, Stainless Steel, 10-24

Washer, Flat, Thin, Stainless Steel, #10 x 1/2”

2 ft

Magnet Wire, Green, 28 ga, Nysol

Zip Tie, 11” Long

1 ft

Magnet Wire, Red, 28 ga, Nysol

Instruction Manual

This kit will typically take between 1 and 2 hours to build.

- 3 -

Assembling the Receive Portable Flag Antenna

1. Assemble the transformer core using the following components:

Binocular Core, Teflon Tube, Green Magnet Wire and Red Magnet Wire.

The core is made into a transformer that uses the Green wire as the Secondary and the Red wire

as the Primary,

2. Using the core as a guide, cut the Teflon tube into 2 pieces the same length as the core.

3. Using the green magnet wire, insert one end into one of the Teflon tubes in the core allowing

approximately 1/2” hanging out. Make 12 turns through the Teflon tubes in the core. Keep the

wire snug. One turn is once through each side of the core.

Using the red magnet wire, insert one end into the core (not through the Teflon tubes)

allowing approximately 1/2” hanging out. Make 3 turns through the core.

Trim the wires so there is approximately 1/2” sticking out both sides of the core.

Cut away view showing Green wires

going through Teflon tubes Red is Primary Green is Secondary

4. Use a sharp knife to carefully scrape the enamel coating off of the ends of the wires as shown.

Take care not to nick or cut the wires.

- 4 -

5. Attach the double sided tape to the feed point PCB, as shown.

Then remove the top paper exposing the adhesive.

6. Press the transformer on the double sided tape on to the feed

point PCB and run the wires through the feed point PCB as

shown. Note colors of the wires in photo. The green wires

(secondary) connect to the “Loop Wire” holes, the red wires

(primary) connect to the holes near the Coax connections.

7. Solder the wire leads in place. Trim wires.

8. Use one zip tie to hold the transformer in place on the feed point PCB as shown. Do not over

tighten the zip tie.

- 5 -

9. Using the 13 feet of the black antenna wire, cut it in half to make 2 wires the

same length. Strip approximately 1/4” to 3/8” off one end of each wire.

10. Route one wire through the resistor PCB as shown and trim as needed. Route

the second wire through the resistor PCB as shown, solder the two ends in

place and trim as needed.

11. Install the 680 ohm 1/4 watt resistor in the resistor PCB, solder in place and trim as needed.

12. Assemble one 1/2” OD cross fiberglass rod to the black starboard center board as shown. Once

the U-bolts are installed, just snug, do not tighten them at this time.

13. To center up the fiberglass rod, use a tape measure and measure one half the length of the rod

from the end of the fiberglass rod to the center of the starboard center board. Once the rod is

centered, tighten the U-bolt hardware for that rod. Do not over tighten. The distance from the

end of one rod to the U-bolt hardware is 21 inches as shown. From the other end of hat same

rod, it should also be 21 inches to the U-bolt hardware on that side as well. Evenly tighten the u-

bolts in place.

14. Repeat for the second fiberglass rod on the other side of the starboard center as shown.

- 6 -

15. Using the element clamp with mounting stud, install one to the each of the ends of the 1/2” OD

fiberglass rods as shown. Note the direction of the mounting studs. One set is the opposite

direction than the other. This keeps the antenna wire centered front to back. Tighten the

element clamps in place.

16. Install one p-clamp, wire guide, flat washer and Nyloc hex nut onto each of the element stud

clamps as shown. Tighten in place.

17. Take the resistor PCB that has the two antenna

wires soldered in place and run each wire

through the wire guides as shown. Note the

position of the center board. Keep the resistor

PCB centered between the two rods as shown.

- 7 -

18. Use the feed point PCB on the other side of the loop and route the antenna wires through the

guides and then through the feed point PCB keeping the feed point PCB centered between the

rods. Ensure the resistor PCB is still also centered. Snug up the wires and make a small mark

on each wire just above where it passes through the PCB eyelets that will be soldered. Remove

the wires from the feed point PCB, trim the wire lengths and insulation back 1/4” to 3/8” on the

ends. Re-route the wire through the feed point PCB ensuring all is centered and snug. Solder

the two wires on the feed point PCB.

19. Prepare the coaxial cable with BNC connector as shown below. Cut approximately one inch of

the black insulation off of the coax end. Take care not to cut or nick the shield.

You want to separate the shield and center insulation as shown using a soldering

pick or other small tool (small Phillips head screwdriver works good). Trim

about 1/2” of the center insulation from the center coax conductor. Take care

not to cut or nick the center conductor strands. Install the shrink tube with

adhesive near the ends of the prepped coax using a heat gun or other hot air

source to shrink the tube as shown. Insert the shield and the center conductor of the coax

assembly through the feed point PCB and solder in place. Use two zip ties to snugly hold the

coax cable against the feed point PCB as shown.

- 8 -

20. Install the 1-1/2” fiberglass rod (handle for the antenna) to the center board using the saddle

clamps as shown below. Evenly tighten the U-Bolts in place. Do not over tighten.

21. Route the coaxial cable as shown and use a zip tie to hold it

in place. Do not over tighten the zip tie, you just want it

snug.

22. Use an antenna analyzer to verify the antenna is properly

assembled and tunes and there is no shorted coaxial cable.

The reading is typically 1:1 to 2:1 when swept as shown in

the photo.

- 9 -

Overall View of completed Receive Loop antenna

Optional Pre-Amplifier and Attenuator

A perfect companion to the DXE-NOISELOOP is the optional

Pre-Amplifier/Attenuator DXE-NL-PRE-ATT-1. It uses an

internal 9 volt battery, has BNC connectors for Input and

Output, Easy to use slide switches and a power on LED when

the Pre-Amp is turned on. Selectable attenuations levels of -10

db, -20 db (and -30 db when both are on), plus an additional

AM filter can be switched in when needed. Note that this is a

Receive Only system. Transmitting RF will damage the unit

and it is not covered by warranty.

Using the DXE-NOISELOOP

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