wf-construction

IV3PRK Pierluigi “Luis” Mansutti

160 Meters: DXing on the Edge

The Waller Flag receiving antenna.

Building Details

This antenna has been originated by Doug Waller, NX4D, and highly developed by Jose Carlos, N4IS, who lately settled the “Top-Beam” which sells very performing systems. See this page TOP-BEAM Systems - Quality low band, high performance receiving systems.…. but recently (November 2024), JC told me that this company is no longer in business.

Nevertheless, both Doug and JC have been very generous in giving me a lot of advice and suggestions for home building my Waller Flag, after having examined all what was wrong in my previous “not performing WF” tried some years before and installed over a grounded all iron tower.

So, at first, I installed a small (12 meters) aluminum tower with the base insulated from ground; then I found on a surplus store a cheap rugged fiberglass 60 mm. tube to use as a mast. The boom is a full length of 8,2 meters’ aluminum tube (from an old ten meters yagi), which contains and shields the phasing lines, but it is well insulated from the vertical structure of the tower, and from the ground.

By Mouser I bought the small Hammond aluminum and plastic boxes for the transformers, the central combiner and the loads, and prepared everything as seen below.

These are their details:

Loads L1, L2: from a bunch of several 2 watts Allen Bradley 1000 and 180 Ohm resistors, I selected two combinations of series-parallel values to get 580 Ohms for L1, the front loop load, and 605 Ohms for L2, the back loop load.

Transformers T1, T2: 6:1 ratio for T1 and T2, that is 5 turns on the primary and 2 turns on the secondary over a long binocular core (Fair-Rite 2873006802).

Combiner balun, T3: 1:1 ratio, that is 2 turns on the primary and 2 turns on the secondary over a long binocular core (Fair-Rite 2873006802).

Phasing lines FL1, FL2: as I could not find, at a reasonable price, a small quantity of the suggested Belden Twinax 100 Ohms balanced coax, I use two lengths of 50 Ohms RG58 cable taped together to get the same impedance line. Their shields are connected together at their ends and to the boom, which acts as a second shield. On the combiner side, both lines are wound on a FT240-31 core (Fair-Rite 2631803802) as common mode chokes; 15 turns of double RG58 can fit on this core, for a length of 2,60 meters which must be added to the phasing line. Thus, FL1 is 7,20 meters and FL2 is 6,70 meters long to keep the difference of 0,50 m. between them. See phasing line lengths graphs on this page.

At the T junction, the resulting impedance is 50 Ohms but be careful to keep the

correct phase and cross the wires “once” to get the necessary 180 degrees phasing between the loops.

This is the drawing of my Waller Flag, with all dimensions in meters:

One of the culprits in my previous attempt was in the loops: half aluminum tubes and half copper wire. Doug and JC recommended keeping the same material and size, so I used normal 1 mm. house wire taped on fiberglass tubes. I bought on Internet eight cheap 5 meters fishing rods, and used the first 3 sections of them, from 29 to 16 mm. diameter. They are attached on the boom to the old aluminum ten meters yagi plates by means of good plastic “Stauffer” clamps available in many sizes in specialized hydraulic material stores. Two big ones of them (60 mm. diameter) have been used to clamp the boom to the fiberglass mast; if I knew that, I could had used a normal metallic mast, being it well insulated from the boom.

The feed line is a “Messi & Paoloni Ultraflex 7” 50 Ohms double shield coax cable, and a lot of care has been put to avoid common mode problems. 15 turns of such coax cable can be fit on a FT240-31 toroidal core as CMC - commom mode choke. I installed ten of them, on both feed line and rotator control cable: on the antenna, at the tower base, at the house entrance, and in the shack, everywhere associated with 1,80-meter ground rods. It's a nonsense the use of high impedance CMC's to block the RF noise flowing on the outside of the feeline, if we don't provide it a low impedance path to the ground.

Beware: it's a must for the efficency of all receiving antennas !

At first, I inserted at the base of the tower, also a rugged 10 dB Norton preamplifier, but I realized that, more than signal, it was amplifyng noise, and thus I took it soon away.

One could worry about the very low signal ( -55 dB ) coming out of the Waller Flag, but - I repeat - the most important issue is to keep it free of common mode noise. The above pictures show my big FT240-31 cores with 15 turns of coax cable installed at the tower base and at the shack entrance (where there are also the same CMCs on the feedlines going to the BOG antennas).

Another big one in the shack ahead my KD9SV BF998 x 5 preamplifier, which is more than enough with its variable 50 dB gain, sufficient at half way, and low noise, thanks Gary!

Luis IV3PRK December 2016