Reflections about a remote mediumwave listeners station

After a long preparation time, a lot of gardening work and a failed attempt to set up the 8 m mast, the double delta antenna is ready and waiting for the connection of the balun / resistance box and the coax cable. As soon as the weather permits, initial tests can be carried out.

The DDA is suspended from 2 guy points at a height of approx. 6 m. A compromise already resulted in the suspension. Anchoring points 8 m high were not possible because a mast bar could not be set up in this length. The horizontal wires run 1 m high. It is fitted with a 16: 1 balun. A terminating resistor has 1 kOhm. The resistor sits in a fuse holder and can be easily replaced with another if necessary. The total scope of the DDA is approx. 78 m. The targeted receiving direction at approx. 325 °. By using quick-change termination boxes, the DDA can also be quickly changed to approx. 155 °.



Pictures (from left to right)
1 Connected balunbox
2 Connected resistorbox
3 The 6m mast with guy lines
4 An aluminum pole in the ash bears the second anchor point
5 + 6 balun box with 16: 1 balun
7 + 8 box with 1kOhm resistor in the fuse holder

Left: The terminating resistor of currently 820 ohms is waterproof in an HT tube. The connections are mounted on lamp terminals, without much effort to remove.

Center: Middle: The mast top in 7.50 meters, to the left of K9AY mast. An aluminum tube of 4 m length carries the tip, attached to the plum tree with clamps, freestanding.

Right: The 9:1 balun also resides in an HT pipe. The 4m long mast made of aluminum stands with only 2 guy wires in a ground pipe, which once served as a prop for a parasol. I still wrap my balune myself ...

For the 40 m long wire I use galvanized uninsulated electric fence wire with a diameter of 1mm. Source: 1000 m / < 33 €

Shot 1: Flag-Loop. The noise level is near -138 dBm, signal at -105.3 dBm. Direction 80°.
Shot 2: K9AY. The noise level is near -130 dBm, signal at -107.1 dBm. Direction 35°.
Shot 3: 50 m longwire. The noise level is near -127 dBm, signal at -108.5 dBm. Direction 30°. Connected two CMCC.

It looks a bit better than I suspected in the last post. The antennas were for comparison without preamplifier.

Note: A precise statement can not be derived from this, all antennas should have had the same direction.

The loop has a total circumference of almost 40 m and closes the gap between northeast and southeast of K9AY. The top of the mast is 7.50 m high. The direction of reception is 80° across the northern Indian subcontinent, via Southeast Asia, western Australia and the New Zealand South Island, huge targets for MW-DX.

The loop can be relocated with a few simple steps, if necessary. For Central America reception, only balun and resistance are reversed. As it is rather quiet without a suitable preamplifier, it is amplified by the RPA-2 from DX-Engineering. This brings 17 dBm, which is still 10 dBm below the noise figure of the the K9AY or the 50-longwire.

The flag loop was built according to the pattern of FO0AAA, but is twice as large. The audible front-to-back ratio is better than K9 and longwire, as is the directivity. It was the only antenna that audibly filtered Palangkaraya, Indonesia at 3325 kHz (31.9.2019, 17z).

So much wood for an antenna that is suspended relatively quickly. Some preliminary work is nevertheless necessary for the measurements to be correct.

More additions to the loop will bring time. Now I'm curious.

Left: In the HT box at 4 m height is a Beverage Antenna matching set. The HT box was overhauled and re-waterproofed.

Middle: the CMCC was connected to the HT box with a 75 ohm coax cable at a distance of 5 meters. The ground rod is a discarded water pipe.

Right: a poplar serves as a holder for 3 long wire antennas, each 50 m in length. Not shown: a 2nd CMCC 5 m away from the receiver.

How are the CMCCs? First tests brought a significantly reduced QRN under thunderstorm disturbances.

Common mode choke coils act as a simple wire against push-pull current (signal), while acting as an inductor against common mode current (noise).

The kit, concerned on the HAM radio, contains all the necessary materials to quickly assemble a CMCC box. Only a 16mm drill for the PL jacks and another narrow drill bit for the screw feedthroughs are required, apart from the soldering iron. The box is IP55 certified and can be waterproof if you work carefully on the holes. The three central ferrite cores are shrink tubing sheathed, the associated thin coax cable is cut to the correct length sufficient. For a tech-savvy hobbyist, the assembly is easy, even if as in my case the instructions are missing and can not be delivered on request. The substitute transmitted by the manufacturer images of the open finished box could not help. In particular, I could only do the screwing with a number of washers at its own discretion. Since the screw connection also affects the water resistance of the box there are a few points deduction at this point. Also because the screws are not retractable as shown on the website, but come as slotted screws therefore. Another point loses the box due to an oversized wing nut that does not want to fit on any of the screws. Replacement by post was announced after a prolonged contact with the manufacturer.

Two of the boxes are inserted into the coax cable, one 5 m from the antenna's feed point, the other one 5 m from the receiver entrance. From the earth connection of the box a grounding line must be applied to the ground spike. These are not included in the kit. The earth connection is small in size, more than a 1 mm Ø line does not allow the eye with the pin. The wing nut would dress better if one had chosen a larger one. At this point, you can only rework yourself and realize your own ideas of a good ground connection.

The kit cost on the HAM radio 27 €, so 54 bucks for 2 CMCC boxes + a can of cold beer for free, which you can easily drink away while writing the many emails to the manufacturer.

The CMCCs significantly reduce thunderstorm disturbances. The 50-m antenna now has 4 grounding points.

Azimuthal Map
Center: 50°35'1"N 8°40'40"E
Courtesy of Tom (NS6T)



QTH: D-35390 Giessen/Germany

All 50 m Antennas are connected through a RPA-2 Preamplifier.
I am working on a 250°/ 70° direction.

Actually, everything was not a problem. The components were assembled, the elements assembled, the wire roll positioned in a bicycle trailer, and we went out to the neighboring meadow. There, first the earth piles with the connection components were cut into the dry soil, then the galvanized 300 m cable was towed from point A (NE) to B (SE), the 80 m long coax was laid out to the hut, and the RPA- 2 connected. The first test showed remarkably good signals over the entire medium wave, no additional amplified noise due to the preamplifier, in short: the perfect antenna for receiving from the NE direction. A two-hour recording showed me later, how good 300 m antenna cable can be.

I sat in my garden hut in front of the waterfall screen and listened intently, likening the reception to the now weak K9AY, it was around 1930z when I heard voices unknown from outside. When they did not stop, I left my seat, walked to the shack, and watched a person slam through the blackberry hedge. I would not want to go through that, I said. Police, was the answer. In the light of the flashlight I could see the lettering on the man's jacket. In fact, I said.

Displaced dog owners carrying their Fiffies on the meadow suspect a power cord, the policeman said, while his companion expertly examined the coaxial cable. It's an antenna, I confirmed, and that's guaranteed no electricity in it. Good - the law did not come to the dicuting. Now the identity card was checked, a radio check was made, and then I was allowed to roll up the quickly mounted antenna again. So that the dog owners can perform their Fiffies again the next morning. We'll check that later, they said before I let them out through the official entrance to the garden. No, we do not want to go through that again, they said, and disappeared in the darkness of the night.

Days later, I realized that the preferred direction of arrival from NE was not guaranteed at all, because one earth point was in the wrong position. So it is not even a pity that the experiment did not work out. It was exciting enough, from planning to firing.

40 safe meters remain me, NE 4-5 m pulled over the impenetrable blackberry hedge, soon. After all, it's my garden, and I do not keep dogs.