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IV3PRK Pierluigi “Luis” Mansutti

160 Meters: DXing on the Edge

My two years in Ecuador as HC1PF - part 2

The electric fence problem.

Quite disappointed by my last serious effort with the K6STI loop, I came to the conclusion that the problem is my electric fence: the loop is inside a big coil of 5 turns, each 183 m. long, as shown in following sketch.

According with the K6STI theory the noise is vertically polarized and the horizontal polarization helps to reduce it, but in my particular case the close coupling with the big horizontal coil is much more dominant and introduces much more noise, whatever is its polarization, and regardless whether the High Voltage is applied or not!

So back to EZNEC and added the electric fence - exactley as measured with 5 turns detalis - to the model. The “antenna view” picture shows the huge currents induced in the fence wires, much stronger than the current on the square loop:

The resulting vertical pattern is completely destroyed, with just a big straight up lobe (Primary black trace) instead of the 45 degrees ones (minor blue trace).

The K6STI loop has been transformed in a DIFFERENT horizontal loop, which corresponds to the realty and explains the high level of noise: more than 15 dB of gain, compared with the original design (blue trace).

The conclusion is that, definitely, I must rethink everything and go back to vertical polarized receiving antennas!

Quito, March 15 2015 Luis HC1PF/IV3PRK

Trying also the DHDL's - from promising models to the sad realty.

As the flag seems to be the only one working in this environment, I went trough EZNEC models at the search of some loops to be installed high enough above the fence, without the need of ground connection. At first, most of the models looked very fine with excellent patterns but, after adding close to them also the TX antenna and the big fence the results were changing dramatically.

I then resumed the documentation from a few years earlier on the DHDL - Double Half Double Loop - an antenna designed by Carlos N4IS and developed by George AA7JV for his DXpedition to TX3A - from which it took its name - that I copied and developed successfully in Italy. Here all the details:

With the available supports - those of the previous pennants, extended with fishing rods - I could reach a height of ten meters; so I decided to try a fixed DHDL towards Japan, and another switchable in the NE - SW directions. The loops are made of very light 1 mm Japanese aluminum wire, but it was not possible to go higher than 9 m., so I looked on EZNEC to find out what the most convenient dimensions were; that is, to choose between a 5 x 9 m. loop with the lower point at a height of 4.5 m., or a 6 x 9 m. loop, but with the lowest point at a height of 3.5 m.

With all those wires in the model, it was clear that the loops with 5 x 9 m. wires above 4.5 m. high (green trace) had better shape and RDF than the bigger ones (blue trace) one meter lower.

Also the horizontal plots seemed not spectacular, but switching directions should have given quite an honest difference - from 15 to 20 dB - taking into consideration the fence and the TX antenna. The following is the complete sketch of one of the switchable loops. There were already coax and a control cable to that area. From the first relay box to the antenna boxes, the 12V are carried through the coax cable.

I put three common mode chokes with 16 turns of RG6 cable wound on a FT240-31 core; one on top of the vertical section of each feed line and one at their switching point with a 1.80 m. ground rod.

The setup was almost the same I had in Italy, but unfortunately I left there those switching and matching boxes, and I had to build them again.

Here, to the rigth, we see the common mode chokes at the antenna boxes connection, and down their placement on the fiberglass poles.

But, these pictures introduced the new enemy, which I had not yet taken into consideration: the outside power and utility lines of the urbanization, running 6 to 8 meters high, closed to my wall… and in face of the DHDL antennas. We see also the rotatable flag and the terminating point of the inverted L, on the roof.

The first “on air” checks were not encouraging, so back to Eznec at the search of an explanation.

I added in the model also those damn power lines….

…..and the reply was terrifying: the presence of the utility lines completely destroyed the previous antenna pattern (blue trace) with an increase of almost 15 dB of noise, all around.

The new primary black trace fills a spheric lobe, with no directivity at all!

The elevation pattern is even more clear:

To the original DHDL model, have been added, one by one:

1) the Inverted L TX antenna (trace blue), which is not interfering too much;

2) the presence of electric fence (trace green) has been managed enough, despite the high angle back lobe;

3) but the addition of the outside utility lines (trace cyan) - bringing a full balloon - seems the final killer!

As I am not yet giving up… what else to try?

Quito, March 25, 2015 Luis HC1PF/IV3PRK

The first BOG's disappointment.

So, after the disappointing experiment with horizontal loops and the DHDL's,, I decided to go on with BOG tests outside of my wall, despite the stealth risks. There was already a coax coming out of the wall and I had tried with a Beverage on ground, laying down a wire under bushes and brambles, and hiding it in the grass. The area is not cultivated and there is only some grazing cow (and humans). Walking one hundred meters from my wall, we see, on the ridge, Quito heigths at about 10 km. distance, on te other side of the valley.

The feeding point, on a 1.80 m. copper ground rod, is just outside of my wall., here on the right picture.

The length of my first BOG should be around 180 m., but I am not sure because a part of the wire, which I left inattentive outside while gone to lunch, has been cut and stolen…! Patiently, I took another roll of wire, better hidden in the grass untill the far end, where I hammered down the termination ground rod.

The transformer is a binocular BN73-202 with 5 turns on primary and 3 turns on secondary to match the 75 ohm RG6 coax. In the shack, after grounding, there is another binocular xfmr to go from 75 to 50 ohms input impedance (5 primary and 4 secondary turns) This is the analyzer impedance plot:

Too perfect match, but useless. The impedance is 50 ohms and SWR curve flat as it should be, but the performance on the air, once more, was DISAPPOINTING !

The BOG should be a “quiet” receiving antenna, nevertheless, the noise level is high. It is terminated in the NW direction, towards Japan, but I began to work my first JA stations and I could copy them only on the rotatable Flag….nothing at all on this Beverage…neither on the horizontal loop, nor on the inverted L. Definitely, flags and pennants are the only possible receiving antennas in my environment.

I had already given up, but somebody told me that probably this BOG was too long, considering the reduced VF of a Beverage on the ground, so I cut it at half and left it unterminated.

Than, after drilling the wall on the opposite side, I brought out a shorter RG6 cable and a new transformer to feed another 80m. long BOG, in a wild area, absolutely free of any wire and structure, facing the East direction, towards Europe and Africa. Which is also opposite to the supposed noise originated by the big city of Quito.

As a first try I left it also unterminated, and the screen images of the midday noise level taken on my SDR-IQ receiver with the different RX antennas available gave these lectures:

Rotatable Flag: from -113 to -118 dB

BOG 80m. unterminated to NW: - 93 dB

BOG 80m. unterminated to East: - 71 dB

Than, I terminated the eastern BOG with a 220 ohm resistor to a 1.80 m. ground rod, and saw a small improvement, to - 80 dB, not yet enough.

As a reference, these are other lectures, taken at the same time:

Inverted L (Tx antenna): -74 dB

No antennas connected: - 127 dB

There is a huge difference between the Flag (and it was the same on the Pennants) within - and despite - the electric fence of my lot, and the outside BOG’s.

Beverages on ground, no matter if long or shortes, trerminated or unterminated: what a disappointment….

What can I try next?

March 2, 2015

Luis HC1PF/IV3PRK

At last, the BOGs begin to work as they should!

My friend Kin JH7PFD suggested me to move the feeding point of the BOG far away, so I put together about 200 m. of RG6 coax, buried it just a bit to not let be seen and stolen, and reached almost the valley ridge, where there are no human activities and walkings.

Beeing asssured that no snakes or dangerous animals are hidden in the vegetatation at this heigth, just gloves are needed to pass the wire through cactus and agaves, and some caution is required only against the eyes of possible thieves.

Here, I'm connecting a common mode choke (8 turns of RG6 through three FT140-J cores) and hiding the new feed point.

And these are my helpers: my wife Luisa and the two local dogs, who adopted us!

Here, I was trying to hammer deep the far-end ground rod, but hard clay beneath, so I added three 30 m. long radials.

I inserted, as usual, two common mode chokes outside and inside the shack (both made with 8 turns of RG6 through three FT140-J cores) and finally I began to see good results.

The BOG is about 90 meters long, aimed to the N-NW direction, and now all NA stations are heard better on it than on the flag..

The screen images of the noise, taken at midday on the SDR-IQ receiver, show quite an improvement over the previous ones, where the difference between the flag and the BOG’s was ranging from 20 to 40 dB. Now the difference is no more than 3 dB !

Rotatable Flag pointed in the direction N-NW: -117 dB

BOG 90 m. terminated with 220 ohm to N-NW: - 115 dB.

In the first two nights of tests I managed to work some low power stations that in the past have been complaining, on DX Summit, that I was unable to hear them. That’s good for sure and this morning, best of all, all the JA’s were much better on the BOG. Unfortunately Europe is 45 to 90 degrees off this direction and I must try something else. In any case this is the way to go, at least one wavelength far from power lines and my electric fence!

In this Google map, I superimposed:

In LIGHT BLUE: almost 200m. of RG6 coax line;

In RED: the 90m. BOGs in the N-NW and East directions with three 30m. radials at each end;

In WHITE: the North direction;

In YELLOW: my electric fence;

In ORANGE: the power (22.8 KV) and utility lines.

Quito, April 5th 2015

A new problem: BCI - Broadcasting interference.

Well, it seems I was getting rid of the noise, finally reduced, but a new problem popped out of it, the “BCI - broadcasting interference”: music and talk spurious signals over all 160 meters band from nearby AM broadcasting stations, less or more loud, during day and nigth.

There is still a plenty of these stations over the Andes, using the upper portion of medium waves; they are not running high power (usually betwenn 1-10 KW) but some of them are pretty close to me and, even if 500 khz down on frequency, their spurious signals are an issue.

Gary, KD9SV, suggested me to improve the common mode chokes isolation by using a bifilar winding on the binocular BN73-202. From the estimated 1500 ohms of my FT140-J chokes, I could had reached more than 3.000 ohms, usually too much and not needed worldwide… but a further help in my particular environment to fight the huge BCI.

With a drill, I twisted two #26 enameled colored wires and could fit 6.5 turns through the binocular cores. I put it in the feeding box with the transformer and a relay to switch the second Bog.

But Andrey, RA6LBS, wrote me that, from his measurements, such a CMC can’t go so high, so I added again also the previous chokes.…”melius abundare quam deficere”!

I put another common mode choke in the shack, in a small aluminium box with a 75 to 50 ohm Xfmr and the blocking circuit to feed 12 VDC through the coax line.

This is the simple schematics of my BOGs feed and switching with all the winding details at both the antenna feeding point and in the shack.

For the moment, I left the new BOG to East unterminated, while the N-NW one is terminated with 220 ohms.

The new readings on SDR-IQ receiver gave, finally, the noise on the terminated BOG down to -118 -120 dB, like on the flag, but on the new unterminated BOG to - 90 dB, about 30 dB higher.

We can see this noise effect better on the AM BC band, centered on 1.360 Khz, my nearest BC station. Down, on this frequency, the noise level worsens by abt. 30 dB and is around - 60 dB on the unterminated BOG (left screenshot) with only the 1360 KHz BC peaking -30 dB (SNR = 30 dB). On the terminated BOG (right screen) the noise level is better as expected, around - 90 dB, while the BC station is still peaking at - 40 dB, thus increasing SNR to 50 dB (+ 20 dB.)

Amazing, on the unterminated BOG, almost all the BC stations are buried in the noise !

At the beginning, I was intended to leave this last 60 m. BOG unterminated, in order to get it bidirectional and cover both East and West directions, but I realized that a good ground connection is needed at the far end.

So terminated it with 220 ohms on a 1.80 m. ground rod with three 20 m. radials also this one (as indicated on the previous Google map) and got a clear improvement.

Anyway, the longer antenna, in the N-NW direction, is still less noisy and I don't know why… for sure the broadcasting signals all around here are playing a big role. No much activity on the band in these last days to test the new one, but definitely, my best receiving antenna now is the N-NW BOG.

Quito, April 14 2015 Luis HC1PF/IV3PRK

In the mean time, my great friend Gary wanted to know which were the frequencies of the strongest AM local broadcasting stations and, in a few days he sent me, as a gift, two specific bandpass filters.

Their insertion was fantastic: both the AM signals on 1.240 and 1.360 khz were reduced on my BOG antennas from 40 to 50 dB!

These are the noise readings on SDR-IQ receiver - with or without - the passband filters, followed by the TS590 S-meter readings of BC spurious.

Amazing: the antenna that mostly benefits from them is the BOG towards East.

Noise level at noon - SDR-IQ readings on 1.830 KHz:

No filters with filters improvement

BOG N-NW -110 dB -114 dB 4 dB

BOG East - 85 dB -114 dB 29 dB

FLAG -115 dB -115 dB 0 dB

These are the S-meter readings of BC AM spurious signals on

TS590 transceiver with KD9SV preamp. in normal op. set-up:

- No filters: BC carrier on 1810 1820 1830 1840 1850 KHz

BOG N-NW S 6 S 7 S 9+10 S 7 S 9

BOG East S 7 S 8 S 9+15 S 8 S 9+15

FLAG S 4 S 4 S 5 S 4 S 5

- With filters: BC carrier on 1810 1820 1830 1840 1850 KHz

BOG N-NW S 4 S 4 S 4 S 4 S 4

BOG East S 4 S 4 S 4 S 4 S 4

FLAG S 4 S 4 S 4 S 4 S 4

What a strange situation: the BCI mix producs were terrible when received through the BOG antennas, and almost null when coming from the Flag. This means that the waves from broadcasting stations mostly propagate over the earth's surface - and not through the ionosphere - and, with the insertion of the bandpass filters, they are completely blocked, thanks Gary!

Quito, April 27 2015 Luis HC1PF/IV3PRK

Sad end of my BOG's story!

But the dream was destined to vanish in a few days, and nights. On the morning of May 7, I heard the clatter of a Caterpillar on the other side of the wall: human progress had arrived there too, in that natural area, never touched before. By the end of the day, all the vegetation had been destroyed, the ground leveled, and all I had to do was search for what remained of my installation.

Luckily the damage was very limited, since the antennas had been moved to the steep slope, and therefore only the coaxial cable that crossed the flat part had been broken. Something easily solvable with my abundant supplies of cables and connectors, but the dilemma was: what future would there be for that so far pristine area?

…and what next for my antennas?

…. See this page

Quito, May 9 2015 Luis HC1PF/IV3PRK