The BOG’s at HC1PF
Finally getting them to work, and definitely the best, but what a sad epilogue!
So, after the disappointing experiment with the horizontal loop, I decided to get out of my wall and try a Beverage on ground.
I had already all the needed stuff and began to lay down the wire under bushes and brambles, hiding it well in the grass. The area is not cultivated and from time to time there is only some grazing cow (and humans).
Here we see Quito, on the heights at abt. 10 km. far, on the other side of the valley
This is the feeding point outside of my wall. The transformer is a binocular BN73-202 with 5 turns on primary and 3 turns on secondary to match the 75 ohm RG6.
The length 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…!
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:
The SWR curve is flat enough as it should be, but the performance on the air is once more DISAPPOINTING !
The BOG should be a “quiet” receiving antenna, but here 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 I put down another 80m. BOG, with a new shorter RG6 cable and a new transformer, in this area wild and absolutely free of any wire and structure, facing the East direction, towards Europe and Africa. That is opposite to the supposed noise originated by the big city of Quito.
As a first try I left it also unterminated, and the following are the screen images of the midday noise level taken on my SDR-IQ receiver with the different RX antennas available:
Horizontal Loop: -116/-119 dB Rotatable Flag: -113/-118 dB
BOG 80m. unterminated to NW: -93 dB BOG 80m. unterminated to E: -71 dB
Than I terminated the Eastern BOG with a 220 ohm resistor connected to a 1.80 m. ground rod and saw a 10 dB improvement, not yet enough.
BOG 80 m. terminated with 220 ohm to E: - 80 dB BOG 80 m. unterminated to NW: -96 dB
As a reference the following are the same lectures taken with the Inverted L and without any antenna connected:
No antennas connected: -127 dB Inverted L (TX antenna): -74 dB
There is a huge difference between the Flag (it was the same on the Pennants) within the electric fence of my lot, and the outside BOG’s.
What can I try next? March 2, 2015
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, buried it just a bit to not be seen and stolen, and reached almost the valley ridge, where there are no human activities.
Connecting a common mode choke (8 turns of RG6 through three FT140-J cores) and hiding the new feed point
These are my helpers: my wife Luisa and the two local dogs who adopted us:
Trying to hammer deep the far-end ground rod, but hard clay beneath, so I added three 30 m. long radials.
I added also 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 almost 100 meters long, aimed in the N-NW direction and now all NA stations are heard best on it.
Here are the screen images of the noise taken at midday on the SDR receiver. Quite an improvement from 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 !
Rot.Flag 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 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 the following Google map I superimposed:
In LIGHT BLUE: almost 200m. of RG6 coax line
In RED: the 100m. BOG in the N-NW direction with three 30m. radials
In WHITE: the North direction
In YELLOW: the brick walls with electric fences
In ORANGE: the power (22.8 KV) and utility lines
In DASHED RED: 60m. BOG to East with three 20 m. radials
Gary, KD9SV, suggested me to improve the common mode chokes isolation by using a bifilar winding on the binocular BN73-202 . From the 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 aluminum box with a 75 to 50 ohm xfmer and the inductance and blocking capacitor to feed 12 VDC through the coax line.
This is the simple schematics of my BOGs feed and switching with all the winding details
Just a check with the AEA analyzer
For the moment I left the new BOG unterminated
These are the noise level images on the SDR receiver
BOG 100m to N-NW terminated 220 ohms BOG 60 m. to East - unterminated
Finally the noise on the terminated BOG is down to 118-120 dB, like on the flag, but the new BOG unterminated is abt 30 dB higher.
We can see this noise effect better on the AM BC band, centered on 1.360 Khz, my nearest BC station:
BOG 100m to N-NW - terminated 220 ohms BOG 60 m. to East - unterminated
Amazing, all the BC stations are buried in the noise on the unterminated BOG! I was intended to leave this last one unterminated, in order to get it bidirectional and cover both East and West directions, but I realized a good ground connection was needed at the far end.
So terminated with 220 ohms on a 1.80 m. ground rod with three 20 m. radials and got a clear improvement:
BOG 100m to N-NW - terminated 220 ohms BOG 60 m. to East – terminated 220 ohms
The longer one, in the N-NW direction, is still less noisy and I don’t know why…for sure the broadcasting signals all around here are doing a big role.
No much activity on the band in these last days to test the new one, but definitely now my best receiving antenna is the N-NW BOG and I keep it in use not only for NA and JA, but also for Europe.
Quito, April 14 2015 Luis HC1PF
April 24: further improved the BOG’s performance thanks to the KD9SV bandpass filters. All the details on this page.
May 7: Human progress arrives for the first time in this area with a bulldozer to destroy all vegetation.
May 9: Sad End of my BOG’s story !