For the expected solar storm of last 3rd August, I’ve planned a continuous 72 hours transmission of my MF station as QRSS10 beacon since 1st of August afternoon.
I’ve monitored my signal on the MF grabber of Stefan DL7FC, comparing it with IQ2MI signal, downloading for the 72 hours a picture any 10 minutes.
Nothing strange appeared over the pictures, signal was about the same for all days like before.
Only to note that IQ2MI signal appear over the grabbers at about 1800 UTC (sun set at my QTH) while mine about 40 minutes later. The same in the morning, my signal disappear 40 minutes before IQ2MI signal.
Here another picture with IK1HGI signal, too:
Even though I’m 500 Km farther from Stefan my signal seems quite solid.
This is my umpteenth upgrade to the TX antenna to try to get better general performance and get the possibility to work on 136 kHz without tons of electrical wires outside the terrace.
The new layout is drawn in the next basic picture: I’ve passed from 4 top wire and a single vertical tube to 6 wires as in the picture. The hat is always 13 meters long (I don’t want to go over the neighbour roof) but now also six wires come down to about 10 meters to the variometer.
The capacitance was raised from 235 pF to 310, not bad. The only doubt is about the vertical side that is not exactly vertical and it shows an angle of about 75/80° to the ground.
The telescopic pole by now is not more a radiating part of the antenna, this simplified my life because I don’t need to insulate the base of the pole for high voltages.
This is the usual photo of the whole antenna with an Unidentified Flying Object up on the left:
Now the target is to tune the antenna for the 136 kHz that should it be possible with a 4.4 mH coil.
Since my antenna was born as monoband for 630 meters, until today I’ve used an autotransformer built around the variometer.
In these days I’ve tried to tune the antenna on 136 kHz, beginning to put some mH over mH to reach my goal. Arrived to 136 kHz I’ve sadly found that the autotrafo was inadequate to reach the correct impedance. So I tought to build a toroid coupler as seen on the web. A short look inside my “oblivion boxes” just to find a big blue toroid, this is a N30 material, usually used for interferences from several-KW triphase motor inverters.
It has a quite hi initial permeability and the work frequency is exactly for our game, from 10 Khz to about 400 Khz. Somebody could turn up one’s nose but since turns on toroid are only ten or so and mine is not a KW station I’ve decided to try to build my new matching unit.
For first I’ve winded 10 turns for primary and then 14 for secondary, here is what I’ve gotten:
I’ve soldered 10 wires for as many as different impedence taps and painted the welds with insulating paint.
The next step was to put the “spider” inside a box to be protected from rain and dust (and cats…).
The matching unit under the front cover
Every screw is provided of an OR rubber.The wingnut give me the possibility to fast retune the antenna The first test on 136 kHz was an immediate success, SWR was 1.14 at first “wingnut touch”! The same coming back to 474! WOW!
It was time to give POWER!!
Just started the trasmission on 136 I’ve seen power going down “rhythmically”: there was something was arching! Testing on 630 the music was about the same. A brief look on my external ammeter was clarifier. My old autotrasformer was not insulated from coaxial cable, common mode current probably was running over the braid. This new solution now shows me a 3 times bigger current on ammeter. The voltage is of course also higher and the antenna wall insulators cannot resist to this new hi voltage.
So at the moment antenna is perfectly tuned but I can use only about few Watts.
Next step is to increase the insulation to use more than few Watts.
Just arrived (10 days from Japan) I’ve worked for a couple of hours to assemble the U3S Deluxe kit from QRP Labs, later I wanted to try the GPS receiver for my LF activity by Spectrum Lab, so I made the smoke test giving 5 volts to the GPS receiver.
After a while all LEDs were working and Spectrum Lab was disciplining my audio board.
The GPS receiver was positioned inside my lab room, close to the window, it was capable to find 7 or 8 satellites.
1pps and Data Out has been connected to the input of sound card of my laptop and finally I saw a perfectly synchronized system.
An now it’s time to try the rest of the kit after winding the LPF.
Because of strong noise at home, in these nights I’m receiving MF signals from Monte Ripoli remote station. There the noise is very low and I can dispose of good performance antennas, not MF/LF dedicated for the moment.
Here is a screenshot of my signal (on the left) while just some minute before (00:18) the signal from DH5RAE was captured.
I should correct the drift of my transverter… a must to do soon.
My signal is always about the same, reaching always 7 or 8 dB. The aerial distance is about 50 Km.
The audio at 474 KHz of BIA NDB is very strong and also IQ2MI is very clear audible.