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.
Stay toroidal tuned!
Fantastic virtual tour inside the SAQ building
Summer don’t stop MF propagation, here some captures from DK7FC grabbers, the last is from Radio Club Ripoli near Rome:
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.
Here is the U3S without the LPF:
Inserisco questi file PDF dell’amico Mimmo in merito al setup delle porte virtuali su PC tramite VSPE, utile per chi ha radio SDR e molti software da far girare insieme con i dati CAT della radio.
To make a clean sweep of spagetti wires on the bottom of the antenna, to make my XYL happier, i tought to use the aluminium strip for the first section of the TX antenna.
After removed copper wires I connected the variometer to an old 4 el triband yagi for HF aluminium boom by a piece of strip taking care to pass as far as possible from the reinforced concrete column.
Then, on the top of the aluminium tube, another strip of 2 meter or so long to connect the vertical pole (the “antenna“…) located on the roof.
Two insulators are ready to be mounted between the brackets in the wall and the aluminium tube so to try to improve the insulation for the high tension present in this zone.
This improvement, of course, lowered the antenna resonance and changed the impedence of the system.
It seems now that the current has risen by 1/8 compared to before.
- UPDATE 28th April 2016 … :
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.
In the last weeks I’ve tested a new antenna for 630m band. To have also something usefull for 2200m I’ve built an helical loaded vertical antenna followed by a 3-wires hat, so to have a longer radiator that resonate about on 350 KHz.
The coil was about a 45 meter long 3 cm aluminium tape with a thickness of 0.3 mm. It was distributed along a 10 meter high fiber pole (used for my old 80m inv-L antenna).
After windings all the turns I’ve fixed the vertical “python” in the final position and tried to stretch the hat wires… after some seconds I heard “crackkkk”… one of the tubes cracked for the strong flexure.
So, the antenna down again, tube repaired with resin-soaked bandage but now I’ve used a second telescopic tube to support the hat.
Very good! To tune the antenna on 475 KHz I’ve inserted a 1200 pF variable vacuum capacitor, it was too long. Tried the antenna for a few days, as long as a in a weak windy day I made this photo:
There was something strange, the twists were too close and the bending was too evident! Again the antenna down on the roof. One of the inner poles was broken!
So why don’t use the telescopic pole as new antenna? It’s a 10m high pole, and I don’t need of the big coil for 630m. So I’ve decided to use the steel pole and with the only variometer I found the perfect tune on the 630m band!
Here it is: …and here the full 10 meter long hat.
The next step will be to fatten the vertical pole to increase performance and probably to strengthen the ties.
So if you at the moment hear my signal it comes out from this thing, an inv-L 10×10 meters about.
Tonight was the second night for my new 630 meter antenna test.
Thanks to the increase of Lowfers fellows I’ve had the possibility to have more receivers that last year.
I’ve been listened by about 40 different stations in more than a dozen of European country.
This image is relative to the night between 7th and 8th of April.
My new personal “record” for DX has been reached with the over 2000 KM of LA8AV.
The power is less than 60 Watts. Some photos of the new antenna arrangement will be posted here soon.
On 630 meter band page a new video about the renewed remote variometer.