I am back at work. The summer was great despite the rainy final week of my summer holidays.
New engine for me dinghy.
I had a brand new Westerbeke 20B, 18 Hp Marine-Diesel installed in my old 21 ft dinghy this spring. The fuel consumption is only half of what it used to be in my 48 years old petrol-powered engine. And the diesel fuel is much cheaper. The low fuel consumption caused us trouble some days ago when we went out to our summerhouse one evening after work when the temperature here started to reach 30 oC here on the mainland. I had completely forgot that routine of checking the fuel left in the tank and on our way back in the sunset, the engine stalled after 10 minutes. The tank was almost empty and driving at cruise-speed made the bow rise to an angle thad got the fuel left run away from the fuel outet. I had to dive into the bulkhead in the bow and get to the tank, jacked it up and tilted it forward using Ingela's slippers so the fuel left could reach the outlet. The cruise continued at some hefty 4 knots and at that speed (well below hull-speed) the boat remained in a level position and the fuel flow was secured.
Computer crashes several.
I had to finalise some documents at home in the beginning of my holidays so I brought my laptop home. It crashed immediately upon bootup. Harddisk trouble. Got it up and working after running diagnostics, CHKDSK and fixing MBR.
Ingelas fairly new laptop (2 years old)crashed one Monday morning. No warranty left. One IC in the internal power supply on the motherboard had erupted, cause unknown. Maybe overvoltage on the main supply, modern switching PSU:s are a pain in the butt. Good old transformers in the front end of PSU:s would save many vulnerable pieces of electronics from being destroyed at home.
Repair at the producers European repair-shop would cost as much as a new laptop with the same specifications. So I built her a new desktop computer instead. I later on found a motherboard for the laptop, used and in working order, on the eBay in UK and I will put the laptop together again any rainy weekend now.
Upon returning to work my laptop crashed again after some few hours. The HDD went FUBAR this time and I am now waiting for a new laptop.
The Who gave a un-f*cking-believable good show in Helsinki. You can find my comments on that further below in this blog.
We are now eagerly waiting for the DVD from that show to show up in our mailbox :)
Another evening we went to the outdoor summer-theatre in Närpes to see a show. All the actors involved are mostly amateurs and what a good show it was.
As much time as possible got spent at the summer-house. July was though a very rainy month here in Finland as well as in many other places in Europe but as usual, the weather out in the middle of the sea between Finland and Sweden is much sunnier than on the mainland where afternoon and evening showers are common.
A new antenna concept for the HF-bands.
All HAM:s (amateur radio operators) know that there is no real multiband-HF-antenna that fulfills all the criteria that could be put down for such a beast:
-resonant (Z = R +-j0) inside all (or the most of) the "classical" WARC- bands like 80, 40 ,20, 15 and 10 m.
- SWR less than 1:3 when resonant, that means R in between 17 to 150 ohms when operated at 50 ohms output which reduces the need for complex matching devices.
Well folks, that is the antenna I built and tested this summer! the OH6MY antenna. Hit the road G5RV and W3DZZ... :)
It all started several years ago when experimenting and testing different loop-antennas for 40 m. in co-operation with my old friend Lars, SM5GQV, former OH6MX, to get a satisfactory configuration to be able to have regular contacts on the airwaves between our QTH:s, he is living in Norrköping, Sweden. This path is a little tricky, sometimes very good propagations on 40 m, sometimes on 80 m and sometimes not at all.
The problem is the space needed for loops, the easiest way is to hang it horisontally but that usually means that it is hanging parallell to the ground at close to 1/4 wavelenght and the radiation will take off at 90 degress vertically. Good for local QSO:s but not for longer distaces and DX-ing.
So, the main objective was to create a loop that could hang at a low level parallell to the ground and have as low radiation angle as possible.
The radiation problem is solved by shifting the phase of the current maximums 180 degrees, then we have radiation in the same plane as the loop with current maximums at the feedpoint and opposite to it. We are from here on discussing a loop shaped as a SQUARE, fed at one corner.
My idea for the phase shift was to insert shorted 1/4-wave stubs at the corners adjacent to the feedpoint and having voltage maximum. A shorted stub is an isolator at its other end and thus perfect for insertion in the voltage maximum point.
Two 1/4-wave stubs introduces a total of 180 degrees phase shift and that is what I wanted. The 1/4-wave stubs are made of 450 ohm ladder-line.
I then modelled this creation into the 4NEC2 (based on MININEC )software, heigth about 8 meters above normal ground and got really promising results when running the simulations.
The radiation angels were as expected and the impedance at 40 m. was much closer to 50 ohm than i a normal 40 m. loop.
The real surprise was that I in the simulations also could find resonances inside the 20, 15 and 10 meters as well! Even in the 6 m. band :)
Everybody trying to get a normal 40 m loop to resonate in the upper bands knows that the resonance points are well below those upper bands.
And the most surprising finding was that this antenna shows some kind of folded-dipole resonance immediately above 80 m. as well and that I could bring this into the 80 m. band by adding a 2.5 m "whisker" to the shorted end of the stubs without affecting the resonance on the other bands and that the impedance was close to 50 ohm at 80 m. as well!
The basic OH6MY multiband antenna for 40 - 10 m. is as follows:
-antenna wire is 2 mm diameter enamelled Cu-wire
-each side of the loop is 11.1 m.
-each stub is 9.1 m. of polyethylene coated 450 ohm ladder line or (theoretically) 10.1 m home-made 450 ohm ladder made from the same wire as the antenna. I built this using the polyethylene coated line.
I built and tested at approx 8 m. above ground at my summer house (sorry Ingela...)the stubs in the corners are falling down perpendiculary to the plane of the antenna for some few meters and then sloping sidways-outwards, the shorted ends are at approx. 1 m. above ground. Added 2.5 m. of the same wire to the end of the stubs, parallell with the ground to bring it into 80 m.
Different heights and/or ground properties would need slightly different stub lengths, start with 9.5 m and search for the point of resonance on 40 m by moving the shorting point upwards in increments of 5 - 10 cm. The resonance is fairly sharp. Whenever it is in resonance on 40 m. it will be on the upper bands as well.
I have tested and worked several QSO:s and it is resonant on all bands and the radiation angle on 40m is very low, in fact too low for me and SM5GQV because from my QTH I hear German and Italian stations on 40 much louder than I hear him. On 80 we have had good QSO:s despite the very low erection for a 80 m. dipole.
I heard stations from the Middle East and the US one evening on 20 m. Did not try to work them because I am only running some 20 - 30 watts from an IC-706 and a old car battery.
I will post some pictures of this creature here from home later on.
73:s es GL
OH6MY aka Hans
