I would like to apologize for the very short activation of OK/PL-022 today. However, I have an excuse. The original plan was to go test a new antenna - a 1.25 lambda dipole on 28MHz and activate at least two hills in a day.
However, in the morning, my 8-year-old son told me he wanted to go to the summit with me, and I couldn’t refuse that. So, I had to slightly change the plan to one easily accessible SOTA. I chose OK/PL-022, even though I had already been there this year.
The weather looked beautiful, but the temperature around 0°C and a light very icy wind didn’t allow me to keep my son on the summit for long. Anyway he kept smiling all the time and enjoyed my CQ SOTA because “CQ” reminded him of “SIKU,” which is his favorite brand of toy cars, HI
Well the WX forecast was for 50% sun, then cloudy then 50% sun. It was 50%sun, cloudy, very heavy showers, more showers. So I quit the summit early.
I got soaked in the first showers but it was windy enough I was drying out nicely but I saw even more rain coming so I pulled the plug and got back to the car just as more rain came down.
Activating in GM in the winter can be hard enough so I can’t imagine how much harder it would be bringing a young child along!
I worked 4x EA stations, 2x OH, G, OE, SP. I did get 2x US and I could hear WP4LG calling me but he couldn’t hear me. This was 1315Z so the band probably just getting useable to USA. But the next set of rains made me shutdown.
So let’s get back on topic… what is the info on the antenna Pavel?
Briefly about my 1.25 lambda antenna. The antenna is inspired by an article of Czech antenna guru OK1VR. The direct link to a PDF with his antenna related articles is here (sorry, all in Czech, but a translator can surely be used) . Essentially, it is an antenna where each arm of the dipole is 5/8 lambda long, and the transformation to 50 Ohms is done according to OK1VR with a 450 Ohm twin-lead of 0.174 lambda length. The theoretical gain of a 1.25 lambda dipole should be around 3dBd and the antenna is more directional.
In my case, the lengths used are:
Length of the each dipole arm (0.75mm² wire with PVC insulation): calculated 6m 42cm. I think it is real but not exactly sure now, because I started with 6m 80cm and then I shortened it for best SWR.
Length of the matching 450 Ohm twin-lead (velocity factor 0.902): 1m 67cm.
Instead of a 1:1 balun at the end of the twin-lead, I placed four ferrite beads (from old PC cables) at the beginning of the H155 cable.
Results at 28.350MHz measured with NanoVNA are SWR about 1,6-1,7 and Z= 61-j28 Ohms which I think is suitable, but I did not play with the length of the twin-lead.
