Saturday, 31 January 2015

G7FEK antenna SWR measurements & LDG RT-100

I noticed that the LDG RT-100 is struggling to tune some bands on the G7FEK.
The antenna is a nested Marconi with two wires tuned for 80 & 40m, with two elevated counterpoises.
G7FEK aerial

80,40,17,15m are ok and the RT-100 re-tunes from memory in fractions of a second.
30,20,12,10m the RT-100 has to perform a full tune to find a match (5-6s, sometimes longer), even when it found a tune previously. I guess this is because the loads are a the limit of what it is capable of. The wind moving the vertical radiators probably does not help either.

I decided to do some measurements today with the VK5JST aerial analyser at the base of the antenna.
At 80m, where the antenna, the measured resistive impedance is 70 Ohm, which I think indicates a poor ground. Radiation resistance should be close 35 Ohm and therefore Rg (ground resistance) is estimated 35 Ohm, giving an approx. efficiency of 50% .

On the higher bands, I don't fully understand why the R is so low. More antenna theory to read & experiments to perform... elevated counterpoises?

F (MHz) R(Ohm) X(Ohm) Impedance(Ohm) SWR
3.600 70 0 70 1.40
7.100 100 55 114 2.74
10.120 22 132 134 18.50
14.050 23 108 110 12.70
18.080 24 55 60 4.88
21.060 29 54 61 4.07
24.890 13 54 56 8.47
28.040 16 38 41 5.05

Sunday, 18 January 2015

SOTA Activations during Christmas break

I activated 6 summits in EA2 & EA5 during the Christmas break. It was great fun to do combined activations with Ignacio EA2BD & Jose EA2KV.

Activation in Navarra with EA2BD

Activation in Zaragoza with EA2KV

In EA5, the WX was simply unbeliable - 17C at 1000m elevation at midday.

EA5/CS -016 Tossal de Saragossa
Very pleasant hike with great weather and ample views of all the valleys and sierras of this part of the province, including various SOTA references: Penyagolosa, Bartolo, Penya, Campanilles, Espaneguera,..
A somehow troublesome activation with a shorted radiator to the coax shield - intermitent conection. Thanks to those who try to contact me.

EA5/CS-020 Campanilles
Acompannied by various family members, fantastic views of the Mediterranean sea. Very sunny and warm WX - about 15C.
Ermita de LLucia, Alcossebre - starting point 
Columbretes Islands 

At the summit, 7m pole, 12m random wire + counterpoise, T1 tuner

Operating position with views. Many thanks to Guru EA2IF & Ignacio EA2BD, who awaited at EA2/NV-097 for our arrival to the summit for a S2S.
After New Years eve, I activated Bartolo & Espaneguera in EA5/CS. Great WX and QSOs again.
73 Angel EA/M0HDF/P