I just realized that the last time I have blogged about my pet project, Gpredict, was back in February 2007. Back then, the big news was the Sky at a Glance function and there has in fact been a lot of evolution since then despite the big silence in the Gpredict Developer Blog. Let me try to sum up the progress from last two years as well as what you can expect to happen in the weeks to come.
Like with any other multi-band vertical the different bands are coupled with each other. This means that modifying the settings on one band will influence the others. This effect is worst on the low bands (40 and below) and less noticeable on the higher bands. If you only have the basic two-band HF2V there are only two bands/parameters to adjust and you can easily get through the alignment by doing a few iterations on each band. However, if you have the 30 or the 160 (or both) extensions mounted, aligning all 3 or 4 bands can become an endless process.
Tuning the 80 meter coil of the HF2V messed up my settings on 40 and 30 meters in a way that I ended up with barely acceptable SWR on all 3 bands. I definitely needed a new tuning strategy.
Now it’s time to adjust the 80 meter coil. The current setting for all three bands are given below
With the current settings on 30m (26cm 2.5 turns shorted), fc on 40 shifted to 7.188 MHz – even with 8 turns shorted. Moving the shorting strap to 7 turns, fc shifts to 6.988 MHz. With 7.5 turns shorted fc = 7.039 MHz.
I have tried to adjust the 30m coil on the HF2V in order to bring the resonance closer to 10.1 MHz. Increasing the length of the coild 17->20 cm did indeed move the cenntre frequency to 9.2 MHz, but going up to 25 cm did not seem to make a big difference; it only moved fc by about 250 kHz.
By studying the graphs in the User Manual I have come to the following parameters, which are supposed to be good enough for CW work. Note that 80 and 40 meters can not be tuned independently, which is why the centre frequency on 80 meters is set to 3.6 MHz.
The resonnance frequency of the ATX-1080 is adjusted by selecting the correct taps to connect (band change) and adjusting the telescope length for fine tuning on the given frequency. The radial length should have different lengths for each band as well. The original document describes which taps need to be connected and how long the telescope should be on each band, but says only that the radial length should be less than 1/4 lambda. Wimo, on the other hand, provides to pages of documentation in German, where they also give some start lengths for the radials. Also, a useful formula l [m] = 54 / f [MHz] is provided.
I felt I should give the FT-817 a fair chance, so I have put the DX-88 up again. Of course, I have new tuning parameters and it seemed, that some of the parameters were not like they should have been.