VHF Contest March 2017

Most of our team met on Friday and we managed to erect 2 of the 5 antenna systems before sunset. After that we prepared our time-proven Wasserkuppe barbecue and enjoyed some technical talks about our new “perfect” preamp setup.

Our old setup included no preamps at the antennas but this meant that our very long 7/8 inch LCF coaxial cables plus 4 x 12 meter flexible coax lines up to the 4-way antenna combiners also attenuated the received signals by some dBs.

That is why we decided to reduce the receiving losses. Therefore Tim and Max built mast mounted preamp boxes for 144Mhz and 432Mhz and overhauled the RX/TX sequencing and switching scheme during the Winter. Well-known “suitable” contest amplifiers were installed in the boxes and everything was supposed to be fine, but it was not!

Important to know is the fact that the Wasserkuppe is an extremely exposed location, which is struck by the elements and any kind of rf radiation. Close neighbours are around 11 FM transmitters on Heidelstein and Kreuzberg with 50-100Kw ERP. These transmitters were measured at average levels of -40 to -20dBm on our 144Mhz antennas (without any preamplifiers involved). Moreover there is local flight traffic (tower) on 128Mhz at -50dBm and an APRS digipeater on 144.800 with -50dBm. To put it into a nutshell, we suffered from heavy intermodulation distortion and our “contest preamps” could not handle these levels of rf exposure. This heavily impaired our 144Mhz activity this time and all our preamps will require bandpass filtering in the future.

Similar problems also disturbed our 70cm activity with two local 70cm relays in close proximity. When these relays were opened listening on 70cm became impossible.

What have we learnt from this experience? What can go wrong, will go wrong! Murphy never sleeps :(.

Our final score:

144Mhz: 672 QSOs 202375 points

432Mhz: 119 QSOs 33620 points

Astonishingly the weather was quite fine this time with just some stormy winds in the night. After the contest we disassembled the station in just 3 hours and left the summit at 6 pm local time.

Cu in May

73 de DA0FF Team