Archive for the ‘Technical Article’ Category

Systematic Investigation of a large fixed 145 MHz Yagi Group

The following investigations have been performed to lay the base for a larger group of yagis for the 145 MHz band to be used for contest operation at mount Schneeberg, JO50WB. It has been inspired by the antenna group used by the DR9A contest group at their portable contest QTH. Mount Schneeberg is the highest peak of the Fichtelgebirge located in the northern part of Bavaria close to the Czech border. It is very demanding with respect to weather condition and high-frequency environment. Antennas will have to be setup in spring and removed in autumn since they won’t survive the winter storms.


Clearing Space

Killing a Birch

P1140038A birch grown to about 25m height over the years became a creeping danger to the house @DL2LSM. Additionally, it came to close to the main antenna mast and damage already the 2m antenna. So, we decided to cut it down.

Unfortunately, the close proximity to the house and the limited space around the birch prevented us from doing the job on our own. We hired professional tree climbers who cut it down piece by piece. They did a marvelous job.


Antenna Survey @DL2LSM

The standard antenna setup @DL2LSM consists of:

  • a three band spider beam at a height of about 13m, and
  • a 2-by-20m dipole fed by a symmetrical antenna tuner AT-502 at about 12m.

The ground conditions are pretty good with ground water close to the soil. In principle the antenna setup is rather small. Nevertheless, it works amazingly well and allowed for some nice contest scores, e.g. the actual World Record of the Single Operator Assisted QRP category of the CQ WWDX contest. Additionally, a couple of different temporary antennas have been used, e.g. 40m delta loop, 2-by-27m double zepp, 80m wire pyramid, and 80m horizontal quad loop. None of these antennas — although often praised as killer antennas with gain several S units above a dipole — has been really convincing. In order to put the practical observation into perspective a numerical analysis with the 4NEC2 package has been performed. The results are presented in the following.


VA6AM Triplexer

P1130798_smallIn order to use the spiderbeam @DL2LSM in parallel on several bands I’ve been looking for a triplexer. Looking at several approaches both commercially as well as homemade, I stumbled across the work of Pavel, VA6AM. He has been developing a triplexer with respectable performance numbers. Additionally, he provides printed circuit boards, parts, as well as entire triplexers. I opted for a full assembled board. It arrived in good conditions. DL2LSM did his usual mechanical magic to mount it in a suitable enclosure.


u2R Upgrade

My u2R from microHam has been working flawlessly for a couple of contests now. Unfortunately, it is recommended to be operated from an isolated power supply in order to prevent ground loops. I have been using some bricolage solution for a while now. It is not clear why there is no solution originally directly on the board.


u2R Reloaded

My old u2R from microHam suffered from low quality solder joints. I have been receiving a new u2R unit about after two weeks I sent the old one back. (more…)

microHAM u2R Failure

Highly Questionable Quality

As mentioned I have had problems with my microHAM u2r station controller (#196) during the last two major contests (CQ WPX CW 2015 and IARU HF World Championship). The following problems showed:

  • The unit wouldn’t go to automatic receive mode when both receive buttons have been pressed for a longer period of time.
  • The microphone switching didn’t work for transceiver I anymore.


Spiderbeam Repair

P1130685_small.JPGThe storm ‘Niklas‘ caused some minor damage on the spiderbeam. One of the lower guy lines got disconnected when a carabiner malfunctioned. These carabiners are kind of low quality and shouldn’t have been used in the first place. They do not have a latch system and therefore do not lock well. Additionally, the lower guy ropes haven’t been very tense anyway. So, the carabiner simply disengaged when the antenna moved heavily in the wind.


Winter Impression @DL2LSM

P1130641_small.JPG The picture of the spiderbeam and DL2LSM QTH has been taken December, 29 2014.

Persistent Antenna Tuner Failure

The 2-by-20m double-zepp antenna with an AT-402 antenna tuner unit has been working flawlessly @DL2LSM for quite a long time. However, an automated AT-502 controller unit has been used to control the tuner during last years CQ WWDX CW 2013. The unit showed intermittent strange behavior since then. Eventually, the problem has been cured.