30th Dorsten GHz-Convention

On 24 February 220 microwave enthusiasts from Germany and neighbouring countries, such as G, PA0, ON and HB9 met for the 30th time in Dorsten. The participants numbered as many as in the previous year, which bode well for the conference.

As always, the convention had been organised by DARC chapter Herrlichkeit Lembeck in cooperation with District N and the Dorsten Adult Education Centre.

While ´holding an event, such as the Microwave Convention, for thirty uninterrupted years represents a noteworthy achievement, the organizers nevertheless resisted the temptation to 'enrich' the proceedings by indulging in endless self-congratulatory eulogies.

However, convention chairman Peter Hörig, DL4BBU, briefly reminded delegates of how the informal get-togethers of a handful of Gunnplexer enthusiasts have grown into the Convention; how it has managed to firmly establish amateur radio on the microwave bands, and Dorsten as the widely recognized venue for the sharing of know-how and experience among microwave amateurs.

Following the introduction of delegates, Alfred Schlendermann, DL9GS, Head of the DARC's radio sport department, honoured the winners in the three categories of the VHF-Cup. There was the 'customary' First in the single-operator station category. Hans Harazim, DK2MN, who secured the cup for the tenth time. Runner-up was another 'regular', Norbert Richter, DL1SUN. DL1SUZ came in third and managed to thus consolidate his place amongst the winners of previous years.

DL0GTH, who secured their first place in the multi-operator category for the ninth time in succession, was represented by several members of their team to receive the cup, as were runners-up DM7A and DF0YY. Newcomer DF0YY is an aspiring team with the potential to improve its placing in future years. Their exemplary efforts to involve younger amateurs in the microwave field alongside their more seasoned peers in no small measure contributed to their success.

For the first time, DARC chapter Elbe-Elster made first place in their chapter-category , narrowly ahead of the Bergkamen and Schwerin-chapters.

DJ7DJ, the leader of the Bergkamen chapter then asked delegates to observe a one-minute silence in remembrance of Wolfgang, DG9DM, who had passed away on 11 September following a heart attack he had suffered while at the chapter's portable operations site, shortly after the close of the last 2 metre-IARU contest.

At the end of the awards ceremony delegates saluted the successful contestants for their achievements and applauded Alfred very warmly for his hard work in evaluating log submissions for the annual VHF-, UHF- and microwave-contests, a role from which he was now resigning, as previously announced.

Anyone undertaking the role of contest evaluator for more than 40 years with such commitment deserves special recognition, and the convention organizers felt that there was no better way than for someone from the ranks of the active contesters to honour Alfred. When they were approached, DL0GTH, (who, after all, had generated most of the work for Alfred in recent years), spontaneously agreed to prepare an encomium. Jens Kosch, DL2AKT, paid tribute to Alfred's achievement in systematically developing the DARC's radio sport department into a meaningful entity. The ensuing extended applause by delegates will have demonstrated to Alfred just how invaluable his work has been for the whole VHF community.

But more accolades awaited Alfred. Aside from his log evaluation work, Alfred was also a very active "activist" on the microwave scene - in the early days even presenting papers at the GHz-Convention - and one of the few attending all 30 events. DJ6XV, father of the Convention, gave recognition to this achievement by awarding Alfred the District's badge of honour. Alfred took the opportunity to introduce his successor, Martin Henz, DL5NAH, who thanked Alfred and promised to continue his work as he would have wished.

Finally, those delegates who, like Alfred, had through the years faithfully attended each and every convention were also honoured. Heinrich Frerichs, DC6CF, who has produced video recordings of all the conferences for the last 30 years was awarded District N's golden badge of honour. And much to everybody's surprise, the conventions 'founding father', DJ6XV, himself was honoured for his contribution to the amateur community. His 'co-organizer', DL4BBU, presented him with District N's golden badge of honour. DJ6XV, who already is a recipient of all of the DARC's awards was visibly moved by the unexpected award by his own district.

Jürgen Dahms, DC0DA, the led off the presentation of the technical papers. His first paper was a retrospective look at 30 years of GHz-Convention from the technical standpoint. In preparing the presentation, Jürgen had singled out the particularly significant era of the nineties, when contacts on the 'high' frequencies were almost exclusively made using portable apparatus, sometimes also known as BBT-equipment. Jürgen had searched his archives, and using a series of photos featuring his own setups of microwave modules, presented a historical summary.

Immediately following this presentation, Jürgen focused on the newly allocated 122 GHz band, first giving an overview of the 'capture' of the band and the contributing amateurs. He then outlined in great detail the theoretical circuit design and the practical realization of a 122 GHz transverter. His step-by-step explanation of the construction and alignment of the local oscillator, the peculiarities of the diode mixer and the alignment of the various modules should allow any interested amateur to construct such a transverter. Jürgen's planned demonstration of a contact on 122 GHz with DJ6BU across the lecture theatre as part of his presentation had to be rescheduled due to pressure of time. Despite this, Jürgen's plan to honour those amateurs most active on 122 GHz for their European distance record was put into action. Karl Ochs, DJ6BU, and Walter Iller, DH6FAE, had bridged a distance of 31 km during the 2006 IARU Microwave-Contest. Jürgen and the organizers congratulated the record holders on their achievement and DL4BBU presented each one with a bottle of special 'soldering fluid' and a certificate.

Having completed his presentation marathon, Jürgen then handed off to Heino Schübbe, DJ6JJ, who embarked on a similarly extensive programme comprising three separate papers. He began by describing the conversion of commercial 23cm-modules for use in the 23cm amateur allocation. Pursuing an original idea by IK8UIF, Heino described the conversion of the module types MHW 1815 and MHW 1915 that cover the bands 1805-1880 MHz and 1905-1930 MHz, respectively. Conversion of these modules, which are available on the surplus market for approx. two Euros, is a rewarding project that can be undertaken by just about any GHz-amateur following Heino's detailed instructions, with each critical step being documented by a series of photographs. Heino has converted a total of 22 of these modules which are capable of a power output of 15 W (P=1dB). The lowest amplification gain measured was 33dB (max. Pin= 17dBm). The modules can also be operated off 13.8 Volts, however output is then limited to approx. 8W (Pin=10dBm).

Heino considers these units suitable for application as a single-stage driver for power amplifiers, measuring amplifier for determination of intermodulation characteristics of power amplifiers and as a four-stage driver ahead of a BLV 958 yielding an output 4 x 60 watts.

Judging by the audience's positive reaction, Heino had clearly managed to deliver the desired impact with his presentation.

Next he reported on a novel design concept for a 13 cm transverter born out of to avoid interference from a new UMTS base station (near his QTH) producing wideband noise on 2320.100 MHz at Heino's location. Research into the UMTS frequency blocks indicated that the highest frequency used was close to the local oscillator frequency of Heino's transverter. A narrow mechanical interdigital filter ahead of the receiver input gave some improvement, but despite this weak DX-signals would have still been buried in the noise. While searching for an engineering solution to overcome this problem, Heino dug up his 'UNILO' (universal oscillator), which he had first introduced at the 1989 convention. Using this as the L.O. in his transverter proved highly successful; the wide band noise had disappeared! Heino concluded that his original transverter design must have allowed mixing of the input frequency with a random frequency multiple. In order to avoid such problems he developed a new, simple-to-build transverter concept and has already produced a prototype. Heino stressed, however, that the design had not yet matured sufficiently to be reliably replicated and presented it only as work in progress to stimulate discussion. He is planning to rework his design and to incorporate state-of-the-art frequency synchronisation (PLL synchronised by a high-accuracy 10 MHz GPS-signal and a 10 MHz OCXO). He will report on progress at the forthcoming GHz-convention.

As a special bonus Heino presented results of a modification of a commercial 23cm power amplifier (XRF286). These units, employing three XRF286s by SPECTRAN, are appearing on the market from various sources. But initial tests were sobering; with only 30 - 40 watts output at 28V and Id=18A!!! Heino has, therefore, decided to design a more efficient 23cm power amplifier based on the XRF286. This is not a new concept as F1ANH has proved by obtaining 330 watts from four XRF286s.

Heino explained first how to remove the FET's from the commercial amplifier's circuit board. He then illustrated the electrical and mechanical "rebirth" with a series of photographs. In this manner he managed to extract 130-150 watts from a single-stage PA (Pin= 16W and Id approx. 15A) - a dramatic improvement in efficiency. Heino wrapped up his presentation by showing how to build a "duo"-amplifier (two coupled single-stage PA's with four XRF286) that is capable of delivering nearly 300W output.

As always, the lunch break created a dilemma for delegates who had to chose between the nose bag and a live demonstration of satellite reception in the 8.4 GHz-band. To this end, Freddy, ON6UG, had brought along his portable station consisting of a one-metre dish, an integrated GHz-converter and the back-end receiver. Freddy's aim was to receive signals from MarsRO. Sadly, as in 2006, these efforts proved unsuccessful as the orbital position of MarsRO at the time was once again unfavourable. But Freddy made the best of the situation by capturing signals from the sun observation satellite STEREO.

There was little respite for Freddy who had to launch into his next presentation immediately following the lunch break. His paper on measures to improve the gain of small parabolic reflectors was of technically high standing. Improving the performance of such reflectors is of particular importance for use in EME and so-called deep space communication where every dB counts. In the microwave bands above 10 GHz the majority of amateurs use dishes with prime focus feeds because of their ease of construction and low cost. But such an arrangement suffers from poor efficiency - typically only 50% to 55% - and other drawbacks, such as a dramatically reduced 'illumination' at the edge of the reflector. This can suffer deterioration of some -10dB relative to the centre which impairs gain further. This 'overspill' effect allows additional unwanted noise to reach the receiver. Also, the centre of the dish is obscured by the feed which causes an additional 1dB loss. Generally, the best approach to improving parabolic dish performance is to incorporate sub-reflectors as in the CASSEGRAIN antenna, whose efficiency can reach 75%. This arrangement also reduces pick-up of unwanted noise by reducing 'overspill'. Further improvements can be achieved by employing specially shaped sub-reflectors which allow the construction of 'axially displaced' antennas; they can achieve extraordinarily high efficiencies of up to 91%. Freddy first outlined the theory behind optimum placement of the feed in the reflector and then showed how to achieve this in practice using amateur techniques. Using a series of diagrams Freddy showed that gain improvements of the order of 3dB are achievable while reducing overspill at the same time. Unfortunately, the time allotted to Freddy for this most interesting paper proved too short as, clearly, he could have gone on about his topic for much, much longer. Freddy received extended applause from delegates for his paper and his live reception demonstration during the lunch break.

The next speaker was Steffen Braun, DJ5AM, from Dresden who attended the convention for the first time and immediately launched into his paper '47GHz transverter - built on the kitchen table (almost)' which delegates had been looking forward to with considerable curiosity. His refreshing, highly stimulating presentation reminded delegates of the spirit of the early years of the Convention. He did not waste time on the well-known circuit design but focused instead on the mechanical 'how to' of getting such a project off the ground. He explained how to home brew the parabolic dish and how to resolve issues associated with matching of the feed, as well as the alignment of the receive/transmit mixer with basic measuring equipment. In order to achieve the necessary mechanical stability the complete transverter is built into a wooden case that also serves to protect the equipment during transportation.

Steffen thus demonstrated that it is still possible to put together a technically demanding project, such as a 47 GHz-transverter, using simple methods and 'attitude'. Delegates applauded his spirit and style and a few may have felt renewed appetite for experimentation and tinkering.

It is hoped that Steffen will soon again give an another paper at one of the forthcoming conventions.

The final speaker was Norbert Richter, DL1SUN, who had obviously 'smelled blood' as a result of presenting a paper together with OZ1FF at the previous year's event. Norbert - the eternal runner-up in the 'UKW-Pokal' - set out to demonstrate how a single-operator station 'at the fringes' of a poor VHF-site can successfully participate in VHF contests. In his presentation he outlined the strategy and tactics he applies during a contest and how he performs contest post-mortems to analyse performance, to identify weaknesses and how to improve the equipment used. Photographs revealing the terrain limitations inherent in his QTH will no doubt have served to encourage others having to operate from similarly poor sites to also 'try their hand' in a contest.

In his wrap-up DJ6XV thanked all presenters on behalf of delegates for their invaluable commitment to, and support of, the Convention. He expressed his delight at the large number of papers submitted for the event, whose inclusion in the programme had proved somewhat of a challenge for the organizers. Delegates' feedback on the format of the Convention had not unearthed any real issues and Peter confirmed the organizers' intent to continue with the time-proven format and style, whose focus on papers concerned with the technical and operational aspects of GHz-amateur activities, has been the key to its enduring success. However, he stressed the importance of participants' readiness to continue to support the convention by presenting technical papers and other contributions.

DL4BBU noted that he had already received a number of commitments to support the next year's event and reminded everyone to follow the status of preparations via the convention's home page and its 'call for papers' section. On behalf of webmaster Ralf, DG6EA, Peter requested delegates to send in photos taken during the Convention to be posted on the on the website.

As always, all papers presented will be published in the proceedings which will be available DJ6XV at-cost (6.00 € + 3.00 € P&P). Past conventions' proceedings and their contents are listed on the website under 'Rückblick'.

Video/DVD recordings of the Convention are available from Heinrich Frerichs, DC6CF, Süderstraße 12, D-26835 Holtland.

Remarks: The corresponding pictures you'll find in the German version on the website under 'Rückblick/2007/Bilder'.

A special thanks to Joe, DK3NG/G4XXW for his "literal work" to bring the German version in a "good English style".