The Swedish EME meeting in Örebro, May 2013
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PA7JB, G4RGK, G3LTF, SM0ERR, RW3BP, UA3AHM, SM7FWZ, UA3TCF, SM5BSZ, DJ8FR, SM2CEW, SM0DFP, SM7GEP, RA3AQ, SM4IVE, SM6PGP, SM5QA, SM7SJR, SM6CKU, OZ4MM, DL1YMK, YMK/Monica, SM7GVF, ON5TA, PA2DW, SM4FXR, SM6FHZ, ON7UN, DL6SH, SM4DHN, PA3DZL, OZ6OL, KE9M, HB9BBD.
Pictures by Ingolf Larsson, SM6FHZ Report compiled by Peter G3LTF. There were 32 attendees at the 2013 Swedish EME meeting at Orebro on May25-26 May who enjoyed a fascinating set of presentations about detailed aspects of EME as well as enjoying the opportunity to meet, greet and discuss with old friends. Thanks of everyone go to Lars SM4IVE for organising the event and to all the presenters and supporters, especially Mart SM0ERR and Leif SM5BSZ who supplied and manned the measurement suite.
Ingolf SM6FHZ described a suite of Kumar (VE4MA) feeds with 5 step septum polarisers, carefully optimised for f/D ratios 0.32 to 0.42 for 23, 6 and 3cm. This is focussed on optimum amplitude and flat phase across the aperture and low cross polarisation. The measured performance of return loss (RL) and isolation shows excellent agreement with the modelling results. The W1GHZ feed efficiency programme is used for evaluation so direct comparisons can be made with other work. All dimensions are given for 23, 6 and 3cm. See http://www.2ingandlin.se/SM6FHZ.htm hopefully, in time, Ingolf will add 9 and 13cm dimensions. With this suite and the septum fed W2IMU described by Marc N2UO (see http://www.ok1dfc.com/EME/emeweb.htm ) we now have for 23cm a set of optimised feeds covering 0.32 to 0.6 f/D. Ingolf cautioned against scaling between frequency bands so we probably need some more work on the septum fed W2IMU for 13-3cm. For those who play with feeds and dishes Ingolf’s slides 13-16 are of great interest because they show that, because of the variation of cross polar response with choke position it is possible to maximise sun noise (randomly polarised) but then find yourself with sub-optimum coherent signal performance.
Hannes SM6PGP described the manufacture of the new design Kumar feeds for 6 and 3cm using his home workshop and for those who build feeds I strongly recommend looking at his slides for some useful tips on manufacture and assembly / alignment. The designs use standard pipe sizes which is a big advantage. Both Hannes and Ingolf have used these feeds in their systems with excellent results. A novel 5 step septum feed suite_A.pdf (Link to Hannes' webpage for updated versions of the document)
Leif SM5BSZ outlined the several potential error sources when making accurate total power measurements of moon (or radio star) noise as a means of evaluating system noise temperature. Very small Y factor ratios are involved. For example because most LNAs gain values are very sensitive to input source impedance a small change in feed position relative to the dish surface could induce an error. A more accurate measurement of moon noise can be made by injecting a small stable signal into the front of the system and making a SINAD measurement instead using LINRAD. Leif was also making a set of precision NF measurements using a special set up described on his webpage http://www.sm5bsz.com/lir/loss/1296/hp8970a/hp8970a-auto.htm
Mart SM0ERR described how accurate measurements of very small losses in components like adaptors and relays can be made. The magnitude S11 of the item to be assessed is measured using precision open and short circuit terminations at its output terminals. By taking the average and dividing by 2, the loss can be measured. This is best done by using an automatic network analyser. (But it can be done manually). Some actual results were presented. Note that at 23cm with NFs now in the 0.2dB region these items have even more effect on Tsys. Mart also measured the Noise Figure of a large number of preamps and the results will be on this webpage when the document is compiled.
Jurgen DJ8FR demonstrated the use of a highly portable VNA made by SDR kits http://www.sdr-kits.net/Webshop/products.php?14&cPath=5 to measure the RL and isolation of a 23cm RA3AQ feed
Sergei RW3BP described the progress with his 76GHz system, the essentials are a 60W twt (that requires 31kV), a 2.4m offset dish, and several 4db LNAs. But that is just the start! Sergei described a long and painstaking process of finding the correct focal point of the dish; and similar efforts in all other areas of the system. The reduced radar cross-section of the moon, libration and atmospheric absorption add extra losses of 25dB in summer, reducing to 19dB in winter (that’s a Moscow winter) He showed clearly visible echo results using stacked up echoes on Spectran. This is a unique set up involving serious engineering and Sergei hopes that someone in NA will soon construct a similar set up for the first 76GHz EME QSO http://www.youtube.com/watch?v=2En_W2EaJFw
Dmitry RA3AQ presented the results of modelling using the OM6AA full dish simulation of some of his feed designs in various dish sizes. With the low sky temperatures at 23 and 13cm especially, and very low noise figures in the 0.2dB region there is much to be gained from careful feed and f/D choices. A lot of very interesting data is available from his presentation and if there is one clear message it is this. Looking at the W1GHZ curves of dish efficiency versus f/D ratio, be sure to stay on the lower (smaller f/D) side of the peak.
Dick PA2DW brought us up to date on the PI9CAM Dwingeloo dish project, he showed the fascinating film that was shown at EME2012 and emphasised the use of the dish for educational outreach. An enormous amount of repair and restoration work has been done by volunteers as well as professionals and the hope is that the dish will be back in operation in November/ December this year. Many hundreds of QSOs were made on 70 and 23cm before the re-build began, hopefully with the dish profile improved from the repairs (with new magic mushrooms!) there will be some more operation on the bands above 23cm.
Ingolf SM6FHZ and Hannes, SM6PGP described a novel 23cm feed for small dishes (1.8 and 2.4m) comprising a patch housed in a cavity with a beam-forming ring in front. Ingolf modelled this comprehensively and optimised its performance for two variants one with the ring covering f/D 0.34 to 0.43 and a second 0.3 to 0.38. Detailed dimensions and construction details are given on his webpage, quoted earlier. There are two orthogonal feed points which can be fed with a 90 degree hybrid to produce the required CP and with SSPAs spatial combining can be utilised, saving a high power combiner. Hannes has used this on his 1.8m dish to make both CW and JT65 QSOs and has copied LX1DB and OK2DL on ssb. Circularly polarized patch feed for 1296 MHz_A.pdf
Dominique HB9BBD showed a fascinating film detailing the obtaining, restoration, installing and then re-installing (to get an improved window) of his 10m dish. This involved substantial amounts of steel and concrete and the use of helicopters and large cranes, definitely not for the faint-hearted! With its hydraulic control system it is a beautiful piece of engineering. The film was also very entertaining and the on-air results speak for themselves. http://hb9bbd.ch/
Michael DL1YMK and Monika described their 2012 EME dxpedition to Corsica. For the first time they added 6cm operation to the bands worked on the 4m stress dish and also (another first) used 10GHz with a separate 1.8m solid dish. For details of QSOs made on 70, 23,13,6 and 3cm see http://www.ok1dfc.com/peditions/ymk2012/dl1ymk2012.htm 9cm is not available in French territories. Michael concludes that the stress dish is not good enough for 6cm, although he did make 5 contacts, and that a 1.8m dish is too small for 10 GHz CW contacts so his plan is to find a way to take a 2.4m dish on future expeditions for those two bands. It has to be both light and transportable in sections. (He is considering offset following discussions after the presentation!) We could not determine the location of this years (possible) planned expedition but were told that a complete absence of small biting insects inside the house is now an essential for the logistics manager. Schweden2013.ppsx (abt 33 Mb to download. You may need Powerpoint viewer to watch the file, available at the Microsoft webpage)
Michael DL1YMK described the design and construction of the two SSPAs that he made for the Corsica expedition. These used devices from ELISRA TV links combined with ring hybrids and needed a significant amount of “snow-flaking” to tune then up. Michael emphasised the need to protect the eyes while doing his as there is a significant radiation from the strip line discontinuities Useful device numbers are FLM1112-8F, FLM1112-12F and TIM 1112-8, Schweden2013_10G.ppsx (8 Mb file)
SM2CEW moderated the Round-up session After thanking everyone who had contributed to organisation and presentation he emphasised three things we needed to do to increase EME activity. Inspiration, Information and Focus. Inspiration came from the excellent technical and operating work that we had heard about at this meeting. Information comes from the distribution of this which will be done by publishing on the http://www.moonbouncers.org/ website and by distributing a summary (this) to the appropriate newsletters and interested groups, and Focus comes from ensuring that there is a solid presence of CW activity in addition to digital operation.
DUBUS Contests Joe CT1HZE, who organises the DUBUS contests asked that there be a discussion on timings, dates etc. Points made were: Please continue to organise the contests. One suggestion made was to have one day only per band and a pairing of bands for the weekend chosen, for example 144 and 432 on Saturday – Sunday. There is of course the risk of bad weather if we go for only one day per band. There was also a call for the weekends chosen to be lower loss (i.e. closer to perigee) but several disagreed citing horizon blockage. (This will be a problem for at least 3 years until high moon declination and perigee get back into synch) In order to get dates into diaries and maximise activity then it’s essential to have the contest dates announced in DUBUS by October at the latest. Activity Weekends Yes, continue, as they are noticeably increasing activity on the bands above 13cm. We will have to change the date of the 2013 9cm weekend as it clashes with the 9cm DUBUS contest. We will move it to share the 6cm AW, 3-4th August. Circular Polarization on 3cm With the availability of the 10.368 / 10.450 GHz septum polariser Kumar feed described by SM6FHZ there was a strong feeling expressed that CP should become standard there as well as on the lower bands. Encouraging cross-mode contacts Suggestions were: replying to JT CQs on 23cm using SSB and, on 70cm, calling CQ on 432.060 (which has worked) but both require the JT audio to be switched on! PI9CAM reported considerable interest in CW operation among young visitors to the big dish, seeing it done on a screen was more commonplace for them. Finally a decision was made to hold the Örebro EME meeting every 2nd year, in between the big international EME conferences. A big thank you to Lars SM4IVE for organizing the meeting again in 2013, see you all in France 2014 and back in Örebro in 2015!
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