Pekka Eskelinen

Problems in estimating some timing uncertainties of commercial frequency and time standards

An end user cannot define the different timing errors of current cesium or GPS clocks properly. Conventional satellite-based techniques are able to detect long-term drifts only larger than 2 ns/day, and momentary receiver time deviations of the order of 100 ns can he expected with no practical improvement due to averaging unless extended to one day which precludes a medium-term analysis of local cesium performance. Bias-type errors, reliably found after a three-month test run and seriously hampering synchronization, with less costly user equipment show a typical offset of 200 ns. The generally applied test periods of 20 to 50 days, particularly for drift analysis, seem short since slow 10 ns to 20 ns fluctuations of the timing difference, lasting 20 days, are found. Many laboratories overlook environmental factors during long-term stability tests and thus unreliable results are produced. For a careful analysis of current commercial cesium clocks several colocated high-quality references are needed.

Novel DFMA-Tools For Passive MW- And RF-Components In Cost-Effective Mass Production

Because of the large production volumes of MW- and RF- technology even slight improvements of design methodologies or manufacturing technologies would give possibilities for cost reduction. Modern tools for cost-effective DFMA (Design for Manufacturing and Assembly) for passive components and modern antenna constructions should be easy to integrate with the tools for electrical design. Furtheron design methodologies for mechanical components should be tuned for this specific branch of science and for the specific product type. Recently this kind of development has been seen in antenna design and the results of reducing the design and manufacturing costs have been promising [1]. We have designed and manufactured a prototype of a smart antenna and its all passive components for mobile communication. To increase the flexibility of the mobile systems those wide band designs are used which are able to provide electronic real-time beam stearing through analog technologies or digital beam forming. We have gathered novel DFMA-aspects [2] during this design project and tested virtual engineering (VE) tools to improve products performance and to increase the cost-effectiveness of the design and manufacturing processes.

Observations on stability measurements of commercial atomic clocks

Besides the known effects of temperature and aging, abrupt changes in barometric pressure or in the Earths three dimensional magnetic field, occuring typically every 100-800 hours and lasting for 20-200 hours. Cause unpredictable 10-100 ns cesium clock deviations in commercial equipment. An air pressure increase of 100 Pa is suspected to induce a 1.2 ns clock bias whereas observations indicate that a 50-200 nT H-field z-component of a magnetic burst initiates in an other design a positive or negative drift having an absolute value of the order of 0.3 ns/hour. Measuring techniques, based on various GPS Disciplined Oscillators, require the extension of similar recordings well over 1000 hours due to internal GPSDO anomalies which exceed 20 ns from the mean timing difference and may have a period of 500-700 hours.

An adaptive high power vector network analyzer for the tuning of NDB transmitter antennas

Reliable impedance measurements of installed HF air navigation antennas are possible with an automatically adjusted high power analyzer using levels above 30 dBm to overcome external interference signals coupled from the environment. Even a bad mismatch of an unknown device cannot cause unpredictable results or test equipment failures if this straightforward method is applied. The proposed adaptive network analyzer covers frequencies between 100 kHz-50 MHz and regulates the test port power down to 10 dBm according to the return loss and, thus, reduces the risk of damage and, at the same time, improves resolution at the other end of the return loss scale above 25 dB. The rejection of the misleading effects of unwanted signals can be further improved by the built-in modulation.

The (r)evolution and stagnation of higher education in EE ever the past decades

The current university education of electrical and electronics engineers has evolved from the well-established system of the 1950s to a wishy-washy mixture operating with lots of ill-motivated or less-qualified students, a process mostly accelerated by the growth in the telecommunications industry. External projects take staff time and the curriculum continues to threaten youngsters with de-focused mathematics. The computer age has reduced the interest in experimental research, and the continuation of science in the systems level may be in danger.

Notes on RF scale testing of tower mounted antennas for cellular communication

Scale model towers with associated antenna installations provide an efficient and fast means to test current and future 1800 MHz mobile communication base station installations prior to site, antenna type or mounting scheme selection. Repeatability better than 1 dB is readily achieved if the scale reduction is between 1:5-1:15. Many measurements are possible with a very short anechoic test range, just fulfilling the far field requirement. Typical findings include the possibility to effectively reduce interference minima caused by adjacent vertical structures by simply positioning a thin absorptive sheet to the optimum location. Improvements of the order of 20 to 30 dB have been measured.

Experiments with numerically controlled atomic clocks

Long term timing stability of present atomic clocks can be considerably improved by simple numerical algorithms which correct both the inherent frequency bias and the effects of supply voltage variations and outside temperature. Rubidium units are demonstrated to operate with less than 100 ns errors per week or any sensible longer interval corresponding to relative uncertainties of 10/sup -13/. Often a linear subtraction of frequency offset which can be realized by a microprocessor controlled digital delay line is sufficient. A cesium clock could be run at 10/sup -15/ level, but reliable and reasonable real-time measurement techniques do not yet exist.