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Single-Side-Band Techniques at Microwave Bands, Chapter VII
@ OK1AIY
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Breaking Point - 1989
This year was a breaking point for all our community. Everyone of us was affected, and for many it was a U-turn in life. Many important views had to be switched, and not all people swallowed it quickly. Our point is not to cover everything. We want to focus on our microwave problems for which new horizons started to open. Gradually we will cover important details. Modern technology just „broke in“ from the outer world, to gradually simplify our life, and brought a new quality to it. Let us focus on the narrow theme- communications- meaning telephones and data transmission: for the sake of simplicity we will treat them together. In some places we will see some funny points as promised in the intro to this series.
The POTS, the wired telephone system, has worked since early times but was not available to everybody. Let us see the typical situation in a small mountain village. The telephone was installed at the meir's home, in Jednota grocery store, in the local school (before the school was closed), then in the local National Committee office, at the bus transport dispatcher's office, and maybe at the parish office. By the end of 1950s, the poles carrying numerous (often faulty) phone wires were replaced with telephone cables, and almost anyone could have his/her line available. Another novelty was the radio-relay link built in TESLA Přelouč, named „VAMka“. This radio replaced cables in mountains but had only one to four channels (VAM 808). It operated at 390-450 Mhz band, but other frequencies were utilized for official use including state entities. The FM signal was not scrambled (offering line tapping ), RF output power was 2 W, and DC power was taken from the power AC line or a spare 12V battery. Despite utilizing old germanium transistors like 153 NU 70, the VAMs were very reliable and stayed in use from the end of 1950s till the beginning of 1990s. Any post office in the view had a small Yagi on the roof, and a base station inside. Another radio telephone was AMR (Automatic Urban Radio Telephone), developed in TESLA Pardubice, the first mobile network in the Eastern Europe. All-state network operated over 161-165 Mhz, regional network over 152-157 Mhz. Vehicle stations had RF output of 10W, duplex separation of 4.5 Mhz, frequency modulation, and no scrambling used. The experimental AMR network started operating in 1979, all-state network since 1982. The systém was terminated in 1999.
The next mobile network in the Czech Republic was NMT450 (Nordic Mobile Telephone), operated by EUROTEL company over 1991-2006. It used 450 Mhz band, duplex without scrambling, the updated NMT allowed for analog scrambling. Vehicle stations had 14W RF output, hanheld ones, 1W. Our radio amateurs know the stations retuned for 70-cm band as „KANISTR“ used also over repeaters.
A very interesting novelty in telephone use was the „torn-away handset“, in fact a cordless set. The terminal was connected as any POTS , or in parallel to one, and the handset separation was quite good. Users welcomed it as they could work and play away from their office desk. Popular devices were sold in stores and imported from abroad. Some were even homologated (licensed), like Panasonic KX-T 9000BS called T5, operated at 900 Mhz. Versions using 50 Mhz were certainly not licensed. Users of these devices discovered fast how to extend cordless range by connecting antennas to the link ends. Some types had antenna connectors, those without needed more technical gist. One construction operator once asked me for such extension. I used then popular UHF TV antenna with radiators cut by some 2 cm, and using some 10 meters of the foam twin-line UHF cable, the antenna operated well from an inaccesible location on a tall pole. The systém operated well over all the city area. Good news, however, propagate fast, so within a week the antenna was stolen and had to be replaced with a new one.
Another case used a Yagi antenna. OK1UFL calculated element lengths from a 70 cm Yagi, and OK1THK made the new Yagi from steel welding wire. The systém operated well over 5 km. It was also admirable how well the „illegal“ 50 Mhz devices operated. The station was connected to a TV dipole antenna, the handset to an auto antenna, and the distance was up to 3 km. One cordless handset „Jaguar“ maybe imported from the USA, was used from a car over 15 km far from the station. When in use, the handset holder reported his cheek being heated... In the 1990s I had no telephone at home, so I tested the mentioned Panasonic KX-T 9000 BS, but the nearest phone line location was the parish office. It was working well over 600 m, and I had a talk with the priest. I needed badly the phone, but after 14 days the priest met me again and said that „ the Vatican does not support this idea“...
At the same time, friendly telephone technicians told me that on Žalý hill they planned to install IRT2000 radio link, so there will be connections for a hundred of interested users. It was designed by TRT Paris-LUCENT, for mountain ranges and protected areas. The TRT2000 network was installed in the Czech Republic since 1994, the territory was finally covered by 23 networks operated by the Czech Telecom. In the first years , 1.5 Ghz was used but later switched to 3.5 Ghz. Fig. 228-230, TNX INFO OK1NK

Fig.228 IRT 2000 Base Station, location at telephone exchange

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Fig.229 IRT2000 Terminal Station (two units) located at a village, users connected by cables

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Fig.230 IRT 2000 User station with a power supply and spare battery (right)

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IRT2000 System provides the users with all services of modern telecommunication networks including DECT systém in 1.8 Ghz band. DECT stands for (Digital European Cordless Phone). DECT is the most important standard for cordless telephony. Products are on the market since 1993, operate over 1880-1900 Mhz. TDMA digital access is used. In a free space, the safe radius is about 300 m. A significant feature is „handover“, switching to another base station during a talk. At the start of 1990s, in some areas plastic pipes were laid under ground for the future optical cables. The action was swift, muscular guys were able to dig down to each dwelling around, even to the location number plaque in a bush. But there was no continuation as the early systems looked cheaper. Optical cables are wonderfully wideband while resistant to lightning. Today the optical fibers extend into apartment blocks in cities. The always decisive points are the cost and revenue. Optical networks already offer (and promise more): telephone, data, internet, TV, and various smart boxes offer guarding homes and signaling whatever needed. What is important are the parameters of end devices (modems), and capabilities of the providers.
The existing „links“ in microwave bands (today even at 70 Ghz) carry not only data but can also carry anything including telephone signals. Depends upon the used terminal devices. Mobile telephone signals from the providers (O2, Vodafone, etc.) are digital and allow to carry telephone, internet and all other information. The mentioned IRT2000 systém was not only useful for telephone but allowed data transmission (low speed), leased lines and back then the popular ISDN (Integrated Network of Digital Services). The fixed (metallic) lines will remain in use for a long time. Everything was laid, all telephone exchanges digitized, and linked by optical cables. Over fixed lines, voice and digital signals are now transmitted for internet, like ADSL, ADSL2+, VDSL and also IPTV (television with many programs incuding HD). Everything runs over a wire pair of an old cable!
Availability of this mode is limited by cable loss. (distance of an user from an exchange) due to the fact that for transmission, frequencies up to several Mhz are used (up to 15 Mhz with VDSL) Like said earlier, at the end user a special modem has to be used for individual service types.
To explain some codes above : ADSL is the asymmetric digital service line. The newer ADSL 2 and ADSL2+, VDSL allows a higher internet connection and to send data back. The VDSL2 is the second generation, uses up to 30 Mhz bandwidth . Allows a high transmission speed in both directions but only over 300 m distance. IPTV is the TV transmission over internet protocol.
To conclude, what all that brought to „creative“ radio amateurs? In the first place, new and more modern components that can be utilized with an advantage in our microwave bands. As the quantity manufacture grows, their cost decreases. Updating process required more modern systems, and the „older“ ones had to be sent to trash. This process brought a relatively cheap material for enthusiast designers, or to modernize the existing systems. If you look at the last picture, nowadays nothing of it can be used. But this is another story...

Fig.231 IRT2000- repeater station located in a container.

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Fig.232 IRT2000 : an open view of a user station

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Fig.233 Location of a IRT2000 station in a protected location (Turnov area)

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Fig.234 Mobile phones of 1990s till today

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47 Ghz Band 1st generation equipment
The next band assigned for radio-amateur experiments is 47 Ghz (exactly 47.088 Ghz, wave length 0.64 cm). Table 2 presents individual band sectors. This is a really short wave , and at the time when the 1st generation was being created, these bands were not yet even used by professionals. For data transmission there was still room at lower bands. The first design was published in DUBUS magazine by DB6NT in the early 1990s. We had some experience from 24 GHz band and what we saw in DUBUS was so attractive that with Míla Skála, OK1UFL, we decided to get into it (Fig.235).
To „command“ a band means to build the simplest design as possible, then go on and improve it by domestic sub-systems and devices: starting by simple indicators, various calibrators, converters to existing spectrum analyzers, small beacons for indoor use, and finishing by real beacons on the hills that may serve the other experimenters. This procedure was valid all the time from the lowest bands. All concerns go away if someone can buy the equipment with accessories and thus becomes an user. In the beginning era such chance was nonexistent, so every designer tried his means. Some components, however, had to be purchased. In this case it was a profesionally built PC board on DUROID material, and diodes for the sub-harmonic mixer. Their size is so tiny (Fig.236) that they cannot be seen by bare eyes. It is easy to lose such component in our „workshop“, devices fly away by only electro-static force. So we asked DB6NT to attach the to the PCB as he had the needed equipment. Some guys glued these diodes, even tried to solder them at home, which is a proof of their skills. (OK1 JHM and OK2BPR). After visiting DB6NT where the diodes were glued on otherwise finished PC boards, we tried to make our first QSO in Cheb (Eger) where we could not stop or park our car, with Michael on the other side of the Czech-German border. (Fig 237) The next day we extended the distance to 4 km approx., with OK1UFL, and then we continued in making contest QSOs in every following contest . (Fig.239 is from a later time, original photo is missing).

Fig. 235 Block diagram of a 1st generation transverter, 47 GHz.

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Fig. 236 Mixer diodes used in the simplest versions of sub-harmonic mixers

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Fig. 237 Michael, DB6NT, in his workshop, 1996

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Fig. 238 The first QSL-card for the first OK-DL QSO at 47 GHz

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Fig. 239 47 GHz Transverter, 1st generation, here a rotary amplifier by DB6NT added

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Tab.2 Assignments in 47 GHz band

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47 GHz Band, 1st generation equipment – oscillators
Now we are at the beginning of 1990s. The simplest designs were adopted also by those who had some experience with 24 Ghz band, so after a short time it became possible to communicate over 100 km. Their designs sre shown in Figs. 240 thru 245.
It is an adventure to start more sophisticated designs. Experience from lower bands is useful but it is important to decide if a problem is essential or as often said, only „cosmetic“. The significant problem was frequency stability requiring to use a well-designed thermo-stabilized oscillator. Earlier designd used oscillators in „cold“ or other thermostats adequate for the lower bands but not usable at higher frequencies. Oscillator type was also important, with the grounded-base transistor which overloaded the new miniature crystals, and the output signal was not clean enough. A temporary solution was to reduce DC voltage to 5V.
The problem of a suitable oscillator we have discussed with Michael, DB6NT who had passed most of the problems before. It was then welcomed that the oscillator problem was to be discussed at the „Danish microwave activity week“ in 1994.

Fig.240 47 GHz Transverter, 1st generation, by OK1UFL

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Fig. 241 Adjusting SP6GWB transverter for 47 GHz at OK1UFL home in Jilemnice

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Fig.242 47 GHz Transverter, 1st generation, OK1EM

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Fig. 243 47 GHz Transverter, 1st generation, OK1JHM

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I was grateful for the invitation by Bjarne, OZ1UM, the „boss“ of PROCOM company which organized the Danish Week annually, as well as by DB6NT, DF9LN and DC0DA, who „took me along“, Fig.252. The activity was described in detail in AMA magazine, 10/1995, but the substantial contribution was brought by Uwe, DF9LN who presented his oscillators, Fig. 246 to 248. I have acquired two component sets, and Míla, OK1UFL, made the first oscillators with a good stability, Fig. 249,250. This was a breaking point in the design, and allowed to start fully the activity on higher bands. Over next several years, Mila built more than 100 units (Fig.251). Oscillators designed by DF9LN are being used in all transverters and new beacons in our country as well as in Poland (SP6), also in some EME equipment. It really made a future for next design generations...

Fig. 246 A schematic diagram of the RF oscillator by DF9LN

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Fig.247 A schematic diagram of the oscillator thermostat by DF9LN

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Fig. 248 A detail of the oscillator thermostat board by DF9LN

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Fig.249 The PC board of the oscillator, DF98LN/OK1UFL is soldered on a copper plate. Except of the crystal, the other large component is Johanson capacitor trimmer.

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Fig.250 DF9LN oscillator by OK1UFL built in a tinned steel sheet box

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Fig.251 DF9LN oscillators, mass -built by OK1UFL

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Fig.252 Danish Microwave Activity Week, 1994, DL team

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The next generation of 47 GHz Transverters, with amplifiers
The described epoch (end of millennium) was marked by a high working activity, and some updated their equipment. The second or third generation of 47 GHz transverters appeared, now with a RF amplifier. Due to the high cost, a practical design was named as „reversible“, the amplifiers could be used to receive or to transmit by reversing the amplifier body by 180 degrees. (who had more money, could use separate amplifiers to receive and transmit, without switching). First amplifiers were offered by Michael, DB6NT, followed later by design of Aleš, OK1FPC.
It is still very difficult to build such amplifier at a home workshop. Instruments to attach tiny dies are so expensive and demanding in use that in our country there are only several. Also the makers must have a real market to get their investment back. (What is important is: one must also have special skills and training is not easy to be taken in a week).
The described amplifier is built on Rogers RG4003 substrate on which two chips are attached, CHA2104 from UMS company. To improve amplifier stability, a 6-dB attenuator was inserted between them. Also corundum „antennas“ are used, from DLI company. They can be contacted with gold wire, and the amplifier has better parameters. On twenty manufactured units, gain was measured to be 37 dB, and NF of 4.5 dB. For amateur communication, output power of 30 mW is so far adequate. (says Aleš, OK1FPC). Figures show the updated 47 GHz transverters, from the simplest with a knob control (operated on a tripod), to the modern, servo-controlled mechanism installed on a pole (Ok1DGI).

Fig. 253 47 GHz Transverter, 2nd generation, by OK1EM, with an amplifier, front view

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Fig. 254 47 GHz Transverter, 2nd generation, OK1FUL, with a new amplifier from OK1FPC

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Fig.255 Rotary mechanism of the RF amplifier at 47 GHz, OK1DGI

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Fig. 256 A side view on the rotary mechanism in the 47 GHz transverter, OK1DGI

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Fig. 257 A set of aligned antennas on a pole during a contest, OK1KKD

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This paper was also published in print in Practical Eectronics magazine, with permissione (PE/AR Magazine – Practical Electronic and Amateur Radio, Czech amateur magazine, in Czech).


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