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Single-Side-Band Techniques at Microwave Bands, Chapter VI
@ OK1AIY
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5670 Mhz Band, 6cm Wave Length
In the past, the 6 cm band was not widely used. The first QSO was made in the eighties by OK1VAM and OK1WFE, and they gradually extended the distance like it was done and is being done on all bands. It started at several kilometers, and over tens up to hundreds kilometers. Only CW and phone modes were used. Design similar to that used on 3 cm allowed the duplex operation: the carrier signal was also used as a local oscillator for the mixer. To receive, the transmitter was keyed ON. Usually the IF was within the 2-meter band , so the frequency distance between the two carriers was close to 145 Mhz. One of such designs survived, see Fig.191
During the initial period, the earlier mentioned RVG 958 communication equipment from East Germany was being replaced by very modern radio link systems from NEC. They operated close to 5.8 Ghz, so the radio amateur traffic was not allowed there to prevent interference. I was even warned by a „friendly“ official , not to even think about transmitting there. I was understandably motivated, and on 1.1.1987 when the band use was released for our experiments, we together with OK1MWD were ready to assemble the simplest version of the transverter (shown in Figs. 192 a, b, and 193), and by 24.2.1987 we made our first SSB QSO. This action happened when also our 24 Ghz equipment was being built. In DUBUS magazine several designs were published, so our effort was not difficult to finish.
In March 1987 there were several transverters in operation, and it was a chance to také a first QSO in a sub-regional contest. Our opposite station was our club-station, OK1KZN, with Míla and Honza as operators.The window from the transmitter room was oriented towards Benecko, but snow „fences“ at road edge were impenetrable. It took us some time to find a fence-free spot through which we could pas our signal from open car door, to finally make the QSO. All this effort was , however, in vain as the 6 cm band had not been officially allowed for use in contests.

Table 1. Frequency assignments over 5650-5850 band, Center frequency is 5760.2 Mhz

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Fig.191 6-cm band Transverter, the professional design by Josef, OK1WFE (1st QSO, 17.6.1982)

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Fig.192a 6-cm Transverter, the first generation. Primary radiator to connect to input connector.

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Fig.192b 6-cm Transverter for SSB, 1st generation

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Fig.193 Block Diagram of the Simplest SSB Transverter for 6-cm Band

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The Simplest Transverter for 5760 Mhz (6cm)
The transverter from Fig.193 of the last section was, although simple, very nicely operational. It allowed to make nice QSOs also in contests, so the most courageous Hams started building it (Figs.194, 195). Integrating the last multiplier and mixer in a waveguide had several advantages. Filters are easily made, with high Q-factors, and there are no leaks from a closed waveguide. The Tesla 33NQ52 or similar diodes were later replaced by Schottky diodes built in similar holders (for an easy swapping), also they allowed to generate a higher output power, of units of a mW. The larger size and weight than today was back then not important. Later one set was built for our Polish friends (SP6), where the activity on microwave bands has started, too (Figs. 196 a, b, c, d).
One of further designs was the sub-harmonic mixer by DC0DA, Fig.197. Juergen's designs were practical, easy to build and very functional, and following the first simple design a second generation appeared with better transverter features. During that time also a new transistor series appeared with better parameters, like BFQ65 (BFG65), and BFQ69. DF6VB invented a new oscillator concept, with multipliers on one PC board, originally for 2808 Mhz (the half frequency for the 6-sm subharmonic mixer). The PC board utilized an „ordinary“ laminate, and allowed adopting different freuencies for up to 3400 Mhz. It became a standard component in many transverters and beacons for different bands, from the 80's till now (Fig.198). The described time period was characterized by a generally high working morale, the designs allowed to build equipment at home, even on a „kitchen board“. The next generation was gradually developed with the sub-harmonic mixers and also receive – and transmit amplifiers with which the first QSOs with surrounding countries were made.

Fig.194 Milan, OK1JHM, with his first rig for 6 cm, 1989

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Fig.195 A 6-cm Transverter, 1st generation, in OK1UFL garden, with a home-made 110-cm dish. On the table, 10 Ghz and 24 Ghz band equipment (1990).

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Fig.196 a,b,c,d A „comfort“ transverter design, 1st generation, to „introduce“ 6-cm band in SP6, the first QSO was made by 14.9.1996 with SP6MLK/p

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Fig.197 A subharmonic mixer DC0DA with the output filter

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Fig.198 An oscillator board after DF6VB (a 9-cm version, 25 mW).

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Transverter with a Sub-Harmonic M ixer and Aplifiers, for 6-cm Band
Fig.199 presents the described transverter, its block diagram is shown in Fig.200. The improvement was done by inserting amplifiers into receive and transmit path. Two coaxial relays were needed for it. In that time, the only suitable switches available were Tesla QN599 27/28, used in some Tesla radio stations. They were quite bulky and used poor connectors. Using BNC connectors from East Germany, usable transitions were made, so the switches could be replaced for improvements. (Details are shown in Fig. 201). The mentioned Fig.199 does not show much but components after a disassembly are seen in Fig. 201. This transverter served us well over many years (Fig.202), and in its 3rd generation, these devices were no more used. New , modern and easy-to-get components were appearing as a new challenge for the designers. In a next section we will present some interesting designs from later years till now.

Fig.199 A 6-cm Transverter , 2nd generation, OK1AIY

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Fig.200 Block Diagram of a 6-cm transverter, 2nd generation, with receive and transmit amplifiers

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Fig.201 Individual components of a 6-cm transverter, 2nd generation, with a sub-harmonic mixer and transmt and receive amplifiers (bottom right).

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Fig.202 A QSL-cards for the first QSO on 6-cm band

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Fig.203 A 6-cm Transverter, 3rd generation, OK1AIY

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A Transverter for 6-cm Band, with a Sub-Harmonic Mixer and Amplifiers
Designs shown in the following figures were built for „terrestrial“ communication. They offer a good sensitivity and output power measured in Watts, and the IF band was selected by their designers in 2-meter or 70-cm range, out of the main frequency segment to avoid interference if another station uses the close frequency. Another favorite IF band is 28-30 Mhz. Fig.204 shows the transverter by Jenda, OK1CJH, and Fig.205 a nicely made primary feeder with a choke collar for a 120 cm parabolic dish. The next transverter generation by Míla, OK1UFL, is shown in Fig.206. The circuitry utilizes ERA3 and ERA5 integrated circuits, the input amplifier is built with GaAs FETs from a satellite TV converter, and the final amplifier is by DB6NT. Operation over 8 bands also needs some limitations, so several QSOs can be made with a small „flat“ antenna from a phased-out professinal radio link.
Eda, OK1EM, has built already several transverters, one is shown in Fig.207. For „outdoor“ operation, the transverters were installed in weatherproof boxes of aluminum or plastic material. The one by Mirek, OK1DGI, must be really weatherproof, Fig.208a shows the open view of his design, Fig.208b then shows his transverter in a box, mounted on a pole. Fig.209 presents the OK1KKD base station with all microwave bands on shared poles.
For more demanding users who cannot build such instruments, some components can be purchased from manufacturers. DB6NT and DL2AM are not alone now, their transverters, preamplifiers and power stages are being used by many stations around the globe. Even purchasing right transistors for a final stage including it PCB is often more expensive than buying a finished product, not mentioning „adrenaline“ feelings during first operations before we can attach the top over...

Fig.204 Transverter for 6-cm band by OK1CJH, top view on the final stage

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Fig.205 a, b Feeder for 6 cm, by OK1CJH, with the choke collar

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Fig.206 TCVR for 6 cm by OK1UFL

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Fig.207 a,b,c,d Transverter for 6 cm, by OK1EM

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Fig.208a 6-cm transverter by OK1DGI, a complete view of the system

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Fig.208b 6-c, transverter by OK1DGI, the covered system on a pole

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Fig.209 Base station, OK1KKD, all bands installed on poles

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EME Equipment for 6-cm Band
Technical requirements for EME -capable equipment are, of course, incomparable with those for the terrestrial communication. Fig.210 shows OK1CA design of 2007. The transverter was by DB6NT, OCXO was of a domestic production (TESLA). 10W output power goes directly into antenna feeder, „horn septum“ as called by EME people. The output to RX goes via a relay controlled by a sequencer: during transmit, load is connected to the semirigid cable, and preamplifier input is disconnected. Fig.211 shows transverter location at the focus of the parabolic dish, 4.2 meter in diameter. In 2014 the transverter was „updated“ by a better preamplifier, and a power amplifier by DL2AM, with 25 W output. This improved transverter is shown in Fig.213 at the focus of a 10-meter dish. Over 10 years, František, OK1CA, has made by EME 78 QSOs with opposite stations on all continents. His comments that „EME is a philosophy“, are being confirmed in general. Fig.214 shows a „portable“ EME equipment by Zdeněk, OK1DFC. A view into his transverter over an open side wall (Fig.215) shows a lot of nice but also expensive components. The basic DB6NT transverter is complemented with a preamplifier with 0.7 dB noise figure. The final stage delivers 110 W output, a sequencer cares for the necessary time delays for TX-RX switching. Monitoring temperatures in selected points as well as DC currents in exposed parts is included. An important part are the receive and transmit filters.
The 5 to 7 Ghz frequency band, due to its positive features, is shared by numerous services. Some are destined to data transmission, they often operate near our 5760 Mhz segment, and cause an interference e.g. by an increased noise. In general they are called WiFi links. Based upon the general license, the internet operators use this band to distribute data streams, and instead of small local cells (for which the band is primarily destined), and optical cables, taking advantage of lower costs and a faster installation. Details on frequency spectrum utilization can be found on Czech Telecom Office (ČTÚ) website, and others.

Fig.210 Original OK1CA transverter, with 10 W output. His first EME QSO was with F2TU, 30.9.2007.

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Fig.211 6-cm transverter, OK1CA, 1st generation, in the focus of a 4.2 meter dish

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Fig.212 6-cm transverter, OK1CA, 2nd generation: a new preamplifier and a new 25 W PA were added, from DL2AM

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Fig.213 6-cm transverter, OK1CA, 2nd generation, in the focus of a 10 m dish

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Fig.214 Zdeněk's transverter, OK1DFC, for EME in 6-cm band. Output power, 110 W, noise figure, 0.7 dB

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Fig.215 6-cm EME station of OK1DFC. During one hour, everything is disassembled, loaded into suitable car, and ready to be moved to another expedition.

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6-cm Band (5.76 Ghz) EME Activity At OK1KIR
The EME equipment at OK1KIR has developed gradually over time. At the start the design conditions were poor, and more initiative and manual work was needed instead. Fig.216 shows the primary radiator for the parabolic dish, and T/R switch. Switch details ae shown in Fig. 217. Toník OK1DAI comments on it:
„6-cm equipment in the old dish comprised of a transverter with a TWT mounted behind dish rim. The signal was led via some 2 meters of R70 waveguide to the focus where there was the primary feed with a polarizer for left-hand (RX) and right-hand (TX) polarization, and a LNA. All focus components were linked with the three-way switch in R70 waveguide. The photograph shows the switch in RX position, where RX line (left-hand polarization) goes via a larger waveguide arc in the rotary „stone“ and is connected with LNA input. LNA output goes via a coaxial cable into a coaxial-waveguide transition, and via the smaller arc in the switch the received signal comes down to the transverter switched to RX. The opposite small R70 arc of the switch connects the TX section to a waveguide load (a pyramid block of an epoxy-powdered Fe, some 100 mm long). When transmitting, the transverter was switched to TX, and the three-way R70 switch was turned 90 degrees, and connected the waveguide with TX output (right.-hand polarization) through the larger arc in the switch. The RX inout was connected to a second load via the smaller switch arc. The third arc has no function under TX mode. This all was designed in 1993 when there were doubts in both loads should be used, so we used them to be sure. Later it was found that thanks to polarizer isolation, under RX mode, the PA may stay permanently connected to TX output. This long way we achieved our experience..“
Fig.218 shows another improvement: a linear feeder for 6 cm. A two-way switch in R70 is used. On antenna port there is a R70 transition to a circular waveguide, 38 mm dia. , and a small DC motor turns a coupling post in R70 (which in the circular waveguide was formed as a loop), to change the polarization. This was used in the old antenna. Before we finished the new antenna, the world came to the circular polarization on 6-cm band, so it was no more needed. Today the circuitry has two coaxial-waveguide transitions on polarizer ports, the TX port stays connected to the PA, and the RX is blocked when transmitting by a SMA relay before LNA on RX port. All above parts with the transverter, LNA and PA is mounted in antenna focus, Fig.220. The new transverter has no TWT amplifier with a high-voltage power supply. It was replaced with a safer and smaller SSPA, giving some 70 W output, Fig.219. When one needs to switch to another band, it requires a lot of moving all blocks over a 7.meter ladder, and many cables must be replugged in the shack.
We have given up the all-band activity. I survived a gall bladder surgery but six months later I developed a hernia which a year later required a new surgery. I would rather forget the diploma for victory. Due to a messy transition between EME bands, my friend F2TU suffered an accident, and died a year later. This we understood as a warning and gave up. Says Toník, OK1DAI.

Fig.216 Primary feeder of a parabolic dish, with a T/R switch

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Fig.217 Detailed view on a switch of Fig.216, in RX position. OK1DAI has made it on a milling machine, not on a CNC

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Fig.218 A 6-cm feeder with a two-way T/R switch. The DC motor at top left is changing polarization

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Fig.219 A new 6-cm TRX in the focus of a new 4.5 meter dish from MRL5 meteo radar.

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Fig.220 The actual version of the EME 6-cm radio-club equipment, OK1KIR, 2017

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EME Activities at 6 cm (5.76 Ghz) in Poland
A successful EME operation, by reflecting signals from the surface of the Moon, requires also a corresponding transmitter power. There are more methods how to achieve the high power, earlier TWT (traveling wave tubes) were used in various versions and sizes, from pencil-like, to large blocks capable of hundreds of Watts. They required a careful handling, and high voltages were unsafe to handle.
Modern semiconductors allow to obtain even in 6-cm band a power of around 10 Watts, and designers then unite two or more blocks to get more. Like in lower bands, Andrzej, SP6JLW used power dividers to unite the output power of four ALCATEL 12W amplifiers, Fig. 221. Such design brought several problems that must be solved, to get the quadrupled power output. A demanding component is a good loss-less coupler, Fig.222. A more expensive professional unit is shown in Fig.223. Couplers are needed at amplifier inputs and outputs, so the completed design becomes a bulky „machine“, also quite expensive, Fig.224. Another problem is to adjust correct phases of input power signals into individual amplifier pairs. The lengths of coaxial cables are different and cannot be varied simply, so the designer used a professional adjustable attenuator to do it, Fig.225.
Fig.226 shows a block diagram of the complete amplifier block. A similar way chose aso Staszek, SP6GWB, for his EME equipment. He utilizes a similar but only two-stage ALCATEL amplifier, originally designed for 8 Ghz. A view of an „optimized“ 5.7 GHZ amplifier is presented in Fig.227.

Fig.221 A four-stage ALCATEL amplifier for 5.7 Ghz, Output 12W, input only 50 mW.

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Fig.222 A detail of the power coupler/divider for 6-cm band, SP6JLW

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Fig.223 A professional coupler/divider for 6-cm band, SP6JLW

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Figs.224 a,b,c,d The 6-cm PA stage, SP6JLW

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Fig.225 An adjustable coaxial attenuator for 6-cm band, SP6JLW

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Fig.226 Block diagram of the complete 6-cm systém, SP6JLW

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Fig.227 A two-stage ALCATEL amplifier optimized for 5.7 Ghz band, SP6GWB. Originally used for 8.4 Ghz.

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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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