Single-Side-Band Techniques at Microwave Bands, Chapter 6
@ 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
Fig.191 6-cm band Transverter, the professional design by Josef, OK1WFE (1st
QSO, 17.6.1982)
Fig.192a 6-cm Transverter, the first generation. Primary radiator to connect
to input connector.
Fig.192b 6-cm Transverter for SSB, 1st generation
Fig.193 Block Diagram of the Simplest SSB Transverter for 6-cm Band
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
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).
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
Fig.197 A subharmonic mixer DC0DA with the output filter
Fig.198 An oscillator board after DF6VB (a 9-cm version, 25 mW).
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
Fig.200 Block Diagram of a 6-cm transverter, 2nd generation, with receive and
transmit amplifiers
Fig.201 Individual components of a 6-cm transverter, 2nd generation, with a
sub-harmonic mixer and transmt and receive amplifiers (bottom right).
Fig.202 A QSL-cards for the first QSO on 6-cm band
Fig.203 A 6-cm Transverter, 3rd generation, OK1AIY
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
Fig.205 a, b Feeder for 6 cm, by OK1CJH, with the choke collar
Fig.206 TCVR for 6 cm by OK1UFL
Fig.207 a,b,c,d Transverter for 6 cm, by OK1EM
Fig.208a 6-cm transverter by OK1DGI, a complete view of the system
Fig.208b 6-c, transverter by OK1DGI, the covered system on a pole
Fig.209 Base station, OK1KKD, all bands installed on poles
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.
Fig.211 6-cm transverter, OK1CA, 1st generation, in the focus of a 4.2 meter
dish
Fig.212 6-cm transverter, OK1CA, 2nd generation: a new preamplifier and a new
25 W PA were added, from DL2AM
Fig.213 6-cm transverter, OK1CA, 2nd generation, in the focus of a 10 m dish
Fig.214 Zdeněk's transverter, OK1DFC, for EME in 6-cm band. Output power, 110
W, noise figure, 0.7 dB
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.
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
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
Fig.218 A 6-cm feeder with a two-way T/R switch. The DC motor at top left is
changing polarization
Fig.219 A new 6-cm TRX in the focus of a new 4.5 meter dish from MRL5 meteo
radar.
Fig.220 The actual version of the EME 6-cm radio-club equipment, OK1KIR, 2017
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.
Fig.222 A detail of the power coupler/divider for 6-cm band, SP6JLW
Fig.223 A professional coupler/divider for 6-cm band, SP6JLW
Figs.224 a,b,c,d The 6-cm PA stage, SP6JLW
Fig.225 An adjustable coaxial attenuator for 6-cm band, SP6JLW
Fig.226 Block diagram of the complete 6-cm systém, SP6JLW
Fig.227 A two-stage ALCATEL amplifier optimized for 5.7 Ghz band, SP6GWB.
Originally used for 8.4 Ghz.
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).
Related links:
Česká verze