SSB Techniques on VHF and UHF Bands, 50 Years Ago
@ OK1AIY
____________
It has not been quite common to describe an equipment after 50 years. There is
no practical reason for it: after such a long time, technology has changed as
well as available materials. Today we cannot find any use for the stuff of the
past. Only the magic of radio-amateur effort persists, its image differs after
many years
The „paradise“state of radio-amateur work that exists today thanks to our
long-time effort, offers a wide range of possibilities to the contemporaries,
while the old-timers often cannot handle all of it correctly. The path to the
recent state was not easy. The entire radio-amateur population has worked and
fought in small steps till now. It is good to look back, to revive the memory,
and show some details to our young colleagues, and refresh nostalgic memories
of the old-timers. The old saying fits here: „a good knowledge of the past
helps to better understand the actual state“.
A detailed view on the state of VHF/UHF technology of the sixties has been
outlined in PE-AR 8 and 9/2011, in a paper „How we ran VHF contests 50 years
ago“. It is also possible to find this paper in this web page. This article is
a good introduction to the following description of SSB equipment which has
pushed forward many VHF activities back then. Let us look how our equipment
looked like in that time period. In the two-meter band , AM and CW was
preferred on fixed frequencies generated from quartz crystals. In 70-cm band,
active stations were counted on one-hand fingers. In higher bands, „solo“
oscillators served as transmitters, and super-regenerative receivers were
common. Power levels ranged from fractions to units of Watts, and
communication quality corresponded to it.
Advantages of SSB traffic were known from short-wave bands and only time was
needed to utilize SSB on higher VHF bands. A wide development activity was
observed. Designers discussed their ideas and circuits on-band, or by letters.
Communication was not so easy as today but the exchange of information worked.
Everybody who tried to use his ideas had to solve similar problems. Here I
will describe my way, and the readers can compare their attempts and designs.
Figs.1 to 3, Photos of my first SSB transmitter of 1960's.
Basics of SSB design
Although everybody knows it, I would mention the basics of SSB, and its
advantages. An AM signal spectrum contains the carrier wave and two side bands
created by carrier modulation. A SSB signal has no carrier (rejected in a
balanced mixer), and one of the side bands is cut off by a filter. Under 10
Mhz, the lower side band is used, over 10 Mhz, the upper one. It means that
without talking to the microphone, there is no output power from the TX. In
the receiver, the beat-frequency oscillator (BFO) signal is added to the mixer
to the spot where the carrier sat in the TX. As the TX only generates one side
band, in the receiver the mixer (also called product-detector) generates a
legible audio output even when the other side band is missing. Advantages are
many: there is no interference due to many carriers even if signals are close,
and more signals can be used over a narrow band. All TX power is concentrated
into one side band, so there is saving of energy. It is said that the
communication efficiency of SSB is the same as CW. If our TX signal is
correctly tuned, we can step into a running communication without affecting
it. With AM or FM this is not possible. To make a SSB signal legible and not
distorted, all amplifiers must operate in a linear mode, without an overdrive.
This, however, is not a disadvantage but a natural thing.
Considerations for the basic design
It was an adventure to start the described design without any experience and
materials and test equipment. The idea was to generate a SSB signal on a
suitable frequency, and mix it with a variable frequency signal, to get an
output at 2 meters. From the very beginning, the TX and RX blocks were
separated. Such approach was the used also on short-wave bands, one complete
block would be too huge, and the advantage was that the RX can be used
immediately. In AR magazine there were SSB filter designs published, but
mostly at lower frequencies, and quite bulky. (Suitable for short-waves). One
OM has made a good SSB filter but on 50 kHz. For 2 meters, such filter could
not be used as it generated a „rake“ spectrum over the full band, a peak every
50 kHz. Another problem was how to find suitable quartz crystals. We managed
to get crystals at 500 kHz with needed frequency differences, and a filter was
created of them. Also , VHF transistors were then not available, so the design
utilized vacuum tubes, Figs 1...3. It consumed a lot of power and was bulky.
Vacuum tubes were then at their peak performance after a long development
(Semiconductors arrived only in 1980's). Some vacuum tubes are still good now,
and we enjoyed them much. Building a transmitter took a long time, several
years. Here the description takes only a couple of lines... The goal was to
get the equipment into operation, and gradually improve it under operation.
During that time, the fall brought improved VHF propagation, and 2-meter band
was alive even during the day hours. I was lucky to find a nice QTH in the AC
room of „Panorama“ hotel in Benecko, 900 meters above sea level, and an open
view from the South to North-West. My antenna systém was not too decorative
for a nice hotel, but back then the human relations were somewhat warmer.
Hotel guests were not annoyed and hotel management did not protest. Mr.Klouda,
hotel manager, even gave me keys from the AC room, so I could visit my
equipment any time. I liked it much, today I doubt it might be possible. And
in the AC room it was warm any time.. Having mentioned „human relations“, I
think the young generation would not understand, and old timers forgot. Many
things were not available to buy in the shops, and we were used to reuse or
repair anything. People knew the value of things, and faulty things were only
discarded if a repair was no more possible. There were good experts who could
repair almost anything, and even use discarded stuff for something useful.
They were recognized by the public, and having one as a colleague at work was
a really good luck. If managers could recognize such individuals is hard to
say but any boss knew his subordinates' capabilities. We had to do many things
by our own hands, so creative people were needed. We knew how to improvise in
design, one could learn from others, and for a long time I have used such
knowledge well.
First Operation Experience
By the end of 1960's the transmitter was not finished. It had no front panel
but it was tested in all operation modes. SSB was not yet common, so the main
mode was AM. Among the stations in our region the SSB was not known, so when
OK1AHO started with it, other stations cautioned him that „his modulation is
poor“. In that time we were taking part in sports events and car races and
used our equipment for „community communication services“. Our cooperation
eased the organization, and we could test our equipment in various conditions.
We had no idea that the saddest „communication service“ was lurking. The week
after 21 August 1968 was infinitely endless. Of course, it was an opportunity
to protest Russian occupation, and many hams faced problems later. I do not
want to tell more now, but many people do not want to recall and the nightmare
will follow us till death.
Fig.4 OK1AIY at his equipment in 1972
More improvements, the new SSB exciter
As the time passed, designs saw technical improvements ,like the SSB signal
generated at a higher frequency, in practice 10 Mhz. The German DL literature
presented a full exciter design, with a VOX and Anti-VOX, with transistors on
a PC board. The board was large (today it could carry a complete transceiver),
and allowed experimenting. In our country it was distributed fast under the
name HS1000 (Fig.6). A simple quartz filter designed by W1ICP became known as
„McCoy“, Fig.7. I used Soviet-made crystals at 5.744 Mhz in bakelite covers
that allowed frequency adjustment by a glass brush or iodine. The design was
easy and nice, the only difficult element was the bifilar coil on a core,
tuned to the operating frequency by a parallel capacitor. (one must not forget
to make the center tap... this did happen). We have found that also crystals
from RM31 radios could be used, B000 to B900 series. If we could find a larger
quantity of them, we could select their frequencies even without opening
covers. Then it was easy to build McCoy filters . Aleš, OK1AGC, had a good
experience from HF bands, and was able to show the frequency response on a
scope, so by varying C and R values, the response could be cleaned. Starting
in 1970's, also TESLA Hradec Králové (a state company manufacturing quartz
crystals and ceramics) had introduced quartz filters for 9 and 10.7 Mhz, for
the cost equal to a monthly salary (today for this money one can buy a
commercial transceiver or two...).
Amateur manufacture of transceivers
During that time period, 2m transceiver production exploded. (likewise in the
former GDR, East Germany). Such devices were not available in shops and there
was no good outlook for the future. There was a story about a Czechoslovak
mariner bringing his brother (a short-wave ham) a transceiver. After some time,
he sold it as his brother mariner brought him a newer and better transceiver.
One can imagine what might follow. Not many people had a friend who would work
on an oil drilling rig, or in diplomacy, so most of us manufactured
transceivers at home. People were creative and proud of their skills to make a
good TRX by their own hands. Some looked like professional products and worked
very well. Successful designs were described in magazines (named Klínovec,
Fantom). Later Kentaur followed which was quite good after minor
modifications. Its author, Jirka, OK1WBK, had manufactured a perfect printed
board, multiplied in masses. Some own it till today.
Fig.5 A view on a chassis of my transmitter
Fig.6 SSB exciter, HS1000
Fig.7 McCoy filter
Fig.8 The basic block diagram of my transmitter
Fig.9 A peek inside with PA uncovered
Fig.10 The rear panel of my transmitter
Professional manufacture of transceivers
This is a bit a hyperbola but in 1974 Kamil Hříbal, OK1NG, launched a mass
production of 2 m transceivers. Following a very successful model by Václav,
OK1MWA, he derived a design named „Sněžka“, and in Hradec Králové Small Square,
in facilities owned by District Committee of Svazarm (Union of Cooperation
with the Military) he started the first 10-piece series. The workshop included
also a PC board-making line in which OK1MHJ's XYL worked, so 11 units were
made. Kamil, however, worked with a limited access to materials, and himself
was no enthusiast in VHF. He even claimed that SSB is not suitable for VHF
operations. He disliked „sardine cans“, the chassis was taken from a
short-wave transceiver „Petr 103“ , the IF amplifier was taken from „Otava“,
all stages used KSY 62 transistors, and N05 ferrite cores. The mentioned unit
No.11 we were bringing to life with OK1MHJ, by using better transistors and
good cores the features gradually improved, and finally we got a quite
well-functioning transceiver. We added a small trick, the VFO signal was
injected via an emitter-follower, along with a signal from a quartz oscillator,
to the gates of MH7474 integrated circuit. The quartz oscillator ran on a
frequency chosen so that to cover 144-146 Mhz, the output from the IC was
4...6 Mhz. Then we could connect an ordinary digital frequency counter and we
had a „fake digital scale“. It was curious that this circuit did not generate
interfering whistles. With an added IF amplifier for FM mode, this was a
really nice piece of equipment. Several years later all that was replaced by
Petržílka's „Sněžka“ from Radiotechnika company which was comparable with
anything created by world renowned companies.
More info on this transceiver can be found on OK2KKW.com page, see external
references at the end of this paper.
Starting 1970's, some design details
I have somehow deviated from describing my TX. Along with the new SSB exciter
at .5.744 Mhz I had to modify oscillator frequencies so I could cover the
entire band. It was of course cumbersome but I knew I had to do it. In
addition to measuring I monitored my signal by the receiver, to check there
was no spur. I would like to mention the balanced mixer with 144 Mhz output. I
used 6CC42 twin triode which was designed for such balanced circuits. The
circuit had to be mechanically symmetrical and fine tuned , then the unwanted
signal was really well rejected. Any tiny mis-balance was immediately seen.
The following 4-stage amplifier had inter-stage band-pass filters. The filters
were 2 Mhz wide and no tuning was expected. A good improvement was the new
available EF 184 that replaced the old EF80. The new tube had the same pinout,
only plug in and fine-tuning was needed. The following stage was EL83, then
QQE 03/12. In my final PA I used GU29, later GI 30. The last one was only
specified for up to 80 Mhz but it worked, and it was easily available.
Operation points of the last two stages were set by potentiometers on the rear
panel, from a regulated negative voltage supply. Steady-state currents were
monitored by a front-panel meter. Also the IG1, grid current, to monitor an
overdrive. As at the fifth grade of my high school we were taught about
linearity and amplifier classes A, AB and B, I could test it at home. The
mechanical design of the resonant circuit, output coupling, correct screening,
reflectometer probe and antenna relay, all required a good care. At the start
it happened that the set screw in the tuning knob burned my finger, but there
was no output power from antenna connector. (I had to make the tuning shaft
from a plastic-Novotex). I tuned and tuned till there was no more improvement.
As I could use Rafena DVM106A RF voltmeter with a professional coaxial test
head, I had no problem with loading my TX with a 70-Ohm load and calculating
power from voltage. My 55W I deemed as a giant power. I had no idea that in
the future there would be the QRP category with a 100 W limit... The long time
when vacuum tubes were used was quite impressive. The magic of glowing
cathodes and the smell of ozone from open PA circuits plus burning dust
fragrance brought an adventure feeling. Such experience will be missed by the
users due to new progress .
Funny design hints ( a man should learn from his mistakes)
At the beginning 1970's my SSB equipment was fully functional including the
front panel and enclosure. A problem was found with a mains transformer. The
commercial one from Dubnica factory was too large and also expensive. I have
found a discarded M-core with a smaller size (after DIN standard). I have
followed high-school instructions to calculate the windings and wound the
transformer using a „novotex“ plastic for the coils. One wire size was just
not available, so I used a novelty, a wire insulated in a green colored
varnish designed for an easy soldering. Once used and loaded to a higher
temperature, the transformer burned. Later I repaired it with a classical
material. Still the size was no adequate and the next transformer was wound on
one higher-size M core. I intended to swap the new transformer for the old but
it never happened. Before one contest I decided to make sure my power supply
would not fail. I attached another transformer by five wires, to only feed my
PA. It was put into a paper box laid on the main enclosure, and stayed so over
time. Another intended improvement was to replace the neon regulators, 11TA31
and 14TA31, with a series-connected Zener diodes. In one worst moment, one
Zener diode „opened“. Fortunately the neon tubes were still at hand as spares,
after plugging them in original sockets they saved the day. One funny event
happened due to electrolytic capacitors in the power supply. They were rated
for 550 VDC but in operation they carried almost 500 V. At home the mains
voltage was stable but during the 1971 VHF Contest on Žalý the gasoline
generator stepped up the AC voltage, and one electrolytic capacitor puffed off
its rubber plug. The witnesses remember the gray smoke shaped after the square
hole in the enclosure that filled our tent. To save the contest I drove my
motorcycle down hill home using field lanes (I would not say why), then filled
my backpack with spare capacitors, auto-transformer (to reduce AC voltage),
and my AVOmeter. After an hour we contested with a full power. Then we secured
capacitors type TC521a and connected them in series for a safety.
Receiver, MWEc with a converter
In that time, most VHF receivers utilized converters to German surplus
receivers. Most popular were E10AK or FuG16. For 800 Kč I purchased a MwEc
which was fully functional after a minor repair. It was a wonderful receiver,
it has a perfect bandwidth control and the scale was quite accurate. In one
Designer magazine I found a list of medium-wave stations across Europe. It was
interesting to find them following indicated frequencies. This receiver
generated almost no inherent noise but I would not point out its features to
prevent being called an „old stuff lover“. A double-conversion converter built
by Pavel, OK1 GV, in Vrchlabí, was just perfect. The IF receiver was tuned 3
to 1 Mhz, and the LO crystal was 10.5 or 21 Mhz. Modifications to MwEc for SSB
operation was described by Jirka OK1FT, in AR 9/1959, and using the
sensitivity control from zero, this receiver became almost a measuring
instrument.
Fig.12 A schematic of a converter for MwEc receiver
Using MwEc to create a transceiver
Even though the described equipment worked quite well, in 1972 I succeeded in
joining both units into a transceiver, by connecting the RF tuning from TX to
RX (MwEc). From a suitable point of the tuned oscilator in MwEc receiver, I
picked up a signal via an emitter follower into a „premixer“ circuit as shown
in Figs. 13 and 14. A tunable crystal oscillator at 17.995 Mhz could set a
zero beat, so both TX and RX operated at one frequency. The only MwEc was used
to tune signal frequency. (A fine tuning was also possible by receiver BFO).
In that time , VHF SSB operation in Europe was common and during improved fall
propagation conditions, tens of far-range QSOs were possible. It cannot be
compared with the recent state, the band was alive even during days. After
several sleepless nights I felt a „pleasant“ tiredness. SSB station quantity
grew also in the Southeast, so the mode switch on my front panel was set to AM
only rarely. Signals were strong as everybody ran almost the same power. Every
year I looked forward to the nice fall time- a nice radio-amateur period.
Fig.13 Premixer block diagram
Fig.14 Premixer full schematic
Fig.15 Block diagram of the transceiver with MwEc receiver
Front panel view, controls
The main control (Fig.16) is the tuning knob with a scale. (It was never
finished, only pencil marks were drawn). At bottom right there is the switch,
TCVR,LAD, RX, TX. The two last positions are „doubled“ by microphone
push-button. The other „mode“ switch selects SSB, CW, AM and FM. Next there is
a potentiometer for a manual mis-balancing the balanced modulator. It
generates a voltage 0 to 1 V, it was used from the start to adjust the
modulator but was left for practical reasons. It allows checking with a RF
power meter that there are no spurs generated in the power chain. When the
potentiometer controls power output, the output power should grow smoothly
without jumps. On bottom left there is the audio level control from the
microphone. Above it there is a DHR3 indicator with a switch to monitor plate
and grid current of two last amplifier stages, and also the forward and
reverse power indication from the built-in reflectometer. On top right there
is a switch for upper and lower MHZ on the two-meter band , under it the knob
for the butterfly capacitor in the plate RF tank of GI30 tube. On the left
there is the fine tuning of the mentioned 17.995 kHz oscillator for the added
premixer, and under it, the VFO/transceiver switch. The indicator LED light,
LQ100, was the first-generation of LEDs: the LEDs did not generate too much
light, so in day light one needed to make a hand-shadow to see the LED active.
(today, a LED under 10 mA current is blinding). The front panel design reminds
the popular Collins KWM-2 face look.
Fig.16 Transmitter front panel
SSB operation at 70-cm band
The start of 1970's was full of important events, technical and personal. It
is unbelievable what all we could achieve but it is a correct saying „the work
is best done when it has good results“. SSB operation was starting at 70 cm,
so the first transverter was made, Figs. 17, 18. Two cnnectors were added to
the rear panel of the described transceiver for 2 meters, Fig. 16. From EL83
amplifier stage some 50 mW power was coupled out by a 2-turn coil, 10 mm
dia. . To the switch with three positions, LAD/TX/RX, one position was added ,
„transverter“. All handling was like on 2 meters, TX/RX switching by
microphone push-button, only 2 m power stage was switched OFF. The separate
transverter was fed from +13 V for TX, and the mentioned 50 mW into TX mixer.
These two controlled the full equipment for 70 cm including the final stage.
My first QSOs were with G3LQR, G3LTF, G8CFQ and F8ZW. Horizon started
„opening“.
Fig.17 Front panel of 432 Mhz transverter (10W). It was used for 20 years in
our club station OK1KZN in Křížlice
Fig.18 Bottom view of the transverter
Transistorized SSB transceiver for 2 m
For portable operations it was needed to have a battery-operated transverter
as my equipment described needed 220 V AC to operate. Contests like BBT
(Bavarian Mountain Day) required battery-operated equipment, and weight was
also limited. In that time transistors as well as other components were
available to design small, lightweight and later powerful equipment. Foreign
magazines presented first detailed descriptions, like from DC6HL in UKW
Berichte which was followed also in my design (Fig.19). Its base was the IF
amplifier at 700 kHz, taken from „Racek“ surplus equipment, using
battery-operated vacuum tubes at 10.7 Mhz. I added other parts to make a
transceiver. The twin-gate field-effect transistors 3N140 or cheaper RCA 40673
were new and easy to use, so I used them in many stages. Design concept was
similar to the vacuum-tube transceiver. It was not a direct transceiver, it
used a SSB exciter at 10.7 Mhz. Controls had the same functions, so the RF
connectors were only swapped. During the following years I was gradually
adding more transverters for higher bands (Figs.19,20). One exciter was not
enough, so later others were added, IC-202, Mizuho SB-2M and FT-290R.
Individual bands could be operated separately. New possibilities arose for VHF
work.
Fig.19 Transistorized transceiver for 144 Hz band, transverters for higher
bands laid on it
Fig.20 Rear panel view
Experience from communication community service
In addition to a frequent activity in experiments and contests I would like to
mention the community communication services offered by radio amateurs during
various actions like automobile Škoda Rallye, or Bohemia Rallye. The operation
only took few hours but we had also longer actions. By the end of 1970's it
was the annually repeated action „Obaleč“, „Tortrix“. We participated in
liquidation of tortrix butterflies whose larvae, one centimeter long,
voraciously ate conifers. For liquidation, during an exactly defined time gap
the forests had to be sprinkled by a chemical before larvae could make it into
pupas. Chemicals were sprayed from helicopters MI6 and specially equipped AN 2
airplanes. Activities were directly coordinated by ministry of Agriculture,
and were run in various regions of Krkonoše mountains by forest workers,
firemen, chemists and other support units. Communication was essential, and
radio amateurs made it well. Full days we spent at our portable stations,
starting at five in the morning. A forest specialist showed pilots where to
drop chemicals, and during the day there was a chain of information running.
Every evening there was an evauation meeting, consume of Actelic and Ambusch
chemicals reported, etc. Central Radio Club coordinated radio amateur
communication activities, some 30 radio amateurs took part, mostly of East
Bohemia region. Some used their own equipment, Union of Army Cooperation had
their new FT-225 and FT-225RD. The joint command was located at Vrchlabí
airport. Each airport had their communication center with one operator, also
one at a meteo station. Every 30 minutes each pilot received a fresh weather
report. Air traffic was off in rain or too hot weather as helicopter load
capacity was low. After having finished in one sector, operations were moved
to higher mountains where pupation cycle started later. For an introduction I
was assigned to the worst location, Harrachov airport. For VHF operation it
was not much suitable, but I had in my Š103 van two transceivers with an
electrically rotated antenna, so the communication worked. In difficult
conditions, the use of SSB was essential. During my activity I overheard , on
other frequencies, the communication from Jizerské Hory where the same
activity was running. I had a QSO with them, and as both separate teams had no
mutual communication, I served as a bridge. It proved very useful. This
communication service had a very nice ending. Every large-scale action
resulted in some kind of a moral promotion. My name was mentioned among
rewarded forest workers and I received a honorary title „ Highest-ranking
company participant“. The Communist party committee in the company I was
employed was very excited as I never was a party member. There was no monetary
reward, so they forgot soon, but the morale effect held for a long time...
Fig.21 Top view on an uncovered transceiver, transverter module on top
Fig.22 Bottom view on an uncovered transceiver
Fig.23 Top view on the transverters for 1296 and 2320 Mhz
Fig.24 Top view on the 432 MHZ section. For a better access the top cover for
23 and 13 cm is mounted on hinges, Fig.23
Fig.25 RF compressor at 100 kHz with electro-mechanical filters after OK2JI
Experience from DX operations and international contests
Thanks to the location of my operations location at Benecko (Fig.30), I had
all chances to make good long-range QSOs at 2 m and 70 cm. I think about using
the Es layer and aurora, occurring then often, as well as some via OSCAR 7
satellite. Mostly the „tropo-layer“ conditions happened, and some data cannot
be forgotten. For example, 19-21.1.1974 or other, it is a fun to look into the
old logs. I remember a long line of Dutch stations waiting to make a QSO with
me, minute by minute. I was happy to have a good communication with the
equipment I made by my hands. A QSO is as we say only the „cherry on top of a
pie“. My equipment worked very well, possibly better than now with a FT-790.
Here I cannot give details on why I think it was. Also during the contests,
the first I had in 1972 from Klínovec, I was very successful even though there
was a competition. From Krkonoše, however, my results were never so good. The
Golden Hill (Zlaté návrší) was not a „winning hill“, the exposed direction is
shaded by Kotel (Boiler), so that a section of North-Western Europe was not
open. Once a year (1981) during better conditions, I was close to winning a
contest, but interfering station some 35 km away made me problems. Only
several more QSOs were needed but the interferer called CQ for long hours, and
victory was claimed by Jirka OK1OA, from Ještěd, thanks to his operation
skills. The described equipment I was using till 1980's , it was excellent but
bulky, and as new bands were added, I had no room enough in my Š1203 van. SSB
operations started then also on 23, 13 and 3 cm bands. So I used the old
equipment in my permanent QTH and ended later in a depository.
Figs. 26...28 Three pictures from „Obaleč“ (Tortrix) activity
The communication center in a shed at a Harrachov heliport. Handheld Tesla
radios served to communicate with workers in the field, and with the joint
command at Jizerka. In the bottom photo, helicopter pilots, Ing.Havelka in
forefront
Fig.28 A full crew on the station (heliport at Jelení Boudy, over Špindlerův
Mlýn)
Fig.29 It was a lucky opportunity to have antennas at 700 meters above sea
level. So we made a club station OK1KZN in the ham-shack of Jenda Skála,
OK1UFP. The antenna systém from 2m up to 3 cm was smashed by a storm in the
1980's.
Fig.30 Antenna systems for 2 m through 13 cm as a „decoration“ on Panorama
hotel, Benecko. Cables run to AC room where my station was located
Fig. 31 a, b VHF contest 34 (Fichtelberg), 432 Mhz station. Operators Jarda,
OK2JI, and Pavel, OK1AIY
Phasing method for SSB signal generation
The above described filter method is not the only one to generate a SSB
signal. It is the simplest, however, and a filter can be also used in the
receiver. Such filters are also used in professional units. The phasing method
has been used in vacuum-tube equipment in 1950's. The design was more
voluminous, so it was no problem to use the phasing method in short-wave bands
and later VHF. Pribin, OK1AHO, used it in his 2-meter equipment at the
beginning of 1960's. Using solid-state devices reduced the size and in 1976,
in Radio Communication magazine, 9/1976, a nice design was described in a
metal box, 115 x 80 x 20 mm. The frequency is 10.7 Mhz which was very suitable
for my transceiver design, so I tested it, too (Fig.32). Mirek, OK2AQ, built
his phasing SSB source directly on 144 Mhz (Fig.34). The author described his
design as follows: „VXO runs at 16 Mhz and is multiplied by 9 times to 144
Mhz. There it is split into I and Q paths. The 90-degree phase shift is set by
a quarter-wave piece of a coaxial cable. Two balanced modulators with GA206
diodes are fed the pair of low-frequency modulation signals, I and Q. As the
audio phasing network a six-stage polyphase network is used. All components of
audio spectrum must be shifted exactly by 90 degrees, over 300 to 3000Hz
range. Outputs of both balanced modulators are summed: this rejects one of the
side bands. To achieve 40 dB rejection, the total phase symmetry must be
better than 1 degree, and amplitude symmetry under 1%. The signal is then
amplified to 0.5 W for the next PA. The transmitter was successfully used
mostly for satellite-transponder traffic as a second transmitter for
cross-band communication. „ From the above description it is clear that there
are quite strict requirements to achieve a good function of phasing SSB
exciter, and this is difficult in amateur conditions. Also in the case I
described, after 10 years the SSB signal quality deteriorated and could not be
improved by tuning. I had no access to apropriate test equipment ( a vector
voltmeter with two probes I had no idea it existed). Listening on another
receiver could not detect any cause, so I had to build another SSB exciter on
the same-size board, with a 10.7 Mhz filter from TESLA Hradec Králové. The
phasing exciter would not ever be checked, so it will remain as a „mute
witness“ of the ancient effort. In 1970's such effort was common among radio
amateurs, many hours and days we spent trying, without a sure result ahead.
Today we can use integrated circuits, using the digital technology the
resulting parameters are quite accurate, and a SSB exciter can be built with
several or even one tiny circuit.
Fig.32 Phasing SSB exciter at 10.7 Mhz, from a paper by Karel Jordán, OK1BMW,
published in Radio Amateur News magazine
Fig.33 Schematic diagram of the SSB exciter from Fig.32
Fig.34 Phasing SSB exciter directly at 144 Mhz, by OK2AQ
Some more notes to the design and documentation
Fig.36 shows that even a „gel“ rechargeable battery was fitted in the 2m
solid-state transceiver. Two cells, 6V/4Ah from „Sonnenschein“ company were a
welcome novelty, and it came for a nice price (130 DM, I have no idea how much
it was then in Czech crowns). Such battery was good for short operations, for
contests we connected a larger external supply, 13.6 V, in parallel. New types
of rechargeable batteries allow Umax when charged of up to 14.5 V. Power
source was used for all connected transverters. Important circuits were
powered from individual regulators at lower voltages. The reader might notice
that there were no 78 xx regulators. In that time they did not exist, we used
Zener diodes in transistor bases, blocked by an electrolytic plus a ceramic
capacitor. Such regulators worked well, today a better regulation is required,
new regulators meet new specifications, (for example, low-drop types with only
1 V drop). Unfortunately, we cannot show the detailed schematic of the vacuum
- tube transmitter described in our series, it did not survive. I probably
gave it to someone for copying. After a week I forgot who it was, after a
month, what it was, and later there was no trace. The described modifications
are from a later time. Such a thing cannot happen today, designers save their
data in computers where they are safe and easy to find. Fortunately, I had
drawn the schematic of my solid-state transceiver. Fully unfolded it covers a
half of a kitchen table, Fig.37. I never needed it... Recent reader would deem
such design no more possible to show as an example. Let us use it as a
„detriment“ . The rare time we spent in experimenting could have been used
otherwise. Maybe we could play golf, wait several decades, and now spend a
couple of bucks and buy it cheap. But everybody who lived the „hard way“ will
tell you that a good feeling is nowhere to buy...
Fig.35 A schematic of the audio phase shifter for a SSB exciter (capacitors
marked „k“ equals „nF“)
Fig.36 a, b Top view on an uncovered 2-m transceiver from 1972. Also the gel
battery can be seen
Fig.37 a, b Schematic of the 2-m transceiver covers almost all of the kitchen
table. Such complex was an amateur design in 1970's
Fig.38 Detail of the schematic of the transmitter in the transceiver
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).
External links:
Source of information: OK1AIY , foto : OK1UFL
Translation: Jiří Polívka
Česká verze