Complete-Transverter-for-Six-Meters.pdf

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complete
transverter
for six meters
If
you have
Every time the six-meter
skip comes in
you're no doubt impressed by the rapidly
increasing number of single sideband sta-
tions. "Maybe it's time to plan for that
sideband rig,'' you think. Then you look at
the price tags on the commercial outfits and
decide, "Not yet." Even the kits are expen-
sive, and whipping one up from scratch
i s
both expensive and complex.
A
much more attractive answer to
a
good
sideband signal
on
six meters i s a combined
receiving and transmitting converter. If you
have a low-band ssb transceiver, a grid-dip
meter and a little homebrew experience, this
can be a very happy solution to the problem.
I
went through these mental gymnastics
for a couple of years before deciding to take
soldering gun in hand and build the 6140
'verter.
One of Mr. Heath's excellent Single-
Banders for forty meters was in the shack.
I
put together a conventional converter to
shift the six-meter sideband signal down to
forty. You've probably had some experience
along this line and this is half the job.
A
somewhat similar converter was built along-
side to swing the forty-meter ssb signal from
the transceiver up to six meters.
A
simple
a
single-band
ssb transceiver,
it's easy to get
on
50
MHz
with the
6/40
'verter
44
a
july
1969
power supply for both converters was added,
and the job was done. Both converters use
the same oscillator, so both the received
and transmitted signals are on the same fre-
quency. Once tuned up, the transverter can
be disregarded, and operation
is
with the
transceiver only.
Right about here you're probably saying,
"It can't be
that
simple. The generation of
ssb signals
is
complex, and homebrewing of
such equipment just isn't for me." You're
absolutely right. But, the difficult part has
all been taken care of by those smart people
at Benton Harbor. All we're talking about
here
is
beating signals to produce hetero-
dynes, as in that ten-dollar table radio in the
bedroom. The fact that one of the signals is
modulated ssb instead of a-m doesn't change
the operation.
meter ssb signal from the Single-Bander
is
inserted at the screen grids of the 5894, and
a six-meter, single-banded signal comes out.
The 5894 dual tetrode is a relatively high-
power, easily driven tube that isn't exactly
cheap, but it can be found in some of the
bargain-priced tube lists.
It does a beautiful job in this application,
but maybe you have an 815 or 6360, or a
couple of 2E26's you'd like to use. A few
component values would require changing,
but these tubes would all work-at lower
power. By the same token, there's no reason
why you can't start with a twenty-meter
signal and end up on two meters. The ap-
proach would be the same. It all depends on
what you have to build with and where you
want to operate.
the circuit
With this description in mind let's exam-
ine the schematic
(fig.
1 .
Note that the top
)
half, consisting of the 6CW4, 6EA8 and as-
sociated circuit is the familiar receiving con-
verter. The one used here isn't original-
it's borrowed from "The Radio Handbook."
It's a good one, but there's no reason to use
this if you have a converter on hand or wish
to buy a commercial unit.
For transmitting, the conversion signal
from the triode-section of the 6EA8 is fed to
a 6DJ8 cascode amplifier. The boosted rf
is
then inserted push-pull into the grids of a
5894 sewing as a mixer-final. The forty-
assembly
Construction practices are standard for
these frequencies. Good grounds, short
leads, many bypasses and shielding are very
important. The layout shown in the photos
is compact, and it works, but it isn't neces-
sarily the last word. The receiving converter
was built on a four- by six-inch sheet of
flashing copper. Good rf grounds are no
problem since many of the components can
be soldered directly to the copper.
The 6CW4
i s
a grounded-grid nuvistor rf
amplifier. It's lightly coupled to the 6EA8
mixer section via C1, which consists of two
lengths of hook-up wire with about one inch
of each parallel with the other, inserted from
opposite sides through a hole in the shield
between the two tubes. Coupling between
oscillator and mixer portions of the 6EAB is
via the spacing of about 314 inch between
L3 and L4. The coax input and output fit-
tings can be eliminated-they're a reminder
of when this converter was used alone.
The same crystal oscillator signal used for
receiving
is
taken from the plate of the con-
verter portion of the 6EA8 via C4 to the
first grid of the 6DJ8. Here i t goes through
two stages of amplification needed for the
transmit conversion. The 6DJ8 output is in-
ductively coupled to the 5894 signal grids.
A very low level forty-meter signal is re-
quired. This
i s
achieved by dissipating most
of the output in a dummy load. A sur-
july 1969
45
0.5 pF gimmick (see text)
capacitive pickup between
L3
and L4
15 pF butterfly
10 turns B&W 3003, tapped 2% turns from
ground end
0.87
pH
(J. W. Miller 40A827CBI)
1.0
pH
(1. W. Miller 40AlWCBI)
Miller 41AOOOCBI wound full with no. 26
enamelled; L16 tapped 15 turns from
ground and
2.2
pH
(J. W. Miller 41A226CBI)
fig.
1
Schematic diagram of the 6/40 'verter.
.
L8
8 turns no. 28 enamelled on a
'14"
slug-
tuned form (J. W. Miller 41AOOOCBI); link
i s 2 turns of hookup wire on the cold end
L9
9
turns B&W 3004, center tapped with 2
turns of hookup wire around center
6 turns no. 12, 1-inch ID, spaced 1 wire
diameter, with 2-turn insulated loop at
wider-spaced center
48 turns B&W 3004; link is 4 turns of hook-
up wire around cold end
L10
L11
PSI, PS2
6
turns no.
18,
spaced one wire diameter,
on high-value, 2 W resistors
plus three-pole, double throw dc relay
switches the antenna circuit alternately
through the receiving and transmitting con-
verter sections and turns on the final for
transmit by grounding its cathode. Any sim-
ilar commercial relay will do this job, and
by choosing a six-volt ac coil, the rectifier
diodes and filter capacitors, which can be
seen in one of the photos, can be elimi-
nated. The Single-Bander has an extra set of
relay contacts that activate the transverter
relay to make the switching automatic.
The entire outfit, including power supply,
fits neatly on a commercial 3x7~12-inch
6DJB; and 150-volts regulated for the 6CW4
and 6EA8. Signal stability
i s
essential on sin-
gle sideband. This depends on your trans-
ceiver, but the voltage regulation provided
here ensures against any frequency drift in
the transverter. Capacitors C1 and C3 are
mounted on insulated bases, and the cans
are insulated to prevent accidental shock.
appearance
Finishing touches include a ventilated top
cover, formed from sheet aluminum, and a
ventilated bottom plate. The shielding
i s
re-
quired for best results. A coat of spray paint
and decal identification of controls will give
a professional appearance.
tuning up
The forty-meter Single-Bander tunes only
100
kHz-from 7.2 MHz to 7.3 MHz. Thus,
a 42.9-MHz crystal will cover 50.1 to 50.2
MHz. This
is
the portion of six meters where
fig.
2.
Power supply for tha
bans-
verter and mlay witching amnga-
ment. Relay Is a 6.3 Vae unit.
Top vlew showing the general layout with the
nceiving converter at the left on its copper
plate, the transmitting converter in the center.
and
power supply on the right.
m
chassis base. A hole was cut in the top at
one end to accept the copper sheet of the
receiving converter. The photos show the
placement of the other components. Note
that C3
is
ungrounded. It mounts on a ver-
tical square of phenolic board to which the
output winding of 110
is
also attached. The
parasitic chokes for the 5894 are soldered
across loops in the copper straps connecting
its plates to C3 and
L10.
The power supply
i s
conventional
(fig.
2)
It provides 500 Vdc at 300-plus mA for the
5894 (which, incidentally, can be pushed
much harder); 300-volts regulated for the
m m m m
d
7
Relay switching arrangement.
july 1969
47
most ssb signals are heard. Crystals can be
chosen, however, to put you anywhere you
want in the band.
Assuming you plan to operate 50.1-50.2
MHz, a grid-dip meter can be used to reso-
nate L2 and L3
a
little under, and a little
over, 50.15 MHz. L4 i s tuned to the crystal
frequency; 7.25 MHz
is
bracketed with L5
and L6. This should give a good, flat response
across the 100 kHz used. When you get far
enough along to copy signals over the air,
these adjustments can be touched up to
produce the best signal-to-noise ratio.
L7, C5-L8, and C6-L9 are resonated to
the crystal frequency. C7
is
adjusted to
peak L11 at 7.25 MHz. Adjust
C3
and the
spacing of L10 to 50.15 MHz. By making
these adjustments to the center of the 100-
kHz segment of interest, it will be unneces-
sary to do any further tuning of the trans-
verter a you change frequency.
s
5894 plate current under 200 mA. Don't let
this tube run red.
Return the transceiver tune control to
transmit, and speak into the mike. The plate
meter should kick on voice peaks to approxi-
mately 300 mA. This completes tune up, and
you're ready for on-the-air tests. Listening
tests will provide the best criteria of correct
adjustment. Important: correct adjustment
should occur when the least amount of ssb
drive, as established with
R 1
and C7, pro-
duces the greatest output. The quality of
your six-meter sideband signal should be as
good as your forty-meter signal. Reports for
the
6/40
'verter have been uniformly good.
on-the-air tests
After checking and rechecking your work,
you're ready for the smoke test. Connect
your
6/40
'verter between your transceiver
and your six-meter antenna. Turn on the
power and listen for signals. Listen on the
upper sideband, because stations on six are
almost always on upper sideband and those
on forty are on lower sideband.
With the receiving converter working, ad-
just L4 for maximum using your dipper as an
absorption wavemeter. Move to L8 and ad-
just L7 and C5 for a peak, which will be
very much stronger. Touch up C6 for a high
reading at L9.
Now, with no forty-meter input, close the
relay manually and adjust R1 for a plate
current of 50 to 75 mA. Connect a dummy
load in the transceiver output to reduce the
forty-meter signal to one or two watts, and
attach a dummy load to the transverter out-
put. Insert a power-output meter between
transverter and dummy load. Interconnect
the relays so the transceiver and transverter
transmit together. Turn the transceiver to
tune position to provide a carrier, and ad-
just C3 and C8 for maximum output. C7
and R1 can be readjusted to peak the out-
put. During tune-up, the injected carrier
level should be low enough to keep the
1
'H
The ventilated cover improves eppear-
once and provides essential shielding
and protection from accidental contact
with the high voltage.
a final note
This probably shouldn't be your first con-
struction project, but you don't have to be
an engineer to achieve good results. Single
sideband isn't all that difficult when you do
it the easy way. The idea i s to proceed
slowly, plan each step, and follow my in-
structions and suggestions. If you can solder
and use simple shop tools, you can build
the
6/40
'verter in a few week ends.
ham radio
48
july 1969

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