Heathkit MR-1-MT-1 Comanche Mobile Receiver Instruction Manual

Compact design: total volume of both units is a mere cubic
foot
Power Supplies: 115-volt AC for home installations, 12-volt DC
transistorized supply for mobile operation

Single-conversion amateur-band superheterodyne receiver
Designed for reception of AM, CW, and SSB signals on amateur
frequencies from 1.5 to 30 MHz

Product Usage Instructions:

Installation:

1. Choose a suitable location for mounting the receiver and
transmitter units.

2. Securely mount the units using the provided mounting
rack.

3. Connect the power supply according to the type suitable for
your operation (115-volt AC for home or 12-volt DC for mobile).

Operation:

1. Power on the units using the appropriate power supply.

2. Adjust the V.F.O. control for the desired frequency.

3. Select the mode of operation (AM, CW, or SSB) based on the
signals you wish to receive.

4. Use the controls such as Noise Limiter, Antenna Trim, RF
Amplifier, etc., as needed for optimal reception.

Maintenance:

1. Regularly check and clean the equipment to ensure proper
functioning.

2. Keep the units away from moisture and extreme temperatures to
prevent damage.

FAQ:

Q: What is the purpose of the crystal filter in the
receiver?

A: The crystal filter provides adjacent-channel selectivity and
helps in image rejection, improving the receiver’s performance in
filtering out unwanted signals.

Q: Can I use this mobile equipment for home installations as
well?

A: Yes, the manufacturer provides power supplies suitable for
both home installations (115-volt AC) and mobile operation (12-volt
DC), allowing flexibility in usage.

“`

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Heathkit Mobile Equipment

AN appropriate title for the units pictured would

.t:l. he a ” cubic-foot QHO” _.- the receiver-

transmitter combination offers v.f.o. control and

80-through lu-mcter operation. yet the total

volume occupied by both units is a mere cubic

foot. The transmitter and receiver, although

primarily designed to be used mobile, also corn-

prise a very «ompar-t and flexible home station.

The manufacturer, more than likely having this

in mind, makes available two different types of

power supplies: one a conventional lI5-volt a.c .

supply for home installations and the other a

12-volt d.c, transistorized supply for mobile

operation.

Comanche Mobile Receiver

The Heathkit J1R-l mohile receiver is a single-

conversion amateur-band superheterodyne using

a bandpass crystal filter in its :~-JIc.

i.f. amplifier.

It is designed for reception of a.m., c.w, and

s.s.b. signals Ol! all amateur frequencies from

a.5 to ao Me. The block diagram of the receiver is

shown in Fig. 1. The front:end uses a 6BZ6 d.

amplifier, and this stage is followed by a 6EA8,

the peutode section of which is the mixer and the

triode section the high-frequency oscillator. The

high-frequency oscillator and mixer tuned cir-

cuits are tracked to give an i.f. output frequency

of 3 Me.

The complete Heathkit mobile installation, including receiver, transmitter, speaker, microphone, and transistorized power supply. The mounting rack, bolted to the back of the receiver and transmitter, is partially visible at the top
of the receiver-transmitter assembly.
The output of the mixer goes into the :3-Mc. crystal filter, which has a bandpass characteristic :~ kc. wide at 6 db. down and a maximum width of
10 kc, at no db. down. The crystal filter con-
tributes tho receiver’s adjacent-channel selectivity and the high intermediate frequency takes care of image rejection. After the crystal filter,
OFF
NOISE LIMITER

ANT. TRIM.

R.F. AMP.

lst.l.F.
MIXER XTAL FILTER AMP.
3Mc.

2nd. 1.1:
AMP.

H.F.
” OSCILLATOR

~6EAe: I ~I

AUDIO

AGC.

-tE~: GAIN IIl.AUDIO OUTPUT

ON oiL

OW SSB
AM

PRODUCT DETECTOR

Fig. I-Block diagram of the Comanche receiver,

April 1960

Top view of the Comanche receiver chassis. Tubes from panel to rear and from right to left in this view are, front row, the 6T8 first audio-noise llmlrer-c.m, detectar, 6BE6 product detector, and 6AQ5 audio output; second row, 6EA8 second i.f. amplifier-S meter amplifier, 6BZ6 first I.f, amplifier, OA2 voltage regulator; third row, 6EA8 mixer-h.t oscillator, 6BZ6 r.f. amplifier. The i.f. coils, in small shield cans, are at the upper right. The crystal filter
is at the center.
another t3BZ6is used as the first i.f. amplifier, and the output of this stage is impodunce-couplcd to the second Lf. amplifier, the pentode section of a t,EA8. The output of this tube is impedancecoupled to the detectors. Automatic gain control is applied to the d. stage and both i.f. stages when the u.v.c, switch is in the don” position. With the a. v.c. “off,” hoth i.f. stages are operated at maximum gain, with the manual r.f. gain COIltrol operative only on the r.f. stage. The triode section of the 6EAS, with the a.g.c. voltage applied to its grid, is used to drive the S meter.
A choice of detectors is available. A (iTS is used us a conventional diode detector for a.m.. as a series noise limiter, and as the first audio amplifier. A 6BE6 product detector is used for c.w, or s.s.b. reception, generating its own b.f.o. signal with a circuit resembling the type used for fraquency conversion, as shown in Fig. 2. The audio output of the detector in usc goes to the first

audio amplifier, the 6’1’8 triode section, and

thence to the 6AQ5 output stage. The 6AQ5 is

transformer-coupled to an external 8-ohm perma-

nent-magnet speaker.

An OA2 regulator is incorporated to supply a

constant voltage to tho high-frequency oscillator

and other critical circuits.

As shown in the bottom view of the receiver,

the tuning mechanism uses five gears. The tuning

capacitor drive gear is spring loaded to prevent

backlash. Band calibrutions are ou a plastic

cylinder which rotates into proper position be-

hind the rectangular Lucite window in the panel

when the band switch is turned. The dial drum is

string driven from the band selector switch. The

Hlide-~ule

dial pointer is also string driven from u

large pulley located on one of the gear shafts, The

dial scale is approximately five inches long, and

thirteen rotations of the tuning knob are required

for covering each band, The dial is eulibratcd

everv 20 kc, on 10 meters and at lO-ke. intervals

on tho rest (,f the bands. If more uceurate fre-

quency interpolation is desired, the flat dial

pointer can be given a half twist, ut the time of

assembly, so that its edge is perpendicular to the

dial drum.

Assembling a kit of this sort is definitely not an

undertaking for the beginner or inexperienced

eonstructor. However, auyone who has previous

kit-building experience under his belt and if’

willing to follow the well-laid-out und detailed

construction manual can come up with a very

satisfying; finished product. Wiring of the r.f.,

high-frequency oscillator and mixer coils in the

front end must be completed before the band

switch is installed. since the coils become fairly

inaccessible afterward. Because of the confine;l

quarters, usc of ll. pencil-type iron is highly roe-

ommcnded.

Alignment of the finished receiver requires an

aceuratc signal generator, or a frequency meter

such as the L:I or BO surplus HI’ries. Included

with the kit is the required alignment tool and a

soft plastic nut starter which is an Invaluable aid

in starting nuts on screws in tight spots.

ln the unit this reviewer constructed, the

r.f. stage was slightly regenerative at maximum

gain setting; however, this was readily cured by

FROM~T’
SECOND I.F. AMPLIFIER
27k 30
10k

.o,uf~
~1
I $27< KO~I
6+

TO FIRST “UDIO STAGE
Fig.2-Product-detectorcircuit uses a converter tube with selfexcitation. The rectified d,c, voltage developed at the oscillator grid (No.1) is one or two volts (negative) a. operated in the Comanche.

QST for

Bottom view of the Comanche receiver. At the right, from bottom to top, are the r.f, coils, mixer coils, oscillator coils, and gear-driven tuning mechanism. The three sets of coil. are shielded from each other, and a vertical partition separates the front end from the i.f. and audio sections.
The rectangular shield compartment at the left houses the product detector.
installing small parasitic chokes in the plate and grid leads of the d. amplifier. When peaking the r.I. stage be sure the antenna trimmer is carefully “d,; its adjustment is critical. One slight improvement which perhaps might be desirable would be to increase the available audio level, which is a little on the low side.
Power requirements for the Comanche re”dver are :l50 volts d.c. at 1:l5 milliamperes, maximum, and either 1:l volts at 1.65 amperes or o volts at ;~. amperes. The finished unit. weighs I.’i pounds and measures (j~ by 1278 by !Jl% inches _… slightly less than a half cubic foot in volume. Our total eonstruction time, including
alignment, was 3U2 hours.

buffer Rt,age iR untuned on 80 meters, slug-tuned

to 40 meters for operation on 40, 20, and 15, and

slug-tuned to 20 meters for final output on 10

meters. The driver is straight-through on 80 and

40. doubles to 20, triples to 15, and doubles to 10

meters. Pi-network interstage coupling is em-

ployed between the driver and the final stage,

and the eorroct coil tap is selected by the exciter-

section wafer of the band switch. The final am-

plifier tank is a pi network, shunt-fed through a

2.5-mh. r.f. choke. For c.w, operation the buffer

and v.f.o, run continuously, with the final am-

plifier and driver cathode-keyed. The metering

circuit in the transmitter can measure either final

amplifier grid current or final amplifier cathode

current.

The modulation svstem is similar to that in

the DX-aS and DX-10 transmitters.” using a

triode as a Series screen modulator. The modula-

tor tube in the Cheyenne is the “heavy” triode

section of the fiDE7. As in the earlier transmit-

ters, the modulator’s average plate current is

adjusted, by means of a control tube which

responds to the average speech level, to vary the

r.f. carrier level to correspond to the modulating

level. The “light” section of the oDE7 is used

for this purpose. The speech amplifier preceding

HlP modulator and control tube is a cuseude

resistance-coupled affair using a 12AX7.

Many of the mechanical det.ailf1 in the Chey-

eune are similar to or identical with those in the

Comanche mobile receiver. Both the dial drive

arrangement and front panel are alike. The dial

length and frequency calibration are also the

same _.. that is, 20 ke, INr division on :l8 Me.

-l<;R~:t

Equipment,’;QST~bcr

1936, p, 2!l.·

Cheyenne Mobile Transmitter
The Heathkit ITT-l mobile transmitter is a v.f.o.-controlled all-band (80 to IO meters, inelusive) rig with a built-in controlled-carrier modulator. Referring to the block diagram. Fig. :. it ran be seen that the r.f. tube lineup is fairly conventional, with a liAU6 v.f.o., (JCLI buffer, 5763 driver, and 6146 final. The audio section has a f:lAX7 speech amplifier and GDE7 screen modulator. The controiied-currior screen modulation system permits peak-envelope inputs up to !10 watts, which should result ill all effective maximum carrier output of about 30 watts at 100 per cent modulation.
The v.f.o. is a series-tuned Colpitts circuit with output on either 1.75 or 7 111′., the proper range being internally selected depending on the setting of the transmitter band switch. A spot.ting switch arrangement allows the v.I.o. to be turned on for frequency checking prior to putting the transmitter on the air. The v.f.o. screen and plate voltages arc regulated by an 0/.2 tube. The

In this view of the Cheyenne mobile transmitter the tube. starting at the top right, are the 5763 driver, 6CL6 buffer ond 6146 final amplifier. The 6AU6 v.f.o. tube is in the center. Along the left are the 12AXl speech amplifier, 6DE7 modulator and carrier control tube, and OA2 voltage regulator. The plate r.f. choke, tank coil, and tuning capacitor are grouped around the 6146 tube at the right. Located from right to left on the rear wall of the chassis are the power plugs, antenna connectors, and key lack.
The microphone connector is mounted on the left-hand chassis wall.

April 1960

MOULATOR
AND CARRIER CONTROL

Fig. 3-Block diagram of the Cheyenne transmitter.

und 10 kc. pCI’ division on all other bands. The v.f.o. is completely shielded, and power
vonnectione are hrought out through feedthrough bypass capacitors, The buffer, driver and amplifier stages arc isolated from one another by rectangular shield plates, minimizing stray coupling between stages which could result in instability. The plate tuning capacitor, mounted above the chassis beside the 61-16, is driven by a right-angle gear arrangement. The loading capnr-itor, underneath the chassis at the rear, is also driven by a set of right-angle gears.
All control switching, including antenna changeover from receive to transmit, is handled by an internal relay. Power input and output rl'(‘cptades are mounted at the back of the (‘hm.. sis, and are wired for the compatible Heathkit power supplies (iIP-l and UT-l) and Comanche receiver. Included with the transmitter is u ceramic-type push-to-talk microphone.

Undemeath the chassis of the Cheyenne transmitter. The

center shield compartment contains the v.f.o. To its left are

the band switch, buffer, driver and final amplifier circuits.

The relay for control switching and antenna changeover is

at the lower left. The speech section is to the right of the

v.f.o. compartment. The 3·section capacitor at bottom

right center is the final amplifier IQadin~

capacitor.

Power requirements for the Cheyenne arc :300 volts d.c. at 100 milliamperes, 500 to !.iOa volts
d.c, at 150 ma .. and either 12 volte at 2.:35 ampores or 6.:3 volts at -l.7 amperes. The finished unit weighs 151,”:2 pounds nud measures 13,I.i
inches high, 12 }’B inches wide, and VIt.l6 inches
deep. Total construction time in our case was
approximately 28 hours.

Transistorized Mobile Power Supply

The Heathkit lIP-l transistorized power SIlP-

ply was designed primarily to furnish all the

necessary power to the Heathkit mobile trans-

mitter and receiver units. This supply is the

usual transistor type having a feed-back winding

on the power trnnsformer to set, the transistors

into oscillatory switching. as has been described

several times in recent issues of <1ST. However.

the rectifier-filter arrnngcmcnt differs from most

of those previously desc~ibd

in using a full-wave

voltage doubler circuit rather than a center-tap

or bridge rectifier. This is apparently a matter of

economics, primarily; the doubler circuit requires

onlv half the number of semiconductor rectifiers

that would be needed with either the center-tap

or bridge circuits to deliver the same output

voltages. (This is because the peak inverse volt-

age on each rectifier group is twice as great with

either of the latter rectifier circuits.) The circuit

is shown in Fig. -1. The 100-ohm resistors between

the first and second filter cupacitors in each lell:

add considerably to the ripple attenuation since

they represent about 20 times the impedance of

the ,W-/lf. output capacitanr-e at the 800-eycle

ripple frequency,

The pilot lamp :I(‘ross the 20-ohm resistor

serves as a current indicator, lighting up to about

liar mal brilliance at the maximum permissible

current drain on the supply.

A 1000-!’f. r-lectrolyti« capacitor is connected

directly across the battery at the primary input

side of the supply to bypass the hat t”ry circuit

and prevent the -lOO-cycle hash from feeding

back into the transmitter and receiver. There is

also a self-contained control relay for turning on

08T for

fi.3V. aeome,

Fig. 4-Rectifier-filter circuit used in the transistori:z:ed power supply.

II
POWER TRANS. SEC.

.!.2Q. 1W.
+

<, <a / 4iOV.”

100
7W:

+ 60 0
+300

lN2071
/

the supply, operated by the auxiliary control circuits in the mobile transmitter and receiver. A manual toggle switch on the chassis offers an alternative means for turning on the supply. The 12-volt primary circuit iH protected by a 15ampere fuse.
After constructing the puwer supply unit it would be wise to cheek the relay contacts with an ohmmeter before applying power. In the unit constructed here these contacts were covered by some type of insulating coating which had to be cleaned off before the supply would function.
Power specifications of the supply are as follows: Input voltage 12 to 14. volts; input current, 4.5 to 15 amperes (varies with load); maximum output power, J20 watts. This maximum power may be taken from either tap alone or distributed as desired between the two taps. In the transmittor-receiver combination the distribution is !)O watts from the high tap (GOO volts at 150 mu.) tind 30 watts from the low tap (300 volts at 100
ma.). Over-all dimensions arc Hh6 byH.’.J: by
5’16 inches. The total weight is 5 lb. 8 oz. Total construction time was approximately () hours.
Mobile Accessories
Optional accessories styled to match the receiver, transmitter and power-supply units include It5-inch speaker (AK-7) to be used in conjunction

The transistorized mobile power-supply chassis. From right to left on front (top) wall are the external power switch, output-current indicator bulb, primary fuse, primary input power cable, and power-supply output plug. The semiconductor diode rectifiers are mounted on the terminal
strip at the lower center. The control relay is to the left of the terminal strip.

with the receiver, and a mobile mounting base

(AK-6) which is designed for mounting of the

mobile transmitter and receiver on the transmis-

sion hump of the car tloor. Also available is an

all-band mobile antenna (Hlvl-L), The munnfac-

turer is the Heath Company, Benton Harbor.

Michigan.

– 1(. C. L.

~Sta.Y

Hams interested in good-paying jobs with

generous vacation, sick leave and retirement

should investigate the civilian positions of elec-

.tronic inspectors for the U. S. Navy. Write to

Executive Secretary, Board of U. S. Civil Service

J~xaminers,

17 Brief Avenue. Upper Darby, Pa.,

for application form 5000-AB. Applicants are

graded on written examinations plus experience.

night KIJWK worked K8II1 and W8:MMM, both of whom are in Novelty, Ohio.
W6TKV gave a call on 80 c.w. the other night and who should answer but W7TKV from Boulder City, Nev., who said he used to be W6TKV back hefore World War II. The present W6TKV uses a ten-meter dipole for an antenna.

A couple of novel QSOs. On aurora the other W9DBO’s post office box number is 73!

April 1960

Documents / Resources

Heathkit MR-1-MT-1 Comanche Mobile Receiver [pdf] Instruction Manual
MR-1-MT-1 Comanche Mobile Receiver, MR-1-MT-1, Comanche Mobile Receiver, Mobile Receiver

References

User Manual

MR-1-MT-1 Comanche Mobile Receiver

Product Information

Specifications:

Product Usage Instructions:

Installation:

Operation:

Maintenance:

FAQ:

Q: What is the purpose of the crystal filter in the
receiver?

Q: Can I use this mobile equipment for home installations as
well?

Documents / Resources

References

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