KWM-1

THE COLLINS KWM-1 TRANSCEIVER

The KWM-1 covers the frequency range of 14-30 mc with an input of 175 watts PEP or SSB. In addition to SSB emission it also utilizes the VOX circuits for break-in CW operation with a built-in monitor. The bands are covered in 100 kc segments with a total of 10 such segments. A box that plugs into the front panel contains the 10 injector oscillator crystals. A standard crystal complement is furnished as detailed in the specifications. For other selections such as MARS or commercial frequencies, extra crystal boxes with the proper crystal complement can be obtained. The front panel meter acts as an S-meter on receive and as the tuning meter on transmit. Frequency stability, receiver sensitivity and selectivity are outstanding.

Maximum convenience in switching between mobile and fixed station is built in. For mobile installation the unit plugs into the mounting rack. The power plug, antenna coax connector, and speaker, are in one plug and connect automatically. Two knobs tighten to hold the unit securely in place. For fixed installations a separate speaker jack is provided. Power connections and antenna coax connection would be made through the same plug used for mobile installation.

A 100 kc crystal calibrator is included.

KWM-1 SPECIFICATIONS

RF POWER INPUT: 175 watts SSB PEP or 160 watts CW.

OUTPUT IMPEDANCE: 52 ohms with not more than 2.5:1 SWR.

POWER SOURCE: 115 vac 50-60 cps, 12 vdc, or 28 vdc

POWER INPUT: Filaments 5.25 a at 12 v; B+ and Bias:
Transmit: 800 v at 200 ma; 265 v at 210 ma; – 50 to -80 v at 3 ma
Receive: 290 v at 170 ma.

SIZE: Transceiver   – 6-1/4″ h, 14″ w, 10″ d
AC Power Supply – 6-1/4” h, 7-5/8″ w, 10″ d
DC Power Supply – 7-19/32″ h, 10-1/8″ w, 5-3/4″ d
Speaker Cabinet – 6-1/4″ h, 7-5/8″ w, 10″ d

WEIGHT: Transceiver – 15 Lbs.
AC Power Supply – 25 Lbs.
DC Power Supply – 15 Lbs.
Speaker Cabinet – 5 Lbs.

FREQUENCY RANGE: 14-30 mc continuous. Choice of any ten 100 kc bands
by crystal switch. Standard complement of crystals:

14.0 – 14.1 mc CW
14.2 – 14.3 mc SSB
14.9 – 15.0 mc calibration with WWV
21.0 – 21.1 mc CW
21.3 – 21.4 mc SSB
21.4 – 21.5 mc SSB
28.0 – 28.1 mc CW
28.1 – 28.2 mc CW
28.5 – 28.6 mc SSB
28.6 – 28.7 mc SSB

FREQUENCY CONTROL: 70K-1 Permeability Tuned VFO

HARMONIC AND SPURIOUS RADIATION: Carrier suppression
-50 db, unwanted sideband 50 db, oscillators and mixer products
-50 db, second harmonic
-50 db, 3rd order products 30 db.

FREQUENCY STABILITY: After 10-minute warm-up, within 100 cps.
Reset within 1 kc throughout range.

AUDIO CHARACTERISTICS: Response 300 – 3,000 cps
noise 40 db below one tone carrier;
transmitter input designed for high impedance crystal or dynamic mike.

PHONE PATCH IMPEDANCE: 600 ohms unbalanced to ground.

CIRCUIT PROTECTION: Primary fuses.

ACCESSORIES REQUIRED: Hi-Z Dynamic or Crystal Microphone and/or
telegraph key, antenna, loudspeaker and/or headphones,
516E-1 dc and/or 516F-1 ac power supply

POWER SOURCE: 115 vac 50-60 cps; 12 vdc; 28 vdc.

RECEIVER SENSITIVITY: 1.0 uv for 6 db S/N ratio with 3 kc bandwidth.

NUMBER OF TUBES: 24 plus 2 rectifiers in ac power supply.

NUMBER OF TRANSISTORS: 6 in dc power supply.


KWM-1 CIRCUITRY

TRANSMITTING FUNCTION

The audio amplifier (V19) consists of a two-stage amplifier and a cathode follower (V18) driving a ring-type balanced modulator, which feeds a 455 kc Mechanical Filter. The 455 kc signal is heterodyned by V6 to a band pass IF frequency of 3.9-4.9 mc by means of the VFO. The band pass IF frequency is then heterodyned by V5 to the desired output frequency by means of crystals. Ten such crystals can be selected from the panel, each allowing operation over a 100 kc portion of the spectrum. The output frequency is amplified by two amplifier stages (V3 and V4) and the driver stage (V2) and applied to the grids of the two 6146’s in parallel (V23 and V24). The output circuit consists of a Pi-L network and will match 52-ohm antennas with up to 2.5:1 SWR. A self-adjusting dual time constant ALC circuit effectively provides higher average talk power. VOX and speaker anti-trip circuits are an integral part of the design. CW operation is obtained by feeding a keyed audio tone into the transmitter audio circuits. A portion of this audio tone is fed to the receiver audio circuits for monitoring.

RECEIVING FUNCTION

During transmit or receive, tubes not being used are biased to cutoff. A received signal is fed through the antenna change-over relay to the grid coil of V4. Since V5 and V3 are cut off, the signal passes through V4 to V7. This tube heterodynes the signal with a crystal oscillator to produce a signal in the range of 3.9-4.0 mc. With V6 and V5 cut off, the signal will pass through the IF transformer to V8. This mixer heterodynes the IF against the VFO to produce a signal at 455 kc. The signal passes through the Mechanical Filter to the grid of V13. Since V18B is cut off, no BFO voltage is fed to the balanced modulator so it is inoperative even though still connected to the Mechanical Filter. The signal passes through V13 and V14, the receiver fixed IF amplifier, and is detected by V15. V12 is the AVC rectifier. The detected signal is amplified by V16 and V17 with audio outputs of 4 ohms and 500 ohms available. V1, a 100 kc calibrator, furnishes calibration signals for the receiver dial, with provision for comparison with WWV on 15 mc.

ELECTRICAL CHARACTERISTICS

The KWM-1 receives or transmits (on the same frequency) SSB or CW signals in the 14.0 to 30.0 mc range. Blocking-bias control circuits switch from receive to transmit function by disabling some of the tubes. The vox and anti-trip circuits permit voice operation on SSB and break-in operation on CW.

RECEIVE-TRANSMIT COMMON CIRCUITS

Circuits common to both receive and transmit functions are:

Receive-transmit amplifier V4 and its tunable grid and plate circuits. (These are gang tuned with other circuits tuned by EXCITER TUNE control on front panel.)

The 3.9- to 4.0-mc band-pass i-f transformer T1.

Mechanical filter FL1.

High-frequency oscillator V11.

Beat-frequency oscillator V9.

Variable frequency oscillator V22.

Control circuits.

RECEIVE CIRCUITS … R-F CIRCUITS

Signals from the antenna are connected from J5-A1 through contacts of relays K1 and K2 to the grid of r-f amplifier V4. Grid circuit (L1, C13, and C15) and plate circuit (L3, C10, and C21) are tracked and ganged to the EXCITER TUNE control on front panel. Output from V4 and high-frequency oscillator signal from V11 are fed to the first receiver mixer (V7).

I-F CIRCUITS

Difference frequency (3.9 to 4.0 mc) is coupled through i-f transformer T1 to the receiver second mixer (V8). The 3.9- to 4.0-mc signal is mixed with the 3.445- to 3.545-mc vfo signal in V8 to produce the 455-kc i-f signal. This i-f signal is coupled through the mechanical filter FL1 to the grid of the receiver i-f amplifier (V13). A two-stage i-f strip, consisting of V13, and V14, amplifies the 455-kc signal and applies it to the agc rectifier (V12A) and the product detector (V15).

A-F CIRCUITS

Beat-frequency oscillator signal is applied to the product detector which mixes the two signals to produce demodulated audio signal. The audio signal is filtered by L17, C86, C89, C88, and C77 and amplified by V16A and V17 for application to phone patch, speaker, and headphone circuits. Negative voltage, developed by V12A, provides automatic gain control to receiver amplifier circuits. The R.F. GAIN control (R116) is used to set the level of operating gain for all receiver r-f and i-f amplifier stages. Audio output level is controlled by A.F. GAIN control R79.

TRANSMIT CIRCUITS … A-F CIRCUITS AND SSB GENERATION

Microphone signal is amplified by V19A and V19B and applied to cathode follower V18A. Signal level applied to the cathode follower is controlled by MIC. GAIN control R92. Output from the cathode follower is filtered (by L18, C96, and C98) and applied to the diode-ring balanced modulator (CR1 through CR4) consisting of four matched 1N67’s. Carrier energy is supplied from the bfo through an isolation stage (V18B) to the balanced modulator. Output of the balanced modulator (with carrier balanced out) is applied to mechanical filter FL1 which passes only the lower sideband energy to the first transmit mixer (V6).

R-F CIRCUITS

Mixer V6 combines the 455-kc sideband signal and the 3.445- to 3.545-mc vfo signal to produce a 3.9- to 4.0-mc output. The 3.9-4.0 mc signal is amplified by V3 and applied to second transmit mixer V5. Tuned circuits T1 and T2, are bandpass transformers. Mixer V5 combines the 3.9- to 4.0-mc signal with the high-frequency oscillator signal and inverts the side-band to produce the desired upper sideband output frequency. This output signal is amplified by V4 and V2 and applied to the final amplifier. Both driver (V2) and final amplifier (V23 and V24) stages are neutralized by the capacity-bridge method, and negative feedback is coupled to the cathode of the driver to improve linearity. The Pi-L power-output circuit consists of C42, L10, L11, C43 and C44, and L12. Output power is connected from L12 through contacts of K1 and connector J5-A1 to the antenna.

CONTROL CIRCUITS … VOX AND ANTI-TRIP CIRCUITS

Vox and anti-trip circuits operate as follows:

A portion of the audio voltage developed across R93 (in output of V19B) is amplified by V20A and rectified by V21A. The positive d-c output of V21A is applied to the grid of V16B causing V16B to conduct current and actuate vox relay K2. Contacts of K2 switch the high-voltage plate power supply into operation, (on d-c supply only; these contacts are jumpered in the a-c supply) disconnect the antenna from V4 grid, and energize relays K1 and K3. Relay K1 switches the meter M1 from receiver S-meter circuits to transmitter multimeter circuits and switches antenna connections so that receiver input is grounded and transmitter output is connected from L12 to the antenna through J1. Relay K3 applies screen voltage to the power amplifier, and plate voltage to V18A turns on transmitter tubes (V2, V5, V6, and V18B) and turns off receiver tubes (V7, V8, V12, V13, V14, and V15).

The anti-trip circuit provides a threshold voltage to prevent loud-speaker output (picked up by the microphone circuits) from tripping the KWM-1 into transmit function. Some of the receiver audio output voltage is connected through C116 and R115 to the anti-trip rectifier (21). Negative d-c output voltage from V21B, connected to the grid of V16B, provides the necessary anti-trip threshold. ANTI-TRIP control R115 adjusts the value of the anti-trip threshold so that loud-speaker output will not produce enough positive d-c output from the vox rectifier to exceed the negative d-c output from V21B and cause V16B to actuate K2. However, speech energy into the microphone will cause the positive vox voltage to overcome the negative anti-trip voltage and produce the desired action of K2.

MANUALLY OPERATED SWITCHES

VOX GAIN control R93 is ganged mechanically to switch S3 which may be used for transmit-standby manual control if desired. When R93 is turned down through minimum, S3 closes and shorts the cathode of V16B to ground, causing the tube to conduct and actuate the switching relays. (Refer to figure 3-1.) As the EXCITER TUNE control is adjusted near 14.0 mc, 21.0 mc, or 30.0 mc, S5 connects pins 15, 16, or 17 (respectively) of J5 to ground to operate any desired combination of antenna selecting relays. Crystal selector switch S1 selects the proper crystal for high-frequency oscillator V11 to put the KWM-l in the desired 100-kc portion of its operating range. Switch S2 selects metering function for M1 when the EMISSION SWITCH S4 is in SSB, CW, or TUNE position.

EMISSION SWITCH section S4A applies PA screen voltage through PA SCREEN switch S6 in all positions except OFF. In TUNE position, the screen voltage is reduced through a voltage divider R154 and R155. Section S4B turns on crystal calibrator V1 in CAL position and turns on tone oscillator V20B in CW and TUNE positions. Section S4C removes cutoff bias from V19B when in SSB, TUNE, and LOCK KEY positions. Section S4D reduces input of V18A and V16A when in SSB and CAL positions and grounds alc voltage in CW, TUNE, and LOCK KEY positions . Section S4E grounds microphone input in CW position and reduces input to V18A and V16A when in TUNE and LOCK KEY positions. Switch S4G, mounted on rear of S4, turns on all low voltage supplies in all positions except OFF.

OSCILLATOR CIRCUITS

The crystal-controlled bfo provides 455-kc (nominal frequency) carrier to the balanced modulator and bfo injection to the frequency product detector. Its crystal is selected to fall at the -20-db point on the high-frequency skirt of the mechanical filter band pass. The vfo is a series-tuned type circuit. Its operating frequency of 3.445 to 3.545 mc is controlled by a permeability-tuned coil. The high-frequency oscillator (V11) is crystal controlled by one often crystals selected by the crystal selector switch on the front panel. These crystals may be selected to operate at any frequency in the operating range. The tone oscillator (V20B) is an RC phase shift type which supplies a 1-kc tone for tuneup and CW operation. The 100-kc crystal calibrator (V1) supplies calibration check points for calibrating the receiver dial.