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Heathkit SB-303 1970–1976
Heathkit SB-303, 1970-1976
Solid-State Amateur receiver. The original price for the kit was $345.00

Frequency Range (Megahertz) 3.5 to 4.0, 7.0 to 7.3, 14.0 to 14.5, 15.0 to 15.3, 21.0 to 21.5, 28.0 to 30.
Intermediate Frequency (IF) 3.395 MHz
Frequency Stability Less than 100 Hz per hour after 10 minutes warmup under normal ambient conditions. Less than 100 Hz drift for ±10% line voltage variation.
Frequency Selection Built-in LMO (Linear Master Oscillator).
Modes of Operations  
SSB Single sideband (suppressed carrier, with selectable upper or lower sideband).
CW Keyed continuous wave.
AM Amplitude modulated continuous wave.
RTTY Radio Teletype (frequency-shift keyed continuous wave).Wide shift, narrow shift and narrow CW shift identification.
Sensitivity Less than 0.25 microvolt for 10 dB signal-plus-noise to noise ratio for SSB operation.
Overall Gain Less than 1.5 microvolt input for 0.5 watts audio output (single tone SSB).
AGC Characteristic  
Blocking Greater than 3.0 V CW/SSB/RTTY.
Dynamic Range Greater than 150 dB CW/SSB.
RF Attenuator Range 0-40 dB nominal.
SSB 2.1 KHz 6 dB down, 5.0 KHz maximum at 60 dB down (crystal filter supplied).
CW 400 Hz at 6 dB down, 2.0 KHz maximum at 60 dB down (crystal filter available as an accessory).
AM 3.75 KHz 6 at dB down, 10 KHz maximum at 60 dB down (crystal filter available as an accessory).
RTTY 2.1 KHz at 6 dB down, 5.0 KHz maximum at 60 dB down (uses SSB crystal filter).
Image Rejection 60 dB or better.
IF Rejection  
3.395 Greater than 55 dB.
8.595 Greater than 50 dB.
Spurious Response All below 1 microvolt equivalent signal input.
Temperature Range 10º C to 50º C ambient.
Dial Accuracy  
Electrical Within 40 Hz after calibration at nearest 100 KHz or 25 KHz point.
Visual Within 200 Hz.
Variation in RTTY shift as LMO is changed (shift can be adjusted to nominal value at any point within the band).  
CW shift (50 Hz nominal) Less than 10 Hz/100 KHz.
Narrow Shift (170 Hz nominal) Less than 20 Hz/100 KHz.
Wide Shift (850 Hz nominal) Less than 100 Hz/100 KHz.
Calibration Every 100 KHz or 25 KHz.
Dial Backlash No more than 50 Hz.
Antenna Input Impedance 50 Ω nominal unbalanced.
Audio Response  
SSB 350 to 2450 Hz nominal at 6 dB.
CW (with accessory filter) 800 to 1200 Hz nominal at 6 dB.
AM (with accessory filter) 200 to 3500 Hz nominal at 6 dB.
RTTY 1840 to 3940 Hz nominal at 6 dB.
Audio Output Impedance  
Matching Speaker 8 Ω.
Matching Headphones Low impedance.
Audio Output Power 4 watts at less than 10% distortion.
Muting Open external ground at Mute socket.
Power Requirements 105 to 130 or 210 to 260 volt ac, 40 watts maximum.
Front Panel Main Tuning dial.
Function switch.
Mode switch.
Band switch.
AGC switch.
Converter switch.
AF Gain control/Power on-off.
RF Gain/Speaker Disable.
RF Attenuator.
Circuit Boards  
IF/Audio Bias adjust.
Meter Zero.
Meter Full Scale.
PS/BFO +15 V adjust.
100 KHz adjust.
RTTY Wide Shift.
Narrow Shift.
CW shift.
Rear Panel Phones.
HF Antenna.
VHF Antenna #1.
VHF Antenna #2.
HFO out.
LMO out.
BFO out.
CW shift.
4-Spare sockets.
3-Wire line cord socket.
Accessory socket (RTTY and VHF converter connections).
NOTE: Specifications measured with 120 Vac line voltage at 25° C.  
Cabinet Dimensions 12-1/4" wide x 6-5/8" high x 13" deep.
Overall Dimensions (with knobs and feet installed) 12-1/4" wide x 7-15/16" high x 14" deep.
Net Weight 15-3/4 lbs.
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