HF-2050 Receiver
![[HF-2050]](hf20501.jpg)
The HF-2050 Receiver is modern in terms of operation as well as technology and performance. The extensive use of digital circuitry for signal processing and control affords the operator convenient command of the LF, MF, and HF spectrum. Front panel controls and displays have been thoughtfully engineered for quick access to all operating parameters of the receiver.
Tuning is accomplished by any of four methods: (1) The numeric keypad may be used for selecting frequency; (2) User preset channels may be recalled; (3) The rate selectable tuning knob may be used; or (4) Tuning may be via the digital remote control interface. A simple user code allows multiple receivers to be controlled from a standard video display unit.
Traditional analog IF amplifiers, filters, mixers, demodulators, and control loops have been replaced with stable and accurate digital signal processing (DSP). No IF alignment or fine tuning is necessary in production or throughout the life of the receiver. First-line maintenance is easily accomplished with the aid of Built-in-Test Equipment (BITE) which quickly isolates faults to the card/module level. DSP also makes it possible to further fault isolate to functional circuitry levels.
The HF-2050's superior performance is not limited to the DSP. Linearity is enhanced by the high performance front-end (25 dBm third-order-intercept) and ultralow noise synthesizer. Frequency stability is better than 0.05 parts-per-million per month. Other standard features include voice squelch, noise blanker, selectable AGC and audio mute.
Standard Features
Digital signal processing technology.
Compact 5.25-inch panel height.
Frequency range of 14 kHz to 29.99999 MHz in 10-Hz increments.
Microprocessor, keypad, and alphanumeric display control
and monitor all receiver functions.
Frequency selection from the keypad or rate selectable tuning control
100 preset channels.
Built-in-Test Equipment (BITE) for fault isolation to the module level.
5000 hour Mean-Time-Between-Failure (MTBF) in ground fixed
environment (predicted).
30 minute Mean-Time-To-Repair (MTTR) to the module level.
Five IF bandwidths with ultra-low delay distortion.
High performance frequency standard.
Noise blanker with adjustable threshold.
Voice squelch with adjustable threshold.
Character-oriented remote control interface.
Optional Features
Independent sideband & external preselector port.
Ability to scan preset channels or frequency bands.
Slide/tilt mechanism.
Desk top case.
Display lighting.
Frequency coverage .......... 14 kHz to 29.99999 MHz in 10-Hz increments.
Frequency stability ......... 11 x 10 8/0 øC to 50 øC; 5 x 10-8/month.
Channeling speed ............ 50 ms maximum.
Digital BFO ................. +/-4.00 kHz, 10 Hz increments.
Noise figure ................ Less than 15 dB 0.5-29.99999 MHz.
Sensitivity ................. 14 kHz to 0.5 MHz 1.25 uV for 10 dB (S+N)/N.
0.5 MHz to 29.99999 MHz 0.42 uV for 10 dB
(S+N)/N.
Modes of operation .......... A1 (CW); A3/A3H (AM); A3J (USB or LSB);
A3B/A9B (ISB optional); F1 (FSK, with
external modem).
Bandwidths .................. CW 0.3 kHz, 1.0 kHz; AM 3.2 kHz, 6.0 kHz;
USB, LSB, ISB 2.8 kH.
RF overload protection ...... Receiver protected to +47 dBm at RF input.
Intermodulation (In-band) ... -40 dB or better for two tones (-13 dBm/tone)
within the IF passband. >200 Hz separation.
Intermodulation (out-of-band) Third order intercept point greater than
+25 dBm. Second order intercept point
greater than +40 dBm.
Spurious responses .......... Image, IF rejection greater than 80 dB.
Internal spurious less than 6 dB S/N.
External spurious rejection greater than
80 dB, 20 kHz removed.
AGC ......................... 13 dB audio output variation for 1 /IV to
0.1 V signal range. Attack less than 30 ms.
250 +/-50 ms fast release. 3.5 10.5 s slow
release. Greater than 100 dB manual range.
Reciprocal mixing ........... For a desired signal of 1 uV and an undesired
signal of 0.7 V located 200 kHz or 5%,
whichever is greater, away from the tuned
frequency (2 to 30 MHz), the signal-to-noise
ratio shall not be degraded to less than 5 dB.
Audio outputs ............... Line: 600 ohms, balanced. -20 to +10 dBm,
1% distortion.
Headphone: up to +10 dBm into 600 ohms,
5% distortion.
Speaker: B ohms nominal, 2.5 W peak,
5% distortion.
Preset channel memory ....... 100 channel capacity, each channel
containing frequency, mode, bandwidth,
AGC and BFO information.
Remote control interface .... Provides serial control and monitor of
frequency, mode, bandwidth, BFO, AGC,
presets, and BITE. Receive/transmit logic
levels compatible with interface selected
(RS-232C or RS-422).
Power requirements .......... 100/120/220/240 V ac 110%, 47-63 Hz,
100 watts nominal.
Temperature ................. Operating: 0 to 50 øC;
Nonoperating: -62 to +71 øC.
Size ........................ 133 H x 483 W x 458D mm (5.25 H x 19 W x
18 D in max).
Weight ...................... 14.5 kg (32 Ibs) max.
Specifications subject to change without notice.
![[HF-2050 top view]](hf20502.jpg)
![[HF-2050 bottom view]](hf20503.jpg)
Overall Description
The primary function of the receiver is to receive RF signals and process them into audio signals. The standard configuration provides 10 Hz incremental coverage of the 14 kHz to 29.999 99 MHz frequency range in the USB, LSB, CW, and AM modes.
Control and monitor of the receiver's operation is performed by a microprocessor which interfaces to each circuit module. Front Panel A1 key pad and rotary tuning switch provide the required control inputs. Monitor information is returned to the front panel for display as frequency, status, or meter information. Remote control of the receiver is also provided through the microprocessor. Control and monitor information is supplied to a remote control unit at the remote control interface.
The signal processing circuitry may be divided into two parts: analog (RF Translator A6) and digital (IF/Audio A3). The analog circuits use conventional mixing and filtering techniques to provide frequency conversion, amplification, and selectivity. Narrow-band filtering, AGC demodulation, and audio amplification are performed by the digital IF/Audio A3.
Input signals from the antenna are preconditioned by bandpass filters or a VLF up-converter prior to their application to the first mixer. Bandpass filters of 0.5 to 2.0 MHz and 2.0 to 30.0 MHz provide a "roofing" function for the first mixer. The up-converter translates the 14 to 500 kHz band up to 12.014 to 12.5 MHz before its application to the first mixer. At the first mixer, the RF input signal and the variable injection (99.5 to 129 MHz) are combined to generate the first conversion IF signal at 99 MHz. Initial front-end selectivity is provided at the 99 MHz IF by a crystal filter. Following the crystal filter is the second mixer which translates the 99 MHz first IF signal to the 3 Hz second IF signal. Additional selectivity is provided by the 3 MHz crystal filter. At the 3 MHz IF, much of the signal amplification and RF AGC is provided. The noise blanker circuit will blank impulsive type signals which could degrade the receiver's performance.
The 3 MHz IF signal from RF Translator A6 is applied to the digital signal processing circuits on IF/Audio A3. At the a/d converter, the analog IF signal is converted to a digital representation. Following the a/d converter is the IF translator circuit which translates the digital representation of the 3 MHz IF to a digital representation of the baseband signal. This translation improves the resolution of the digital representation and prepares the signal for the digital filters. The output signals from the IF translator are in the form of digital in-phase (I) and quadrature-phase (Q) signals. Amplitude and phase information (necessary for signal demodulation) are maintained by using the I and Q representation. The digital filtering is performed by using finite impulse response (FIR) filter algorithms. Within the filter signal processors are the software algorithms to perform the AM, CW and SSB filter responses.
AGC and signal demodulation are provided by the AGC/demodulator signal processor. The amplitude of the digital signal is controlled by the RF AGC to the RF translator and a digital scaling factor to the digital signal processors. Attack and decay times are controlled by software algorithms. Signal demodulation results from software algorithms being performed on the I and Q baseband signals. Digital-to-analog converters and low-pass filters produce the desired analog audio outputs from the demodulated signals. For those applications requiring independent sideband, an optional signal processor may be added which contains the ISB gain control and audio demodulator algorithms. In the ISB mode, both USB and LSB signals are simultaneously available at the rear panel.
The analog audio signals are amplified and supplied through the audio output transformer to provide a balanced 600-ohm output at the rear panel. In addition to the line audio output, a speaker or headphone output is provided at the front panel. The speaker amplifier is capable of 2.5 watts into 8 ohms. Part of the audio output is applied to a squelch control circuit. Active filters and signal-to-noise detectors sense the amount of noise (high-frequency components) and signal (low-frequency components) in the audio signal. The outputs from the detectors are compared in a signal-to-noise comparator. A predominance of high-frequency noise will activate threshold detectors which generate a muting control for the speaker and headphone outputs.
Synthesizer A5 provides the signal injection frequencies required by the receiving circuits. All injection signals are derived from the 48 MHz voltage-controlled crystal oscillator (vcxo) which is locked to the oven stabilized frequency standard A5A3, or an external 100 kHz reference. This 48 MHz signal is also supplied as an output for use by the digital signal processing in generation of clock/control signals. The 96 MHz injection signal for use by the second mixer in the RF translator is obtained by using a simple frequency doubler. An amplifier follows the doubler to provide a boost for the signal and load isolation. The 12 MHz signal used by the LF converter mixer is obtained by dividing the 48 MHz vcxo signal by 4 and is supplied through a low-pass filter for use by the LF converter. The 400 kHz signal used as an internal reference signal is obtained by dividing the 48 MHz vcxo signal by 6 and then dividing the resulting 8 MHz reference by 20. The internal 400 kHz reference is supplied to a divide-by-4 network to provide an internal 100 kHz reference output. The variable injection source uses two phase-locked loops, the 48 MHz base frequency multiplied by 3 to produce a 144 MHz reference, the 400 kHz internal reference, and two programmable loop dividers to produce the required 99.500 00 to 128.999 99 MHz variable injection signal.
Built-in test (BIT) capabilities are initiated from Front Panel A1 or through the remote interface. When initiated from Front Panel A1 or through the remote interface, the BIT will isolate faults to the module level. During normal receiver operation, the microprocessor continuously monitors various circuit functions to confirm correct operation.
The remote control interface permits remote serial control and monitoring of the receiver by a remote control unit. The interface will receive and transmit data at logic levels compatible with EIA Standard RS-422. Characteristics of the remote control functions such as format and baud rate are controlled by the microprocessor control circuits.
Power Distribution
Input power to the radio receiver is connected to J1 on the receiver rear panel and supplied through fuse (P/O J1 on rear panel) and A1A1S1 (front panel) to Power Supply A4. Power Supply A4 is a linear power supply and develops the following output voltages: +5.2, +15, and -15 V dc. These voltages are supplied to cards and modules in the receiver using IF/Audio A3 as the power interface.
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This Home Page was created by wa3key, Wednesday, June 14, 2000
Most recent revision Wednesday, June 14, 2000