WJ-8711A | Watkins-Johnson

Watkins-Johnson » WJ-8711A

High performance, triple-conversion, HF desktop receiver with last IF in digital technology. Frequency range 0.005-30 MHz all-mode. Ideated in USA.

Reference market : professional and mil/gov

General :
Frequency coverage 0.0050 ~ 30.0000 MHz
Modulation mode CW / LSB / USB / ISB / AM / FM
Tuning step 1 Hz
Receiver :
Sensitivity CW [1] 28 uV (0.005~0.02 MHz, pre. OFF, 16dB S+N/N)
1.27 uV (0.02~0.05 MHz, pre. OFF, 16dB S+N/N)
0.5 uV (0.05~0.5 MHz, pre. OFF, 16dB S+N/N)
0.35 uV (0.5~30 MHz, pre. OFF, 16dB S+N/N)
SSB/ISB [2] 0.56 uV (0.5~30 MHz, pre. OFF, 10dB S+N/N)
AM 1.6 uV (0.5~30 MHz, pre. OFF, 10dB S+N/N)
FM 2.5 uV (0.5~30 MHz, pre. OFF, 10dB S+N/N)
Selectivity [3] CW
300 Hz
0.35 KHz (-6dB)
0.45 KHz (-60dB)
CW
1000 Hz
1.1 KHz (-6dB)
1.5 KHz (-60dB)
SSB
3.2 KHz
3.2 KHz (-6dB)
4.0 KHz (-60dB)
AM
6 KHz
6.0 KHz (-6dB)
7.5 KHz (-60dB)
FM
16 KHz
16 KHz (-6dB)
20 KHz (-60dB)
IF-filter ultimate attenuation > 80 dB
Group-delay < 0.06 ms (-3dB band)
NF (Noise figure) 14 dB (preamplifier OFF)
11 dB (preamplifier ON)
IP2 (2nd order intercept point) +60 dBm
IP3 (3rd order intercept point) +30 dBm (preamplifier OFF)
Image rejection 90 dB typ
IF rejection > 85 dB (90 dB typ)
Spurious carriers < 0.4 uV (referenced to RF input)
AGC Adjustable
Frequency stability ± 0.7ppm with temperature from 0°C to +50°C
± 0.2ppm with temperature from 0°C to +50°C [4]
Synthesizer settling time 10 ms
Intermediate frequency 45.455 MHz
455 KHz
25 KHz
Features :
Memory 100 regular memories
Display 1 Hz frequency resolution
Antenna BNC 50Ω connector
Power supply 97 ~ 253 VAC
Power consumption 35 W typ
Audio power 1 W with an 8Ω load
Audio output Jack 6.35 mm headphone
Connections RS232C (control)
BNC (IF 455 KHz output)
BNC (monitor 455 KHz output, BW 30 KHz)
BNC (frequency reference input)
Terminal jack (audio
Mechanical and environmental data :
Operating temperature from 0°C to +50°C
Dimensions 482 (W) x 133 (H) x 508 (D) mm
Weight 6.78kg

[1] 300 Hz bandwidth
[2] 3200 Hz bandwidth
[3] Standard values, 66 bandwidths are available between 0.056~16 KHz
[4] With WJ-8711/REF optional reference

Description :

The WJ-8711A uses the SDR technology in hybrid form, ie adopting a superheterodyne configuration with the last IF digitized to perform the filter and demodulation functions. The equipment has professional features both in terms of RF performance and reliability, the manufacturer Watkins-Johnson has in fact designed this model mainly to the military and for this reason the operational specifications include resistance to vibration, shock, humidity, atmospheric pressure, storage temperature according to the MIL-STD-810D standard. The receiver offers a lower limit of only 5 KHz, although tuning can go down to 0Hz under the operational aspect. In fact the WJ8711A, starting from hundreds of KHz and up to the 30 MHz, guarantees a precision in the detection of the amplitude displayed by the S-meter equivalent to a measuring instrument in standard S-points/dBm. The automatic gain control operates in analog and digital sections for a total of 1OOdB, the response time is extremely rapid, taking 5 milliseconds while the release time is selectable between slow, medium and fast. After the ADC conversion stage operating at 100 Ksps with 16 Bit resolution a DSP processor is responsible for defining selectivity and making the PBT, notch, BFO adjustable functions available (within ±8000Hz in 10Hz steps), multi-mode demodulation including also the ISB or independent sidebands with two audio channels.

The apparatus has 66 different bandwidths to choose from a minimum of 56 Hz to a maximum of 16 KHz, the form factor of the filters is always better than 1.5 at 1 (6/60dB). In the following table the nominal bandwidths referred to 3 dB:

Hz Hz Hz Hz Hz Hz Hz Hz Hz
56 113 225 450 900 1800 3600 7200 14400
63 125 250 500 1000 2000 4000 8000 16000
69 138 275 550 1100 2200 4400 8800  
75 150 300 600 1200 2400 4800 9600  
81 163 325 650 1300 2600 5200 10400  
88 175 350 700 1400 2800 5600 11200  
94 188 375 750 1500 3000 6000 12000  
100 200 400 800 1600 3200 6400 12800  

The front-end is characterized by excellent IP2 and IP3, to shift the dynamic range at the input you can insert a 10dB preamplifier or a 15dB attenuator. However, there is not a preselector stage which is supplied only as an optional accessory (model HF-8711 - PRE), this integrates no less than eleven preset bandpass cells with a width of less than one octave and can be switched off when necessary.

The receiver uses a high stability TCXO with ±0.7ppm for an excursion of 50°C in temperature. Installing the internal option WJ-8711 - REF the stability can be further improved. An input is also dedicated for an external frequency reference that accepts signal at 1, 2, 5, 10 MHz. The receiver automatically detects its presence and adopts this master signal. The audio is usable for loudspeakers, headphones and via fixed-level outputs for connection to recording systems. The volume control is separate for audio intended for the speaker and headphones. Two IF outputs at 455 KHz with different bandwidth makes possible to connect a spectrum-scope and even a specific demodulators that make use of the selectivity determined by the WJ-8711A. An RS232 serial interface with baud rates of 75/9600bps allows remote use of this WJ. The apparatus has standard size measurements so as to be possibly mounted in a standard 19 inch rack.

Performance and practical notes :

The 8711A is a superior class receiver for reliability and repeatability in performance. Its characteristics are similar to the WJ-1000A intended for the civil market, but there are significant variations with respect to the latter as the maximum bandwidth of selectivity. Having been designed in the first half of the '90s this Watkins-Johnson inevitably suffers from some weaknesses when compared to the most recent radio-set but expresses the ergonomics guaranteed by a front panel where each command is rationally enslaved to specific buttons and rotary controls.

Valuation :

Sensitivity
Selectivity
Dynamic range
Spurious response
Audio
Signal functions
Control functions
User friendly

Stars: 1=insufficient, 2=just sufficient, 3=mediocre, 4=good, 5=excellent

Review :

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