WJ-1000A

The WJ-1000A was one of the first receivers for the amateur market to implement the SDR technology in hybrid form, ie. adopting a triple frequency conversion with the last digitized to perform the filter and demodulation functions. The equipment has professional characteristics both in terms of RF performance and reliability, the producer WJ in fact works in the military as well as in the civil sector, always linking its name to products of the highest quality. The receiver offers a lower frequency limit of only 5 KHz, although tuning can go down to zero under the operational aspect, thus covering even the lowest radio frequencies with substantially constant sensitivity and dynamics over the entire range. In fact, this model, starting from hundreds of KHz and up to the upper limit, guarantees a precision in the detection of the amplitude displayed by the S-meter. Equivalent to a measuring instrument with reading both in S points and in dBm. The AGC operates in analog and digital sections for a total of 100 dB, the response time is extremely rapid, taking 5 milliseconds while the release time is selectable between slow, medium and fast in the interval of 0.01 ~ 5 seconds so as to adapt to each type of emission. After the ADC conversion stage operating at 100 Ksps for 16 Bit a DSP processor is responsible for defining selectivity, with high attenuation slope bandpass filters, and making the PBT, notch, BFO adjustable functions available (within ±8 kHz in 10 Hz steps), multi-mode demodulation including also the ISB (independent side bands with two audio outputs) and the synchronous-AM.

The WJ1000A has 58 different bandwidths to choose from a minimum of 56 Hz to a maximum of 8 KHz, the form factor of the filters is always better than 1.5:1 at 6/60 dB. In the following table the nominal bandwidths referred to 3 dB:

The front-end module is characterized by excellent levels in IP2 and IP3 parameters, to change the dynamic range at the input you can insert a 10 dB preamplifier or a 15 dB attenuator. However, there is not a preselector stage that is only provided as an optional accessory (model HF-1000PRE), this integrates eleven preset bandpass cells with a width of less than one octave and can be switched off when necessary.

The internal clock uses a high stability TCXO with a maximum deviation of ±1 ppm for a temperature change of 50°C. An input is dedicated for an external master clock reference that accepts 1, 2, 5 or 10 MHz signal. The receiver automatically adopts this reference and detects its presence. The audio is usable for loudspeakers, headphones and via fixed-level outputs on 600Ω for connection to recording systems. The volume control is also separate for audio intended for the speaker and headphones. Two the IF outputs both at 455 KHz but with different bandwidth, this makes it possible to connect instruments that display the spectrum around the tuned frequency or even specific demodulators that make use of the selectivity determined by the user. A multi-standard interface on a 25-pin connector with baud rates of 75 ~ 9600 bps allows remote use of the WJ-1000A. The apparatus has standard size measurements so as to be possibly mounted in a 19-inch rack.

WJ-1000A performance and practical notes :

Certainly the WJ1000 is a superior class receiver for reliability and repeatability in performance, it is also taken care of in every detail both in terms of electronics and mechanics. Being born in the first half of the 90s this Watkins-Johnson (WJ) model inevitably suffers from some weaknesses when compared to the recent SDR, more flexible on some aspects, but nevertheless expresses an ergonomic that perfectly fit the needs of the operators who prefer a traditional front panel instead of the combination of monitor and mouse. It should be noted that the receiver is in practice the version for the civil market, with few but significant variations, of the WJ-8711A model of the same manufacturer. Apparatus that was originally intended solely for military and government users.