[Radio Wrangler]

The bullet-proof front end of the H2900 was standard, there were no options in this area. The one I had was a prototype and fully loaded with full diversity and ISB, so there were two front ends and four final IFs all sharing one synthesiser.

The RF amplifiers were 2N4391 JFETs, run at quit high quiescent currents. I'd always seen the 2N4391, 2N4392, 2N4393 FETs as analogue switch devices. It was an enlightenment to see them used as amplifiers.

The front end started with a multipole preselector tuned by a mechanical variable capacitor operated by a servo motor and gearbox.... very low intermod.

The first LO was a bank of crystal oscillators at 1MHz intervals mixing signals up to 70 or 80 MHz (can't remember) where they met a helical filter a bit over 1MHz wide.

The second LO was the PLL, but it used the first LO selected crystal oscillator as a component frequency giving it an offset which corrected any error or drift in that crystal. This converted signals down to 2MHz where they met the main bank of crystal filters.

The crystal oscillators gave very good phase noise performance, and the PLL had to tune only 1MHz.

Its weak spot was the PLL. A horrible stack of boards all wire-wrapped together. All inaccessible without unwrapping all its wires. Lock time was very slow. There would be no point in trying to adapt it for a tuning knob. You set the thumb-wheel switches and waited for the lock light.

When I got one (Swapped for a Redifon HFA125) the switching transistors in the SMPS had been raided by someone building an HF PA, and, of course, the synthesiser was faulty.

One weird thing is this receiver has no rear panel connectors. They are all behind a removable section of front panel and there is a cable duct to the rear.

David