The 08662-60001 low noise VCO: the heart of the HP 8662A

This is certainly one of the electronic antiques and marvels, which had the most hidden and non-spectacular impact on mankind and development of mobile communications in the 80s and 90s – the VCO of the 8662A/8663A, the defacto standard for low close-in phase noise signal generators.

The concept, it is a switch reactance oscillator, i.e., the inductances will be switched, to cover the 320 to 640 MHz range, rather than doing this all by varactor diode tuning.

For low phase noise, you need an oscillator with high Q – this is achieved by strongly biasing the varactor diode over the full tuning range, and by low resistance PIN diodes (two in parallel, see below!), that switch the thin-film inductances embedded between lexane disks.

Note the small indent on the golden patch on the PCB? This is where the copper bolt reaches in to adjust the frequency offset.

All this is housed in extruded aluminum, end a layer of special steel which absorbs magnetic fields. So far, I never had the chance to look inside of these – but a kind reader this block, Martin, shared this picture and I put it up here for those interested.

The designer of this marvelous and magic device, his name, Dieter Scherer, a German fellow of HP, unfortunately, I have never met him and don’t know if he is still alive. Sure he left behind great achievement and a legacy of high frequency engineering.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.