In yesterdays post, I mentioned the need to update the flex cable design. The flex cables connect the vacuum tight cable feed through to the ladder PCBs. The idea is to have a resilient mount between the attenuator ladder sections and the enclosure and the flex cable is part of the resilient mounting system. The resilient mount breaks the mechanical transmission from the relays to the outside world and the vacuum breaks the air-borne transmission path.

While assembling the v2.2 version of the atttenuator, I found two problems with the flex cables: 1) the flex cables are too long which pinned the ladder attenuator PCBs to the top of the vacuum enclosure; 2) the flex cables are too stiff. To correct these two problems I are going to use a narrower, more flexible cables and lower the mounting point to make better use of the available flex cable length. Two inches is a standard length flex cable length and the next shorter length is a bit longer than one inch which is far too short. The current cables are 1 mm pitch flex cables and I am going to modify the design to use 0.5 mm pitch flex cable.

The picture below compares the 1 mm pitch cable I have been using to the 0.5 mm pitch cable I am going to use. Both cables have 12 conductors and are two inches long. The 0.5 mm pitch is significantly more flexible that the 1 mm pitch cable. I need to make a minor revision to three PCBs to accommodate the change to the narrower cable. I should complete the design and order the new PCBs this week and be back at it in a couple of weeks when the new boards arrive.

Comparison between 1 mm pitch (left) and 0.5 mm pitch (right) flex cables. Note that the 0.5 mm cable has a connector attached at the top.