Routing coax and/or balanced-feeder into the average Shack can be problematic – whether you’re trying to get large coax through an air-brick or attempting to keep balanced-line away from metal objects, it sure tests your skills (and patience!). The PZT Shack has used a 3″ square 45-degree drain-pipe fitting in the wall for a number of years – The problem is routing new cables through which involves removing the bit of rag wedged inside it and threading the new cable through. What I wanted was a convenient way to add/remove aerial feeders as well as being able to do it quickly.
My solution was to make use of the large fan-vent which had previously been used to extract warm air from a computer shelf where 2 tower PCs used to sit. This has been idle for a few years and just happens to be about 30cm from the back of the ATU and radios – A great way to introduce signals into the Shack, surely?
I wanted to make it a flexible solution so I opted for 3x SO239 connectors plus 2 pairs of 4mm terminals for balanced-feeder. This panel would appear on the outside of the Shack and also remove about 2-3m from the overall feeder lengths had they taken the “drain-pipe” route.
However, behind the panel lies the really useful aspect: Some FT-240 ferrite toroids. There are 3 FT240-31 toroids each wound with 8 turns of RG58 coax. These form a resistive 1:1: Choke/Balun for 3.5MHz-30MHz and are wired to 1 pair of the 4mm terminals and 2 of the SO239 sockets. The 2nd 4mm terminal pair is direct to the “balanced” terminals on my MFJ-948 which has its own internal 4:1 voltage balun. The remaining SO239 is direct to PL-259 in the Shack
Here’s a simplified wiring diagram – I used 8 turns of coax around each ferrite:
Here’s the plan – click for a larger image:
The drilled plate as supplied by Aerial Parts of Colchester:
…and with the 4mm terminals and SO239 connectors fitted:
450ohm ladder-line and 2 RG213 coax connections into the PZT Shack…
Much better than a drain-pipe fitting and an old rag!