03 Nov Automatic Antenna Selector
by Steven Pemberton, VK3PBJ
According to the kit manufacturer’s website, The FA-AS Automatic Antenna Selector enables four different antennas to be connected to the IC-7300, for example, and to have them selected automatically depending on the operating frequency. Operation and programming are simple and intuitive, the operating status is indicated by multi-coloured LEDs. Operation with separate transmitting and receiving antennas is possible. Each of the four antenna connections can be assigned to any amateur radio band.
An aspect of the hobby that I enjoy is building and testing various antenna designs. I’m constrained to a typical suburban block, so it’s not that I have an extensive antenna farm, though I usually have 3-4 HF antennae strung about the yard. So like most hams, I have a variety of manual coax switches to select which antenna to use at any particular time and to quickly swap between them when making comparisons.
That convenience comes at a cost of course; some cabling complexity, but also the coax switches are not inexpensive. A Diamond 2-way switch is ~AU$90, and the 3-way version is ~AU$180. So I was interested to read online about a kit for a 4-way automatic antenna switch, and relatively inexpensive for ~EU$125 (~AU$208 at the current exchange rate).
I liked that the kit would automatically switch to the preferred antenna for the given frequency, as well as push-button manual selection. It also has a fifth output with inbuilt attenuation for connecting a transverter. Note that although it’s designed to match the IC-7300 it also supports CI-V control from a number of Icom transceivers, and in manual mode could work with any model or brand.
The first hurdle was ordering the kit, as the site is entirely in German. Although Google translate could render the text into English pretty well, it didn’t work for the online ordering process. So I set about manually translating each phrase as required. In short order, I completed the order and set about waiting for the kit to arrive. It took almost 6 weeks for delivery, but I suppose that’s to be expected with the current impact of Covid on parcel post services. Order the kit here.
Like a kid on Christmas morning, I eagerly opened the parcel to see what goodies lay inside. That the build instructions were all in German gave me an initial pause, but David Cray, via a post on the SPARC Facebook page, helpfully pointed out there was an English version available for download.
I found the instructions quite easy to follow, and the build itself was very simple. There are no surface mount components, with everything being through-hole construction.
This is only the second kit that I’ve built, and even my modest skills sufficed. I’d describe my style as slow and cautious. Double-check everything and think before you solder. But before long I had the kit completed and ready for testing. The hardest part of the build was connecting the control cable to a 13-pin accessory plug to suit the IC-7300. Only four wires but fiddly, and not terribly well described. I realised later that you can probably skip this step and instead use a 3.5mm plug for CI-V control. In some cases, this may even be preferable, though an advantage of the accessory plug is that it also provides power to the switch.
After completing some simple power-up testing and confirming the transceiver could hear a test tone on 18.4320 MHz I connected it to my IC-7300 and the various antennae I wanted to use.
At this point, I discovered that the second antenna output was intermittently failing to switch completely. Further testing on the workbench confirmed that the coax centre on that port would sometimes not switch at all, and when it did it measured approx 10 Ohm resistance through to the input’s coax centre (compared to only 1-2 Ohm for the correctly functioning antennae outputs).
I opted to “phone a friend” and after advice from Paul Whitaker (VK3DPW) tested my work and those few components between the coax socket and an IC. I was suspicious of the #2 relay, so desoldered it in preparation of swapping it with one of the others to see if the fault followed it.
I decided not to risk damaging the PCB of the automatic antenna selector by desoldering another relay and purchased a compatible relay from Jaycar. Unfortunately, though it was several millimetres too tall for the case and was therefore not usable. So I ordered a substitute relay of the correct dimensions from Element14 and again set about waiting for delivery.
This time the delivery was very prompt via a Toll overnight service, but to make things interesting it was delivered to the wrong address. According to the tracking details it was even signed for by someone named Sean. I guess the “Signature Required” on a parcel actually means any signature will do!
On a hunch, I searched for similarly named streets in the same suburb, went for a little drive, and there was my parcel sitting beside their front door. So a successful delivery regardless of Toll’s efforts. After fitting the new relay and retesting the kit everything worked as designed.
After resolving the faulty relay I’m very happy with the end result. The cascade of coaxial switches are banished from my desk, and the correct antenna is now automatically selected per the transceiver’s selected frequency. I’m very impressed with the quality and price of the kit. The powder-coated metal box of the FA-AS Automatic Antenna Selector is very robust and matches the IC-7300 perfectly. Some good, over-engineered German design!