N3QO » antenna switch

Antenna switch project

jeff — Mon, 21 Mar 2011 18:58:44 +0000

In the weeks leading up to the ARRL DX Phone contest this year, Eric, WG3J and I did some extensive antenna planning at his QTH in Maryland in preparation for the upcoming contest. One of this biggest concerns was the amount of coax coming into the station. During a contest last year, we encountered a ton of RF affecting computers and audio causing an RF burn or two. Fun times.

How to resolve this? Reduce your coax run length and quantity by using antenna switches.

I reviewed a number of designs online and ended up designing my own, 2 position antenna switch which injects 12VDC onto the coax, so we didn’t require additional long lengths of control wire which could end up resonating RF.
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For the next 3 weeks part of my station would be turned into an assembly line, etching circuit boards, fabricating cases, etc.

A week before the contest, Eric and I put the switches through their paces by dumping 2.5kW at 100% duty cycle for about 10-20 seconds. This would help us assure that they would hold up to the contest pace.

I ended up building five switches, 2 rated at 10kW and 3 rated at 5kW. I’m happy to report success with the design with no smoke emissions. One thing we did find was a high SWR at 15m and above, which I believe I have a fix, that needs future testing.

Antenna switch label

jeff — Fri, 05 Feb 2010 23:58:33 +0000

After working some 40m PSK this evening, I found I had to move the switch positions around a little. With the updated configuration, I can work someone off the Vee, and then make one switch movement to get to the vertical for DX. Doesn’t sound like much, but in a QSO or contest, this allows for quick change in antenna take-off angles. The label is a custom label template in Microsoft Visio.
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The chores before the storm…

jeff — Fri, 05 Feb 2010 21:29:25 +0000

With the upcoming snow storm that’s predicted to hit the Northeast US in the next few hours I decided to move my Ameritron RCS-8V antenna switch to it’s permanent home so it doesn’t get buried under the supposed 18″ of snow. I used my new RG8/U cable to connect it into the shack. I swept the 110 foot coax run with .3 db loss at 1.9mhz and 1.1db at 29.7.
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Antenna switch panel

jeff — Mon, 02 Nov 2009 15:36:40 +0000

After building my desk rack a few months back, it’s time to actually start using it. My plan was to have anything shared between operators to be place in the middle of the desk or in the rack. One of these things is antenna switching.

Starting with 2 Alpha Delta switches I already had, I went out and bought 2 3U blank rack panels. I drilled out the panels for screw mounting, control switch and GAS fuse. I have enough room now for 6 switches. I also created labels in Microsoft Visio for the panels.

The idea is to assign an antenna to each individual switch, which is where you would select the radio. On the next row, you would select your antenna on a specific radio switch.
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