Antenna switch (or golden Czech hands)

We sell quite a few antenna switches. to be honest – I didn't look for them. Until one moment.

My initial interest in switches was sparked by a QSL from an operator in Argentina, who had this guy in the background above his desk, whom I have not yet met in person, although I quite often visit various exchanges or radio amateur meetings such as Holice etc. I must point out, that it was his e-mail that made me make this antenna switch, in which he wrote me all the parameters. After which the next line contained a query, if I don't want to send it for just $50. With regard to it regarding to it, that the exchange rate to the dollar was just over 40,- I recognized the crowns, that it's a little too much for me. So why not actually make one, that?

Because I knew what I wanted (according to the picture), I was actually limited only by a suitable switch. The choice fell on a switch from discarded military equipment. It was an 11 position switch on a ceramic plate. It was necessary to remove every second contact, so that the switch has 5 position and output. I carefully unscrewed the rivets, which held these contacts, but that was the least of the jobs.

This was followed by the drawing of the drawing, according to which the body of the entire switch was subsequently turned and milled. As a former machinist, this did not cause any major problems for me and the drawing was completed in one evening. I had the material and if I had the proper tools at home, so I would dial it and process it myself. But unfortunately.

It's a different time today, but even so, many things can be arranged. And so I was not lazy, took the drawing and visited a few acquaintances, who performed this task extremely well. And it wasn't the first time. I thank them for that. Only a few corrections in the drawings were needed, to finish minor imperfections – and the skeleton was born.

Another problem arose, when I started looking for PL connectors with Teflon. It is indeed a scarce commodity. But in the end it worked.

After screwing the connectors onto the frame, I continued to modify the switch. This consisted in its complete disassembly and removal of the locking wheel from the axis of the switch, which determines the position of the switch. optimally nailed, that I could leave it in its original form, but why switch one extra position, which will not be equally involved, when I don't have to. I got a piece of approx 1,5 mm of thick stainless steel sheet and I started filing new positions with it, that I missed every other one. Next, it was necessary to hit with a hole on the axis of the switch, because it is rectangular, and if you miss a shot, the position after screwing the entire switch together will not fit you and as such will not be functional. It worked the first time. The only one, what had to be done, it was, that the locking wheel was welded with CO2 and I had its surface modified by chrome plating. The original was pressed and I couldn't find a better solution. The back is closed with a cap with six screws, to which the bracket is assigned.

I was thinking, what toggle button could i use. Unfortunately, we do not offer any decent buttons, so the choice fell on our own proposal, which was again realized according to the drawing by my acquaintances.

I envisioned using a switch both in one place, so the possibility of using it on a portable. The result was a pedestal made from the rest of the stainless steel sheet, on which the switch holds nicely when switching antennas on the table (thanks to the rubber grommets), or which can be screwed to the wall.

In the end, it was enough to mark the antenna inputs with numbers 1 – 6 using self-adhesive double-sided insulation tape and self-adhesive transparent film, over which I pasted a label printed from a laser printer.

And the result is quite worth it. Judge for yourself.

Vlado

This is where the article could end. However, Vlado turned to me with a question about the maximum possible performance, which such a switch can bear, but I couldn't answer him responsibly, so I asked Honzu OK2BNG for help:

William,

Greetings from Klimkovice.
I know these switches intimately. They were used in PA type ZZ 1002,1003,1004, where the lamp is GU74b with Pout approx 800 W.
I think, that they can transfer power to KV around “One kW” under certain conditions:

• the switch must switch WITHOUT load, otherwise it will burn the pen

 

• there must not be a large reactive component on the antenna, max do xj cca 20, otherwise it will jump to the ground screw, if such an antenna is connected there

 

• for illustration, they connect several photo-like switches, but if you have CD PA1, you will find the photo there

 

• I also used similar antenna switches for contests, but it always burned out, because the operators switch in the heat of battle even when the foot pedal is on. That's why I ended up solving it with R-type relays 700, where connected in parallel with the contacts conveniently transfer to KV i 3 KW. Switching antennas during pause, when no PA is active, is sometimes a nut, but it is not unsolvable. But that's another topic.

 

In the end, it applies from general VF technique, that the transient resistance is area x pressure. Then it can easily happen, that there is also a large silver-plated surface, but the pressure is not there. On the other hand I see in PA 2 kW small switches, where there is enormous pressure on the springs. Then the area is minimized.
Some time ago I did research on such contacts in a simplified way. You can overdrive the VF approx 10 MHz with a current of approx. 6A and you measure the voltage drop with an oscilloscope. So I compared different vacuum relays and these switches.
One of you recorded an ISS crew, I can't find it right now, that in one of the Russian Spravochnik they reported a current of around 3A permanently on these switches. When I consider some that “duck” operation, that's how those come out 5 A , which is at 75 ohmech cca 1875 W at real load. And because the real load is a utopia, so those 1250 W will definitely carry it under the above conditions.

He wishes all the best

John , OK2BNG

I want to thank both of them – To Vlad for the excellent article and to Honz for the technical data. TNX! OM0AAO, William