Use Toggle Switch for RF?

[RCHRDM]

I built a simple switch box to choose between two antennas in my ham radio shack.  I used a toggle switch in a box with SO-239 connectors.  The switch handles up to 100 watts, 1 to 30 MHz.

I am wondering if it is OK to use a general purpose toggle switch for this purpose.  RF does not behave like mains AC.

Richard

[TheMG]

It's certainly not ideal but with HF (30MHz or less) you can usually get away with it just fine.

[RCHRDM]

Thanks.  I have been using it for several years but have been wondering if it is the best choice.

I know that there are many antenna switches available.  I was trying to copy this switch that has the feature of switching the offline transceiver to a dummy load.  MFJ has one of these, but it looks like they are just using a simple slide switch.

https://www.universal-radio.com/catalog/switch/5901.html

Is there a better kind of mechanical switch I could use for this purpose?

Richard

[German_EE]

I don't see a problem using a big chunky toggle switch at HF RF frequencies. Things might get a bit interesting above 50 MHz but that's why it's fun to experiment. On the subject of experimentation I have not had good results with using slide switches at RF, either for signal selection or selecting attenuators, all the ones I have tried went bad within twelve months.

[RCHRDM]

Thanks.  I had wondered why MFJ apparently used a slide switch.

I'll stick with my good 'ole toggle switch!

Richard

[German_EE]

MFJ =

Manufactured
Foreign
Junk

[RCHRDM]

I've also heard "Mighty Fine Junk."

Richard

[unitedatoms]

That 100V pk-pk of RF. Through possibly capacitively coupled metal toggle. Will it burn fingers if the leaking RF will find a sudden match to human body?

[German_EE]

If that toggle is designed to switch mains power then the isolation between the switch lever and the contacts will be very high, this reduces the risk to almost zero. To reduce the risk TO zero you build your project into a grounded metal box with the switches mounted to the metal front panel.

[RCHRDM]

Thanks.  Yes, I have it in an aluminum box.

Richard

[Bud]

I'v seen bakelite switches burning down to charcoal on 10m band, though it was at kW level.

[RCHRDM]

Hmm... Interesting

The maximum power for this switch would be 100 watts.

Richard

[David Hess]

If you route the ground (shield) returns properly to minimize loop area and approximate a 50 ohm transmission line, then toggle switches work well to 100s of MHz.  I have a toggle switch 1 GHz attenuator where the switches are embedded into 50 ohm cavities with adjustment screws to trim the response.

[RCHRDM]

Should I connect the metal box directly to my station's ground bus?

Thanks for reminding me about the attenuator.  I have one of those too.

Richard

[David Hess]

Should I connect the metal box directly to my station's ground bus?

That is not a bad idea also but the idea is to run coaxial lines between the connectors and switches and tie the coaxial grounds together at the switches.  If the enclosure is small then just wires can be used at lower frequencies but doing so will compromise isolation.

[RCHRDM]

The SO-239 connector grounds on the box are all tied together by the metal.

Richard

[m3vuv]

dont you mean MORE FUCKING JUNK ??

[David Hess]

The SO-239 connector grounds on the box are all tied together by the metal.

That is right but without running grounds parallel to the signal wires, inductance increases because of the increased loop area even inside the metal chassis.

[tkamiya]

Maker such as DIAMOND from Japan manufacturers something like that in die-cast box.  I've used toggle switches, rotary switches, and just about any switches on HF.  Never had an issue.  If you keep your power down (100 watts?), pretty much anything goes.

"Keep your lines short" is a standard advice but even at 28MHz, few cm won't have any impact. 

I typically don't care much until it goes into VHF range.

[RCHRDM]

Thanks!  Good discussions on this forum!

Richard

[vk6zgo]

That's not a switch--That's a switch!

https://commons.wikimedia.org/wiki/File:Two_pole_knife_switch.png

except that yours would be a DPDT type.
https://www.lockhaven.edu/~dsimanek/scenario/labman4/switches.htm

"Frankenstein" switches are very good to use with balanced feeders.

I had an interesting experience, many years ago, when a temporary Radio Australia transmission was tried at my old workplace, using one of our existing HF broadcast transmitters.
A changeover knife switch was put in place, which when switched to the "RA" position put the transmitter on a Rhombic pointing to South Africa.

The normal routine was to turn off the Tx, call out " I'm going up to switch the aerial to the Radio Australia position".
I thought I was loud & clear enough, but when I reached the switch hut & operated the knife switch, it drew a huge blue arc.
I quickly slammed the switch back to its original position, & walked, shaken to the core, back to the main building.

It turned out that someone had some tests they wanted to do on the transmitter & turned the HT back on!
The Tx didn't even "grunt" when I opened the switch, & blithely continued to transmit 10kW through the nice blue "plasma" connection, for a fraction of a second the switch was open.
The switch showed no ill effects, either!

Smaller switches might not fare as well, so make sure your TX is off before changeover.

[RCHRDM]

Yikes!

Great story! 

I do have a rather small DPDT knife switch that I used to use to switch between two "ladder line" fed antennas.  I found one on eBay that even had a vintage white ceramic base!

Richard

[unitedatoms]

10kW. Thanks to skin effect and fast reflexes the marrow in your bones was not overcooked. There was a professor in military space academy telling the story about lunar projects (USSR). The guidance of transmitter to moon probes failed. So the turning of antenna had to be done by muscle power. A soldiers were sent one by one for 30 sec shifts to keep antenna oriented correctly. Everyone got a home trip as a reward. And possibly bone marrow cancer, which I just assume.

[tkamiya]

If OP looks at "3 way switch" on hardware store, that's exactly what he needs.  Then pick an electrical box and cover.  Then preferably a metallic face plate.

[coppercone2]

10kW. Thanks to skin effect and fast reflexes the marrow in your bones was not overcooked. There was a professor in military space academy telling the story about lunar projects (USSR). The guidance of transmitter to moon probes failed. So the turning of antenna had to be done by muscle power. A soldiers were sent one by one for 30 sec shifts to keep antenna oriented correctly. Everyone got a home trip as a reward. And possibly bone marrow cancer, which I just assume.

why dont they make a wooden clamp with some lumber, you can make big pliers using table legs and pants leg, or shoe lace