Use Toggle Switch for RF? - Page 1
Forum section: electronics / rf-microwave

author: RCHRDM
author_rank: Regular Contributor
timestamp: January 01, 2020, 07:31:06 pm
content: 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

author: TheMG
author_rank: Frequent Contributor
timestamp: January 01, 2020, 08:03:51 pm
content: It's certainly not ideal but with HF (30MHz or less) you can usually get away with it just fine.

author: RCHRDM
author_rank: Regular Contributor
timestamp: January 01, 2020, 08:13:43 pm
content: 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.htmlIs there a better kind of mechanical switch I could use for this purpose?Richard

author: German_EE
author_rank: Super Contributor
timestamp: January 02, 2020, 05:13:06 pm
content: 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.

author: RCHRDM
author_rank: Regular Contributor
timestamp: January 02, 2020, 05:17:09 pm
content: Thanks. I had wondered why MFJ apparently used a slide switch.I'll stick with my good 'ole toggle switch!Richard

author: German_EE
author_rank: Super Contributor
timestamp: January 02, 2020, 05:39:50 pm
content: MFJ =ManufacturedForeignJunk

author: RCHRDM
author_rank: Regular Contributor
timestamp: January 02, 2020, 05:41:12 pm
content: I've also heard "Mighty Fine Junk."Richard

author: unitedatoms
author_rank: Frequent Contributor
timestamp: January 02, 2020, 06:28:16 pm
content: 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?

author: German_EE
author_rank: Super Contributor
timestamp: January 02, 2020, 06:55:43 pm
content: 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.

author: RCHRDM
author_rank: Regular Contributor
timestamp: January 02, 2020, 07:29:28 pm
content: Thanks. Yes, I have it in an aluminum box.Richard

author: Bud
author_rank: Super Contributor
timestamp: January 02, 2020, 08:03:24 pm
content: I'v seen bakelite switches burning down to charcoal on 10m band, though it was at kW level.

author: RCHRDM
author_rank: Regular Contributor
timestamp: January 02, 2020, 08:08:41 pm
content: Hmm... InterestingThe maximum power for this switch would be 100 watts.Richard

author: David Hess
author_rank: Super Contributor
timestamp: January 02, 2020, 11:14:47 pm
content: 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.

author: RCHRDM
author_rank: Regular Contributor
timestamp: January 02, 2020, 11:17:37 pm
content: 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

author: David Hess
author_rank: Super Contributor
timestamp: January 03, 2020, 01:26:21 am
content: Quote from: RCHRDM on January 02, 2020, 11:17:37 pmThat 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.

author: RCHRDM
author_rank: Regular Contributor
timestamp: January 03, 2020, 02:38:33 am
content: The SO-239 connector grounds on the box are all tied together by the metal.Richard

author: m3vuv
author_rank: Super Contributor
timestamp: January 03, 2020, 12:15:29 pm
content: dont you mean MORE FUCKING JUNK ??

author: David Hess
author_rank: Super Contributor
timestamp: January 03, 2020, 02:12:01 pm
content: Quote from: RCHRDM on January 03, 2020, 02:38:33 amThat is right but without running grounds parallel to the signal wires, inductance increases because of the increased loop area even inside the metal chassis.

author: tkamiya
author_rank: Super Contributor
timestamp: January 04, 2020, 12:33:14 am
content: 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.

author: RCHRDM
author_rank: Regular Contributor
timestamp: January 04, 2020, 02:25:06 am
content: Thanks! Good discussions on this forum!Richard

author: vk6zgo
author_rank: Super Contributor
timestamp: January 04, 2020, 03:24:21 am
content: That's not a switch--That'sa switch!https://commons.wikimedia.org/wiki/File:Two_pole_knife_switch.pngexcept 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.

author: RCHRDM
author_rank: Regular Contributor
timestamp: January 04, 2020, 03:31:46 am
content: 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

author: unitedatoms
author_rank: Frequent Contributor
timestamp: January 04, 2020, 03:35:45 am
content: 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.

author: tkamiya
author_rank: Super Contributor
timestamp: January 04, 2020, 03:50:37 am
content: 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.

author: coppercone2
author_rank: Super Contributor
timestamp: January 04, 2020, 04:21:13 am
content: Quote from: unitedatoms on January 04, 2020, 03:35:45 amwhy dont they make a wooden clamp with some lumber, you can make big pliers using table legs and pants leg, or shoe lace

author: unitedatoms
author_rank: Frequent Contributor
timestamp: January 04, 2020, 04:37:51 am
content: You think like an engineer, but not like soldier. They used a wooden stick of a mop to nudge the azimuth and other angle of the antenna.Edit for even more dramatization: … while the grass under their boots was steaming from raw AM CW pulses pumped by multi hundred kWatt Freaking klistrons

author: coppercone2
author_rank: Super Contributor
timestamp: January 04, 2020, 04:50:40 am
content: Quote from: unitedatoms on January 04, 2020, 04:37:51 amit sounds fine if they were a broom distance away, I thought someone decided to give them leather gloves

author: unitedatoms
author_rank: Frequent Contributor
timestamp: January 04, 2020, 04:59:18 am
content: Right. On biological level every living creature is aware of inverse square law. The cancer is best you can get in situation offering instant microwave baking, when eyes are exploding from inner steam pressure

author: coppercone2
author_rank: Super Contributor
timestamp: January 04, 2020, 05:40:10 am
content: Quote from: unitedatoms on January 04, 2020, 04:59:18 amwhy do you think it would cause cancer? it would need to be linked to thermal spot heating or electrochemical modulation of some kind

author: unitedatoms
author_rank: Frequent Contributor
timestamp: January 04, 2020, 06:25:06 am
content: Because I am not a doctor, so I dont know, and just beleive. Because biological moleculas have absorption lines with some exact MHz and GHz values. It takes a picojoule to rip a DNA, so then after that happened, the cell keeps replicating in wrong way, non-stop. Which is cancer. Cancer is caused by damaging the DNA. It can be damaged even mechanically by some sharp asbestous needle even. Or tiny radioactive dust particle, if it stay long enough embedded in the tissue. Or by UV light, or radio waves.

author: coppercone2
author_rank: Super Contributor
timestamp: January 04, 2020, 05:04:56 pm
content: Quote from: unitedatoms on January 04, 2020, 06:25:06 amI feel like its very well shielded by water, if there was a DNA ribbon suspended in a vacuum then I could see something happening, maybeThere is very very little written about non-thermal chemical reaction effect effected by microwave energy in bulk solutions (this can be read about in synthetic chemistry articles), a very interesting question to a synthetic chemist determining if buying a microwave reactor is a ripoff.Usually the effect of microwave chemistry is due to phase dispersion (multiphase solutions i.e. oil and water) and heating peculiarity, such that the reactor can be made cleaner, or that a precipitate is heated in a different manner etc. (say, less stirring is required, so there is no vortex to suck in air and effect the reaction in one example). So a heavily stirred reaction (vortex) that had to occur under inert gas may occur in a 'simple' vessel.Not to say heating is totally safe (heat does not normally enter a body in this way). I also believe this is THz region stuff (when talking about actual resonance), the gradient must be different when the body is heated by microwave, but typically blood flow will change to account for this to regulate temperature. I believe that the fact that our body is basically salt water shorts everything out like a big shunt.https://en.wikipedia.org/wiki/Non-thermal_microwave_effect"Non-thermal effects in liquids are almost certainly non-existent," Keep in mind when this is studied,you are talking small vessels (100mL) heated by something like 100W+ of microwave energy, so its VERY powerful and contained. Like tanning with a reflection screen, at least. Same thing with UV chemistry, typically you are talking a probe thats quartz and water cooled irradiating a solution. Hard to compare these things to natural exposures due to sheer power density.Not to mention other defenses (i.e. I believe your skin has a quite abnormally salty layer close to the epidermis in order to combat bacteria with salt), as evidenced by people who consume high salt diets having less chance of serious skin infection, and things like dead-sea salt bath treatments.Perhaps a good reason for a radio technician to eat salty fries with a extra large cup of ice water lol, sleeping on the job may also effect health in a positive way, since your eyes are shielded.

author: David Hess
author_rank: Super Contributor
timestamp: January 04, 2020, 07:52:09 pm
content: Quote from: vk6zgo on January 04, 2020, 03:24:21 amThat is why climbers rig their own harness and someone doing maintenance should remove a part which is required for operation and carry it with them.https://en.wikipedia.org/wiki/Lockout-tagout