Safety Warning - When RF Breaks your SH*T

[@G6EJD]

I don't understand some of the commentator comments: For example 1500W at 50R equates to 273v and 5.5A or at a high VSWR say 10R then its 122v and 12A. The only time that you can get very high voltages is when the antenna impedance is very high say 300R then the voltage is 670v and 2.2A, so at these voltages nearly any modern wire insulation can withstand the voltages...

[@DXCommanderHQ]

John corrected himself in one of the comments. Don't worry - it's just a bit of math! The problem of being on the spot - and recorded!

[@ham-radio]

Hi Guys, It is not 16-18 amps on those open frame relay contacts as stated as fact during the video. It would be the current squared times the impedance equals the power. So at 1500 watts it would be about 5.5 amps. Now here's the rub, a (not vacuum) relay contact rated at 5.5 amps is fine at 60Hz but not so fine at 28million Hz. So some derating of the contact current handling is necessary. Also, relay contacts do bounce so the transmitter needs to give the amp a few fractions of a seconds to close then send RF. Many modern transceivers have a way to delay the RF for that fraction. I have built many amplifiers with some large tubes. I currently live in a very tight neighborhood where the lots of 6000 square feet. And I have had just one complaint from a lady who said that I was turn a ceiling paddle fan on and off. I recommended that she have it serviced, and it was not my problem. The amp I built when I moved here uses a Russian triode. I used two vacuum relays inside. The external antenna relay boxes I built each have 5 large Russian relays connected to 5 SO239 connectors that have Teflon dielectric. They are all silver plated. The vacuum relays are rated at 10KW. I don't use end fed antennas because in my view, they are not a good design. I prefer something like a dipole. The impedance can be close to 50ohms as opposed to 5000ohms(and more) at an end fed. I evaluate antennas by looking at them as if they are a dipole. It could be a vertical with radials or an off center fed dipole for example. High voltage is at the end of the element. It is wise to eliminate corona discharge. During a test with a homemade vertical and QRO power a few years ago, I created arcs that were about 4 to 6 inches long from the capacity hat. There is much more to talk about, but this comment is already too long. Just keep in mind that 1500 watts can be run at a ham radio station when a few simple points are kept in mind. 73, Jim Heath W6LG KZbin Elmer

[@FromthehamshackwithNJ4Z]

Jim I corrected myself down in the comments. I misstated the Amperage. thanks for catching that as well.

[@DXCommanderHQ]

Jim, check John's reply. He did mention that - but as you know, once edited and uploaded, there's not much we can do. Thanks old friend!

[@ham-radio]

Yes I do. If I had a dollar or a pound for every misspoken word or mistake, I could afford to live in California. Despite watching and editing, I make lots of mistakes; lots! 73 Jim

[@roasttoe]

Fascinating discussion, thanks gents!

[@glenmartin2437]

Thanks for the video , Callum. Thanks, all, for the comments. This reminds me of working in the laboratory with 4 kv to 10 kv equipment. !!! Around 400 volts AC, a corona can develop about leads and equipment. If you are grounded and get into the corona or charge cloud, GAME OVER!!!

[@DXCommanderHQ]

Interesting!

[@WECB640]

The issue is in both the dielectric insulator and the inductance of the lead contacts in those "chunky relays". Plastic dielectrics break down under HV stress and heating. There is good reason why RF switches use ceramics as the base insulating material between the contacts. Most people understand breakdown voltage, but their schooling only dealt with DC HV. RF is AC, so there is agitation between the molecules in the dielectric material and this is a great catalyst to the destruction of the insulating material under stress. Wide and flat conductors are also very important to keep ohmic losses low at RF.

[@DXCommanderHQ]

Nice comment. Tnx.

[@G6EJD]

Also most plastics are no-longer pure, the use of recycled materials is prevalent and inevitably small amounts of metal find their way into the recycling process and plastics become conductive. In addition water can be within the dielectric material which in the presence of an electromagnetic field (like a uWave) will heat up leading to material deformation.

[@joel5921]

Energy is heat and heat starts breaking all the weak spots. Then the corona flash starts and gives a nice glow. I would not want this to happen with the coax running through the house

[@thomasperina2990]

Hello Lord Callum: Thank you for this real life video sir. Well if you are running the juice everything's got to be in perfect condition or you will be getting a 4th of July light show. Loved the video + with your talent very inspiring OLD CHAP. God Bless, & my best to Wendy & the dogs. TMP, Unit 22 from N.J.

[@polomint46]

Worth making up some ultrasound sniffer kits to put at critical joint areas, early warning partial discharge, before something goes pop!

[@321CatboxWA]

I placed a flicker bulb or imitation flame bulb (two closely spaced flame shaped elements in place of tungsten wire) on top of my 5 ft firestick and on top of my steel whip . Instead of the normal yellow/orange flicker I get a bright purple/red glow that varys with modulation below a certain level. It did effect the SWR raising it some but that was easy to correct. I recommend coating the glass with hot glue for durability. The bulbs come in two sizes. The smaller bulbs base fits snugly inside a decapitated Firestick cap snugly . The bulbs do not have to be electrically connected but it helps when setting SWR . Remember you are changing the antenna length with this. It takes more than 5watts to light them up.

[@DXCommanderHQ]

Love it!

[@michaelgreenwood1162]

You should see how fast a room fills with black smoke when a switch carrying 40kw uhf, goes faulty. The transmitter trip was also faulty. The black smoke came from ptfe insulators in 6 inch feeder burning. Very acrid smoke and dangerous to breath.

[@DXCommanderHQ]

Woah!!

[@robertabbott7770]

I am guessing the repair shops are going to be busy !!!!! A reminder to all , your EMF calculations will change as well .

[@Jim_2E0HKM]

We're all foundation guys when it comes to the EMF forms 😂

[@1958johndeere620]

My 4k rated Palstar 4 to1 balun would overheat on 160 with 300 watts or more power. My loop was not great resonance on 160. I had to trim it several times to get it better so the balun wouldn't have the china syndrome. As the balun heat soaked the srw would climb steadily.

[@DXCommanderHQ]

Yes, I also had saturation on 160m..

[@basshorseman998]

Years ago on 160, high power had my tuner zapping in very interesting ways...

[@DXCommanderHQ]

Yeah, 160m can saturate baluns pretty fast..

[@mikesradiorepair]

Just emailed you some pictures of a failed PL-259 connector. Water, freezing temperatures, a improperly waterproofed connector and high power don't mix.

[@DXCommanderHQ]

Ah OK!

[@DonzLockz]

No issues with QRP here.😂

[@WR3ND]

Can still be an issue even on the receiving side. But yeah, it tends to be safer playing with matches than it does playing with flame throwers. 😅 Cheers.

[@MirlitronOne]

What amuses me is that I can now initiate a QSO on 10m at 1kW, and then I can observe the rule of "using the minimum amount of power necessary for the contact" and turn down to 10W! 😂

[@DXCommanderHQ]

You COULD - and lose the frequency!

[@FromthehamshackwithNJ4Z]

Correcting myself at 1500watts 275V RMS, 775 V peak to peak, 5.477 amps per leg. I lost my train of thought and quoted the relay specs most equipment has for 1500w, which is are 16-amp relays. Also realize you have to account for frequency when you calculate for your relays, the higher the frequency the less amperage the relay will handle need to check the manufacture specs. For example, if you had a 10amp rated relay the power handling capability using Ohms law should be I^2 x R=P (10A^2 X 50ohms) = 5000watts, but that is at DC or 60hz AC. That same relay may only be rated at 4amps at 30MHz so that changes the power handling. 4^2 x 50ohms = 800watts. In my research I have read to derate relays between 40 and 60% of the DC/AC60hz rating for HF. I typically will use 60% to be safe and will typically use 20 or 30amp relays for my projects. When in question go bigger to be sure your relays will handle the power you are using. Also be aware of Duty Cycle... those contacts will heat up, so high power in the digital modes will create more stress on the system.

[@xszl]

So, is that a yes to testing with your tongue ?

[@FromthehamshackwithNJ4Z]

I was also fighting off a sneeze....

[@FromthehamshackwithNJ4Z]

(volts gives you a pretty good pop on the tongue, I don't think I want to find out what 275v of AC is like. @@xszl

[@DXCommanderHQ]

Good reply John!!

[@FromthehamshackwithNJ4Z]

Callum can you pin this please. @@DXCommanderHQ

[@ianxfs]

Just don’t use your tongue to test anything ⚡️ 😛

[@highflyermw0lkx311]

🤣🤣🤣

[@vk2lq]

LOL yr no fun for testing LOL

[@DXCommanderHQ]

HAHA Ian!

[@markramsay6399]

PP3 batteries every time!

[@garyh8315]

There goes the voice of experience 😂😂

[@Andy2e0ree]

Fantastic work and talk many thanks Guys 73

[@robertmeyer4744]

That was great. yes things change at 1 Kw. even types of plastic start to react to high power RF. may be fine 400 watt. the ends of a dipole is where the highest voltage is. a loop back soldered back on it self prevents the arc ball from forming. even ladder line and window line can be a problem at high power. the voltage john talked about is for 50 ohm feed point. you go up to 450 or 600 ohm feeder the voltage goes way up. and can arc across to near buy metal like a gutter on side of house. same with end fed dipoles. which is about 2500 ohm impedance . not only the UNUN can heat up the antenna side can arc around. for high power RG 213/214 is what you need for feed line at 50 ohm. can be M & P or ABR coax. That yellow Pota flex7 from M & P can handle a KW . that 7 mil . but if needed to go long go even bigger. line loss . it really adds up at 1Kw . 73's

[@DXCommanderHQ]

Nice comment. Thank! Didn't know about the bbalanced feeder. Interesting!

[@g0fvt]

Related directly to this is "hot switching" which itself destroys amplifier relays. Ideally the amplifier relays should be put in "transmit mode" before the radio begins to produce RF and stay in that position briefly when the radio goes to receive. Some radios do have a parameter that can be adjusted to delay the RF output, you only need 10mS or so of delay. Many VHF/UHF high power stations (with mast head pre-amplifiers) have to be even more careful and often use a "sequencer" to ensure the chain of equipment is keyed in the correct sequence. Even moderate SWRs increase the voltage and current stress on the feeders and connectors, an SWR of 2 will increase both by 40% approx. Most 0.5" cables have plenty of leeway though... 73

[@ZeroHarry]

Cal, I believe that the power increase is to create more sales for the Ham Radio suppliers. 🙂

[@DXCommanderHQ]

Oh yes!

[@BurninWires]

Great to see Roly again, wondered what happened to him ?

[@FromthehamshackwithNJ4Z]

an amazing guy!

[@BurninWires]

Funnily enough, I’m from NZ and mentioned him at a Club meeting. No one knew who he was, nor for that matter, who Callum was, heathens and luddites 🤣

[@Kevin_KC0SHO]

Personal experience, DX50 wire does hold up better to QRO digital than DX10. I’ve not QRO’d my element ends yet, as mentioned in the DXC build manual. I will do so next time I drop the 12.4.

[@FromthehamshackwithNJ4Z]

Wire Diameter has an impact on power handling capability.

[@Tantalicdavid]

So glad you put out this video Callum.

[@vk2lq]

Want to see how power affects your antenna, use a stainless steel whip at night with some power and watch it glow red :)

[@Dennis35793]

ty

[@W1TEA]

Is this a short clip of a longer show? This is great information and experience shared here.

[@DXCommanderHQ]

No.. It's the tail end of something else I am currently editing..

[@W1TEA]

@@DXCommanderHQ thanks! Looking forward to watching that when you drop it. Love your work and your content. Very informative especially for newer (and a few older) hams/amateur radio enthusiasts, “radio curious”, and ham adjacents (spouses, etc). 😄

[@k9eihamradio]

These are some great tips! Thanks for the corona discussion!

[@DXCommanderHQ]

You are so welcome!

[@MINI-4X4-RADIO]

Pretty sure quite a few UK Hams will not comply with EMF Levels @ 1000W

[@DXCommanderHQ]

They will be driving over the speed limit next!

[@MINI-4X4-RADIO]

That's a personal choice, neighbours/public will be oblivious

[@markramsay6399]

I have a Acom 1000 amp which I purchased to push me towards the full licence - so far I am still only 2E0MSR as other things got in the way. I was doing some checks in tuning it to my DXC (without transmitting at high power). I got it wrong and pushed out nearly 1000W on 20m (carrier signal etc). Next minute family are shouting at me - I have set the house alarm off! Anyway, not been able to use it in anger etc. Other thing of course - all very well having that power to use, but how far away are you from the antenna? ! My office is back of garden and my DXC is about 3m away - probably not so good for 1000 W (even if I could!). Mark, 2E0MSR.

[@DXCommanderHQ]

Very good!

[@Joe-KN4IFI]

Great video guys. Important information for people wanting to run high power. 73 Joe

[@vk2lq]

A TDR will locate the fault A time domain reflectometer

[@michaelgreenwood1162]

My 1kw traps popped on 40m with 600w.

[@plproductions8887]

Are M&P coax and connectors the best to get?

[@DXCommanderHQ]

For ham radio? Possibly. Not silver-plated mil-spec but close.

[@plproductions8887]

@@DXCommanderHQ yes for amateur radio purposes what would be the best for future proofing my system coax and connector wise.

[@JustMe-dv5ix]

Run QRP and avoid all of this, much more fun making DX on 5 watts or less. Good discussion, TU.

[@xsean]

Hmm... Maybe i will just stick with 100 watts.

[@timg5tm941]

Good luck running QRO with neighbours surrounding you.

[@DXCommanderHQ]

Did it at the house for years.. Gradually nailed every problem apart from 40m - next door's alarm!

[@alanyoung261]

Hi commander why is SW13790 in china such a good reception here in England and everything OTHER is below PAR. Thanks alan.

[@DXCommanderHQ]

Alan.. They use HUGE amounts of power.. I tried looking it up but failed.

[@alanyoung261]

Just surprised then, we 1st world countries are so far BEHIND.@@DXCommanderHQ

[@alanyoung261]

Even the USA is so far behind China.@@DXCommanderHQ

[@kevinmatthews2620]

lol Roly , rip the coax out and get Messi & Paoloni coax :), exactly the coax i have, Roly forgot to mention the M&P plugs too :) :)

[@Thomas-ZET]

Think I’ll stick with my 600 watt amplifier

[@davidc5027]

600 seems to be a sweet spot IMHO.

[@DK5ONV]

💯👍👍👍

[@DnBclassictunes]

25 watts. Qro here lol

[@winstonchurchill6506]

And this week competition is what’s the missing letter 😅😅😅

[@winstonchurchill6506]

And this week competition is what’s the missing letter 😅😅😅

[@DXCommanderHQ]

Haha