Build Yourself a Cheap Efficient End Fed Half Wave for High Power

[@lpbkdotnet]

For a quick and dirty “did this get warm?” check in kit I can’t reach quickly - I sometimes stuff a till receipt into the enclosure. Thermal receipt paper changes colour somewhere between 60-100C - if it went black, you got to at least 60 Obviously this is a really crude measurement approach, and only suitable where you’re sure it’s not going to get hot enough to ignite (although that’s presumably useful info too!) But it gives you some idea without worrying about data logging a probe with kit that may or may not cope being near that much rf

[@MM0OPXFieldRadio]

Great shout. I have thermal labels here somewhere here.

[@acestudioscouk-Ace-G0ACE]

You raise some very good points here and I hope our new-found privileges are used sensibly as you advocate.

[@MM0OPXFieldRadio]

I think many will have been running more already but yes no doubt some will "jump in" and do something silly. I hope not though.

[@timg5tm941]

Superb presentation as always Colin

[@MM0OPXFieldRadio]

Thanks mate 👍

[@charlieoscar09]

Thankyou for the video Colin excellent work as always

[@MM0OPXFieldRadio]

Appreciated 👍

[@StuartM0TTQAmateurRadio]

I've put up a reflector behind a vertical half wave and even without optimising the spacing you start to see some useful gain

[@MM0OPXFieldRadio]

Excellent Stu. I need to try it.

[@jameski5oeb668]

Love it! Great information as usual.

[@MM0OPXFieldRadio]

Thanks again 👍

[@ndkohlman]

Fantastic! Thanks Colin, I really appreciate the work you've put in and your video content

[@MM0OPXFieldRadio]

Thanks, your welcome 🙏

[@reedreamer9518]

I have not yet felt the needed for an amplifier. I have always operated with 100 watts and everyone that I can hear can always hear me at least as well. I even do well on 75m without an amplifier, but I use a very efficient home-brew double magnetic loop, which does not suffer from ground losses compared to the inverted-V that most people use.

[@MM0OPXFieldRadio]

Yes its not for everyone. 100w is ample nearly all the time.

[@hankaajindrich8622]

Pay attention to the attachment of the ferrite with a wire. It's a painted wire, but it's enough to break the paint and the core will be short-circuited.

[@MM0OPXFieldRadio]

Agreed, that's why I'm very careful when winding.

[@hankaajindrich8622]

@@MM0OPXFieldRadio I guess I explained wrong. I point to the copper wire attaching the toroid to the box.

[@MM0OPXFieldRadio]

I'm not sure what you mean then. There is little risk of any shorting here. My Acom 1000 has the protection anyway for issues like this.

[@VoSo_]

@@MM0OPXFieldRadio Colin, the wire (that holds the core to the box) represents an additional (secondary) turn with a short circuit.

[@DonzLockz]

Only top quality parts and workmaship from you, Colin. Very inspiring, I love your work.💪🤠🇦🇺

[@MM0OPXFieldRadio]

Thanks, cant muck about with a KW.

[@cthoadmin7458]

I used teflon coated silvered wire for mine (something worth looking for in hamfest junk boxes cos it's pricey new). Not sure if it made much difference to the heating. Is the EFHW a good antenna to use at high power? Be interesting to see how the losses increase with increasing power. Thanks for taking the time to make these Colin.

[@MM0OPXFieldRadio]

Thanks, if had some I would measure the loss. No problem for high power as long as its built right. I would much rather use my Hexbeam with some power as a pileup buster. More power means more heat so that's whynI say it needs to be built right.

[@mikesradiorepair]

In the USA we can operate up to 14.350 MHz. KC3OSD

[@MM0OPXFieldRadio]

So can we but I looked at the band plan and 14.300 is the centre of activity for global emergency comms. Nothing illegal what I did but should be kept free.

[@m0aze611]

Thermal camera at the ready. Well it will be some months before I’m back on the air from my new QTH but hope to do some /p QRP with my KX3 once the weather improves. Not sure about upping the power but will monitor things as I’m starting afresh. Great vid as usual. Regards Mike

[@MM0OPXFieldRadio]

Hope your settling in well Mike. Portable is a much fun as anything.

[@mortimersnerd801]

.... a thermal camera is nice but, they can get pricey... if $ and price point is a prime consideration, another option might be to get one of those inexpensive trigger thermometers that became popular during COVID... they are accurate and not that expensive.

[@clifficus]

Says a lot Colin, for running 1Kw.

[@MM0OPXFieldRadio]

I can see why some folks want to do it but not for me on, especially on a zero gain antenna.

[@andymcdonald8878]

Maybe a ESP32 would fit you needs for a Temp sensor Colin ? !! Heltec esp32's are very small and work well in enclosures.

[@MM0OPXFieldRadio]

Most likely but I need to try and learn some coding with Rpi or arduino.

[@101blog]

A nice bit of fun, nice to see it stand up to that well, how about epoxying a thermister to the core to measure the temperature or a sacrificial K type and put a meter out there and video it as you operate it. Somewhat heathrobbinson but would give you the answers on the core heating

[@MM0OPXFieldRadio]

Good simple idea, thats the type of thing I had in mind.

[@robertmeyer4744]

very good. love the testing on the FT 240-52 cores. I have been using mix 61 that I have. run great 10 and 12 meters. not much heating on 800 PEP watts or so on 2 stack wound 49:1 and 10 AWG wire. using 2KV 100 PH cap. I have thermal imagining camera . was watching my type 61 cores . at took 500 watt FT8 to heat them up. I have 4 572/B tube amp so I wont run hard very long. I was using 10 and 12 meters. same DX commander pole but veritable with ground plain wires. end fed cut 1/2 wave cut mono band 10/12 meters. I fold end back to tune. I have Pota Flex 7 M & P coax. just bright yellow. nice choke on coax. when you go QRO the counterpoise and CMC choke more important. don't want that RF getting back in the shack. 73's

[@MM0OPXFieldRadio]

Sounds like a great setup. I've yet to try 61 material.

[@robertmeyer4744]

@@MM0OPXFieldRadio from what I can tell. type 61 better than 43 on 12 threw 6 meters. I do not have type 52 to try . good cores in the us is about $15 each, give or take for type . that for FT 240. then add shipping to that. just got a few .

[@CharltonSupporter]

Would a transformer designed for high power have any detriment to say a system running 100w?

[@MM0OPXFieldRadio]

None, buts its extra spend you perhaps not need to layout.

[@CharltonSupporter]

​@@MM0OPXFieldRadio Thanks for the reply.

[@TomG2NV]

Interesting as always Colin, Sorry if I missed it in the video, But I'm guessing you used 43 mix material for this transformer? 73 Tom.

[@johnk8091]

He said 240 #52 mix

[@MM0OPXFieldRadio]

Its the 52's Tom 👍

[@R50_J0]

1KW! Congratulations.

[@MM0OPXFieldRadio]

Thanks although I won't be using all of it much.

[@BenWorrell]

Good video good info Sounds like you have a lot of noise compared to what I hear on 20m using either of my EFHWs which are cut for 80 and 40m 73 de NE5B

[@MM0OPXFieldRadio]

Its local noise. Shortly after it disappeared.

[@KS0JD]

How about a LORA temp sensor in the box. Only use it when not xmiting. command and voltage could be sent over the antenna wire. Just a thought. Interesting antenna! 73

[@MM0OPXFieldRadio]

Yes good idea. I really need to learn coding with likes of Rpi and arduino.

[@40over86]

If you are running high power you need to keep in mind that this system offers zero second harmonic suppression. If your amp has a pi network, instead of pi-L network, you will likely be transmitting a readable signal on your second harmonic.

[@MM0OPXFieldRadio]

Which system? My Acom 1000 takes care of harmonic suppression for me.

[@Andy2e0ree]

Great lot of information Collin 73

[@MM0OPXFieldRadio]

Thanks Andy 👍

[@vetinger]

Can you provide the specification of components which you used in your antenna? Thank you and "73"

[@MM0OPXFieldRadio]

I don't have the time to do this for everything. Its pretry straightforward.

[@geirha75]

Thanks for great information on high power efhw with the transformer. I've got a couple of questions. Did you use a choke next to your high power amplifier? No complaints from your neighbors, emi audio/radio/TV?

[@MM0OPXFieldRadio]

Install the choke 5% of a wavelength back from the feedpoint. It can be a bit more though. Zero interference issues.

[@chuckk5358]

Nice video Colin. Did you build or buy the choke you showed? If you bought it, where? If you built it, do you have a video on that? Thanks. Chuck KE5LY

[@MM0OPXFieldRadio]

I build it Chuck. Search for GM3SEK common mode choke. Super simple to make.

[@K1ZEK]

Hello Q. Do you have a video on winding that unun? I would like to try my hand at making one. 73 Leo.

[@MM0OPXFieldRadio]

Google EFHW Autotransformer. I will make a video on this but likely a few weeks away.

[@K1ZEK]

@@MM0OPXFieldRadio Thank You. 73 Leo

[@WILLIAMPERRELLI]

I hv an 80-10 efhw with a 49/1, 130 feet long. My antennas brand. Very good on all bands. Adding a counterpoise off of the ground rod, I am able to work 160 decently! If I put up a 173 or 202 foot 9-1, wld it gv me better results on the bands, especially 80 n 160?? Ps…I am running an Mfj 998 tuner. Thanku. William

[@TonyM7CVK]

Colin you mentioned about the cap is it absolutely necessary to use one ? M7CVK Tony

[@MM0OPXFieldRadio]

Generally needed for bands above 20m as the SWR is high otherwise. It also improves transformer efficiency to better to have IMO. These are pennies.

[@TonyM7CVK]

@@MM0OPXFieldRadio cheers Colin for the prompt reply I have a few I have gathered so will try them on my home made units

[@MM0OPXFieldRadio]

Good luck 👍

[@BenjaminPieres]

Will work for QRP? Thanks

[@MM0OPXFieldRadio]

Yes but your way overspending if your only running QRP.

[@stewartrv]

The fact that the insulation tape didn't melt or just come off means you didn't get it hot I'd say! 😃

[@MM0OPXFieldRadio]

So inside the box I used liquid electrical tape just in case of arcing. Definitely no issue on 20m.

[@markfeltham9456]

In truth, I can’t understand why the power was upped via the governing bodies.. It was perfectly ok as it was, ample power for all, the problem now is of course measuring antenna performance if someone is blasting obscene amounts of power into the ether. I get from your hesitance in the video delivery that you too are not sold on the idea. It’s totally ridiculous . Sometimes, just sometimes less is more and things don’t need fixing M 73

[@MM0OPXFieldRadio]

I wouldn't say I'm not sold on the idea as I believe we should have the choice. Just because we can doesn't mean we should. For some peolple with big amps this is merely a paperwork exercise so now they can tell the truth. Since this video, my amp has not been on at all. I bought it so it had loads of headroom not to stress the valve and that's the way I see it. I wont be changing my operating.

[@markfeltham9456]

Sensible talk