Running an End-Fed Half Wave Beyond Its Limits (

[@steinshaw2490]

Ft8 is a low signal mode, not a low power mode. I remember being surprised when I first read this. Then I continued reading that low signal modes were primarily developed for moon bounce and moon bounce is not low power. I would agree 30w is plenty for most digital work but as you said sometimes you want to reach out a bit further.

[@johnrees44..G4EIJ]

Hi Dave..Many thanks for this comprehensive ‘plain language’ explanation.. It has answered so many questions for me, that needed to be answered. Best 73.. John..G4EIJ

[@hammathguy3995]

Hi Dave. Nice discussion of magnetic cores. Magnetic flux saturation not something we often think about.

[@d3w4yn3]

I've been playing with my home-made EFHW, based almost exactly on DL2MAN's U01 emergency communications antenna, and I've noticed a few variables that I did not anticipate having to pay attention to: core size (mainly to make sure I'm not losing efficiency or over-powering), diameter of the wire I'm using to make the antenna, and most unexpected, the length of my coax - which kind of functions as a radial. If I make any drastic changes to any of these, I see a huge difference. Kind of reminds me of making sight changes on a rifle scope, the smallest change at the point of change results in an exponential effect at the target, or in the case of my QRP rig, at the point of radiation.

[@dougtaylor7724]

I heard a similar discussion on the OCF. They tend to heat up more than other baluns. Their response was to build a balun rated to 3k watts. But then it only seemed good for 150 watts on FT8. But anything over 50 watts is usually overkill.

[@n5pa]

From the questions he asked, he is wanting to run more power on the Digital Modes. My suggestion is not for him to run less power, but to build or buy something like the MyAntennas EFHW-8010-2K-Plus. This is a 49:1 UNUN Transformer with 3 of the 2.9 inch cores. But even with this, they advertise a Digital Power Limit of 350 watts to prevent either of the two issues that could arise as you talked about in your video. And yes, these are modes for Weak Signal Reception, not low power transmission as such. You should run the lowest power to make the transmission. But to work FT8WW on Crozet Island on FT8, 100 watts would not get you a confirmed QSO at all times.

[@Roddy1965]

The duty cycle should or could also be lowered if the operator feels the need to run 'high' power, because you need to give the materials a chance to experience some cooling time.

[@ronjoseph7973]

Unless you want A LOT of common mode current in your shack, you absolutely need a line isolator or choke balun for a EFHW where proper grounding, which is almost always the case, is not possible. KC5RJL

[@davelapp4740]

Is this an EFHW or OFCD? The description at the begining of video says OCFD and mentions a feedpoint at (I think ~29%???) which sounds like an OCFD

[@glenmartin2437]

Thank you, Dave. N0QFT Is that still called punching a hole in the envelope in flying?

[@watthairston1483]

The steady-state nature of digital modes is confused with SSB power levels thus cores take a beating. Thanks for stating digital modes are "QRP" modes. 49:1 autotransformers are typically rated at SSB power levels. One core 100 watts SSB; two core ~500 watts SSB and three cores about 1000 watts SSB. I would refrain from operating anymore than 25% of these SSB levels using a digital (steady-state) mode. Your autotransformer, baluns, radios and amps will like you a lot more and last longer.... 73' de K4WRF

[@BusDriverRFI]

1. He said "I like to run some power on digital bands". Amateurs running RTTY (which is a digital mode) have always run a lot of power. Also FT8 is a "weak signal" mode and not necessarily a a low power mode. Even you said you run some power on FT8 and maybe this amateur is only going after the difficult stations. 2. You said to add cores to the balun. The real reason it is heating is the XL of the primary winding is too low. You can increase the XL with more cores OR you can increase the number of windings. You still need a 2:1 windings ratio or equivalent for your 4:1 impedance ratio. But his core is heating up from the high current losses in the primary winding. A nanoVNA can help in these required changes. 3. Telling someone to run less power to avoid these issues is like a mechanic telling a customer to not drive over 25mph to avoid a shimmy. This is irresponsible.

[@geirha75]

I presume you guys here, have some experience. What would be the best choice for EFHW antenna, 49:1 or 64:1 transformer ? And why?