kx4o

kx4o

23p

18 comments posted · 45 followers · following 0

6 weeks ago @ Ham Radio . me - Mast Mountable J-Pole ... · 0 replies · +1 points

The stub should work at or near the third harmonic, just as the radiator and impedance transformer section does, but the awkward beam angles put this as a low priority at this time.

6 weeks ago @ Ham Radio . me - Mast Mountable J-Pole ... · 0 replies · +1 points

In the prototype with 3/4 inch tubing it was a bit difficult to arrange the coaxial cable within, but it did work. The larger problem is soldering the final piece of copper at the feed point with the cable inside. The large amount of heat moving through the pipes might damage the coax. I'm still working on a solution for that, but what I'm really hoping to finalize is the scheme using the pipe itself as coaxial transmission line.

6 weeks ago @ Ham Radio . me - Mast Mountable J-Pole ... · 0 replies · +1 points

I built one prototype for 2m that works well although it uses the internal coaxial cable technique rather than making the tube itself the transmission line. The patent just received approval and will publish in a few weeks. I will work on a 445 MHz model with 1/2 inch copper tubing first and see where that goes.

7 weeks ago @ Ham Radio . me - Simulating the end-fed... · 2 replies · +1 points

Yes, absolutely. The "end-fed" moniker does seem to imply a single terminal source, but all power sources are certainly two terminal devices. It's a game of semantics isn't it? In my mind "end-fed" refers to the radiator feed, but I could be wrong. The larger question is if point #2 requires "extra" treatment of ground, lengthly counterpoise or other ideas to get radiation from the dipole radiator. This simulation suggests no as does my experiment with a 10 MHz dipole here...
https://www.hamradio.me/antennas/electrically-iso...

The problem, of course, is we can never really get a power source infinitely small so even its body will be a bit of electrical "mass" (or counterpoise if you like) to push against, but the data seems to be suggesting it doesn't have to be electrically large. Put another way, there's nothing about the EFHW that is fighting our ability to energize it so long as we handle the impedance transformation... and that's the larger point here.

45 weeks ago @ Ham Radio . me - J-pole: Where a choke ... · 0 replies · +1 points

"because it's not a whole, proper antenna and choking it doesn't make it so!!"
By the same reasoning, neither is the quarter-wave ground-plane antenna, but they can be made more functional with an additional set of radials or equiv... just like the J antenna... and that's only if they need a connection to a conductive mast. Independently, both are whole and proper antennas and the rollup J antenna, yes with a feedline choke, personifies the near ideal antenna.

"Why keep building and promoting these pieces of crap?"
Well because they aren't bad as tests and research easily confirm. Yeah they have their idiosyncrasies like any antenna topology, but work fine in the hands of the skilled.

45 weeks ago @ Ham Radio . me - Winlink and Modems: Wh... · 0 replies · +1 points

The FCC isn't making it easy, but if you follow the winding path of restrictions set by reference to other mode limitations you will see they say unlimited bandwidth for only a short list of approved/published/etc. modes. I wanted to open this up to completely experimental and, yes, profit driven, modes, but with the 500-600 Hz limit. So unlimited bandwidth for the elsewhere limited list of modes, and 500-600 Hz for anything at all. I think I said 500 Hz on the actual FCC application because of a typo, but you get the point.

Of course my larger point is to not mix Layers 7 and 1 into the broader demonization of Winlink. There are responsible ways to use broad bandwidth digital modes... especially when it can finish the transfer faster and then stay out of the way for a good while. Think of it as TDMA in super slo-mo... something stunningly ignored by some in the anti Winlink parade. I'd rather not see one application's alleged abuse of the digital landscape needlessly demonize the mode used during the data transfers. It's quite unfair to the modem designers be it SCS or open-source soundcard techniques. I have no dog in the hunt for Winlink. They can fight their own fights. Consider me a "mode warrior."

58 weeks ago @ Ham Radio . me - Superbowl HDTV Antenna · 1 reply · +1 points

John,
The original Hoverman design had limited frequency range. That ~5 inch length is indeed the primary refinement of the more recent Hoverman designs (7") and it extends the frequency range of the overall design quite a bit upwards. With the abandonment of the upper television channels this is less important now. To answer your question more directly... While 16ths of an inch precision might matter in a perfect NEC model, I'm not convinced manufacturing tolerances for any given build are going to be accurate enough to make the length of that last element more critical than, say, 1/2 inch precision. That was certainly the case with my example above and it tested very very well in chamber measurements.

59 weeks ago @ Ham Radio . me - Where a choke chokes · 0 replies · +1 points

Hmmm, well I can convert the S21 measurements to amperage as a percentage. Let me see what I can add.

63 weeks ago @ Ham Radio . me - Have your J-Pole and g... · 0 replies · +1 points

Ask right here.

65 weeks ago @ Ham Radio . me - Slim Jim vs. Tradition... · 1 reply · +1 points

Yes the grounds do have a profound effect on the real-world lobes from the antenna based on, more or less, the height of the antenna's center of radiation above the ground. In this example both the slimjim and traditional J have practically identical free space radiation so both will interact with the ground the same way. Generally the higher they are the more compressed the lowest radiation lobe.