gdp's Comments

Ham Radio . me : Electrically isolated end-fed vs. center-fed dipole radiation

Sat, 23 Nov 2019 09:05:58 +0000

Bear in mind the tests above were to specifically verify if the EFHW with 49:1 transformer actually radiates with no extra gear, counterpoise or what have you as that was specifically the question at hand. Comparing resulting antenna current magnitude (via H-field magnitude) provides the evidence. However, further testing with the things you mention is certainly next on the list not for the sake of verifying a halfwave aerial with 49:1 (or so) transformer and independent CW transmitter can actually work, but to see what connections made to the system with feedline, etc. mess with the system's natural ability to function. I do like the WSPRLite transmitters if they can be configured to produce a steady signal for testing. Other than for "hey it kinda works" experiments, WSPR is too inaccurate for any meaningful absolute measurements. This might change if the WSPR network reported the absolute signal level rather than S/N. Don't understand why they don't since the information is available. Oh well.

Ham Radio . me : Mast Mountable J-Pole Antenna

Sun, 29 Sep 2019 14:23:22 +0000

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.

Ham Radio . me : Mast Mountable J-Pole Antenna

Sun, 29 Sep 2019 14:21:59 +0000

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.

Ham Radio . me : Mast Mountable J-Pole Antenna

Sun, 29 Sep 2019 14:19:25 +0000

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.

Ham Radio . me : Simulating the end-fed half-wave (EFHW) dipole antenna

Thu, 19 Sep 2019 12:40:32 +0000

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.

Ham Radio . me : J-pole: Where a choke is no joke

Tue, 25 Dec 2018 17:22:17 +0000

"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.

Ham Radio . me : Winlink and Modems: When to not cross the streams

Tue, 25 Dec 2018 16:32:44 +0000

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."

Ham Radio . me : Superbowl HDTV Antenna

Thu, 27 Sep 2018 12:35:12 +0000

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.

Ham Radio . me : Where a choke chokes

Sun, 23 Sep 2018 00:43:45 +0000

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

Ham Radio . me : Have your J-Pole and ground it too

Sun, 26 Aug 2018 01:22:31 +0000

Ask right here.

Ham Radio . me : Slim Jim vs. Traditional J-pole Antenna

Sun, 12 Aug 2018 04:53:23 +0000

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.

Ham Radio . me : Slim Jim vs. Traditional J-pole Antenna

Sun, 12 Aug 2018 00:19:23 +0000

"Does the slim Jim have lower takeoff angles vs j-pole as many state which can attribute to more received energy at distances vs in a test box?" No. Refer to figures 1 and 2 above. "Also, does the comparison change for 2m or 70cm as all the data was obtained at higher frequencies, e.g. 650mhz and 1ghz." So long as the antennas are built in proportion to the wavelength of the desired frequency, they result in practically identical patterns. Often the mounting structure and feedline perturb the resulting pattern greatly highlighting the need to mitigate rouge currents, but when you control for them, the patterns match.

Ham Radio . me : 'UHF' Connector Test Results

Mon, 16 Jul 2018 13:36:40 +0000

I don't disagree, but it's their connector for now. Since we are delving into important semantics, your point of referring to this connector family as PL-259/SO-239 is technically incorrect since these two numbers refer to two specific connectors for a specific cable/purpose among dozens in the group. It's a hot mess.

Ham Radio . me : 'UHF' Connector Test Results

Mon, 16 Jul 2018 01:49:02 +0000

Sure... right after Amphenol stops calling it a UHF connector. https://www.amphenolrf.com/connectors/uhf.html

Ham Radio . me : NVIS works very well... except when it doesn't

Mon, 9 Jul 2018 23:56:50 +0000

Certain antenna profiles can increase your signal strength to overcome weak skip conditions, but once the ionosphere shuts down, it's done until it comes back no matter what gear you have. Good gear is still good to have, we just have to understand HF will fail us if we rely on it 24/7.

Ham Radio . me : 'UHF' Connector Test Results

Thu, 28 Apr 2016 16:21:23 +0000

Your observation the UHF connector folks don't claim a 50 ohm surge impedance is spot on. However, the often implied useability at VHF and UHF frequencies suggests it has to function in 50 ohm systems. So they won't claim 50 ohms, but do say it works well in 50 ohm VHF/UHF systems - conflicting requirements at a minimum.

Ham Radio . me : Slim Jim vs. Traditional J-pole Antenna

Wed, 27 Apr 2016 14:59:00 +0000

Electrically there is no benefit. To obtain a benefit, the extra copper requires arranging in a way to increase the "capture area" you refer to. The classic example is a vertical collinear antenna... http://www.hamradio.me/antennas/improving-the-sup... The conductors in the SlimJim, while in phase, are much too close to each other to be anything more than a slightly fatter single conductor. The parallel conductors work just like a folded dipole in almost every way.

Ham Radio . me : 1/2 Wave vs. 5/4 Wave VHF EZNEC Shootout

Wed, 27 Nov 2013 18:17:21 +0000

Your correct Keith... I really don't know what the maker of the 5/4 wave antenna design wants. The only operating parameter his web page discusses is gain... "Although not actually measured, this antenna should give at least 6 dB gain if mounted high enough." I do assume the phrase "mounted high enough" reflects a desire to provide better performance towards the horizon. Assumptions aside, the 5/4 wave designer doesn't really say what the antenna is good for... thus the stimulus for this article. If, as you suggest, the designer meant to focus energy to high elevation angles at the expense of terrestrial service, he definitely achieved this. Finally your assertion high radiation angles make for good repeater use is counter to the trigonometric realities you are either very close to the repeater and don't need much gain at any angle or well away (often just a couple miles or more) and need gain with low radiation angles. A high gain, high angle antenna has little use in typical repeater service.

Ham Radio . me : 2 Meter, 5/4 Wave Antenna Revealed

Wed, 27 Nov 2013 17:20:18 +0000

If you do the trigonometry it is true repeater users against the mountain deal with a high elevation angle. Using your example repeater height of 3,000 (several thousand) feet we have: 1/2 mile away - 49 degree elevation angle, 1 mile away - 30 degree elevation angle, 2 miles away - 16 degrees elevation angle, 5 miles away - 6 degrees elevation angle, 10 miles away - 3 degrees elevation angle, 20 or more miles away - less than 2 degrees elevation angle. Much depends on the purpose and service area of the repeater. I venture to guess most repeater sponsors desire to service a large area on the order of 10 to 30 mile max radius... or perhaps more. If the user is close to the repeater, a high angle with low or no gain antenna will suffice. A simple 1/4 wave ground plane or even a rubber duck antenna and 1/2 watt should be more than adequate. If the user is a few miles or more away, an antenna with higher gain and lower take off angle begins to make sense. The 5/4 wave antenna provides higher gain at higher elevation angles which doesn't fit the repeater user scenarios above. I argue the 5/4 wave antenna is not an ideal use of resources for the typical repeater user.