160-20m LOG loop-on-ground

[nanZor]

Just note that there are 3 versions - EZnec "demo" (limited to 20 segments), the normal paid EZnec with a lot of segments for more complicated antennas, and then "pro" which has a LOT more features mostly for those in the antenna / military business. Which of course needs another license for NEC4 to use. Well, actually there are TWO versions of the "pro" depending on if you are satisfied with NEC2, or need NEC4 with it's own separate license.)

For us normal folk, that usually means demo or the standard paid-for version. More than good enough!

One "outside the box" overlooked by many modelers is of course the common-mode ground interaction of coax cables. I use that feature frequently to determine the effect on pattern, match, and how much resistive ferrite choking it takes to keep it under control.

For example, any modeler trying to get closer to reality would add a "third wire" to a 2-wire dipole connected to one of the sides, drop that wire straight to ground, and run the pattern plots. Add a resistive load and find out how much impedance is needed to actually do some useful choking.

Similar to the above is the "inverted vertical" which I talked about in another thread, where you puposely use the common mode of a vertical coax run, and the top wire are your radials. Choke the bottom of the coax of course, and attach the center conductor to the flat-top, and leave the braid unconnected.

That's kind of out of the box. Now, the feedpoint is up in the air, instead of being fed down low like a conventional vertical, which gets the feedpoint well above ground clutter. Pattern is similar. But what is really cool is after running a pattern plot, is to view the antenna right afterwards, and now EZnec will display the current running through the elements in pink lines.

But of course, modeling is one thing, and real-world another. That's why the smart modeler will back up EZnec with other methods to see if the general trend is being broken. Ie, SWR, rf currents etc. If it doesn't follow the general trend, then something (usually failing to incorporate the common-mode of coax) is the culprit. Or the reason for magical antennas that purport to be out of the box, but are just fancy random wires.

EZnec can save a lot of $$ in wasted wire and guesswork - basically you can trust it to get you VERY CLOSE to the real world, but smart folk back that up with other measurement techniques to see where things it can't predict in the environment would have an effect.

Heh, well maybe with the pro version, one could model what a water-tower 12 feet away from your monster log-periodic would do in 3D wireframe. Us normal guys running the demo or standard version will just have to eyeball that and put the antenna somewhere else ....

 

[nanZor]

A little OT I guess, but just a warning about EZnec, or other modeling aids ...

While they have been a great help to swl / amateurs in general for normal antennas, yes they are also very helpful in ferreting out a lot of "out of box" antennas that prove to be fancy common-mode random wires.

BUT, in the fervor of protecting the consumer, some have taken that sleuthing to a new level, where they put decent manufacturers on trial, based solely upon EZnec and yes time-proven theory (usually quoting Terman 1943 et al), demanding that what appears to be a shortcut or consumer convenience for basically the same performance, is a con job.

Rather than put boots on the ground and build the *exact* thing themselves, or better yet purchase one and put it through actual measurements, they rely solely on EZnec results as the only proof to sustain a never ending FUD campaign.

Some may be disguised competitors, or those who want exact details so they can merely *copy* the design later, letting the original DECENT manufacturer do all the R&D for them.

Realizing that it would not be cost effective to put a copy of Terman, Moxon etc in along with their product, they suffer the slings and arrows of FUD from armchair engineers, or wannabe competitors now or possibly in the future.

Sure there are some bad apples out there. EZnec can point those out. But taken to a different level, it can also be an attack vector for product that actually DO work, but not exactly like EZnec proposes. That takes measurements with other items, and actual physical measurements with other instruments.

Sorry about that - rant over....

 

[Ubbe]

For us normal folk, that usually means demo or the standard paid-for version. More than good enough!

My point where that it is just a dumb program, not some kind of intelligence that can evolve by itself. A program only works the way a programmer guy have coded it and if you do something that the coder haven't thought of, like design a new antenna model, then the result may be totally false.

/Ubbe

 

[nanZor]

Of course. At some point though, a lot of coders - initially Lawrence Livermore Labs for the Navy with NEC in fortran, people have put many eyes on the code, such as W7EL and a whole slew of others over the decades stomping the bugs.

So far, I don't thing any new antenna model can fool it - *much*. Part of not fooling it is the human error input checking. Throw something studid at EZnec, and it either won't let you, or warn you about the consequences.

 

[nanZor]

Speaking of real world testing of the log and dog (one on each side of my house), it would be easy to throw an expensive receiver at it. I've put a Kenwood 590s and Alinco SR8 / R8T on it. Pretty much as expected with apples to oranges comparison, but very pleased with both ends of the performance spectrum.

But I wanted a second opinion on the low end. So for the third time in over 20 years, I put a venerable beginners radio, a recent model Icom 718 transceiver online. I know what the front-end is like (very reasonable if you drive it properly), but never did so with an on-ground antenna. Transmit disabled so I don't blow out Dale's 9:1 rx transformer, nor Danny's rx-only choke by mistake.

I could have thrown an Icom R8600 on it, but that's not challenging enough. Let's see what happens to this 20 year old design. So far, so good. Like driving a sports-car manually. We'll see how 160m holds up later.

 

[Ubbe]

SI could have thrown an Icom R8600 on it, but that's not challenging enough. Let's see what happens to this 20 year old design. So far, so good. Like driving a sports-car manually. We'll see how 160m holds up later.

You're testing the receiver more than the antenna itself with a less superior radio. You must throw the best you have at it to rule out a receiver weakness rather than an antenna one.

/Ubbe

 

[nanZor]

Yup - done that. Best I could do was borrow my clubs' Yaesu FTDX-3000 for a week and put it on the LOG. Me want!
It's a grade above the Kenwood 590s, that's for sure.

So yes, worked great. Not a problem. Expected performance (that Yaesu 3K really dug down deep!).

But how does a radio like the Icom 718, with a performance level that is not at the top of Sherwood's list do? I'm real familiar with the "beginner's" type of front-end performance, and how it needs to be a bit more hands on to get the best out of it having owned it 3 times.

In a word - the Icom 718 took to the LOG and DOG like a duck to water! I guess like any other lower-end radio would do that is prone to overload / IMD / etc etc.

It didn't turn a pumpkin into a prince, but the LOG antenna did do the following to it:

1) Allowed me to listen to the 160m CW contest still raging. No preamps necessary, BUT I did activate the preamp (usually a big no-no on the low bands), and was not penalized in the least! The front end did not crumble or go noisy. CW agc just fine with wall to wall local and distant stations. Could hear the weak underlying station when stacked two deep right on top of each other without blocking! Took some concentration to do that, but possible. With no cw filter I couldn't do that all night of course. Plenty of cw reverse and if-shift going on that's for sure.

I didn't buy this thing for cw contesting, but man, now that I know it can handle the LOG, I may just have to scrounge a cw filter up somewhere.

So that's the good thing - the limited front end of the '718 has no troubles with the log, and from an IMD standpoint of hitting the first mixer too hard - no problem even with a cw contest in full swing. A bit of rf-gain and even 20 db of attenuation (on 160 no less!) hands on here and there, but still - WOW!

The truest test was that after listening for a few hours non-stop to the cw contest with no filter - I took the headphones off, and no fatigue! When I had my first 718, I didn't know how to operate it really, and after an hour or so my ears felt like they just got back from a concert. But not this time. No ringing - hallelujah!

Anyway - I'm stoked about the loop and dipole on ground. A kilobuck radio - yeah sure no sweat. But the loop on ground is a *great* way to put any older rig, or one on the lower end of the scale that may not be contest-worthy initially, back to good use!

 

[nanZor]

Forgot to mention that the 20 year old AF-DSP noise limiter and auto-notch work *much* better than expected with the log.

Like many with severe noise issues, when using the DSP features on my first '718, they seemed like glorified tone-controls. Now that the front end isn't getting hit so hard, I can go much further in dsp depth without that waterfall sound.

One major concern about the LOG and DOG having both low and high angle reception is the possibility of more useless sky-noise. I *think* hear more of that than I do my verticals, but just barely tickling the DSP at a 1 or 2 setting cleans up the top end, but is allowing me to finally hear through some local noise on 40m at night so I can hear the Triple-H net. Didn't think the '718's dsp could handle it, but with the log, it gets through. It isn't a glorified tone control after all!

 

[Ubbe]

It isn't a glorified tone control after all!

But could it be a glorified attenuator? Perhaps the result are the same with a variable attenuator between antenna and receiver to set the input level where the front-end and the AGC works at its optimum designed range? Do you have a cheap $20 CATV variable attenuator you can test with both your vertical and horisontal antennas? Would be interesting to know.

/Ubbe

 

[nanZor]

Nah, it's different than mere attenuation optimization. When the filter is actually used, *after* attenuation / rf-gain optimization, and the noise peaks are still cutting into the signal to be bothersome or tiring, you can hear a somewhat processed sound.

But that means the difference between copying a net on a noisy freq for hours, rather than just listen - albeit optimized for s/n, for 30 minutes.

But one can only go so far - it isn't something I leave activated all the time.