Latest posts of: Steve

"What do you think of the the SteppIR?"

Let's get to a core issue right at the start - gain.

Gain claims. Regarding the 2 and 3 element Yagis -- the ad information states, "...gain and front to back figures for our 2 element 57 inch boom antenna rivals most 3 element beams." Can this be true?

Let's take a realistic look at the claimed gain for 20 meters, which is 4.2dBd. This hardly "rivals" any 3 element beam I know of. In fact, our small C-3S, which is a trio of 2 element Yagis for 20-15-10 has more gain (also verified). Let's take a look:
Antenna Regular Price 20m Gain & F/B 15m Gain & F/B 10m Gain & F/B
C-3S $ 699 (Aug 2006) 4.5dBd / 15dB 4.7dBd / 16dB 4.4dBd / 16dB
2-el SteppIR $ 995 (2005) 4.2dBd / 18dB 4.1dBd / 13.7dB 3.8dBd / 9.3dB

Check the figures for yourself! Staying with the 2 element motorized Yagi, the SteppIR free space model shows the gain specified for 20 meters is 6.6dBi, meaning 6.6dB compared to the isotropic radiator in free space. The front to rear is given as 20.5dB. If you have some Yagi modeling software handy, try it for yourself - set up a boom length of 57" and remember that the feed point impedance must be in the vicinity of 22 ohms, because there is a 22 to 50 ohm transformer in the antenna feed circuit.

Notice that the motorized Yagi never equals the 2 element tubing antenna. A good thing to keep in mind when looking at other claimed gain figures.

Notice also the progressive drop in gain and especially the dramatic drop in the SteppIr 10 meter gain. A boom length of 57" is pretty good for a 2 element 10 meter Yagi. It is more optimum than for 15 or 20. Why is the gain on 10 less than on 15 and 20? Maybe the wound up conductor (a lumped inductor?) at the center? The 10 meter is down 0.6dB from a similar antenna with tubing elements. That amounts to about 14% loss for some reason. If you add more elements, the loss continues to degrade the hoped-for gain.

One of the big selling points is a low VSWR, right? (I thought we were past that issue long ago!) Anyway, run your software with the antenna in free space and see what you get. With a (small diameter) reflector length of 214", a driver of 200", element spacing of 57" and a feed point impedance of 21 ohms, the free space gain is 5.54dBi and average front to rear of 12.5dB. Peak front to rear is 9.6dB. Let the numbers speak for themselves. By the way, 5.54dBi is 3.4dBd (5.54 - 2.14). If you optimize for gain at the 6.6dBi mark, the feed point drops to 12 ohms and the average front to rear is reduced to less than 14dB. At a feed point of 12 ohms running through the transformer, your VSWR would be close to 2:1. Maybe our software isn't the same..........?

Reasonableness - On all the claims, ask for the back-up information. Some make no sense at all. For example, the feed has a fixed value (e.g. 22 ohms and stepped up to 50 ohms through a matching device). This means the feed point for all configurations on all bands must be 22 ohms for the claimed "1:1 SWR - on every frequency." Anyone can run various software to see how this affects the designs on the bands, which will be a compromise due to the fixed element spacing and fixed feed point. Given this situation, how can the product meet the other claim that "Our 3 element Yagi on a 16' boom outperforms much larger arrays"? The main contributor to gain on Yagis is boom length (and number of elements on larger arrays), so to think a 16' boom 3 element 20 meter Yagi can outperform a 28' boom 3 element Yagi (with no feed point impedance, nor element spacing restrictions) is not reasonable. On the higher end of the frequency range, try modeling a 16' boom 3 element 10 meter Yagi and see how it does - this is very wide spacing (almost a half wave long boom) and nothing you will find on any 10 meter monobander for only 3 elements.

Reasonableness again - the conductor in the SteppIR is not round, it is flat. As noted by a professor at a University I spoke at, a flat conductor is not as effective for RF as round. Not only that, but it is much smaller dimensionally. Both these factors make the SteppIR efficiency lower.

Try the pattern and see how it is - the pattern on the SteppIR is not as well defined, nor as sharp as one will find on monoband Yagis. Why not? How about loss for one? When all is said and done, the bottom line is gain and being on the air, not waiting for a motor to run.

Let's go back to the claim that the "2 element version rivals most 3 element Yagis in performance - on a 57" boom." This apparently depends on someone's interpretation of what the word, "rivals" means. Maybe its the same as the often used hype description, "Killer Tribander." There has been too much misinformation in the amateur antenna market for way too long - aren't we past all of this?

A reasonable thought is that one can purchase a time-proven multi-band Yagi of at least equal performance, instant band changing, no moving parts and multiple feed line capability for less money. A related question is whether or not the company will be around when there is a problem with the mechanical and/or software, as all motors have a mean time between failure. Force 12 has been around for 15 years, with >140,000 elements in the air world wide and has the knowledge and experience, plus dedication and continual customer support for >20,000 customers.

At the last several forums where I've been a speaker, I've been asked about the motorized Yagis in the market and how they compare. My surprise was that people in the audience answered the question for me - they don't compare. Some of the issues brought out by the audience are:

a) there is only one feed line, so you are immediately limited for the new dual-watch rigs and SO2R operating and chasing DX on 2 bands at a time;

b) the motorized antennas are much more expensive and they have the potential of a motor failure in the air. As everyone knows, all electro-mechanical devices have a mean time between failure (even the simple fan on your computer);

c) changing element lengths cannot make up for fixed element position; the gain and F/B ratios claimed cannot be done at the same time;

d) there is a reasonable question that the gain numbers cannot be achieved. Their ads note an antenna range test they did and the 10 meter gain on their 2 element is lower than the gain on 20 mtrs. This is odd, as the boom length for 10 mtrs is very favorable for 10 and not favorable for 20. The gain they measured on 10 is much less than any 2 element Yagi you could put up using dimensions out of a book;

e) the power limitation is some clue that there is loss in the system, all the coiled up conductor at the center most likely is not helping the situation, the conductor is not round, which is the most efficient radiator shape;

f) if you do emergency work, you cannot afford to have something fail in the antenna (like a motor) - you are off the air;

g) you have to wait to change bands - a long time

Why wait to change bands? The manufacturer states the motors move the antenna about 1 MHz per second. Besides this, some report so much hash during band transition that they cannot hear while they wait for the motors to stop.

How long does it take to change bands? OK - we are chasing a DXpedition that is on 20 and 15 and we are making calls in both pile-ups. These bands are 7 MHz apart. Using the manufacturer's specification, it takes 7 seconds to change bands. Add to this 1 or 2 seconds of hitting the button and waiting a second to be sure it is ready, a reasonable time is 9 seconds. . Wow - 9 seconds every time we want to try and make a call? How about between 20 and 10 mtrs? They are 14 MHz apart. This gives us twice the time, or 14 seconds plus our wait time, because we can't transmit while the motors are running.

How about in a contest? You can easily do 400 band changes in a weekend DX pile-up or contest listening and calling stations on other bands. Let's take adjacent bands, such as 20 and 15 mtrs. We know the least time for one band change is 7 seconds, but in real life, let's use 9. All right, then 400 changes x 9 seconds = 3,600 seconds -- a full 60 minutes you are off the air. Right - one whole hour of waiting to change bands. If you are really active, 800 band changes is not unreasonable and that is at least 2 hours lost to waiting for the antenna to change bands. If you wanted to change between 20 and 10, the time lost is much more. When you factor in that you might not be able to even listen while the antenna is changing bands, you have lost significant operating time. That new country might have gone away and your contest position will certainly not be improved when you have to wait like this.

Why do you need to track your frequency to tweak the antenna every 25kHz? These thoughts come to mind right away: a) if the antenna is so delicate that the gain or pattern degrades when moving 25 kHz, what does it look like at +/-20 or 24kHz?; b) why do you want to wait and be off the air for the antenna to change when you cross the 25kHz barrier?

There are some important questions that should be prompted by their ad copy.

First, on the MonstIR ad, it should be obvious that although this antenna covers a wide frequency range, it has only one feed line, so using more than one radio at a time on different bands is not possible.

Second, for practical situations, if one element is broken, you are basically off the air. You also have to wait to be sure the antenna actually did change bands. Do you like anxiety? Imagine waiting for your expensive antenna to (hopefully) change bands every time you want to call a rare DXpedition on a different band.

Next, in the ad, they state, "Currently, most multi-band antennas use traps, log cells or interlaced elements as a means to cover several frequency bands. All of these methods have one thing in common - they significantly compromise performance... So, instead of trying to 'trick' the antenna into thinking it is a different length, or simply adding more elements that may destructively interact, ..." What a misleading ad! Anyone who is reasonably prudent in their thinking will immediately recognize that lumping several designs and calling all of them "compromise" antennas is false. The ad ignores reliable and verified multi-band Yagi designs that have been in the field for over a decade, namely Force 12 multi-monobanders. These are not compromise designs. They have set the standard of performance.

The ad copy contains a table of gains and F/B ratios. On 40 meters, the table claims 7.8dBi and a F/B of 25dB, which would be peak figures for a full size, well-tuned, tubular 3 element Yagi with a fairly long boom. You can model this for yourself. There is an asterisk indicating an optional passive element kit, but no more information (maybe this is for 6 meters??). There is no mention of the number of elements used on each band, nor the element spacing for someone to do their own model verification. Be careful - designs rarely have the peak gain and peak F/B occurring on the same frequency as their table implies. The gain and F/B curves do not overlay. On 2 and 3 element Yagis, they intersect; they run in different directions, meaning one is rising and the other is decreasing. To have them overlay requires more elements in a particular spacing arrangement than typical Yagi designs; this is evident in our direct 50 ohm feed designs, such at our Magnum 620, first produced back in 1993. This 6 element 20 meter monobander is on a 44' boom and the gain varies about 0.1dB over the whole band and the F/B varies only 1dB. We use this basic design on production antennas 20 meters through 2 meters and have also built direct 50 ohm feed Yagis up to 5.8 GHz. This design is so good that it has been copied by several others.

In this "monster" motorized antenna, the element positions are fixed and the number of elements is minimal. This is a condition that cannot be overcome by only changing the element lengths.