Hygain Vertical Performance

The Hygain Vertical I purchased has been working well. I hope to run it thru more on-the-air tests over the next few weeks. But during the ARRL /140 contest, it performed well and I made contacts on 10M, 20M, and 40M with it. I have learned a lot about short vertical antennas and I hope to try some other things with it.

For a quick review, the antenna is the Hygain 18VS model. Total cost is $100. It is 18 feet tall and has a loading coil at the base. This is just about as simple as an antenna gets.

I have mine put in an umbrella stand so I can move it to the patio when we mow the lawn. I have a number of radials (minimum of 4) that I attach to the base of the antenna and one ground wire from the antenna base to a 12 inch stake driven into the ground.

This week, I have 10 radials attached to the antenna. Four of the radials are 17 feet and 6 are 13 feet. They are just laid on the grass.

The loading coil tap can be set to make the antenna resonant on just about any frequency from 10M to 80M. I set the tap so the antenna is resonant on 10M. So when I switch to 10M, I do not need my antenna tuner. When I am on 20M, 30M, or 40M I have to use my antenna tuner to get the SWR down under 2.

One of the ideas I have been thinking about is purchasing an antenna tuner to fit at the base of the antenna. These are a little pricy at about $260. That would make the antenna an all-band for sure. But, if I did that, the total cost of the antenna and tuner would be about what a screwdriver-type antenna would cost.

So, the addition of an automatic tuner and more radials are in the plans. I will install the antenna permanently after mowing season is gone. I'll drive a post in the ground to mount the antenna on. I think this will give a much better ground and perhaps improve the way the radials work. The antenna will really be ground mounted instead of 10 inches off the ground.

...AR

Vertical Antenna Ground System

When I come across really useful information, I just have to pass it along. Rudy Severns, N6LF, did an incredible amount of work during the spring of 2008 to evaluate the effect of radials on the effectiveness of 1/4 wave vertical antennas.

For the whole set of articles, click here:

N6LF Antenna Study

In his Vertical Antenna Ground System Experiment No. 4, he makes the following observations:

1. If you are limited to 4 radials for whatever reason, you can SHORTEN the radials (from a 1/4 wave) by up to 40 percent and improve your gain by 2.9 dB. Or you can add a ground rod (4 ft.) and improve your signal gain by almost 3 dB. But doing both does not seem to improve things any more than doing either one. I know, read it for yourself.

2. If at all possible, use at least 8 radials. With the 8 radials you improve your signal gain by about 2.5 dB over the 4 radials and the gain can be improved to 3.9 dB by shortening your radials by about 40%.

3. If you can get to 16 radials, then you have overcome most of the ground losses and shortening the radials is no longer a major factor. He says, "I would think that with 32 or more radials, you wouldn't worry about resonances in the radial screen. The problem is only important when fewer than 16 radials are deployed over average or better soil."

There is a lot more information at his web site and I have not made it through all of it yet. Very good stuff!

... AR

Something You Already Knew - Maybe?

"My Feed Line Tunes My Antenna"... This article was written in the March 1956 issue of QST by Byron Goodman, W1DX. It has been reprinted twice since then - once in 1977 and once in 1991 so it has some good insight that has lasted with time.

Here are my excerpts from this ... basically, main points for me to remember. I hope these bits are useful reminders. I have to read this about once a day to keep it fresh in my mind ...

When we say 50 ohm coax or 300 ohm twin-lead, we are talking about the characteristic impedance of the line. "Characteristic impedance of a transmission line is the value of resistance that when used as a termination for the line, makes the input impedance of the line independant of the electrical length of the line."

The simple view of this: A 50 ohm load (antenna or other resistance) on one end of your 50 ohm coax feed line will measure as a 50 ohm load at the other end of the line regardless of the actual length of the line. No tuner needed here because the load matches the characteristic impedance.

SO: The system is resonant and the whole load is resistance only.

But what if your antenna is measured as a 100 ohm load and you are using a 50 ohm feedline? You no longer match the characteristic impedance of the line. The impedance you measure at the end of the line will vary depending on the electrical length of the line.

The electrical length of the feedline is measured in wavelengths. To calculate the electrical length of the feed line, you must know the frequency, the actual length (in feet) and the velocity factor. So your physical feed line might be 75 feet but the electrical length changes as you change frequencies.

When the antenna load is different from the feed line characteristic impedance then the impedance we measure changes as we move down the line.

The Half Wave Rule to remember:
Every 1/2 wavelength down the line, the impedance we measure equals the antenna load and, obviously, this changes with frequency. And this load is resistance only.

The Quarter Wave Rule to remeber:
Every quarter wavelength, the impedance we measure is resistance only but the value is not equal to the antenna load.

Who Cares? Well, I guess I do. The reminder here is that the antenna load is really a reactive load. The antenna load is a combination of resistance plus capacitance (capacitor) OR resistance plus inductance (coil). The tuners we use help to bring the reactance of the load to pure resistance.

Short Antennas & Automatic Tuners

Or, when do automatic tuners make sense over a manual tuner?

I just found a fascinating article in the May 2008 QST ... actually, it was a short response under Technical Correspondence to an article on automatic tuners. But it answered a question I've had for a long time.

One quote that caught my attention: "...typically, the [automatic] tuners have a tough time when coupling to 'short' antennas whose RR (feedline impedance, if you will) is lower than the prescribed 50 ohms."

The author continues, "...you'll note that in the general instance of the longer -- lower frequency -- antennas, where the feed point (Load) Z is below 50 ohms, the automatic tuners are reticent to couple efficiently, whereas if the feed line Z is above 50 ohms, the tuner is efficient."

A couple of things come to mind ... first, in dealing with short vertical antennas, the antenna Z can be very low, hence the need for radials and/or baluns to match closer to 50 ohms.

Second, if your antenna is "short", whether a shortened 160M dipole or a short vertical, with an impedance of less than 50 ohms, you might want to consider using a manual tuner for better matching range.

If your antenna sports a Z close to or even higher than 50 ohms, the automatic tuners can handle the match easier. The antenna design impedance is affected by a combination of antenna length and height above ground.

This does explain why my auto tuner in my KW TS-440 cranks and cranks to match my NVIS antenna (G5RV at 6 feet high) but quickly tunes on my 40 meter doublet at 20 feet high.

One of these days, I'll have to measure what the impedance is on each of these two antennas.

Something to consider ... AR