A 40 & 80 Meter Vertical Antenna
A friend gave me a Butternut HF-2V 40 and 80 meter vertical antenna to play around with. This antenna is a full-size quarter wave on 40 meters and it is 1/8 wave on 80 meters. It is approximately 32 feet tall. Given the current sunspot conditions, most of the bands are pretty "dead" after dark, with the possible exception of 20 meters (at times). Also, it is currently winter in the norther hemisphere, bringing us more hours of nighttime propagation and fairly low noise levels on the three lowest bands, 40, 80, and 160 meters. An accessory 160 meter loading coil is available for use with the HF-2V, and it was originally my intention to set up the antenna to use it. However, when I tested the 160 meter coil, I had a difficult time achieving resonance within the 160 meter band (it was around 2.3 MHz instead) and the resonant frequencies in the 40 and 80 meter bands were thrown way off as well. Given the very narrow SWR bandwidth on 160 meters and the relatively low efficiency of a 1/16 wave vertical, I decided to give up on the idea of using the antenna on 160 and optimize it for 40 and 80 instead. I disconnected the 160 meter coil and set about tuning the antenna to resonance on the other bands. I discovered that there is some interaction between the tuning on 40 and 80 meters. I used a short coax jumper to a Rig Expert antenna meter and this helped to quickly get the antenna tuned to my desired frequencies.
On 40 meters, with the coil adjusted for resonance at around 7150 kHz, the antenna pretty well covers the entire band from 7000 to 7300 at the 2:1 VSWR points. At band center, it's about 1.4:1. The advantage of having a full size quarter wave radiator is clearly seen. On 80 meters, the 2:1 bandwidth is about 90 kHz with the antenna tuned around 3860 kHz. I will probably move it down to a lower frequency eventually, but this splits the difference between a regional sideband net that I like to check into and the AM window at 3885. Actually, this is not the right antenna for my operating needs on these two frequencies since most of those contacts are "short hop" within about 200 miles. A low dipole works much better for these distances. But it gave me an opportunity to test it.
It would be desirable to use at least 32 1/4 wave long radials on 40 meters with this antenna, but I went with the ones I had previously installed, and they are only about 13 feet long. They were optimized for use with the 17M vertical that I put up earlier. So this is definitely a bit of a compromise, but I find that it does work. When Spring arrives I will make some impedance measurements at the base of the antenna to determine what the ground resistance is on each band.
Not long after I put up this antenna, a friend messaged me to say that he had just worked ZS6CCY in South Africa on 40M SSB and received a 5x6 report. Hearing this, I made a beeline for the shack and tuned around until I heard him. It took a few tries but eventually I broke through and put my first ever contact with that area in the log using the new vertical. He was a solid S9 on my receiver and I got a 5x9 from him as well. His signal was about 4-5 S-points stronger on the vertical than on my (low) dipole. Verticals do work, especially for DX!
So here are my observations about the use of vertical antennas, in case they are of interest. Do not think of a vertical as a "space saving" antenna because you need to install a decent radial field for them to work efficiently. If you can't put out a good radial system, choose a different type of antenna. In the city, with buildings and trees around, I would not recommend a ground mounted vertical especially on 20 meters and above. If you can elevate it to roof level or higher, it may work reasonably well. Ground mounting is OK for the lower three bands (40, 80, and 160) and in any case, it is difficult to get longer antennas up high. If you have a choice between installing many short radials or a few longer ones, definitely go with lots of shorter ones. A "sparse" radial field does not work well because there is too much space between the wires and a lot of the RF energy leaks into the lossy earth instead of being returned to the antenna base through the radials.
Radial systems serve two purposes. First, they provide the return path for antenna currents. Without them, these currents will flow through lossy earth and much of your power will be used to "warm the worms". I often see remarks from hams stating that they aren't using any radials, yet they still work lots of stations. Yes, you can do this, but your signal is nowhere near as good as it would be if you were using an efficient antenna. The second thing a good radial system does is to reduce ground losses in the vicinity of the antenna. This is important for achieving good low angle radiation, which you need if you are trying to work DX. However, although you can reduce ground losses right around the antenna, you don't have any control over ground quality at greater distances. I have read some papers that claim that vertical antenna performance is affected by ground quality out to 50 or more wavelengths from the antenna. So, if you live in an area with poor ground conductivity, don't expect vertical antennas to be hot performers.
Situations where verticals are a good choice:
You do not have to go out and spend hundreds of dollars on a commercially made vertical antenna. That is a ridiculous waste of money in most cases! For example, you can build a single band vertical monopole antenna very inexpensively. Several suppliers like DX Engineering and Texas Towers sell aluminum tubing very inexpensively that you can use to make a self-supporting vertical antenna. If you have a tall support such as a tree, you can hang a wire for almost no cost, and it will work just as well. Do not skimp on the radial system, however!
What about those expensive "no radial" vertical antennas? They work because they have been designed to function as a vertical dipole. That does not mean that they will work efficiently if you have poor (low conductivity) ground quality in your area. However, if you can get them up high, performance will improve because less RF current will flow through lossy ground. If you mount them on the ground, they do need a good radial systems in most cases, unless the ground is of excellent quality! You just can't believe everything you read in antenna advertisements.
On 40 meters, with the coil adjusted for resonance at around 7150 kHz, the antenna pretty well covers the entire band from 7000 to 7300 at the 2:1 VSWR points. At band center, it's about 1.4:1. The advantage of having a full size quarter wave radiator is clearly seen. On 80 meters, the 2:1 bandwidth is about 90 kHz with the antenna tuned around 3860 kHz. I will probably move it down to a lower frequency eventually, but this splits the difference between a regional sideband net that I like to check into and the AM window at 3885. Actually, this is not the right antenna for my operating needs on these two frequencies since most of those contacts are "short hop" within about 200 miles. A low dipole works much better for these distances. But it gave me an opportunity to test it.
It would be desirable to use at least 32 1/4 wave long radials on 40 meters with this antenna, but I went with the ones I had previously installed, and they are only about 13 feet long. They were optimized for use with the 17M vertical that I put up earlier. So this is definitely a bit of a compromise, but I find that it does work. When Spring arrives I will make some impedance measurements at the base of the antenna to determine what the ground resistance is on each band.
Not long after I put up this antenna, a friend messaged me to say that he had just worked ZS6CCY in South Africa on 40M SSB and received a 5x6 report. Hearing this, I made a beeline for the shack and tuned around until I heard him. It took a few tries but eventually I broke through and put my first ever contact with that area in the log using the new vertical. He was a solid S9 on my receiver and I got a 5x9 from him as well. His signal was about 4-5 S-points stronger on the vertical than on my (low) dipole. Verticals do work, especially for DX!
So here are my observations about the use of vertical antennas, in case they are of interest. Do not think of a vertical as a "space saving" antenna because you need to install a decent radial field for them to work efficiently. If you can't put out a good radial system, choose a different type of antenna. In the city, with buildings and trees around, I would not recommend a ground mounted vertical especially on 20 meters and above. If you can elevate it to roof level or higher, it may work reasonably well. Ground mounting is OK for the lower three bands (40, 80, and 160) and in any case, it is difficult to get longer antennas up high. If you have a choice between installing many short radials or a few longer ones, definitely go with lots of shorter ones. A "sparse" radial field does not work well because there is too much space between the wires and a lot of the RF energy leaks into the lossy earth instead of being returned to the antenna base through the radials.
Radial systems serve two purposes. First, they provide the return path for antenna currents. Without them, these currents will flow through lossy earth and much of your power will be used to "warm the worms". I often see remarks from hams stating that they aren't using any radials, yet they still work lots of stations. Yes, you can do this, but your signal is nowhere near as good as it would be if you were using an efficient antenna. The second thing a good radial system does is to reduce ground losses in the vicinity of the antenna. This is important for achieving good low angle radiation, which you need if you are trying to work DX. However, although you can reduce ground losses right around the antenna, you don't have any control over ground quality at greater distances. I have read some papers that claim that vertical antenna performance is affected by ground quality out to 50 or more wavelengths from the antenna. So, if you live in an area with poor ground conductivity, don't expect vertical antennas to be hot performers.
Situations where verticals are a good choice:
- You want to work DX (not short distances)
- Excellent ground quality is available (including seaside locations!)
- You want to operate on lower bands (40/80/160M) where you can't get a horizontal antenna up high enough to work efficiently
- The antenna can be installed "in the clear" with no obstructions for at least 1/2 wavelength around it
- You are able to install a good radial system, with 32 or more radial wires at least as long as the antenna height at a minimum
- You don't have a lot of local electrical noise to contend with
- If considering operation on higher bands (20/17/15/12/10M), you can mount the vertical antenna on a roof, tower, or other elevated location
You do not have to go out and spend hundreds of dollars on a commercially made vertical antenna. That is a ridiculous waste of money in most cases! For example, you can build a single band vertical monopole antenna very inexpensively. Several suppliers like DX Engineering and Texas Towers sell aluminum tubing very inexpensively that you can use to make a self-supporting vertical antenna. If you have a tall support such as a tree, you can hang a wire for almost no cost, and it will work just as well. Do not skimp on the radial system, however!
What about those expensive "no radial" vertical antennas? They work because they have been designed to function as a vertical dipole. That does not mean that they will work efficiently if you have poor (low conductivity) ground quality in your area. However, if you can get them up high, performance will improve because less RF current will flow through lossy ground. If you mount them on the ground, they do need a good radial systems in most cases, unless the ground is of excellent quality! You just can't believe everything you read in antenna advertisements.