Building a Quarter Wave Vertical Antenna for the 17M Band
Recently, a ham radio friend suggested that I check out the 17M band. I figured that with the current low in the sunspot cycle, there wouldn't be much activity, but I was wrong. The band has been reasonably productive for both long haul domestic contacts and working DX.
I wanted a dedicated, fairly efficient antenna for 17M rather than an add-on for one of my existing antennas. I had a Hy-Gain 18V vertical that wasn't in use, so I thought that would make a decent start. The 18V is supposedly adjustable for operation on any single Amateur band by means of a small loading coil at the base (supplied). I decided to get rid of that and just adjust the antenna for resonance on 17M (around 13'). The aluminum sections can be telescoped together somewhat equally to achieve any desired length up to 18'. Thus, it is a full-size quarter wavelength monopole.
I mounted the antenna in the clearest available spot in my back yard. It is very light, so I used a short length (4') of 1-1/2" steel water pipe for the mounting post. To this, I attached a ground radial plate and installed 40 radial wires, each 13' long. Due to the relatively short length of the wires, I was able to install them in a full radial configuration. After mounting the antenna, it was straightforward to adjust its length for resonance at 18.125 MHz. The SWR at the base is around 1.4:1. I did not bother with any matching networks to reduce it further. It would be easy enough to lengthen the antenna slightly and add a series capacitance to get a match that is closer to 50 Ohms. I fed the antenna with a convenient length of RG-8X coaxial cable, inserting a coaxial choke at the base to reduce the possibility of RF current flowing on the feed line.
Verticals are noted for being noisy antennas, and this one did not disappoint in that regard, although the noise level was not too bad. It averages around S3-S4 most of the time, which is low enough to only be a problem for really weak signals. In several weeks of testing, I found that this antenna was satisfactory for working stations in the southwestern part of the U.S. and up and down the west coast with good signals, when the band is open. I have seen signals up to 20/9 at times. Other areas come through at reduced levels. I could barely hear European stations, which mostly come in during the morning hours. I did manage to work a few stations in the Carribbean and Central and South America but signals were not very strong. Once I heard a couple of VK stations (Australia) but they were very near the noise level and I did not try to contact them.
This antenna got me on the air and whetted my appetite for a better antenna, if I could build one. That will be the subject of my next antenna article. My conclusion is that although it is functional, a ground mounted quarter wave vertical is not optimum for operation on the higher bands from 20 meters on up. It is adversely affected by nearby bushes, trees, and buildings, at least in my situation. If you have a large open field to erect it, perhaps it would work well. My guideline is to avoid ground mounting any vertical antenna for any frequency where the size of the antenna is relatively comparable to any surrounding objects. Using this criterion, ground mounting would be suitable for the 160, 80, or 40 meter bands but not for the 20, 17, 15, 12, or 10 meter bands. However, it does work and operation is very stable, mechanically and electrically. This antenna can take the full Amateur power limit of 1.5 kW PEP. In my next post, I will share what I replaced this antenna with, and how they compared.
I wanted a dedicated, fairly efficient antenna for 17M rather than an add-on for one of my existing antennas. I had a Hy-Gain 18V vertical that wasn't in use, so I thought that would make a decent start. The 18V is supposedly adjustable for operation on any single Amateur band by means of a small loading coil at the base (supplied). I decided to get rid of that and just adjust the antenna for resonance on 17M (around 13'). The aluminum sections can be telescoped together somewhat equally to achieve any desired length up to 18'. Thus, it is a full-size quarter wavelength monopole.
I mounted the antenna in the clearest available spot in my back yard. It is very light, so I used a short length (4') of 1-1/2" steel water pipe for the mounting post. To this, I attached a ground radial plate and installed 40 radial wires, each 13' long. Due to the relatively short length of the wires, I was able to install them in a full radial configuration. After mounting the antenna, it was straightforward to adjust its length for resonance at 18.125 MHz. The SWR at the base is around 1.4:1. I did not bother with any matching networks to reduce it further. It would be easy enough to lengthen the antenna slightly and add a series capacitance to get a match that is closer to 50 Ohms. I fed the antenna with a convenient length of RG-8X coaxial cable, inserting a coaxial choke at the base to reduce the possibility of RF current flowing on the feed line.
Verticals are noted for being noisy antennas, and this one did not disappoint in that regard, although the noise level was not too bad. It averages around S3-S4 most of the time, which is low enough to only be a problem for really weak signals. In several weeks of testing, I found that this antenna was satisfactory for working stations in the southwestern part of the U.S. and up and down the west coast with good signals, when the band is open. I have seen signals up to 20/9 at times. Other areas come through at reduced levels. I could barely hear European stations, which mostly come in during the morning hours. I did manage to work a few stations in the Carribbean and Central and South America but signals were not very strong. Once I heard a couple of VK stations (Australia) but they were very near the noise level and I did not try to contact them.
This antenna got me on the air and whetted my appetite for a better antenna, if I could build one. That will be the subject of my next antenna article. My conclusion is that although it is functional, a ground mounted quarter wave vertical is not optimum for operation on the higher bands from 20 meters on up. It is adversely affected by nearby bushes, trees, and buildings, at least in my situation. If you have a large open field to erect it, perhaps it would work well. My guideline is to avoid ground mounting any vertical antenna for any frequency where the size of the antenna is relatively comparable to any surrounding objects. Using this criterion, ground mounting would be suitable for the 160, 80, or 40 meter bands but not for the 20, 17, 15, 12, or 10 meter bands. However, it does work and operation is very stable, mechanically and electrically. This antenna can take the full Amateur power limit of 1.5 kW PEP. In my next post, I will share what I replaced this antenna with, and how they compared.