My last project was to built an antenna to be able to improve my score on 40 as I don’t presently own anything correct for this band. I choose to built a 1/4 wave vertical even if I know in forecast that I don’t have enough place to built a correct earth ground system, if things got really wrong I will be able to reuse everything for another project later.
Why did I choose to built an 1/4 wave vertical, because it’s easy, it’s fool proof and about no mathematic is involved.
I modeled this antenna before building it, you can view the results at the very bottom of this article. The antenna is a quarter-wave vertical using 4 radials but the more radials you use the better. To find the necessary length of each elements (meaning the vertical one and each radials) use the formula 75/F for results in meter or use 234/F for results in feet, F is the frequency to be used in MHz, this length can be prune a little if necessary. If the radials are horizontally mounted the impedance of the antenna will be about 35 ohms, if the radials droop down to about 45° the impedance will be around 50 ohms so you can also play with this angle to get a perfect match if necessary.
You can see right and left a picture of this antenna, and as you can see the antenna is
perfectly free space mounted in all direction, actually the antenna is about 2 meters away from a wall for about 2/3 from here height ‘heading’ east and about six meters away from a concret wall on here west ‘heading’. Even with this poor mounting case the SWR stay below 1.5 for 170 KHz frequency window, really close to the predicted value from the MMANA-GAL antenna analysing tool on 40 meters band. The SPIDERBEAM pole is not fully extended as I only need a little less as 10 meters, so about three meters are still in pole. Perfect pole for an outside activation, solid, light, an easy one man job.
I built this antenna in January 2012 in just 1 day, using a 12 meters SPIDERBEAM pole, I loose hours trying to adjust this antenna till I found a defect UHF 90° male to female elbow (not delivered with antenna). The antenna prove to be as efficient as I had imagine. From January I worked 68 dxccs on PSK with power running from 30 watts pushed in rare case to 100 watts, contact include BY, VU, YV, HI8, PY, ZS and more. As I need a lot of countries in PSK on 40 and on others bands I will use this antenna for some time for sure. This antenna proves also to be very noisy, no sign of static just a constant noise never going down below S8 , so it won't be easy to suppress the noise. Don’t forget I leave only 200 meters away from a major train station, just in the center of my city. In a picture below you will see how big is my lot...
I must say that the quality of the SPIDERBEAM fiberglass pole is very high and the black finish coating looks perfect to me. One of my next project will be a receiving magnetic loop to get a more noise free reception. From the beginning I use a common current choke at the base of the antenna, just in case, see the picture below on the left, you will also see the optional radial plate sold by SPIDERBEAM and which perfectly match with the pole .
I already choose my next project, and it will be an 1/2 wave EndFed Antenna ( for High Power). If I don’t have place for a good ground system, then next step is not to use it at all anymore HI.
More to come.