Slopers Galore
75 Meters
The first antenna tried on the tower was a quarter wave sloper to the northeast for 75 meters. Twenty nine feet is as high as I can go with wire antennas so I started with some misgivings. The 75 meter sloper worked about as good as the 100-foot inverted V fed with tuned feeders we had been using for 75, with the apex at thirty eight feet. There was a null to the southeast since that is off the back of the antenna.
40 Meters
The 75 meter antenna worked so well, now how about adding 40 meters? The first 40 meter antenna was an inverted V half sloper off of the front of the tower. The lower ends were about five feet off the ground and again we had some misgivings about it too. It didn’t work as well as the inverted V trapped antenna for 40 and 20 meters with its apex at thirty eight feet.
The next step was to add a 40 meter trap to the 80 meter sloper. This worked better than the half wave sloper. I think this was because the lower end is about twelve feet above ground.
180 Meters
Having gone this far, what about 160 meters? My transceiver covered the band and I hadn’t worked it since the mid-fifties. This was done by adding a loading coil to the end of the 75 meter sloper. Not having an antenna on 160 to compare with, we didn’t know how well it really worked. We have made contacts around the Midwest running barefoot with the OMNI on 160.
Better or Worse?
The old wire antennas are all down and the thought kept bugging me…..have I settled for an inferior antenna just to make the grounds look better? One way to find out is to do some field strength measurements.
In the past we had tried a Marconi patterned after the one W6SAI wrote up in CQ a number of years ago. In place of a sixty-foot horizontal section, he used a sixty-eight foot long wire as the horizontal section and tuned it to resonance with a series capacitor of 400 pF. This antenna worked as well as a half wave doublet we were using at the time. But, it didn’t work any better and we took it down. This antenna only needed to be twenty four feet high and could be held up on one end by a TV mast on the house chimney and supported on the other end by the tower.
Checking with my old friend WOMDM, in Esterville, Iowa, with whom we have kept schedules for twenty five years, Mel couldn’t tell any difference between the two antennas. The next step was to borrow a field strength meter from a local radio station and make a few field measurements. I didn’t expect very high readings because we are in a typical housing addition with tall trees, power lines and expressways.
Field Measurements
To the south at one mile in the clear we measured 5 mV/m on the sloper and 8 mV on the Marconi. In all fairness, as the sloper ran northwest and this point was due south, it was not in the favored direction for the sloper. That measurement gave the Marconi a 2.56 dB advantage in that direction. Measurements at the one mile point in other directions were about the same for both antennas varying from 1.5 mV/m behind expressways to 2.5 mV/m in other places. At no other time could the antenna be seen from the measurement point.
Power to the antenna during the measurements was 50 watts. The whole point of this little exercise was to see if the sloper would hold its own with an antenna we knew worked well.
The overall height of the tower and antennas is about forty-eight feet. One time the tower was used as a 40 meter vertical with eleven radials, some as long as sixty feet along with three eight-foot ground rods. The Marconi used this ground system along with a sixty-three foot counterpoise run afoot high along the back fence afoot above ground.
One Null
The only null we found with the sloper is to the southeast off of the back of the antenna. In this direction reports from the southeast coastal areas are usually two S units higher on the Marconi. If I was a one-band operator on 75, I would give the Marconi a real try. I like to work many bands but, I will keep the Marconi because it fills in the coverage in the southeastern part of the country.
Even with the 160 loading coil added, the overall length is only sixty eight feet. The tower and antennas, being only forty-eight feet high makes for a small antenna on 160. Our measurements bore this out as the 160 readings run from 1.5 to 2 dB less than on 75 where the tower height is near a quarter wave and the sloper is a full quarter wave long
DXing
The DX we work is usually on 10 meters with some on 15 meters and, once in a while on 20. We can keep in touch with old friends around the country on the low bands and make new ones whenever we find the time to operate. After 41 years as a ham and now retired, there still never seems to be enough time.
Originally posted on the AntennaX Online Magazine by Glenn Thomas, W5INU
Last Updated : 25th April 2024