Real World Comparison Vertical vs Dipole
I have both a vertical and a dipole for 40 & 15m and thought it might be useful to some of the new hams to do a comparison. In this first installment I'll describe the basic configuration, show the SWRs, and some noise level information. Next installment will include some comparisons of signal strengths from each antenna for stations at various distances.
Butternut HF2V with the 30 meter add-on coil. It is ground mounted with 33 buried radials, ranging from 25 to 50 feet long. Radials are insulated 14-gage solid copper house wire from Lowes. The antenna was tuned for minimum SWR in the middle of the 40m band.
Feedline from antenna base to outdoor common ground point is about 70 feet of RG-213, buried. No balun is used.
Horizontal between two trees. Oriented NorthEast - SouthWest. Height at feedpoint is about 30 feet. Height at ends about 35 feet. Length probably about 68-69 feet - exact length unknown - it was initially installed at about 70 feet overall length, then trimmed back to obtain lowest SWR in the middle of 15 meters. Constructed with 14 gage stranded copperweld.
Feedline from outside common ground point to antenna is approximately 70 feet of RG-8x, with a 8-turn, 9 inch diameter choke balun a couple feet below the feedpoint.
Cabling from outside common ground point to radio:
For both antennas, there are Alpha-Delta arrestors at the common ground panel on the outside of the masonry wall of the house. Transmission line from the common ground point through the the wall and to antenna switch is about 15 feet of LMR-240. Patch cables in the shack from Alpha-Delta antenna switch to antenna tuner about 2 feet of RG-8X. Patch cables from tuner to radio or analyzer is about 4 feet of RG-8X.
SWR Measurements and Tuner settings:
An MFJ-259B was used. First the SWR was measured for antennas without using a tuner. It was found that the vertical had low enough SWR without a tuner, but the dipole SWR was a bit higher. Then the Palstar AT-500 manual tuner was used to adjust the SWR of the dipole to 1:1 in the middle of the bands, then the dipole SWR remeasured across the bands. This is how I generally use it, rather than tuning for each individual frequency. I don't usually use the autotuner in the radio.
Background Noise Measurements:
Rig used was an FT-897D. To avoid having the Automatic Gain Control (AGC) skew the results, it was turned OFF. The RF gain was adjusted to 100% and the Attenuator (ATT) turned on to avoid strong signals saturating. The same radio settings were used for both antennas.
Since the S-Meter in the FT-897D relies upon AGC to work, another method of measuring signal and noise levels was needed when the AGC is off. A Rigblaster Plug and Play was used to interface the rig to the soundcard in a PC. The PC Line-In volume was set to 100%. The spectrum display in HRD/DM780 was set to 100 dB dynamic range and signal and noise levels were estimated from the spectrum display.
Background Noise Levels - No Signals in Pass Band:
Measurements taken at about noon local time today (Saturday). Additional measurements will be taken at other times to see if there's a difference. At noon the background noise from the Vertical was about 6 dB higher than from the Dipole on 40 meters, but about the same on both antennas on 15 meters.
Next installment will include some comparisons of signal strengths from the two antennas and noise levels at nighttime.
Last edited by NN4RH; 08-08-2009 at 06:17 PM.
Early AM Noise Levels:
Same noise level measurement set up as before but measured at 0500 local time. The noise levels for both antennas are about the same as they were around noon yesterday. If anything, the noise from the dipole got a few dB higher and now the difference between the vertical and dipole is only a few dB - not even noticable listening by ear. This surprised me a little - I expected it to be quieter at this time of the morning but it really wasn't.
Signal Comparisons Vertical vs Dipole:
Now to signal comparisons. The same method was used - with the AGC turned off and using the spectrum display in the DM780 program to estimate signal and noise levels. Note I never would actually operate with AGC turned off and RF gain maxed out. Normally I'd reduce the RF gain and use filters to achieve best perceived signal to noise and the AGC would usually be left on. But the purpose here is to compare the antennas on a level playing field, so the AGC has to be out of the picture and the RF Gain the same for both.
Anyway, I chose to tune to PSK-31 and RTTY signals since they provide a fairly steady signal level for a minute or two at a time, long enough to switch back and forth between antennas several times. Estimate the signal to noise on one antenna, and then signal to noise on the other. Then the difference between the two antennas. One example where the station was about 1800 miles away is attached below to illustrate the method used.
Obviously this is not an exact science as the noise and signal levels fluctuate around. Some sort of average is estimated.
The callsign is looked up in the QRZ data base to get the distance and bearing from my QTH. And I plot the difference between vertical and dipole versus distance to station. These are the results for eighteen stations last night between 9pm and 11pm local (0100-0300 UTC).
The vertical is expected to do better at long distances and the dipole better at short distances. While such a correlation seems to be there for the farthest stations heard last night, there is a lot of scatter in the trend at shorter distances. Sometimes the vertical is much better and sometimes the dipole is much better. And sometimes the difference is quite large and is opposite to what you might expect, even accounting for bearing from my QTH (i.e. whether the station is off the ends or the sides of the dipole). But, at least based on this small sample of stations, the vertical appears to have the expected advantage over the dipole at the farthest stations.
I'll add more stations to this compilation over a period of days and different times of the day, since the propagation conditions will affect this scatter plot.
Last edited by NN4RH; 08-09-2009 at 02:20 PM.
I added 16 daytime measurements during the day today. The closest one 80 miles away. The graph shows both these daytime stations and the ones from last night on the same graph.
Given the small sample size so far, it's not at all clear cut what the conclusion should be. Arguably there's still a trend of dipole being better for closer and vertical better for farther. But I'll continue to add more data points over the next several days.
More importantly, I think these data so far show that you can't just spend a few minutes doing an A-B comparison of S-meter readings on a two or three stations and conclude anything definitive about which antenna is "better". You have to collect a lot of data under different conditions.
That's why I have two kinds of antennas for 40 meters. If I'm trying to work a weak one, I try both and use whichever one is better for that particular case.
Good stuff, and agrees with my own observations on 40m.
I also have a HF2V with the 30 meter kit, ground mounted with 16 radials. Instead of a dipole, I have a G5RV up 30 feet, with the center supported on a TV mast on the roof of the house.
In my case, the G5RV is usually significantly more noisy than the vertical. It is much closer to all of the noise makers in the house.
Like you, I found that the vertical is usually better for DX, and the horizontal is usually better for closer stations. The difference becomes very significant with longer distances. For example, I easily worked VQ9 (9,326 miles) on the vertical, but could not hear him at all on the G5RV.
But sometimes, the result is not what I expect, and close stations will be louder on the vertical, or far stations will be louder on the G5RV. And sometimes that will change over the course of a few minutes. That's why it is good to have different types of antennas installed.
73, Ron KR2D
Added some more data during the week. Total of about 75 stations on this plot.
I think the conclusions are about the same. The gross trend is for the vertical to be better at the longer distances and the dipole better at the shorter distances. Between about 300 miles and 1000 miles, about the same.
There's a lot of scatter. As '2D said, about all you can say about the trends is usually.
And the differences may not even be noticable depending on how you use your filters, AGC, RF Gain etc.. to tweak your S/N for any particular station.
If the dipole was much higher, it would probably usually be better than the vertical in some directions and usually worse in other directions.
Basically, either type of antenna will serve quite well. If you can't have both then don't spend too much time fretting about it or overintellectualizing about it - just pick whatever fits your yard and your budget, and it will work just fine. It's more important to learn how to use your radio.