Antenna Summer – part 2
With some unavoidable chores out of the way I finally went further on my quest to erect a better antenna for 20 meters. The question asked last time on why the rooftop vertical performed below par was solved pretty quickly: the ground connection to the coax lead had come loose and after I fixed that it performed better, but still not as well as the garden vertical (the garden vertical about 10 dB better than the rooftop vertical).
VK3DZ made an interesting remark in the comments on my last article: “keep VHF antennas at least 12 meters high to avoid short-range noise.” My antenna is for HF, but the more distance from noise sources the better and maybe more distance from the metal roof would also help. So I got my fiberglass poles out and put the garden vertical up on the roof, 4 meters above the metal roof.
A good comparison could be made with the other vertical, but the difference was minimal: signals strengths were comparable and noise levels were the same. After a couple of days I put the garden vertical back in the garden and put my delta loop for 6 meters on the roof.
In a private e-mail exchange a while back Steve (VE7SL) wondered if tying the ground connection directly to the metal roof would have an effect. The question was related to long- and medium wave reception, however it would be a good experiment to see if it would have an effect on my rooftop vertical. Up till now my ground connection has been a single 90 cm ground rod, which did a good job of syphoning off some noise. When I bought that rod my local hardware store said that the longest one they had was 90 centimeters (3 foot), but when I went out to buy some more there recently they gave me 180 centimeter ones (6 foot). I got two for about US$15, so well within my budget. I connected them with twin solid core electrical copper wire and after an hour of pounding on them in 35 degree heat (Celsius, not Fahrenheit) they were in.On medium- and longwave the difference was huge: a 10+ dB gain across those two bands. On 20 meters it didn’t matter at all, but it was a nice experiment and at least I have a better ground system now.
Unfortunately we had a typhoon coming through and it damaged the garden vertical. After fixing it I will have to make plans for the next antenna experiment.
Pounding in those ground rods and be made much easier with a tool that is designed to pound in metal fence posts. It consists of a section of heavy pipe about one to 1/2 ft long with a cap on the end and a couple of metal handles formed from an elongated U-shaped rod that is welded on opposite sides of the heavy pipe. The pipe is then capped with a metal disk that is welded on one end. This “tool” is then slipped over the end of the metal fence post, or over the end of the ground rod in this case, and a series of lifting the “tool” and forcing it down with some force will then make the fence post/ground rod down into the earth. Such “tools” can be bought at places like Lowes and Home Depot for somewhere around $20 US. Cannot find this in an online search but I bought two at Lowes at two different times. They were found near the T-posts.
Several good videos are available for driving in ground rods. Here is one:
Here’s one showing how to use a common hammer drill (recommended method):
I have also used a water pipe connected to a 10-ft section of conduit with water forced into the end. The pipe “migrates” down into the earth very quickly and leaves a hole that a ground rod falls into plus allows one to add some salt for better conductivity. This will not get far in rocky soil of soil with layers of clay as is sometimes encountered. Note that I have also read that kitty litter also forms a good connection between the ground rod and ground…
Note that the video of the “recommended method” has a notice that it is dangerous to weld to galvanized material. I have read that this can release Phosgene gas but welders advise that when you weld zinc-related material, use a fan to blow the gases away from you as you weld. Of course, you can merely use “black pipe” fittings and avoid this “warning” completely.
so what about producing antennas which do not comply to the normal criteria.
a good example is the standard half wave dipole for a particular band.
By making it two or three wavelengths longer it will give a better capture of the signals and does produce gain as well.
so i just want to float these ideas past you.
Best regards Robert G6LLP
WHERE YOU WANT GROUND ROD.
1 DIG A “BOWL” SHAPED HOLE 6I 8 IN. DEEP.
2 FILL W/ WATER AND LET STAND ABOUT 2 MINS.
3 PUT END OF ROD DOWN IN CENTER OF HOLE AND SINK
AS DEEP AS U CAN BY PUSHING DOWN ON IT.
ADD MORE WATER AND BEGIN “CHURNING” WITH AN
UP AND DOWN MOTION UNTIL IT BEGINS TO SINK MORE.
4 I KEEP IT UP AND YOU WILL SINK IT W/O MUSHROOMING THE
END OF IT.
THE POST DRIVERS ARE CALLED “SLIDE HAMMERS” U CAN MAKE UR OWN
BY WELDING A WEIGHT OF SOME SORT ON THE END OF A PIECE OF PIPE.
PROB. IS; THEYRE NOT VERY LONG 24 – 30″
BTW, HR LIVE NR ST. LOUIS, MO.- SEVERAL OIL REFINERIES NEARBY.
EACH OF THEIR STORAGE TANKS HAS 40 – 10′ GROUND RODS AROUND THE PERIPHERY.
OLD DAYS THAT WAS HOW THEY DID IT.
STILL DO ARND HR FOR 1 OR 2 RODS.
’73 RICH KF9F
I would think you didn’t see improvement on 20 meters due to the length of the conductors to the new ground rods. At lower frequencies the new ground is functioning as an RF ground as the conductors are well under a quarter wavelength. Hence, very low inductance/ reactance at those freqs. As you go higher the length of those conductors makes them more ‘interesting’ to the antenna system. RF grounds at higher frequencies can be difficult due to the ground system conductors starting to act like transmission lines.
@Lowell NE4EB – Yes, I realized that, too. I didn’t think reception would improve on 20 meters, but I hoped that it would have a positive influence on the noise floor, even a little.
With the winter approaching it is still good to have a decent earth system. I hope I can do some top band DX the coming season.
Rich KF9F’s comment about the name of the driver being a Slide Hammer was the trick. Putting this term into startpage.com gave me a video that demonstrates the tool and shows how it is used. One can be made easily with a section of heavy pipe about 20-inches long and access to a welder.
Here is the video:
Where I live, the soil is part of a valley that once was flooded every year so the ground system is relatively good. Of course, though, the number of ground rods is always a factor…!!! But living in a near swamp is not a problem as it would be for someone who lives in the desert where everything is dry.
As for dipole antennas as suggested by Robert G6LLP, where I live I’ve found that an end-fed dipole with a radiating element 53-ft long and a 16-ft counterpoise gives me access to 160-10 Meters plus 6 Meters. I use the built-in tuner on the FT-450 and it never fails to give a useful match. It is also good as an AM broadcast antenna rivaling the 80M G5RV on the MW band and for SW broadcasters. Note that the way the feedline is dressed is crucial: It must be dressed away from the main element and is under the 16-ft counterpoise. I use a 9:1 unun at the feedpoint and about 20-ft from the feedpoint, I use a 1:1 balun to eliminate RF possibly feeding back into the shack. The 20-ft of coax forms another part of the counterpoise. Note that if the coax is not fed away from the 53-ft section and back under the counterpoise, it does not allow use of the lower HF bands. In fact, this arrangement gives me 160M and 80M where it was not tunable before. I’m not prepared to say how efficient the antenna is actually but it does load up and is a relatively low-noise antenna on MW and SW broadcase, comparable to the OCF MFJ 40M dipole and the G5RV. For the amount of investment, I like it and must praise it.
Here is another T-post (or ground rod) driver video and shows another source for them. I still like the idea of the hammer drill and must try it soon.
Here’s the video: