Radials

[Jeff W9GY]

When I got my 70 ft. shunt fed tower going on 160, initially I had only a few radials (and short ones, too boot, since I live on a postage stamp).  As I added radials, the main thing that I noticed was the improved stability of the tuning at the base of the shunt wire.  This unit is adjusted to match the shunt wire to the 50 ohm coax from the transmitter. Now that there are lots of (short) radials, the match to the 50 ohm coax essentially doesn't change with season of the year, or other weather conditions.

[Gito]

Hallo


Say that we can get a SWR 1:1 and use lost free  CO-ax to feed the Antenna.

Js said that the input resistance is 43 Ohm,the Question is is this the Ra (radiation resistance) ,I think it consist of Ra +R ground+ R of the cable/wire

If we used an 50 foot (15 meter ) vertical and top loaded with 20 meter right and 20 meter left (half of the dipole) ,how big is the radiation resistance?

As We know top loading does not make the Ra of the antenna bigger,the purpose is making the C as big as possible ,so we can resonant the Antenna without a Loading coil,because the R of the coil add looses

So the 15 meter vertical Antenna is the part that actually radiate ,and such a short Antenna on 160 meter band has only +/-  8 ohm Ra (radiation resistance)

So the input resistance Antenna is 43 Ohm,since the Ra is 8 Ohm,The ground and cable resistance is 43-8 Ohm=35 Ohm,So the eficiency of this Antenna is 8/43 X 100%= 18 %

Don is right, maybe 1 or 2 radials won't affect  the ground resistance,using more radials will make your antenna more efficient.and using antenna tuner or anything to get a low SWR.

Thanks


Gito.

[k4kyv]

If you want to see some real bone-headed hammy hambone ideas about installing radials, check out this link, and be sure to read the follow-ups:

http://www.eham.net/articles/21438

[kz0e]

Any opinions on screens? Sherwood engineering has a pdf up on his site, he's pretty positive about relatively small sections of screen under a vertical. Could be a good solution for limited real estate.

http://www.sherweng.com/documents/GroundScreen-sm.pdf

Larry

[W2DU]

Don, I'm long overdue in reporting that I'm constantly impressed with the writing in your posts--clear, concise, grammatically correct, and always on the money for accuracy. Creative, too, especially in your use of hypotheticals with square-wave cw pulses in your explanation of amplitude modulation--awesome! And it's obvious that your posts reflect wide experience in a number of areas. I don't know your background, but if you have been a teacher I would loved to have been one of your students.

I read the responses concerning the sink drain as a termination of radials. It's positively amazing that nearly all of the responses thought it a great idea, while only one or two recognized (as you did) the possibility (no, the probability) that the bolt-nut combination would loosen, resulting in a poor and intermittent connection. Your emphasizing the necessity of brazing the connections to avoid corrosion was right on.

Unless he was thinking only of elevated radials, one poster considered having radials cut for the correct length for various bands, instead of understanding that radials designed for the lowest-frequency band are just great for the higher-frequency bands as well.

Keep your posts coming, Don, I enjoy reading every one of them!

Walt, W2DU