The 1010 Organization held their Summer Phone contest this past weekend. It gave me a chance to check out my "small vertical" and I was pleased with the antenna over all. I ended with 31 QSOs and 14 states distributed across the U.S.
My antenna is a Hygain 18 foot vertical with a loading coil at the base. It is ground mounted with 4 radials of 13 feet each and one ground rod. The loading coil is not needed on 20 meters, but I did have to use a couple of turns for 10 meters. I was able to work just about everyone I could hear.
On Saturday, contacts were few and far between. I only made about 5 the whole day. Sunday, however, things opened up and I made the rest of the contacts from about 10 a.m. until 3 p.m. IF I had started earlier, I'm sure I could have doubled my count.
Anyway, it was fun. Click here for the 1010 website.
...AR
Showing posts with label vertical. Show all posts
Showing posts with label vertical. Show all posts
Wednesday, August 05, 2009
Sunday, July 12, 2009
Vertical Antenna Ground System
When I come across really useful information, I just have to pass it along. Rudy Severns, N6LF, did an incredible amount of work during the spring of 2008 to evaluate the effect of radials on the effectiveness of 1/4 wave vertical antennas.
For the whole set of articles, click here:
In his Vertical Antenna Ground System Experiment No. 4, he makes the following observations:
1. If you are limited to 4 radials for whatever reason, you can SHORTEN the radials (from a 1/4 wave) by up to 40 percent and improve your gain by 2.9 dB. Or you can add a ground rod (4 ft.) and improve your signal gain by almost 3 dB. But doing both does not seem to improve things any more than doing either one. I know, read it for yourself.
2. If at all possible, use at least 8 radials. With the 8 radials you improve your signal gain by about 2.5 dB over the 4 radials and the gain can be improved to 3.9 dB by shortening your radials by about 40%.
3. If you can get to 16 radials, then you have overcome most of the ground losses and shortening the radials is no longer a major factor. He says, "I would think that with 32 or more radials, you wouldn't worry about resonances in the radial screen. The problem is only important when fewer than 16 radials are deployed over average or better soil."
There is a lot more information at his web site and I have not made it through all of it yet. Very good stuff!
... AR
For the whole set of articles, click here:
In his Vertical Antenna Ground System Experiment No. 4, he makes the following observations:
1. If you are limited to 4 radials for whatever reason, you can SHORTEN the radials (from a 1/4 wave) by up to 40 percent and improve your gain by 2.9 dB. Or you can add a ground rod (4 ft.) and improve your signal gain by almost 3 dB. But doing both does not seem to improve things any more than doing either one. I know, read it for yourself.
2. If at all possible, use at least 8 radials. With the 8 radials you improve your signal gain by about 2.5 dB over the 4 radials and the gain can be improved to 3.9 dB by shortening your radials by about 40%.
3. If you can get to 16 radials, then you have overcome most of the ground losses and shortening the radials is no longer a major factor. He says, "I would think that with 32 or more radials, you wouldn't worry about resonances in the radial screen. The problem is only important when fewer than 16 radials are deployed over average or better soil."
There is a lot more information at his web site and I have not made it through all of it yet. Very good stuff!
... AR
Sunday, July 05, 2009
Something You Already Knew - Maybe?
"My Feed Line Tunes My Antenna"... This article was written in the March 1956 issue of QST by Byron Goodman, W1DX. It has been reprinted twice since then - once in 1977 and once in 1991 so it has some good insight that has lasted with time.
Here are my excerpts from this ... basically, main points for me to remember. I hope these bits are useful reminders. I have to read this about once a day to keep it fresh in my mind ...
Here are my excerpts from this ... basically, main points for me to remember. I hope these bits are useful reminders. I have to read this about once a day to keep it fresh in my mind ...
When we say 50 ohm coax or 300 ohm twin-lead, we are talking about the characteristic impedance of the line. "Characteristic impedance of a transmission line is the value of resistance that when used as a termination for the line, makes the input impedance of the line independant of the electrical length of the line."
The simple view of this: A 50 ohm load (antenna or other resistance) on one end of your 50 ohm coax feed line will measure as a 50 ohm load at the other end of the line regardless of the actual length of the line. No tuner needed here because the load matches the characteristic impedance.
SO: The system is resonant and the whole load is resistance only.
SO: The system is resonant and the whole load is resistance only.
But what if your antenna is measured as a 100 ohm load and you are using a 50 ohm feedline? You no longer match the characteristic impedance of the line. The impedance you measure at the end of the line will vary depending on the electrical length of the line.
The electrical length of the feedline is measured in wavelengths. To calculate the electrical length of the feed line, you must know the frequency, the actual length (in feet) and the velocity factor. So your physical feed line might be 75 feet but the electrical length changes as you change frequencies.
When the antenna load is different from the feed line characteristic impedance then the impedance we measure changes as we move down the line.
The Half Wave Rule to remember:
Every 1/2 wavelength down the line, the impedance we measure equals the antenna load and, obviously, this changes with frequency. And this load is resistance only.
The Quarter Wave Rule to remeber:
Every quarter wavelength, the impedance we measure is resistance only but the value is not equal to the antenna load.
Who Cares? Well, I guess I do. The reminder here is that the antenna load is really a reactive load. The antenna load is a combination of resistance plus capacitance (capacitor) OR resistance plus inductance (coil). The tuners we use help to bring the reactance of the load to pure resistance.
The Half Wave Rule to remember:
Every 1/2 wavelength down the line, the impedance we measure equals the antenna load and, obviously, this changes with frequency. And this load is resistance only.
The Quarter Wave Rule to remeber:
Every quarter wavelength, the impedance we measure is resistance only but the value is not equal to the antenna load.
Who Cares? Well, I guess I do. The reminder here is that the antenna load is really a reactive load. The antenna load is a combination of resistance plus capacitance (capacitor) OR resistance plus inductance (coil). The tuners we use help to bring the reactance of the load to pure resistance.
Saturday, April 18, 2009
Short Antennas & Automatic Tuners
Or, when do automatic tuners make sense over a manual tuner?
I just found a fascinating article in the May 2008 QST ... actually, it was a short response under Technical Correspondence to an article on automatic tuners. But it answered a question I've had for a long time.
One quote that caught my attention: "...typically, the [automatic] tuners have a tough time when coupling to 'short' antennas whose RR (feedline impedance, if you will) is lower than the prescribed 50 ohms."
The author continues, "...you'll note that in the general instance of the longer -- lower frequency -- antennas, where the feed point (Load) Z is below 50 ohms, the automatic tuners are reticent to couple efficiently, whereas if the feed line Z is above 50 ohms, the tuner is efficient."
A couple of things come to mind ... first, in dealing with short vertical antennas, the antenna Z can be very low, hence the need for radials and/or baluns to match closer to 50 ohms.
Second, if your antenna is "short", whether a shortened 160M dipole or a short vertical, with an impedance of less than 50 ohms, you might want to consider using a manual tuner for better matching range.
If your antenna sports a Z close to or even higher than 50 ohms, the automatic tuners can handle the match easier. The antenna design impedance is affected by a combination of antenna length and height above ground.
This does explain why my auto tuner in my KW TS-440 cranks and cranks to match my NVIS antenna (G5RV at 6 feet high) but quickly tunes on my 40 meter doublet at 20 feet high.
One of these days, I'll have to measure what the impedance is on each of these two antennas.
Something to consider ... AR
I just found a fascinating article in the May 2008 QST ... actually, it was a short response under Technical Correspondence to an article on automatic tuners. But it answered a question I've had for a long time.
One quote that caught my attention: "...typically, the [automatic] tuners have a tough time when coupling to 'short' antennas whose RR (feedline impedance, if you will) is lower than the prescribed 50 ohms."
The author continues, "...you'll note that in the general instance of the longer -- lower frequency -- antennas, where the feed point (Load) Z is below 50 ohms, the automatic tuners are reticent to couple efficiently, whereas if the feed line Z is above 50 ohms, the tuner is efficient."
A couple of things come to mind ... first, in dealing with short vertical antennas, the antenna Z can be very low, hence the need for radials and/or baluns to match closer to 50 ohms.
Second, if your antenna is "short", whether a shortened 160M dipole or a short vertical, with an impedance of less than 50 ohms, you might want to consider using a manual tuner for better matching range.
If your antenna sports a Z close to or even higher than 50 ohms, the automatic tuners can handle the match easier. The antenna design impedance is affected by a combination of antenna length and height above ground.
This does explain why my auto tuner in my KW TS-440 cranks and cranks to match my NVIS antenna (G5RV at 6 feet high) but quickly tunes on my 40 meter doublet at 20 feet high.
One of these days, I'll have to measure what the impedance is on each of these two antennas.
Something to consider ... AR
Wednesday, March 25, 2009
What is a Short Vertical Antenna?
I'm quoting from Jerry Sevick's (W2FMI) book "The Short Vertical Antenna and Ground Radial". A short antenna has been defined as one that is small compared to a wavelength.
He gives the following equation on p. 10:
Beta*h less than 0.5
where Beta equals 2*pi / wavelength and h is the height of a ground-mounted vertical.
BTW: the "less than" sign confused the HTML publishing process so had to remove it.
Solving for h gives us the following equation:
h less than 0.5 * wavelength / 6.283
For 40m antenna, the h is less than 3.2 m. If we use 130 feet for the wavelength, then h is less than 10.35 feet. The author uses 11 feet for his purposes.
He maintains that a 40m 1/4 wavelength ground-mounted antenna has a power gain of 1.62 when compared to the mythical isotropic radiator. This antenna is 33 feet high. The 11 foot vertical has a power gain of 1.513! Pretty impressive, don't you think? But HOW?
He further comments that "the very small value of its input resistance" is the important property that makes its capture cross-section nearly equivalent of a full 1/4 wave vertical. A ground mounted 1/4 wavelength vertical has a theoretical input resistance of 35 ohms and a 20 foot has an input resistance of about 8 ohms while the 10 foot antenna has about 2.5 ohms input resistance.
I'm not sure I understand all of this either, but it is very interesting (to me anyway). Well, I have some more to reading to do....AR
He gives the following equation on p. 10:
Beta*h less than 0.5
where Beta equals 2*pi / wavelength and h is the height of a ground-mounted vertical.
BTW: the "less than" sign confused the HTML publishing process so had to remove it.
Solving for h gives us the following equation:
h less than 0.5 * wavelength / 6.283
For 40m antenna, the h is less than 3.2 m. If we use 130 feet for the wavelength, then h is less than 10.35 feet. The author uses 11 feet for his purposes.
He maintains that a 40m 1/4 wavelength ground-mounted antenna has a power gain of 1.62 when compared to the mythical isotropic radiator. This antenna is 33 feet high. The 11 foot vertical has a power gain of 1.513! Pretty impressive, don't you think? But HOW?
He further comments that "the very small value of its input resistance" is the important property that makes its capture cross-section nearly equivalent of a full 1/4 wave vertical. A ground mounted 1/4 wavelength vertical has a theoretical input resistance of 35 ohms and a 20 foot has an input resistance of about 8 ohms while the 10 foot antenna has about 2.5 ohms input resistance.
I'm not sure I understand all of this either, but it is very interesting (to me anyway). Well, I have some more to reading to do....AR
Short Wave Listening
Just listening to short wave broadcasts from Vietnam and China. Right now, I am using my 10M vertical - The antenna is 8 feet long and is ground mounted. Receiver is my FT-840 on AM. Times are UTC.
0340 - 0355 on 6175 kHz is the Voice of Vietnam. Signal is s7 to s8 on my s-meter with some QSB. The Listener's Service program is giving reports received from all over the world. This is an English language broadcast!
0355 - 0400 on 6190 kHz is the China Radio International signal. Signal is S9+. They just signed off from their English language broadcast, but the news program that came on at 0400 is also in English. Strange to hear our news from the Chinese perspective.
0430 - 0500 on 6140 kHz is the Radio Havana Cuba. Signal is S9. Had English language news followed by music. Great if you enjoy Cuban rhythm.
0340 - 0355 on 6175 kHz is the Voice of Vietnam. Signal is s7 to s8 on my s-meter with some QSB. The Listener's Service program is giving reports received from all over the world. This is an English language broadcast!
0355 - 0400 on 6190 kHz is the China Radio International signal. Signal is S9+. They just signed off from their English language broadcast, but the news program that came on at 0400 is also in English. Strange to hear our news from the Chinese perspective.
0430 - 0500 on 6140 kHz is the Radio Havana Cuba. Signal is S9. Had English language news followed by music. Great if you enjoy Cuban rhythm.
Monday, March 02, 2009
Short Vertical Antennas
"The Short Vertical Antenna and Ground Radial" book by Jerry Sevick, W2FMI, is loaded with thought-provoking information. I have been reviewing this book because I'm using a home-brew vertical produced by Tulsa Amateur Radio Club for $20. The 10 meter portion of this antenna just fits on my patio cover support post (4x4 wood post and I used a bunge cord to secure the antenna to it). I have been tuning this for 10 meters as a 1/4 wave-length and on 20 meters as a 1/8 wave-length. I have made contacts on both bands so I'm looking for ways to improve the efficiency of the antenna, i.e. more radials perhaps. So I've returned to Sevick's book for some insights.
In the preface, he says "...a very short antenna had about the same power gain and radiation pattern as a full size half-wave antenna. The main difference was that the resistive component of the input impedance, the radiation resistance, was very small in comparison to that of a 1/2-wavelength antenna and, depending on length, could be a matter of a few ohms. In turn, the short antenna has a very high capacitive reactance, which has to be canceled by various loading techniques. A short vertical has an even lower radiation resistance and, depending upon height, can be a matter of only 1 or 2 ohms."
A little background to put this in perspective might help. The antenna referred to is ground mounted and, as such, one of the main features of performance is signal loss to the earth. A half-wave that is ground mounted will have an impedance of about 35 ohms maximum when the ground losses are minimized. A short vertical will have a 1 or 2 ohm impedance with no radials.
One of the charts in the book shows that as radials are added, the antenna load impedance goes up (or gets better) because ground losses are lowered and eventually reaches a max of 35 ohms with 60 radials. Right now I'm using only 4 so I have lots of room for improvement.
His book spends a lot of time developing a short vertical for 40 meters, so my 20 meter antenna should be a little easier(?) ... AR
In the preface, he says "...a very short antenna had about the same power gain and radiation pattern as a full size half-wave antenna. The main difference was that the resistive component of the input impedance, the radiation resistance, was very small in comparison to that of a 1/2-wavelength antenna and, depending on length, could be a matter of a few ohms. In turn, the short antenna has a very high capacitive reactance, which has to be canceled by various loading techniques. A short vertical has an even lower radiation resistance and, depending upon height, can be a matter of only 1 or 2 ohms."
A little background to put this in perspective might help. The antenna referred to is ground mounted and, as such, one of the main features of performance is signal loss to the earth. A half-wave that is ground mounted will have an impedance of about 35 ohms maximum when the ground losses are minimized. A short vertical will have a 1 or 2 ohm impedance with no radials.
One of the charts in the book shows that as radials are added, the antenna load impedance goes up (or gets better) because ground losses are lowered and eventually reaches a max of 35 ohms with 60 radials. Right now I'm using only 4 so I have lots of room for improvement.
His book spends a lot of time developing a short vertical for 40 meters, so my 20 meter antenna should be a little easier(?) ... AR
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