Antenna Basics

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Antenna Basics

Radio Waves

Radio energy waves are waves of energy that are similar to light waves. In fact signals (radio waves) travel through the air at the speed of light. To understand how an antenna works you must first have a basic idea of the makeup of a radio wave. A radio wave can be visualized as a sine wave, shown in figure 1. The distance a wave travels to complete one cycle is known as the wavelength of the signal. A CB signal completes a cycle as it travels through the air at roughly 36 feet. For every 36 feet the wave travels it has completed one cycle. Since we have defined wavelength as the distance a wave travels to complete one cycle, we now know that one wavelength on CB frequency is approximately 36 feet. So, radio waves are similar to light? What is the wavelength of visible light in feet? Smaller than two inches! Figure 2 show the relationship of CB frequencies to other bands. Continue reading→

Directional Antennas : Cubical Quad

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Directional Antennas

An antenna is known as “directional” if its pattern strongly favors a certain direction. A directional works by concentrating the signal in one direction at the expense of other directions. Also known as the “Beam” antenna.

Read the section on Yagi antennas if you are not familiar with directional (“beam”) antennas and how they work. Since the Cubical Quad works off the same principles, you must first understand the Yagi antenna. Continue reading→

Magnetic Loops by W2BRI

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Article by W2BRI

After many requests by Ben W4KSY*, someone I consider to be my loop mentor, I decided to post a page about my 80 meter magnetic loop. The idea for this loop began with my purchase of a new vertical antenna. Now when you think of 26 feet of antenna, it doesn’t seem that large until you put it together. Now add a couple of 1/4 wavelength 80 meter radials, and the vertical antenna solution starts to get big. Now, I’m into efficiency, and I wanted to string four radials five feet above ground at 90 degrees, and set the whole system up in the best possible way. However, when I moved into my new house, I had the disturbing reality that I had many power lines running across my property and I also didn’t have close to the room for 1/4 wavelength or even 1/8 wavelength radials (even for 40 meters). So I figured I’d never get on the low bands and I’d have to live with 20 meters forever. Don’t get me wrong, I love 20 Meters.

It’s no secret, I am a big fan of Force-12 antennas. I own a Force-12 C3SS triband beam, and can’t complain a bit about it. I call CQ on that antenna, and I get five people coming back to me almost every time. While I was at the ARRL conference last year I met Tom, N6BT one of the owners of Force-12, and picked up his book “Array of Light.” The book chronicles his experiences designing, building, and putting up thousands of antennas (yes, thousands!). It is a great book in my opinion, and a must read for those interested in understanding the ‘reality’ of antennas. As I went through the book I found a chapter on magnetic loop antennas and their high efficiency. The wheels in my head started turning, and I thought, I could manage putting up an 80 meter loop in my backyard. Maybe 80 meters isn’t out of my grasp.

So I picked up the phone and called Tom at Force-12 and asked him what he thought. He told me sure, he’d be happy to build a loop for me but the capacitor arrangement and the loop support would be my problem. I agreed and after several emails back and forth and a couple of months (and dollars), I received a very large box on the door steps of my house. The box was filled with 2 inch 4 foot lengths of aluminum. Each piece was tapered at the end so it would fit into another piece with about 3 inches of overlap. Then a bolt was inserted between the connected pieces, and each section was completed. the corners had a similar tapering, and it took a whole 15 minutes to put it together by the garage.

At first I used coaxial stubs for a capacitor. Tom suggested this strategy. You can cut coax and use it as a capacitor — take several different lengths of coaxial stubs equaling different amounts of capacitance, and move from band to band. I even loaded the loop onto 160 meters, but that’s another story for later. I built two wooden supports for the loop with my friend Steve, and we attached the loop into place. I was ready for 80 meter action.

Great, I had the loop built, but getting it to match and work was a whole different story. I had read many articles by Ben W4KSY about loops, so I thought since I was having some problems I’d ask him via email what to do. Well he was kind enough to instruct me about how the feed system works (the one from Tom was too small), and how to re-work it and what to expect. We emailed a bunch of times and I finally got it where I wanted it, 3.863 at 1.1 VSWR with about 10 KHZ in either side of bandwith (remember, with loops you don’t want a whole lot of bandwith — but this was an acceptable range).

With excitment that first night I turned on the rig to 3.863, and heard a bunch of guys in the bay area (from my QTH in Los Angeles). I popped my call in with 100 watts, and they came back first time around. I heard everyone in the round table, and everyone heard me. Night after night, QSO after QSO, 99% of the time, everyone hears me and I hear them. No problem. And this was during summer conditions. I worked many stations regularly from Oregon to mobiles in Wyoming, stations in Arizona, and others up and down the coast. Now when the propagation changes in early fall I am working stations farther out, Texas, Colorado, and Oklahoma. I am looking forward to winter conditions to give more reports.

I eventually upgraded the capacitor to a Jennings vacuum variable 5-750 pf with a over 12KV rating (cost around 200 bucks), and fixed on a motor to drive the capacitor up and down the bands. The motor controller is in the shack and I use a pair of DPDT relays connected to momentary pushbuttons to pulse the motor onto frequency. It works like a champ.

So, can you work 80 meters with a 12×12 loop 6 inches off the ground, yes! And you’ll have a blast doing it.

For more technical explanations I plan on adding more info relating to large loops on the site, and will be happy to email.

73,

Brian, W2BRI

this article was previously available at http://www.standpipe.com/w2bri/80meter.htm

Yamaha CM500 Replacement Ear Pads Cushions

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My Yamaha CM500 with deteriorated cushions

Replacing Yamaha CM500 Parts

Since some years I’m using the Yamaha CM500 headset. It’s a very comfortable headset, with a good microphone and it costs around 50 USD. I bought it directly in the USA since in europe this product was not available.

Recently I’ve noticed tha the ear pads of my Yamaha CM500 headset has started deteriorating, and therefore I’ve started looking for some replacement cushions or ear pads.

I’ve looked for them on ebay, on amazon and google, but with no success, no results came out from my extensive researches.

A post in my Facebook account, seeking for help, sorted out a link to an interesting audio shop

But even there, thought the assortment is really impressive, it ended up with a not-found.

Unfortunately, after having googled a lot, I arrive at the conclusion that Yamaha does not provide replacement parts at all for this kind of product.

The KOSS SB40

Thanks to a post in a forum I discovered that the Yamaha CM500 is the same of the KOSS SB40 headset, that is available in Italy also via Amazon

<br />

At a very reasonable price.

KEY FEATURES:

Noise cancelling microphone
Full range of sound brings games to life
Microphone eliminates excessive background noise for greater ease of use with PC voice applications, such as speech recognition
Soft leatherette ear cushions envelop ears for long-lasting comfort and maximum isolation without excess pressure
Adjustable headband fits most head sizes
Independent 3.5mm plugs for easy headphone and microphone connection

Yamaha CM500 Cushions

After having discovered this alternative, I started looking for replacement cushions or ear pads for the KOSS SB40, that is also the sister of the KOSS UB20 model, but without boom microphone.

A search for cushions for UB20 returned several options, under the 10 euros even in Amazon.

So, if you are looking to replace ear pads (cushions) for the Yamaha CM500 you could also look for the KOSS UB20 headsets that are more popular and well indexed in several online stores.

Update: Cushions Replaced

Received the new Yamaha CM500 compatible cushions in two days from Amazon, and I’ve replaced them.

Original Yamaha vs Compatible

As you can note the new cushions are very similar but not identical.
They are half centimeter larger that the original ones, but the internal space half centimeter smaller that is even better!

Quality from my point of view is better, than originals, keep in mind that these cushions also replace sennheiser headsets….

The fact that they are a little bit larger is not really a big problem since they fit very well and make te assembling process easier.

Just a note about the final assembling, the original ones have 3 pre-made holes in correspondence of the 3 screws thay are used to close the eard pads. I hade to make it with the screwdriver. Dismantle is very eady, reassembly has been more problematic in the earpad hosting the mic boom. But over all easy.

Yamaha CM 500 ear pad cushions replaced with new spare parts

An effective 3 Band Wire DX Antenna

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First, please excuse my artistic abilities. The diagrams are basic but show the rudiments of this excellent aerial, which is ideal for the newcomer to HF and those on a small budget as well as those with little space to erect large arrays!

Please note that my calculations are worked out using feet and inches because that’s what I grew up with! The reader who understands the Metric System should have no difficulty in converting to Centimetres and Millimetres but this article will use Feet and Inches.

Before outlining the construction, I would just add that when I was first licensed, I tried various aerials, verticals; inverted V’s, inverted L’s and wire dipoles. I finally gave this design a go. It was a brilliant success and I had a confirmed (QSL Card) contact with CE0ERY Hector on Easter Island on 30/04/1984 quickly followed by VK’s, ZL’s, and a string of exotic DX throughout the Indian and Pacific oceans.

YES using this same design I am about to explain to you in the following paragraphs!

WHAT YOU WILL NEED

You will need some wire…I have always found that old or new house wiring cable is an excellent source of wire but will need to be stripped from the grey outer insulation. The red and black pair of wires needs to be further stripped from their coverings. If you don’t fancy this task, it will still work, BUT it’s better to use naked copper wire for best results.

Here’s how I strip wire in long lengths.

First I use side cutters and cut into the wire from the end, trying to keep close to the bare earth wire that is in the centre of the cable and which runs along the length.

Once I can get a grip on the end of this earth wire with a pair of long nose pliers, I twist a few turns around the nose of the pliers and gently pull. Soon there will be enough slack grey outer sleeve to allow it to be held in place with the feet standing on it firmly. I have also tied the end of the grey insulation (with red and black wires) to a door handle or vice handle.

Once the thin earth wire starts to strip it usually comes easily as long as a steady firm pressure is applied and sudden jerks are avoided. When the thin wire has been removed from the entire length, having acted like a cheese cutting wire, the red and black should peel out without any bother.

Continue reading→

HF antennas for high rise dwellers

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If you have ever tried transmitting on HF from a tall block of apartments, where it’s just not possible to erect a substantial aerial system, then this article is for YOU!

If you have never had to try…consider yourself extremely fortunate!

The limitations imposed are not so much that of limited space (although this can be a problem) but strict Rules and Regulations that prevent the erection of any beam or vertical rod aerial.

However, the very fact that the signal is going to leap into space from a good height above ground can be, in certain respects, a bonus, so all is not lost.

It IS possible to install an aerial…a wire aerial and using low power to enjoy some interesting contacts. The satisfaction of making contacts can be most rewarding.

What we need to do is be a little sneaky here. By this, I mean that we should just fit a length of wire, discreetly, tune it up and have a go! Perhaps you have already discovered or learned from others that applying in the normal way for permission will, almost certainly, result in the request being denied.

Continue reading→

Getting started on FT8

Posted in Ham Radio 2.0, Ham Radio Software 3 Comments

Last night I’ve finally found the time to start experimenting the new FT8 digital mode, directy from my iMac.

FT8 QSOs

It’s still too early to give a feedback, but I’ve been really impressed by the automatic (auto sequence) mode, that allows automatic QSOs starting from the Calling CQ till the final 73!.

Well, honestly I’ve found it very easy to setup, but also too much automatic, allowing my iMac to conduct several QSOs in behalf of me without requiring my interaction. Absolutely inpersonal and totally asectic.

At the very first, I’ve downloaded the current stable WSJT-X version 1.7, but I’ve suddenly realized that FT8 was not implemented in that version, and therefore I’ve decided to download the 1.8 rc2.

Configuration, required some changes on OSX settings, and a reboot, while the connection to my TS-590S required some tricks. I copied the settings from the RUMlog configuration, and it worked immediately.

TS-590S MacOSX

Comet CHA250B Review

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While evaluating HF multiband vertical antenna I found this interesting review about the CHA250B by Comet.

I saved for further reference, author is K3DAV whose site is gone qrt.

Comet CHA250B HF Vertical

By David – K3DAV (2/7/2012)

There are a few compromise HF vertical antennas within the same class as the Comet CHA250B on the market.

“BUTTERNUT” makes the HF6VX, but you need to buy extra kits to add some of the bands. That
doesn’t make much sense.

“DIAMOND” has one similar to the Comet called the BB7V. It has a cheap design with a separate
add-on load coil with a flimsy wire that connects the coil to the main element. That doesn’t
make much sense either.

“GAP ANTENNA” makes the TITAN-DX. But in reality, it is a center fed vertical dipole. Only the
top half is a main radiator. And this thing has way too many ugly radials sticking out in all
directions that can break off in the wind. This thing is an eye-sore.

“HUSTLER” has the 6-BTV. Not a bad antenna, but it is loaded with several power robbing
band traps. Again this makes no sense.

“HY-GAIN” has the AV-18AVQII, but again with all of those power thieving traps for certain
bands, and a separate add-on load coil for 80 meters. What’s up with that?

“JETSTREAM” makes a real look-a-like, copycat version of the CHA250B called the JTV680. But
the JTV680 is made of thinner lower grade aluminum that will break easier in the wind, and
the coil is basically a fat 50 ohm resistor type that sucks power away.

And every one of those antennas have high SWR throughout the HF band that requires you to have or purchase an antenna tuner. That means they all have a poor impeadence match which robs even MORE of your power. (Except the JTV680 which just uses a big fat resistor to rob your power.)

Then there is my favorite.

The little antenna that could.

Just to reassure you, I do not work for NCG Company, (the parent company of Comet antennas), and they do not pay me for this review. I am just so impressed by the performance of the CHA250B, that I thought it was worth a page on my website. So take every word I say here as pure and quite honest. And I never exaggerate.

The Comet CHA250B HF Vertical.

I fondly call it my 24 foot dummy load. The design of this antenna is so simple it is almost stupid. At first glance, it is pleasing to the eye. Nice shiney aluminum standing tall, and that’s it. No big ugly radials anywhere from head to toe. More importantly, there are NO FREQUENCY TRAP COILS to suck away your power. The entire length is one continuous piece of aluminum tubing, and the whole element radiates RF at all times. Actually, it kinda looks like an old style CB antenna. My first thought was, how can this thing work? It’s just a balun with aluminum tubing far too short for frequencies below 15 meters. But after my experiences using this antenna, I can tell you, IT WORKS pretty damn good. At least much better than I ever expected it would.

A diagram of the matching transformer built-into the big round black housing within the mounting bracket.

Before you decide to purchase one, keep in mind that this antenna is a compromise antenna. It will not give you top performance like a monster yagi or a perfectly cut dipole up high. But if you are space restricted like me, and want a good HF vertical to get you talking on HF, this is the one antenna to own. As I have told many hams who laugh at this antenna, “You may not give the guy in Australia a big 20 or 30dB signal, but I gave them an S-9 signal, and we had a very nice QSO.” And isn’t that the whole point of ham radio? Making the contact, and possibly a new friend? Also keep in mind that you can NEVER use a linear on this antenna. It can handle a maximum of 250 watts SSB, but only 125 watts on AM & FM. This antenna is for the space restricted ham who only uses the 100 watts of power out the back of the radio.

These are quotes from the NCG website about their own product….

“If you have the space, budget and desire to erect a full size antenna system we suggest you do so… bigger IS better. However…if you live in an antenna restricted area and must manage with antenna or space restrictions, or you simply wish to operate incognito, you will be forced to make significant antenna compromises. The CHA-250B will make the most of these circumstances!”
“The Comet CHA-250B is a newly design broadband vertical with NO GROUND RADIALS. This antenna is EXTREMELY easy to assemble, requires no tuning or adjustments and VSWR is under 1.6:1 from 3.5MHz – 57MHz!”

And for you guys who already have yagis or dipoles on huge towers, the CHA250B is a good standby, or can be used as just a good omnidirectional monitoring antenna to see what’s on the bands. This antenna is quiet with great ears. And it covers the entire HF spectrum, so it makes a fantastic general coverage antenna. It also covers TX on the MARS/CAP frequencies.

The CHA250B comes in 5 pieces. Assembly took me 20 minutes. The entire antenna is 6068 aircraft aluminum, and fits together easily. Each section going up fits inside the one below it. Two of the sections are pre measured with pre tapped holes for inserting a small sheet metal screw. The other two sections must be measured to set them correctly. They too slide inside the lower section, but are held in place with a hose clamp. You only need to measure the element a few inches from the bottom end that slides into the other section. The instructions give you the exact measurements to use. Mark the measurement with a marker or a scratch, then insert the element exactly to the mark, then tighten the clamp. Then you are ready to raise the antenna into it’s new home. From opening the box to complete installation took about an hour.

The specifications for the CHA250B are very simple. Here is how the NCG website list them.

Broadband: TX 3.5 – 57MHz RX 2.0 – 90MHz
VSWR: 1.6:1 or less
Max Power: 250W SSB, 125W AM-FM
Impedance: 50 Ohm
Length: 23’5″
Weight: 7 lbs 1 oz
Connector: SO-239
Mast Size Required: 1″-2″ diameter
Max Wind Speed: 67MPH

The following is the measured wavelengths on particular bands for the CHA250B. No tuner is needed except for 160M as this antenna is not designed for use on 160 meters.

At 1.900MHz this antenna equals a 0.045 wave. (Ant. Tuner Required)
At 3.600MHz = 0.084 wave.
At 60 meters = 0.120 1/8) wave.
At 7.100MHz = 0.166 wave.
At 10.130MHz = 0.236 (1/4) wave.
At 14.200MHz = 0.331 (1/3) wave.
At 18.170MHz = 0.424 wave.
At 21.200MHz = 0.495 (1/2) wave.
At 24.950MHz = 0.582 (5/8) wave.
At 28.500MHz = 0.665 (2/3) wave.
And finally at 50.000MHz = 1.165 wave. Too long for 6M, but still works.

NO TUNER REQUIRED FOR HF. NO KIDDING!

The entire antenna is just over 24 feet tall including the base load coil and mounting bracket. The coil is built into the bracket, and is the most important part of the antenna. The coil is built like a transformer, and provides a nice 50 ohm load on all bands. NO JOKING! I put my MFJ-269 analyzer on this antenna including the 60 feet of coax into the shack. I can spin the tune dial on the analyzer from 3.5MHz continuously scanning the entire HF spectrum through 54 MHz, and the SWR never goes above a 1.6. It is usually near flat except for a few band edges. When I checked below 3.5MHz or above 54MHz, the SWR starts to climb fast. But between those two frequencies, it is great. Even on 60 meters. I am not exaggerating. It really is that good. You do not need a tuner with this antenna on any HF band. As I said, the load coil is a transformer, but it acts sort of like a dummy load. They take a tap from the coil through capacitance to feed the main element.

There is only one exception, and that is on 160 meters. The CHA250B is not designed to cover 160M, so a tuner is necessary. See down below for more details about this antenna and 160 meters.

No counterpoise or radials required. REALLY!

But they can help.

Because of the load coil design which uses the coax or metal mounting pole as a counterpoise, you do not need ground radials or counterpoise wires with the CHA250B. It works quite well without them. I can tell you this from my experience. My first contact on this antenna was a ham in Scotland on 20 meters. I only use the 100 watts from my Icom 746PRO. We talked for about 15 minutes and he gave me a signal report of S-9 to 10dB. I had about the same on him. He never seemed to have any problems hearing what I said, as he always responded to the points or questions I made. I knew at that point that this antenna was pretty good. By the way, I only use LMR-400 coax with all of my antennas including the CHA250B.

I used to talk with a few guys in a free-for-all QSO just before sundown every night on 75 meters. 3805kc to be exact. I am in central PA near Harrisburg. The others were all around PA with one guy in upstate NY. He would get an S-5 or S-6 from my little antenna over 120 miles away. But after the sun went down, I talked up and down the eastern seaboard. A friend close by to me suggested I install a couple of counterpoise wires. So we cut 2 wires, one at a 1/4 wave on 75 meters, and the other to a 1/4 wave on 40 meters. My friend in upstate NY said my signal went up to an S-9, bordering on 10dB. So it made an improvement. This is something to note about the CHA250B. It can run without the counterpoise wires, but it helps to add them.

BUT! There’s A Bonus Feature I didn’t Count On.

160 METERS.

The CHA250B antenna is not designed to work below 80 meters. At least according to the manufacturer. But just out of curiosity, I tried it on 160 meters. Keep in mind that my CHA250B is only 20 feet from it’s mounting bracket to the ground, and I use LMR-400 coax. So as they say, “your milage may vary”. The SWR on 160M is right on a 3.0. I hit the button for the auto-tuner in my 746PRO, and in 5 seconds it tuned it to flat. So far on 160 meters, I have worked NY, NJ, IA,OH, IN, VA, and NC. Not too shaby for a 23.8 foot dummy load. I know it is nothing compared to a good 160M dipole, but it works and I made contacts.

As for performance the CHA250B actually covers the frequencies as advertised, but it has it’s limits. I have found the CHA250B to work very well on 75/80, 60, 40, and 20 meters. I have now worked all continents (Except Antartica) on those bands with it. Usually with good reports. I have even broken through pile-ups with just 100 watts. But as you go above in frequency, the performance slightly drops off, but not so bad that you can’t still make good DX contacts. I find 17 and 15 meters to be pretty good. 12 and 10 meters is fair to OK, but it could be better. But even though the manufacturer says it works on 6 meters, it is fair to poor on 6 meter performance. It is over a full wave on 6M, so I didn’t expect too much up there. My old GP-15 was 200% better on 6 meters. But it does work there.

So I have come to certain conclusions on my antennas. The CHA250B works very well for me on 160 through 20 meters. So they are the bands I use this antenna for. I have a Solarcon I-MAX 2000 for 17 through 10 meters. The I-MAX 2000 is the best vertical antenna for these bands. It performs better on 17 and 15 meters, but a whole lot better on 12 and 10 meters than the CHA250B. And I already have a Comet GP-9 for 2M/440, and a Dominator 6M for 6 meters.

I know of several hams that have purchased the other brand name verticals I mentioned at the beginning of this article, and they were not all that happy. I talked them into trying the CHA250B, and they were very surprised at how well it works for what it is. They all agreed it was an improvement over their original HF vertical purchases. All of us so far believe that it works at least better than we thought it would for a compromise antenna with such a simple design.If you have any questions about the CHA250B contact me at kedav@msn.com

Vertical antenna for ham radio 40 meter band

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PY1BEK Vertical antenna for ham radio – 40-meter ham band (7 MHz)

This self-supported vertical antenna was made with aluminum tubes of 3 m in length that have an external diameter of 32 mm and a wall thickness of 1.2 mm. The total length of the radiating system is 10.33 m and its square-shaped base measures 25 cm on a side.
To the theoretical length (1/4 lambda) was added 4% due to the width of the antenna.

The various lateral stabilizing and connecting rods of the tower are made from rectangular shaped aluminum bar (17.0 mm x 6.5 mm) and are secured to the tubes with pop-rivets that are 1/2″x 3/16″ in diameter.
Those rivets are much better than bolts and nuts – completely free of galvanic corrosion (same metal) and the pressure achieved with an hand tool will be more than sufficient to make a solid mechanical and electrical connection good for many years.

Here is a summarized list of materials: a total of nine (9) 3.0 m aluminum tubes have been used, one (1) 50mm diameter PVC tube, 2.5 m in length, 12 meters of aluminum bar (the stabilizing rods), 140 aluminum pop-rivets, and 9 inox steel braces of 45 mm in diameter.
The total weight of the radiating system is less than 15 kg, perfectly supporting winds of 90 Km/h as a lower limit in a computerized simulation and without the necessity of stays.
Since the revision date of this article, the antenna is already more than 3 years old and its efficiency is the same as when it was mounted.

The unions between the aluminum tubes was made with small pieces of copper pipe 20 cm in length and whose external diameters fit perfectly in the interiors of the aluminum tubes.
Small longitudinal “ridge” cuts (10 mm) on the tips of the aluminum tubes have allowed them to be firmly pressed, with the inox steel braces, onto the copper pipes and make good electric and mechanical contact.
The four insulators of the base of the antenna are made with Brazilian “TIGRE” PVC reducer unions.
Four (4) sections of weldable PVC (brown core), 50 mm in diameter have been used, with 60 cm of length embedded in the center of the concrete base and on the exterior tips (80 mm) two reducer unions have been joined with “TIGRE” PVC glue.
In the center are positioned 32/40 mm reducers that are then coupled via 40/50mm reducers to the 50 mm diameter PVC.
Glue is also applied on the tip of the pipe displayed above of the concrete mass.
In these insulators the four feet of the antenna are placed.
They are introduced 30 mm inside of the lesser sleeve, until they’re jammed inside.
Completing the setting, four screws of 3/16″ x 2″ cross the interior of each insulator, thus securing the antenna to the support.
The tower properly set has an upper part formed by a 6 m mast with a single tube sliding portion of 5m by which Standing Wave Ratio (SWR) adjustments can be made. After the adjustment, single inox steel brace will keep the upper mast in position.

The support insulator was buried to the soil with concrete (cement, rock dust, and 20mm stone aggregate at ratio of 1:4:4) in a squared hole of 40 cm width and 80 cm deep. In the deep end of the hole four linked 2.4 m copperweld poles had been inserted and interconnected with 25 mm2 flexible cable so they will be part of the grounding.
Measurements made with a milli-ohmmeter resulted in a 3.6 ohm when all the poles were in place.
Beyond the copperweld poles, a system of 13 radial of 10 m length, using sections of flexible copper wire (1.5 mm in 2 sections) were attached to the ground terminal.
These wires are embedded and hidden to a depth of 10 cm underground and complete the grounding.
The fact that, as embedded, the radials lose their resonance means that their exact length is not very significant.
However, their combined effect on impedance is not negligible. In practice, the ground impedance obtained was around 20 ohms.
This was then added to the theoretical impedance (35 ohms) of the 1/4 wave antenna which then became close to the 50 ohms necessary for correct adaptation to the coax cable RG-213. With the low Q of the antenna, the SWR over the whole band was well below 1.2:1.

In the top, an element was placed as a driver for the 50 MHz band, transforming the upper part of the antenna to a 1/2 wave radiator for 6 meters (3 DB of gain over isotropic). The J-Pole was made with copper pipe of 15 mm diameter and whose length was 1.47 m. It has an independent coax cable of RG-213 that goes down into the interior of one of the tubes of the antenna. This element for 50 MHz does not interfere with the main antenna that continues to resonate at 7 MHz. The SWR at 50.500 MHz is 1.0:1 and reaches 1.2:1 between 50.000 and 51.000 MHz.
My next experiment will be in making a radiating system with a J-Pole for 10 meters whose photos will be published upon its successful completion.

More information on vertical antennas can be found at this excellent site of L. B. Cebik, W4RNL.

Also, I would sincerely thanks the impressive cooperation of Ken Beck, WI7B helping us with this English translation.

73, Sergio Valente, PY1BEK

http://svcglobal.com/antena/index.html