# Antennas

I’ve been scratching my head for years how to model an appropriate ground with my ground mounted Vertical Antenna radials.

I’d like to thank Sigi, DG9BFC for clearing this up for me.

HOW TO:

NOTE: I like to draw a small feedpoint in all my HF antenna models, like a 5cm length of wire where my “source” (coax) is connected to. Particularly useful for fan dipoles and for making other adjustments. I’ve left that part out for simplicity on this How To since I’m trying to make this super easy.

• Go to Edit > Wire Edit (CTRL-W) and click on the XZ (or YZ) button, bottom right of the Wire Edit screen.
• Click on the New Wire button and draw a line from Z=0 (the ground) straight up for 10m length.
• Click OK.
• Go to the Geometry tab and in Sources (bottom left), type W1B (Wire 1, Base).
• Click the View tab and ensure that the source is at the bottom of the antenna.
• Now head over to Calculate and type in the Freq box “7.2”.
• In the Ground section, click on “Real” and also click the “Ground setup” button.
• You may the leave the Dielec and Ground conductivity as the default. If you want some accuracy, check my link at bottom of this article. I am often near the sea at my holiday QTH so I adjust these up a little bit to 20 and 10 respectively. Pure salt water is much higher than that.
• Click OK and you are now “Good to go”. Hit the Start button and you should see an impedance of around 35 ohms and SWR around 1.5:1. The antenna is actually fractionally short, so you may lengthen to suit.

That’s it! Years of work trying to figure this out and Sigi showed me today.

Of course, do NOT raise the antenna off the ground. The antenna needs to touch. So if you find something it wrong, you may find the antenna wire that you are feeding isn’t touching ground with Z=0.

Note: if your feedpoint ends up at the top of the wire and not the bottom, change W1B to W1E (Wire 1 Base -to- Wire 1 End). That’s it.

Ground Conductivity. A very heavy article can be found here: https://www.qrz.ru/schemes/contribute/arrl/chap3.pdf however for sake of simplicity, see the chart in the last picture in the gallery on this page.

# DX Commander now shipping to USA / Canada / Aus

After much research, I’ve managed to get the price to under £30 for USA, an additional £10 for Canada with Russia and Australia incurring extra costs. I’m doing this shipping at cost folks via a tracked parcel. You can buy shipping cheaper – but with horror stories I’m afraid.

• Still a hugely economical antenna for what you get.

PS Postage for USA is only £30 using MyHermes for delivery to OCS in UK and on to United Parcels Service for local delivery in USA.

Experience is suggesting that due to the low price, no customs or duty should be paid when it lands your end for most countries (although I can’t guarantee that – although my shipping people tell me it’s under the threshold).

Start here:

# Vertical Antenna – How many Ground Mounted Radials Do I Need

I’m often asked this question and after 5 years of development, I think I finally have the answer thanks to both real-worl experience and the work that Ruby Severns, N6LF did in a controlled scientifically based experiment.

Raised Radials are a completely different kettle of fish. These are tuned to the frequency i question and can give varied results.

PS – Another superb read for the very clever folks is here:

Good luck!

# M0MCX Banana Antenna – an end-fed choke sleeve resonant feedline T2LT antenna design

A new document fully documenting the design of the Banana Antenna has now been released entitled, “Banana, a Half Wave End-Fed Choked Coax Antenna”.

Banana Antenna

Antenna can be known as – and is similar to:

Sleeve Dipole / Flowerpot Antenna

The Sleeve dipole has traditionally been used by VHF antenna designers by sliding an external metal sleeve over the coax and connecting the sleeve to the braid of the coax so that the antenna appears to be centre-fed with an outboard “sleeve”. Some commercial CB antennas are also made this way.

Banana

Resonant Feed-line Dipole (J Taylor, W2OZH, 1971)

The first time that I can find any mention of an end-fed Resonant Feed-line Dipole was an article written by James Taylor (W2OZH) in the August 1991 edition of QST entitled the “Resonant Feed-line Dipole”. He discusses the idea of using the coax itself as both part of transmission line – and a resonant element. Again, it apparently behaves like a centre-fed dipole – and extremely similar to the Sleeve antenna mentioned above. Various aerial builders have made this antenna, mostly with variable – or in most cases, poor results.

Tuned Transmission Line Trap, T2LT (CB folks)

CB folks call this type of antenna the T2LT. This terminology appears to be from a German Patent by Prof F. Fischer (Patent Number 733697) from 1939 who apparently mentions “Die T2LT”. But the patent surrounds only the use of a tuned choke which has a capacitor across the choke for tuning, not the actual antenna. The term T2LT is perhaps a misnomer.

# 20m band End-Fed Choked Coax Dipoles (T2LT)

WARNING: This post has been replaced with the following analysis and design:

Banana Antenna Design May 2017

– – –

The Resonant Feedline Antenna is also known as:

• Sleeve Dipole (& Flowerpot Antenna)
• Resonant Feedline Dipole (J Taylor, W2OZH)
• Tuned Transmission Line Trap, T2LT (CB folks)

Pictures of this experiment follow including the 10-25 MHz >8K choke follow.

# 75 ohm to 50 ohm transmission line matching coax stub

Coax Transmission line coax stubs are frequency dependent. Making a stub for one frequency means it WILL NOT work for another frequency. My example is for a 20m Resonant Feedline Dipole, sometimes called a Sleeve Dipole or Resonant Coax Dipole or Tuned Choked Coax Dipole.

NOTE: CBers tend to call this T2LT. I have no idea why they refer to this antenna by that name because it stands for Tuned Transmission Line Trap which means it should be a TTLT – but then it doesn’t have a Trap? I digress. CB for you.

So you have an approx 75 ohm impedance antenna and you want to get the best match you can. Take the wavelength of the frequency, multiply it by the velocity factor of your 75 ohm matching coax and multiply again by 0.0815.

For example.

14.225 MHz = 21.089 metres
21.089 * 0.66 (what ever your velocity factor is) = 13.19
Multiply 13.91 * 0.0815 = 1.134m

Therefore, your transmission line coaxial transformer will be 1.134m long which is apparently about 29 degrees around the 360 degree circle.

Data found here: PA0FRI page.

Finally, I discovered MANY pages on eHam and QRZ forums of people asking the same question but most answers are with people answering questions which were not asked – or giving advice how to fix the antenna, or live with it. Why Americans need to argue the toss when others just need answers beggers belief

# 40m compact fan dipole for 40, 30 and 20m bands

One of my aerials has just come down in the wind, a 40m compact dipole arranged as an inverted V with the ends coming down as far as the 6 feet fence height.

My garden is about 15m wide (actually it’s 51 feet wide, so a whisker over) however it’s too small to fit in full-sized flat-top dipole but an inverted V works well. Whilst you are at it, why not add in elements for 30m and 20m and have three bands on one feeder?

Width of this antenna is 15m. You can make it smaller to suit.

I have designed this antenna to be a flat top with droopy legs. The centre will be held up with a very sturdy aluminium scaffold pole with a 4.6m sailboard mast sleeved over the top. The aluminium mast will cross-bolt to an already installed steel scaffold bar already concreted in the ground. Bottom line is that I should achieve around 10m in height (30 feet or so).

# DX Commander pre-production testing all-band vertical

I finally found some time this year to pull all the components together to test out in a real-world setting, the idea of using multiple elements on a single vertical fibreglass pole to achieve very good SWR and radiation patterns.

The problem with verticals is than in the main, people need either ATUs or they use that awful UNUN business with a single radial. The 9:1 UNUN business is just inefficient and the only way to to use an ATU effectively is at the feedpoint, not at the rig-end due to the severe losses.

A feedpoint ATU is expensive and generally requires a 12V power source. And long verticals have awful radiation patterns beyond 5/8th of a wavelength.

So the only way to reliably install a vertical and dispense with any worries about SWR and power handling is to build a mono-bander.

Regulars will know that I’ve been playing with the idea of adding separate elements to a 40m vertical mono-bander to add in the odd frequency, say 20m – but the interaction between elements can cause impedance issues (read SWR).

With development, I’ve discovered the optimum spacing between elements to achieve pure quarter-waves on 40m, 30m, 20m, 17m and 12m. It happens that the 40m vertical will resonate on 15m for excellent very-low radiation patterns and with the addition of a shorter-then-normal 10m element (around 2.6m in length) one can get radiation with a regular quarter-wave pattern, although the idea of using a ground-mounted vertical for 10m is slightly off-putting. There are other methods to get good radiation on the 10m band.

A picture speaks a thousand words, so, without further waffling, here is the prototype in action. It uses a regular DX Commander fibreglass pole which is around 9.7m in length with stainless hose-clamps using 8mm ID aquarium tubing (softened in hot water to push over the clamps). These clamps don’t scratch the tubing and securely hold each section from slipping down in a gale.

The base plate (radial plate) in the prototype is an aluminium angle with an SO239 fitted. The centre conductor is soldered with added heat-shrink and flooded with hot-glue. Connectors are used to connect to what I’m calling the “driven” plate with stainless nuts. RF enters the driven plate and self-selects the band it wants, just as a fan-dipole would. A guying point made from Nylon 66 keeps the elements optimally spaced as well as securely hold the mast upright at 1.2m off the ground to three guy stakes.

At the 5m point, a “spreader” plate houses the 20m and 17m elements on 3mm bungee cord with the 30m and 40m elements passing straight through. At the time I took the pictures, I had dispensed with the 15m and 12m elements.

In operation, I achieved better than 1:1.5 SWR across the operational bands selected. It was fun leaving WSPR mode running and allowing it to change bands without any ATU etc.

This antenna will comfortably handle 5000 Watts, although of course, the author only ran 400W RTTY for long periods for practical testing.

Hand-production of this system is extremely time-consuming so I am about to launch this with slightly lighter-weight and machined components to reduce cost. Target consumer price will be around £99. You’ll just need to add the wire and follow the instructions.

If you’d like to stay informed about progress, let me know.

# Compact half-square for 40m band

I’ve just had an interesting discussion on 40m this evening with Peter, OH6GHI, also an antenna enthusiast. I happened to mention that I was listening to him on both VFOs. VFO A on my dipole and VFO B on my vertical and I found the stereo image very interesting as the polarisation of his signal to me changed.

We got talking about half-squares and I confirmed that we were talking about the same thing, basically 2 x 10m verticals separated by a 20m top section. The half square is fed in one corner and according to my MMANA model, this should present 50 ohms and a great SWR curve across the whole of 40m.

# Bidirectional switchable 40m wire yagi

I switched on the other evening and heard a very quiet DX caller on 7.142. It was YC0LOU from Indonesia and I could only pick up parts of his call. He called and called and had no takers. In fairness, he was extremely quiet but as the sun was gradually moving around the sky, he finally became audible and it was worth giving him a shout. 400w off my inverted V at 7m height got his attention but I needed a few blasts for him to get my call right. I put him on the cluster and he had a pile up.

Now, the point is, had I had more gain, I’d have not only heard him better, but he’d have heard me quicker too.

So I could add more height to my Inverted V but the difference between 7m and 10m isn’t actually that much at 5 degrees off the horizon – not even a db. Hardly worth writing home about.

Anyway, this was the QSO that made me sit up and take stock of what I could do. I was seriously considering phased verticals for DX when I thought up the idea of having a switchable wire yagi. Either firing East or firing West.

Like me, you may already have an inverted V dipole up for 40m, all you need to is build another one about a quarterwave in front – or behind your existing dipole but out of a single wire. You don’t need to feed this with coax, it’s a parasitic element, like a 2 element yagi.

# How to use dual coax feeders as ladder line

Having recently taken delivery of a Palstar AT4K manual tuner, I was keen to get her into production to replace my CG5000 in the attic.

Problem: the route to the attic from the shack is complex but I have a number of spare coax runs going that way including a couple of RG58 cables that I installed about 10 years ago as backups. Actually I originally installed three RG58 lines but I’ve been using one of them to send 12V up the line to the ATU.

After MUCH research, I finally used about 20 feet of parallel coax feeders, connecting ladder line to both ends. To clarify, I run about 12 feet of ladder line from the ATU to the parallel RG58 cables. I soldered the ladder line to the inner core of the RG58 coax and shorted the braid-to-braid. My 20 feet of RG58 runs to the attic, through walls, up ceilings etc and in reverse, I connected the ladder line to the RG58. Again, I shorted the braids of each line to each other with a solder blob. My ladder line then has another run to the feedpoint of a large 60m loop that runs through the attic and around the garden.

The results have been quite amazing. Comparing my 40m reference dipole to the the CG5000 (SG230 type) ATU feeding the 60m loop has always shown that the loop was about an S point lower than my reference dipole for most stations.

# Working 15m band on a 40m vertical antenna

Note: This article discusses the merits of a 3/4 (three quarter wave) vertical -vs- a 1/4 (quarter wave) antenna.

You can build a 40m vertical quarter wave antenna and ground mount it with 16 x 4m radials and operate it at the third harmonic; 21MHz.

Actually, all my experimentation has shown that if you multiply the quarter wave resonance by 3.03, you’ll have the next available usable band. In this case, if you tune a 40m vertical to 7.00Mhz, you’ll have the whole of the 15m band to play with with a centre-point of 21.300Mhz. Oh, and you’ll still have the whole of 40m band under 1.3:1.

Now here’s the controversy:

Most people who read antenna publications or the ARRL handbook believe that if you actually make this antenna, you’re creating a cloud-burner on 15m.

Technically correct (sort of) – but for DX, wrong.

On the surface, the 10m long 40m vertical that’s used on 21.225MHz does indeed look like a cloud burner. Here it is. 15m band in green -vs- a pure quarter-wave in red).

(click to expand quarter-wave in red, three-quarter wavelength in green)

# How heavy is a Cushcraft A3S TriBander Yagi?

The A3S is 14Kg (That’s 30 pounds in US money )

I was worried that the combined weight of a Create Rotator an aluminium pole *and* an A3S Cushcraft might be too much for my little lighting rig.

To test it out, I fitted the Create Rotator to the mast and added a 20Kg dumb-bell weight and started the motor.

It lifted without an issue so I’ll go ahead and plan to use the A3S for next field day.