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.
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.
– – –
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)
For more about common mode chokes, see this article:
Pictures of this experiment follow including the 10-25 MHz >8K choke follow.
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.
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
In the UK therefore, there’s a couple of simple steps to take to make sure you won’t transmit out of band.
If you don’t have JT65 already, get it here: http://jt65-hf.com/downloads/.
Run the installer and interface your rig as you would any other piece of software that connects to your computer. If you are after help with that part of the problem, there are other places to hunt solutions down, not this blog.
Go to file > Settings and click the Frequency tab at the top and edit the frequency for the 5 MHz band so it reads 5.356.
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?
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).
In the UK, this boils down to 100 Watts maximum transmitter power and 200 Watts effective radiated power (* see note). Only Advanced licence holders are allowed on 60M band. You used to obtain a NOV however I believe that’s finished now.
To get around remembering everything, it’s probably best just to set up some memories in your HF set. I don’t know about you, but all these fancy rigs come with memories – and we never use them. Well, I didn’t up until now. 60m is ideal for getting up to speed with these Memories (and you can scan the channels too which is something else few of us know how to work!).
The following table should be able to set you up for your HF set memories (as at February 2017).
Frequencies: Upper Side Band (USB)
AM is a mode I remember from my youth. All the original imported CB sets were AM at that time and I seem to recall that I enjoyed the sound quality. Somehow it’s more relaxing than FM. Maybe its because you don’t need squelch, I really don’t know. FM has great clarify but AM just has a roundness to it.
Most modern radio sets come with the ability to transmit on AM but there’s an element of setting up, for instance with an old fashioned AM CB radio, you probably don’t set up the carrier and then adjust the microphone gain to achieve the modulation.The good news is that out the box, my TS990s seemed to transmit AM pretty well. I have an additional benefit in that the AM carrier on the TS990s is 50 watts, with voice peaks naturally falling at around 100 watts, perfect for maximum juice on the 60m band which limits our power to 100 watts anyway.
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.
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.
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.
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.
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)
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.
How mad is that? !
A couple of times, I used Audacity (software) to record out the back of my Kenwood TS-990s and caught some interesting sound-tracks.
Mostly, I forgot to hit the record button, particularly when I hit a very fast pile-up to the US but I found time to catch the tail end of this one after it had slowed down a bit.
Here’s a “perfect” example of a CQWW “rubber stamp” contact. (read more…)