Aerials – Some thoughts and ideas

June 27th, 2009 by g4lds
Having recently moved to Morecambe (Good Move!!), I had my dreams of a 80 foot tower with a rotary HF beam popped as the garden is only 25 x 35 feet!!! MMM Back to plan B.  Which is wire aerials that i have used to good effect in the past.
Doublet for 80 - 10 fed by balanced feeder

Doublet for 80 - 10 fed by balanced feeder

The doublet works I found on all bands.  A dipole is really a one band aerial, cut for 1/2 λ on the band you want to work on and fed by 50 Ω coax (really it should 75 Ω as that's the correct value of a 1/2 wave dipole but rigs are 50 Ω!!) A doublet is a balanced aerial around 1/2 λ on the lowest frequency you wish to work on however in practice, it can be 85% of this value with minimum effect of efficiency.  I find that a top of 84 feet (ie 42 x 2) is good for 80m upwards.  I fed this by 300 Ω slotted ribbon cable.  It can be feed by open wire feeder between 300 - 600  Ω shop brought or homemade.It should be fed into a balanced Aerial Matching Unit (AMU or called ATU) or to a 4:1 or 6:1 Balun to coax. I have used this both Horizontal and Inverted Vee.  During a contest on 40 meters I managed to work Stateside using this at 15 feet!
w3edp2
Another aerial which I have used is the W3EDP. This appears to be in use from around the 1930s.  Check on the net for its history. This can be laid out in really any layout with bends, kinks and it still works!  It rocks on 5 Mhz as using 5 watts I have covered round the UK no problem.  It again should be fed to a 4:1 balun before the AMU or a balance Z-Type AMU. Very useful for portable use, laying along a hedge, thrown up a tree.
This should be feed via a balanced AMU like a Zee match or via a 4:1 balun to an unblanced AMU. If using a balun, the long length goes to the "hot" terminal and the short to the "earthy" terminal. The notes indicate that on 3.5 Mhz, the counterpoise does not need to be connected(it acts as a endfed around 19 feet longer than a 1/4 λ), 7Mhz its a halfwave with eightth wave feeder, 14Mhz its a fullwave endfed beyond the end of the counterpoise 17', 21Mhz its one and a half wavelengths with the 17' counterpoce acts as twin feeder! 28Mhz it does neeed the counterpoise as it two and half wavelenghts long (85')
Now having used these aerials at my new QTH, I found that the local noise was producing a S8 level on HF so operating was not very successful!.  My thoughts turned to going portable in the wonderful countryside and sea front around Morecambe.
Non counterpoise aerial (See table for variants)

Non counterpoise aerial (See table for variants)

I had read early about the non-counterpoise aerial on the G-QRP forum. A couple of years ago, you could buy a version of this aerial from Stateside via E-Bay. There has been lot of thought of what this aerial is, I think it looks and works like a "J" pole, or a Zepp or even an Off Centre Diople.  A lot of work has been carried out by Pete M3KXZ (see www.outsideshack.com) and also look on the wonderful Cebik site  http://www.cebik.com/content/a10/wire/m3kxz.html.
Table for different coverage

Table for different coverage

After reading up the published info and mailing Pete, i thought that this might be worth a try.  I decided to build a 20-6 metre version. I cut a length of speaker cable (or called low voltage twin cable) 12.5 feet long, and a length of 24/0.2 connecting wire 12.5 feet long.  I soldered this single wire on the end of one of the twin cables, making note that this would be the "hot" or radiating element.  I then used insulating tape to cover the joint and to "weatherproof" the cut ends. I then wound 10 turns on a ferrite core to act as a 1:1 balun or RF insulator at the "feed point" of the aerial. I then used insulating tape on the soldered joints and to avoid the winding moving, I used Tye-wraps.

1:1 balun or feedpoint for my portable non-counterpoise

1:1 balun or feedpoint for my portable non-counterpoise

Having made this I connected around 10 feet of twin cable to act as ribbon feeder to an AMU which had a 4:1 balun built in. Having used my aerial analyser, checked that it could be resonated on 20 - 10 meters using the AMU, noting the settings.  I then connected the FT-817 to see how it worked and found the noise level had dropped to S1  and signals were heard!  A rush into the shack and the noise level was still S8 so the non-counterpoise was connected via a coax lead to the shack, and switching between the two aerials, the noise was there or not depending on the selected aerial!!!  I moved the non-counterpoise aerial near to the house and the noise level shot up. So a quick re-think took place and I made another version for the base station, using a  4:1 balun at the feed point so I could use a direct 50 Ω coax feeder to the shack.

4:1 balun eed point of my base version of the non-counterpoise

4:1 balun feed point of my base version of the non-counterpoise

My base version is set up with the feed point on the fence and sloping towards the house, which blends in with the rest of the domestic site. Currently  the noise level is around S1-2, I am able to work on 20m upwards.  During recent sporadic E openings on 10 meters, I worked from North to South Europe. Later I tried the portable version on the stone jetty here in Morecambe, wound helically around a 6m pole, I heard around Europe and Stateside on 20m. (would have tried longer and maybe tried working but the batteries went on the '817!

My next plan is to make a 50 foot version for operating on 40 meters upwards but firstly I need to find out the local noise one source is from the street lights and I hope to get the local authority to find the cause.  the other local

My portable version wound on a kite winder
My portable version wound on a kite winder

source I hope OfCom will help in deaing with.The next version, I may make from 300 Ω ribbon cable as it may be more weatherproof!

UPDATE (28 July 2009)

Have re-read the notes and replaced the 4:1 balun with a 1:1 choke ( 8 - 10 turns on a ferrite bead) and will try this out now. First tests make it seem a bit "more lively!". When can afford it! will replace this with 450Ω ribbon as it should decrease the losses

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Baluns

June 20th, 2009 by g4lds

This is a recent project that I have carried out.  A simple balun

4:1 balun using ferrite ring

A balun using ferrite ring

Balun using ferrite rod

A balun using ferrite rod

Baluns - you either swear at them or swear by them!

So what do they do? They simply allow a balanced item like a centre fed dipole to be fed with an unbalanced system like coax (or balanced feeder (open wire balanced) to an unbalanced ATU) to try to reduce RF currents causing EMC or tuning problems. Now the next step is which one to use, a voltage or current balun?. Now I have only built and used a simple current balun so these thoughts are based on my experience.
Back in time before I held a license and was still a SWL, I built a trap dipole and needed a 1:1 balun at the feed point, saw a kit for a balun and sent off for it. Having got the kit and instructions my next problem was trying to understand what was meant by trifilar windings. I thus learnt it means three parallel windings (and of course bifilar is two windings!). Having understood this, I made it and it seemed to work. Later on I started to read up more on baluns and trifilar and bifilar windings. A look in Les Moxon’s book on aerials explained more and thus made me realize how simple baluns are to make. A 4:1 balun is even simpler to make than a 1:1 balun due to having one less winding to make!

Making a simple current balun

I feel that anything you make you learn a lot from both the practical and theory so here’s some tips to help you make 1:1 and 4:1 current type Baluns that will save you some cash! You need a ferrite rod or core, a smallish box, suitable connectors some wire (either hard drawn copper or heavy duty PVC covered different colour wires) fixings and your soldering iron, cutters etc.

Now to get the ferrite rod. You may have a defective MW portable radio, which a great source for the ferrite rod for a balun if not then a ferrite ring can be used.

My Method

The wire I have used is 18 SWG enameled wire.
Straighten the wire (tie one end around a door handle, pull gently until straight if you don’t have a vice) to remove any kinks etc and cut three lengths around 18’ long.
Lay the three straight wires in a triangular bundle with no twists and wrap in PTFE tape (as used by plumbers and stocked by most DIY stores) firmly but not too tight. (Helps to keep the wires straight and in one line! Wind 12 – 18 turns of the bundle onto the ferrite former (rod/ring) leaving NO GAPS between turns (wind slowly and carefully to ensure this). The method I used was to find the middle of the bundle and wind onto the former from this point towards the two ends. I then use a tie-wrap to hold the two ends in position on the former. If using a rod, ensure that the bundle usually lays flat on the rod but if not gently squeeze in the vice jaws taking care not to break the rod or scratch the enamel). Now define which end of the windings are your start and which is your finish. Scrape off the enamel on the end of the separate wires, buzz through to identify the individual windings (A, B & C) and connect up as per circuit diagram. (I show the connections for both 1:1 and 4:1 and using a switch you could make a 1:1 and 4:1 balun in one unit) If you are making a 1:1 balun connect a 50 Ohm dummy load to the balanced side (or output side) and aerial analyzer to the unbalanced (or input side) via a short coax lead. (If you're using a low power transmitter ensure the 50 Ohm load can handle the power, 4 x 220W 1w resistors in parallel should be ok) to check the VSWR. (Likewise if you built a 4:1 balun, put a 200 Ohm load on the output or balanced side). If the measured VSWR is high i.e. greater than 2:1 check your wiring!

I used a simple ABS box to mount the transformer with a SO259 connector on the input and bolts on the output for the aerial feeder or elements.. The transformer can be glued in the bottom of the box for mechanical strength.

I have used both ferrite rings and ferrite rods.  The pictures, I hope explain more. I also attach a Excel plot of one balun I made, fairly flat upto around 33 MHz!

And to prove it here is a picture of it being measured on 29Mhz.

4:1 Balun under test @ 29 Mhz

Info on types of cores

ferrite-core-info

Cct diags

1-1-balun

1:1 Balun

4-1-balun1

4:1 Balun

vswr1

Plotted response curve

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