Canvey Island, Essex, England Justin@g0ksc.co.uk
Twin boom quad
144MHz LFA Yagis
144MHz LFA Yagis

Low Noise LFA Yagis designed by G0KSC free to build for personal use.

144MHz LFA Yagis
70cms LFA Yagis
70cms LFA Yagis
Twin-Boom G0KSC Quads
G0KSC Twin-Boom Quads
Twin-Boom G0KSC Quads
G0KSC Custom Dish feeds - Above installation @ HB9Q
Custom low-noise dish feeds
Custom low-noise dish feeds
G0KSC Custom Dish Feeds

Above installation @ HB9Q

G0KSC Custom Dish feeds - Above installation @ HB9Q
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Read Time: 3 - 5 minutes

The G0KSC Element Insulators

 

COMMERCIALLY MADE INSULATORS NOW AVAILABLE IN OUR SHOP

 

Amendment 21/7/2010 I have established that insulators should be as small as possible, extending either side of the boom by an absolute minimum. A commercial offering by Stauff (www.stauff.com) provide an excellent alternative to home making and these clamps are just 30mm wide.

Please Read This section - If your antenna(s) is 6m or above and your insulators are more than 30mm wide and or electrically connected to the boom, any antenna you build with them my need correction. If you are stuck or unsure and want to explore this option, do let me know via Email.

 

Probably the most important part of your Yagi antenna are the insulators you will be using and sadly, there are not too many good quality insulators commercially available (without buying the whole antenna system!). To this end, I decided to design an insulator that would be relatively easy to make and provide excellent performance at the same time.

The main consideration for me when looking for the material to use was to find something which would be easily available to most Hams in most places in the World. Step in Plexiglass and Perspex. Used in anything from signs to tables, both brands of acrylic are available to buy widely and at reasonable prices. This is in addition to offering excellent insulation properties and being relatively lightweight too.

I buy mine from Ebay in A4 or A3 sizes and purchase 15mm thick sheets of clear Plexiglass. Buying sheets sizes much greater than A3 becomes a little expensive and as a result, a little less economic.

 

Insulator Sizing

For 50 and 70 Mhz I cut my insulators to 30mm wide by 100mm long. This 100mm can be reduced for 220 or 144 Mhz and increased in both width and depth for 28 Mhz and lower bands. I have not experimented with these insulators on bands other than 50 and 70 Mhz but will report on my findings (ideal sizes) once I have. However, logic suggested there should be no degridation in performance on the other bands and the associated strength should allow for the supporting of elements down to and below 28 Mhz.

Tutorial - Making the Insulators

I have a table saw and table router which does make things a little easier. However, the same job can be carried out with hand-held devices too. If you really do get stuck, let me know. For a fee and can supply some of my own.

The insulators are cut from the 15mm thick Plexiglass/Perspex and are 100mm long by 30mm wide. First, I cut a 100mm wide strip from top to bottom of the A4 sized plexiglass and routed a 1 inch grove in the centre from one end to the other (assuming your boom is 1 inch square, if using metric sizing, adjust accordingly)which should be between 1 and 2mm deep. When you have done this, you can test your work by placing the Plexiglass onto the square boom length and if you have completed the task correctly, the piece should not move side to side.

Now cut the 100mm length into 30mm strips, you will have around 9 pieces from a strip this size so you have a few spares in most cases. As we did with the 100mm strip, we now need to route a grove in these 30mm wide strips from the elements to sit within. These need not be ½ inch. I made this around 4 to 5 mm wide In order that the elements sit above the insulator just touching it on each side of the grove. 4 to 5 mm give enough to keep the elements in place with minimum insulator effect on the elements themselves. Check out the photos of the insulators to ensure yours look like these!

For most of the insulators you are done but we need to do a little more work with the driven element insulator which we will cover now.

Driven Element Insulator

The dipole section will have a nylon 8mm (60 to 100mm total length) rod inserted into each piece of the dipole and just 10mm of nylon showing between the 2 aluminium lengths. These again are available on Ebay along with Plexiglass rods which are also acceptable to use albeit a little more brittle.

The driven element is the only element where the stainless steel bolt will NOT go through the element itself. Instead we need to countersink the drilled M6 hole in the insulator with a hole big enough to fit the head of our bolt into.

 This should be 5mm deep into the insulator in order that the bolt sits well below the dipole centre. Next we need to align the dipole upon the insulator and measure along each side 5mm from the nylon joint on the dipole and drill through both the element and the insulator (see pic). This time, we need to countersink the holes as we did above but this time, the countersink will be from the bottom of the insulator. Insert stainless bolts (50mm M6) from the bottom up into the elements, place a washer upon these with a nut and tighten them. The protruding portions of the bolt will be used to bolt our coax to.

 You should be now done and ready to install your remaining insulators and coax! If you have any problems or suggestions, do let me know justin '@' g0ksc.co.uk

73 Justin G0KSC  

 

 

 

 

 

Read Time: 2 - 4 minutes

OWA stands for 'Optimised Wideband Array'. Generally this type of antenna is designed with maximum performance whilst retaining a 50 Ohm impedance in order to help ensure minimum losses and maximum radiating efficiency. It is this point which is often missed by many when selecting an antenna design, one tends to get 'blinkered' by  'formed' opinions and high performance, on paper figures regardless of the hidden losses and inefficiencies there may be.

Many antennas available today show huge gain and front to back figures and sometimes ( not always) these figures stack up within simulation software. However, it is more often than not that when you analyze further, radiating efficiency means many of the on paper benefits are lost in the real world.

Read Time: 2 - 4 minutes

 Why compromise?

When building antennas commercially, compromises have to be made for many reasons, tapered elements being one such area. The thicker the elements, the better the bandwidth of your beam so why would we choose to have thin elements that get thinner towards the ends? Having a single piece element on a 14 Mhz beam with 2 inch diameter elements is just not practical and therefore, tapering is common place. The second reason for tapering and why even 50 Mhz and 70 Mhz antennas are tapered is to allow for easy postage, another commercial benefit. If the antenna when broken into component form is nice and compact, it can be posted easily and cheaply. This methodology however does not lend itself well to long-term, uncompromised performance.

Whilst I do allow for this method of construction in some of my designs, the 'ideal' models I present generally have minimal connections or one piece elements. This is for the same reason I chose to use isolated elements within my antennas as this method of construction (multiple connections, tapered elements, elements to etc.) provides the basis of an antenna that can be de-tuned by the least amount of third party factors. Allow me to explain more fully.

It has been common place over the years for Yagi antennas to be designed with elements electrically connected to the boom. Often a gamma match is used on this type of antenna in order to match the system in these cases. Consider how many electrical connections there are within such an antenna. Have you ever dismantled one and notice the corrosion within each of these joints? Each of these corroding joints can produce a resistance and with this comes de-tuning of the antenna. If we use single piece, isolated (from the boom) elements, there are no areas for resistance to occur and as such, less opportunity for the antenna to be de-tuned. Furthermore, it’s performance will be sustained with the highest level of efficiency remaining, without change.

This is one of the reasons stainless steel hardware is provided with good quality beams. It ensures minimal reistance occuring due to it's tendancy not to corrode and create high resistance. This said, even using stainless steel in the above examples does not exclude such an antenna from having any resistance at all. Can you imagine building your perfect beam, tailoring it to provide the best performance in the section of the band you favour only to find in a few months time, the antenna has shifted to another, less desirable section of the band. Now imagine an antenna that you have built that performs admirably on the whole band regardless of your favoured portion and one that does not shift in frequency or performance, no matter how long it is in the air.

 

G0KSC Mechanical Design Summary

  • Where ever possible, my designs will have single piece elements to ensure NO resistance and as a result, no aging will occur along any element length
  • Insulated elements increase the ability to ensure no resistance and therefore no de-tuning will occur due to age or weather
  • Thick, high stand off insulators are used to ensure limited (if any) effect on element length is made by the boom
  • Quality, thick wall components should be use to ensure durability and longevity of life in addition to 'no sag' elements
  • No feed point tuning or matching mechanisum is required which ensures minimal losses and maximum radiation
  • Highest power rating antennas are the result -  the power rating of my antennas (in most cases) being limited to the feeding coax only

 

If you are looking for a no compromise antenna with great performance, look no further, you have come to the right place!