10m QUAD

Welcome to the 10m Quad page

My "little" 10m quad

I was listening on 15m one night shortly after getting my class A license and heard a local station in qso with a Brazilian station. The local guy commented that the Brazilian had faded down to 5/7 so he would now turn his "Quad" more in the direction of South America to bring the signal back up........on my dipole the Brazilian was non existent! The local station was using a 2 element Gem Quad at 25 feet above ground. I needed to find out more!!

After reading "All About Cubical Quads" by William Ore and the section on Quads in the RSGB Radiocommunication Handbook i decided to build a single band Quad for 10m, the sunspot numbers were just starting to rise so this was perfect timing.

I built this aerial on a low budget using bamboo canes (better quality "thicker" bean sticks) instead of the more common fiberglass rods. This is ok for 6, 10, 12 and possibly even 15m but you need to use something more substantial if you want to go any bigger. I cleaned the canes thoroughly with foaming cleaner and then tightly spiral wrapped them in All Weather Electrical Insulation Tape (RS 176-523) making sure that there are no gaps or kinks. This tape is thicker than ordinary electrical insulation tape and is UV resistant. Immediately you can feel that the canes are much more robust and weatherproof. Tip: Leave the tape in a warm room over night before using and this will make it more pliable, also cut the tape with scissors at the beginning and end of the wind and it will seal down nicely. 

Quad reflector

The boom is 1½in O/D aluminum tube and the crosses at each end on which to mount the canes are made from 12in lengths of angle welded onto short pieces of 1½in I/D tube. These then slide over the boom and are secured with a bolt through the middle. The cane spreaders are then clamped to the cross pieces using good quality UV resistant cable ties. For a larger aerial stainless steel hose clips would be better. The whole assembly is then given 2 coats of black gloss paint to match the spreaders.

The 2 loops are made from hard drawn enameled copper wire and are fastened to the canes with a 4in length of ¼in I/D reinforced hose and cable ties. DO NOT drill the canes and pass the wires through, there is no provision for adjustment and the loops WILL fall off/the canes WILL break when the moisture gets in.....which won't take long in the UK! The idea of the short length of hose is to pass the wire through to stop it sawing through the cable ties and to brace some tension into the loops (quads are 3 dimensional anti-social monsters as it is, so sloppy untidy loops only make matters worse).

Quad driven element and feed point

The driven element is fed at the bottom for horizontal polarity with a dipole centre and an electrical ¼ wavelength of 75 ohm coax, then 50 ohm coax into the shack. The length of 75 ohm acts as a matching transformer to raise the feed impedance, without it the VSWR will be high due to the mismatch. I cut my 75 ohm transformer using the tracking generator facility on the spectrum analyzer (see picture). If you don't have this facility available use RG59 coax and the formula 300/frequency x 0.66 = wavelength in meters, then divide by 4 for a quarter wave.  This is a balanced aerial that should not really be fed directly with an unbalanced feeder so as a precaution i've placed 8 ferrite sleeves over the 75 ohm section just where it connects to the dipole center to act as a choke balun. This will help to prevent any current flowing on the shield of the coax. Feeding the aerial with a Gamma Match system would probably produce a better match but i think this would be more of a problem to make waterproof.

Spectrum Analyzer used for cutting 75 ohm transformer 

75 ohm transformers with ferrite sleeves

Dimensions for the 2 element Quad that i've used are 1005/f = driven element (feet), 1035/f = reflector (feet), 0.12 wavelength spacing and f x 0.666 (velocity factor, dependant on cable used) for the 75 ohm matching transformer section. If you use a wider spacing the aerial will have slightly more forward gain, less f/b ratio and bigger nulls off the side of the aerial. I wanted maximum f/b ratio and with tests i've made using a dipole, HP spectrum analyzer and local amateurs there's 25db peak f/b ratio falling off to 10db at band edges and 6dbd forward gain. The Quad has a very low angle of radiation which for DX is one of the reasons this aerial performs so well. Compared with a dipole, G5RV and 10m vertical the signals on the Quad are way up.....plus you call and get answered!!

Happy DXing on 10m.  

AB2KC's quad with 4 elements on 10m and dual/circular polarity

A crane prepares to lift VA7DX's monster 40m quad off the scaffolding and over the house onto the tower in the back yard!