Quadrifilar Helix Antenna Mk2

 

Quadrifilar Helix Antenna for the 137MHz APT weather satellite bandBackground
After moving house my original Tall Thin QHA failed to perform well when I erected it at the new location as a solo antenna. It had performed well in conjunction with the turnstile before but the mechanics were poor. I initially constructed a quick and dirty turnstile to my original design and have now replaced that with this QHA.

The new antenna seems to outperform all my earlier constructions by a fair margin. The better low elevation performance of this antenna which produces such excellent results from the satellites makes the station far more vulnerable to pager interference from a transmitter which is less than a mile away. Images received on the Sunday showed just how good the performance would be were it not for the ridiculous UK pager frequency allocation. There is no viable filter that can block the pagers but if I lower the antenna a little there will be some attenuation afforded by my roof as this is lined with foil covered insulation just under the tiles. I need to experiment.

Design and Construction
Built using 32mm plumbing waste pipe and 8mm microbore tubing to the dimensions produced by Bill Sykes (G2HCG) and Bob Cobey (G0HPO) and published as Taming the Quadrifilar Helix.

I connected the plastic waste pipe to an aluminium pipe with a plastic joint moulding. This joint was strengthened and the tendency of plastic pipe to bend in the heat of the sun overcome by the simple expedient of inserting a length of wood inside and screwing through the two pipes into it.

I deviated from the suggested design for the connections. Instead of using a PCB and screws I soldered short lengths of copper wire to the 8mm tubes and then in turn soldered the coax directly to these.

Wire soldered to 8mm tube for coax connection

 

I also used plastic furniture blocks to reinforce the top connection area.

Hopefully pictures can replace a thousand words and save me from typing them….
Furniture block re-inforcement Coax connection point detail

Teamwork is essential - it allows you to blame someone else.


  4 Responses to “Quadrifilar Helix Antenna Mk2”

  1. I am impressed abaut the sophisticated design of these antenas . Unfortunatly I am living in an flat with poor opportunitities to receive satellites.
    What type of 137MHz receiver do you use ? Have you ever bulit yourselv one ? Plessy devices I think are not available any more.
    Best regards from Vienna,#
    Karl

  2. Hi
    Going to give building a QFH antenna a shot after reading your website. Hope to get some good results :-)
    Neil

  3. Good luck Neil.

    I’ve built a couple of designs now. In the UK Toolstation is an excellent source for the tubing and elbows.

    Mark

  4. Hello Mark,
    Nice to see the QFH is serving you well, I still get lots of enquiries from all over the world so glad design has and is still helping others to receive the Polar Orbiting weather satellites.
    Best wishes
    Bob G0HPO

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