137MHz QFH Antenna for NOAA Satellites

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This page last updated 05/12/2023.

 

(Price: £85 + shipping.  Price correct December, 2023)

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This page describes how this antenna can be used for receiving images on the weather satellite band.  Please expand each item below for a comprehensive explanation.  If you are interested in buying one of these antennas, you will  find an order form in the “How to Buy” section.

Receiving Weather satellite pictures is one of the easiest and most rewarding areas of radio to explore. No licence or special permission is needed, and the equipment required is extremely cheap and easy to obtain.

The satellites which are easiest to receive pictures from are called Low-Earth-Orbit, or LEO sats. Some of these satellites send a type of transmission called Automatic Picture Transmission, or APT. The LEO Satellites are continuously orbiting the earth at an altitude of around 800-850km and each one will pass over any given location approximately three times a day. These satellites send a continuous picture stream as they travel, rather like a continuous fax transmission. When you receive and decode this transmission, you will receive the portion of the picture which the satellite sees as it passes over your location.

The only thing which limits how much of the picture you can receive, is how long the satellite is ‘visible’ above the horizon from your location. Being visible refers to the satellite being within ‘line of sight’ from a radio signal point of view. An antenna mounted at a good height in a location clear of obstacles will help greatly. Having said that, where I live in the centre of the UK, I can receive a portion of picture stretching from North Africa up to Greenland , so the whole of the UK can easily be identified, all using a loft-mounted QFH antenna.  

In the early days, it would have been fairly difficult to decode a transmission from these satellites. VHF reception equipment was expensive, a computer was an expensive device, and you would need a demodulator of some description. Thankfully, nowadays you can buy a VHF receiver for £20, everyone has a personal computer, and you can decode the pictures using the computer’s soundcard.

BUT (see next item):

 

The most important part of any radio station is the antenna. An incorrectly selected antenna can mark the difference between success and failure. While you can receive signals from satellites using a fairly simple dipole or monopole antenna, you will find that the signal fades in and out as the satellite’s antenna changes polarisation, and you may get loss of signal when the satellite is directly overhead or near the horizon.

The answer: Use a Quadrifilar Helix Antenna! This strange-looking antenna, often named the egg-beater antenna (for obvious reasons), was invented in the 1940s and has become something of a stablemate for modern satellite communications, and also other uses such as wifi. These antennas have a fundamental ability to demonstrate high gain with regard to signals presented from the side, and less gain to signals presented from above (when the satellite is overhead the signal is strong and unobstructed). The QFH antenna also has a unique capability of receiving wanted signals for which it was designed, and rejecting unwanted signals.

The signals sent from satellites are of circular polarisation. This polarisation is used because satellites are constantly moving and changing orientation. Therefore relative orientation between linear polarized transmitting and receiving antennas is not guaranteed, i.e both transmitting and receiving antennas vertical, or both horizontal. The polarisation of linear signals is also changed as it travels through space, while circular polarisation is not affected.

The QFH antennas I build and sell are carefully designed to be effective both in operation and in cost. They are built from copper tubing which is formed into the required helix shape using a 3D tube bender, and is soldered at the joints for reliability. The antenna structure is supported using solvent-welded tubing and associated fittings for mechanical strength and weatherproofing. There is a screw-cap fitted at the top for easy access to the coax feed point. I also polish the copper tubing and lacquer it to prevent corrosion and weathering. This antenna could surely be excused as a garden ornament, Christmas decoration, or similar! Whatever happens, your better half won’t mind too much.

Antennas are built to order, priced at £85 each plus shipping in a huge box!  (Antenna is approximately 95cm high with a diameter of 40cm.  Price correct December, 2023.)

If you need a coax feeder for your antenna, I can offer various options from stock.  Full details are provided on this page.

Feedback from customers is always good, with reception results always reported as being nothing short of excellent. These antennas will always beat crossed-dipole antennas, and turnstile antennas by some margin, simply by their design.

My aim is to produce these antennas at cost in the spirit of the hobby. A few people have suggested that the antenna is overpriced, and the materials cost around £30 at their local DIY store. Of course these people omitted to realise that when you buy the components, they don’t just magic themselves into a complex antenna of exact dimensions and set up to perform as required! This takes a few hours of work, and requires the following materials and equipment:

  • Pipe straightener
  • Pipe cutter
  • 3D pipe bender
  • Tube drilling jig
  • Copper tubing
  • Steel wool
  • Solder
  • Soldering flux
  • Soldering torch
  • Gas for soldering torch
  • Flux remover
  • Degreaser
  • Lacquer
  • Sealant
  • PVC solvent cement
  • Wet & dry paper
  • Heatshrink tubing
  • Antenna Analyser

If you are interested in having a go at receiving weather satellite pictures using one of these antennas, please contact me by emailing  joe@ft8.co.uk.

I haven’t gone into too much detail regarding actually receiving and decoding pictures here as this is already well documented on the internet. I recommend downloading a program called WXtoIMG, the full version of which is now free. This can automatically track and receive the weather satellites, and can also add colour to what would normally be a monochrome picture. You can also add country boundary lines to really identify the area which you have received.

The price of an antenna is currently £85 (price correct December, 2023) excluding shipping.  Please use the contact webform below to place a provisional order.  Once I have all your details I will send you a firm quotation for the full price, including shipping costs to your address.  If you prefer, you can just send an email to joe@ft8.co.uk. Please remember to include your full postal address so we can work out the shipping cost.

Because of occasional difficulties when attempting to reply to a Gmail address, please also include a telephone or mobile contact number in case I can’t reach you by email.

 

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