CobWebb Balun Box

CobWebb Balun Box
CobWebb Balun Box CobWebb Balun Box
Product Code: HG-COBBOX
Availability: 4
Price: £55.00
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The CobWebb is a popular antenna due to its small size - it's a 5-band HF aerial, under 8ft square, and is ideal for the small QTH.  One of the issues for home-constructors has been how to cut+tune the folded-dipole elements.  Fortunately, G3TXQ came up with the idea of using single dipole wires and feeding the aerial via a 1:4 balun which transforms the 12.5-ohm aerial back to 50-ohms to match your transceiver.

Following requests from a number of USA/EU based Hams, we're pleased to annouce that a QRO version of the balun is in production and will be available early December.  It'll handle around 1kW, use the same enclosure as this standard one but just be a little heavier due to the larger toroids.

There are plenty of articles online about this balun and how it's built - but construction is not for everyone and it's probably not a beginner's project so we've done the hard work for you.  This is a no-solder product and ready for mounting onto your CobWeb metalwork and spreaders.  The rugged box houses a 1:4 balun for use with the G3TXQ CobWeb design (the original, by G3TPW is known as the CobWebb) and is rated at well over 100w continuous and up to 400w SSB.  The box is filled with casting resin so fully weather-proof.

Want to build your own balun?  Just order 2x FT140-61 toroids and 3m of RG316 coax.

  • Weather-proof balun solution using 2x FT140-61 ferrites and RG-316 coax
  • 2x 1" Stauff clamps for boom mounting
  • 10x M4 screw-terminals (plus washers and lock-nuts) for wires
  • Box dimensions: 120(d)x80(w)x40(h)mm
  • Overall weight: 660g
  • Fitting and tuning instructions supplied

This is not a complete aerial!  You will need to add some metalwork, fibreglass spreaders and 5 sets of dipole wires (we use CPC CB19907 for ours).  For the metal, we suggest the Aerial-Parts metalwork from John G4ZTR and a set of fibreglass spreaders (Sandpiper) to form a complete 20m-10m HF aerial solution that can be assembled with a just a spanner, a pair of wire-cutters and an SWR meter or antenna analyzer.  Read details of John's own CobWebb build here.

What about the MFJ CobWebb?  Yes, what about it?  For starters, we've seen the balun: Only 2 terminals to mount the 10 wires (ours has 1 terminal per wire). They've also got ferrite beads on the coax as it comes out of the box - Why? The 1:4 Balun is a Current Balun and doesn't need additional choking. This suggests that they've cut corners on the balun or are selling you non-essential "window-dressing". The mounting plate only permits the aerial to be mounted at the top of a pole - if you want a VHF/UHF colinear above, tough luck! G4ZTR's metalwork kit (our design) allows you to mount it anywhere up a 1.5-2" pole.

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