Yet Another EFHW Matcher

While on the lookout for a more compact housing for the End Fed Half Wave matcher, I came across this perfectly sized enclosure at Altronics (Hammond 1551).  At 50mm x 35mm x 20mm, it is just right to hold the FT-82-43 core, a BNC socket at one end and a terminal at the other. The case is just a bit too small to fit a banana jack as it would protrude too far inside, so a 4mm bolt, washers, nut and wingnut make the antenna connection.  A 4mm nylock nut holds the wingnut from coming off.

The toroid is the same one as used here, with a 3 turns bifilar wound primary over a 24 turn secondary.  A 100 pF and 45 pF capacitor are in parallel across the primary to improve the match.

This is quite a bit smaller than the earlier versions and is a better fit with the KX2 and antenna in the case.  Total weight is 38 grams.

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11 Responses to Yet Another EFHW Matcher

  1. Andrew VK1AD says:

    Hi Glenn, your SOTA kit is getting lighter, what’s the total weight now?
    Nice project well done. I still find my EFHW plus the impedance matcher a favourite antenna. Thanks for sharing the design update. BTW I’m looking forward to summer 6 m sporadic E contacts.
    73 Andrew VK1AD

  2. vk5bje says:

    Hi Glenn
    Is this coupler designed just for 40 metres? And how much band width do you get before the VSWR climbs too high? It is beautifully made Glenn and I notice Andrew has commented on the space and weight saving. I have been thinking about making a parallel tuned circuit coupler with a variable capacitor. I have a very small variable and I could get the total size down to a quite small package. I have a QRO one with variable inductance (switched) and a hefty capacitor and it does a great job.
    cheers
    John D
    VK5BJE/VK5PF

  3. vk5bje says:

    Hi Glenn, thanks for the comment. Well done and I amazed it works over such a wide frequency range.
    Cheers
    John D
    VK5BJE/VK5PF

  4. vk3jbl says:

    Nicely implemented as always Glenn. Are you using the amp with this matcher? I’m looking at a new smaller matcher as well for the MTR and am thinking of dropping down to a ft50-43 given the lower power. I’m not yet willing to part with my combined screw/banana jack though 🙂

    Andrew

    • vk3yy says:

      Hi Andrew, yes, the reason I chose the larger core was so that the amplifier could be used. It was tested to 50W and seemed to be happy. There may be room for the 82/43 core and a banana jack, particularly if the jack was offset to the top of the case, but it would be a squeeze.
      There is a table here: http://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1988/12/page33/
      that suggests the FT 50/43 core is good for 5W. The KX2 puts out 10W, and I understand that ferrite cores are prone to permanent changes if overheated. Cheers, Glenn.

      • vk3jbl says:

        Thanks. Dropping to the ft50-43 would allow a decent saving in weight and size.

        I’ve been tempted to move to the ft140 size for use with the amp to avoid any risk over heating, however the existing matching unit is so good, I’m loathe to touch it!

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