KW E-ZEE Match


Date: Mon Nov 10 1997 - 09:51:09 EST

  As I was looking for some wide spaced capacitors at a local rally
  yesterday, which I wanted to use to build a balanced ASTU, I came across
  an unit made by a company called KW (which was a well known and respected
  maker of radio gear in the UK, originally started by a gentleman with the
  callsign G5KW I believe) called an "E-ZEE Match".

  Since I managed to haggle the price down to a reasonable level I bought
  the unit and opened the covers when I got home. By tracing the circuit
  and checking a few of my books, I found that it was a 'Z Match' type of
  ASTU, which was ideal as I wanted a unit to load up a doublet fed with
  open wire feeder. If anyone hasn't come across this design, I'll put a
  simple circuit diagram at the end of this message.

  Now comes the questions; on loading up my doublet consisting of 5 metres
  of open wire feeder and a 40 metre length of wire as an inverted Vee, fed
  in the centre (i.e., a dipole for 80M), I found that the one set of
  terminals would load the antenna on 80M (which was as per the circuit
  diagrams which I had found) but would not load on 40M. However it would
  load up on 30M using the 80/40M terminals. Using the other set of
  terminals, I could find reasonable matches on all the HF bands to 10M,
  including the other WARC bands of 17 and 12M. Have I just hit a strange
  impedance on 40M with the length of feeder, or is the top section being
  about a full wavelength on 40M causing me problems?

  Also, on examining the unit I noticed that the capacitors are what I
  would term 'receiver' types, that is the spacing between the plates is
  quite small. I have noticed a tendency for such capacitors to flash over
  in the past, even when running low power, as the voltage across these
  capacitors can be quite large at times. So, what experience have others
  had with using the KW E-ZEE match please, or other Z match units? What
  sorts of voltage levels do people think that these capacitors can handle?
  I would guess that the worst case is going to be a half wave end fed
  antenna, which David (G4HYY) suggested might be possible using a similar
  circuit in the QRP Antenna Handbook.

  Any information on the unit would be gratefully received, although it is
  a fairly straightforward unit to work out what does what, there was no
  instruction manual with the unit, so I wonder what maximum power input
  was recommended by the original manufacturer and what, if any, advice was
  given about feeding certain systems, where the voltage at the feed point
  might be quite high?

  Thanks very much - de Dave (G0DJA)

  Circuit of the KW E-ZEE Match (Z Match type ASTU)

     Coax input VC1
                                                               /| |
   __|__ GND
  / / / / a ____ /
  | L3 \
  _________ b
  \ \ L1 ___|/__ VC2a
  / /
                                                                     L2 /
  / ______
  \ \ L4
  \ \ / |________________
  / /
  / ___|/___ VC2b |
  \ \__________ b
  \ _______ __|__ GND
  / / | / / /
  / |
  __|__ GND
  / / / /

  VC1 = Single section variable capacitor (value unknown)
  VC2a and VC2a = Dual section variable capacitor, shaft earthed (values
  L1 = 7 turns silvered wire inside L2
  L2 = 6 turns silvered wire outside L1
  L3 = 10 turns silvered wire inside L4
  L4 = 7 turns silvered wire outside L3

  terminals a - a used for HF bands ( 20/17/15/12/10M)
  terminals b - b used for LF bands (80/40/30M)

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