[Premium-Rx] The 'Ideal' Logwire

[John Miles]

I have seen good results from the AMRAD active-antenna preamp
(http://www.amrad.org/projects/lf/actant/index.htm), using a plain old
Mini-Circuits T1-1T broadband transformer.  It works well on 12V with a J310
FET, as long as you don't live right next to any serious IMD-causing
sources.

Check out the September 2001 issue of QST.

You can use a T2-1 or T4-1 transformer if you want some voltage gain, but I
haven't spent enough time playing with the circuit to tell if that's really
a good idea.

-- jm

  -----Original Message-----
  From: premium-rx-admin at ml.skirrow.org
[mailto:premium-rx-admin at ml.skirrow.org]On Behalf Of Carcia, Frank A. HS
  Sent: Monday, January 06, 2003 12:43 PM
  To: 'NewRadioChap at aol.com'; premium-rx at ml.skirrow.org
  Subject: RE: [Premium-Rx] The 'Ideal' Logwire


      I would use a protected gate FET as a source follower positioned at
the antenna driving the coax. The problem
      with broad band transformers is the swing in reactance over frequency.
A FET gate as an antenna termination
      would have a minimal effect over frequency. Then there is the issue of
protection.  The only way to reduce the effect
      of reactance swing is to load the antenna which also reduces the
signal level. The FET gate will require some
      type of load resistor to bleed off any static but the value could be
high compared to the typical 600 ohm
      termination. You might also consider grounding the far end of the
antenna but a smart guy with a computer
      can tell you the difference.                fc
    -----Original Message-----
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