Topband: 160 RX Loops

[Herbert Schoenbohm]

Pete Parisetti wrote:
> Initially I have used the KC2TX coax loops, with rather dismal results.
> Then, I have done exactly what Herb suggests
> (loop.jpg<http://www.chmusiq.com/ham/img/loop.jpg>),
> and was initially very pleased. Upon more careful evaluation, though, I
> found that there is no real gain in terms of s/n: the loop is a lot less
> noisy than the TX antenna (inverted L, 17 m tall), but in reality I can hear
> just as well (or as bad...)
Pete,

 From your picture it appears that the feed line dress is along the 
horizontal support. Correct me if I am wrong.....But this could cause 
real performance deterioration.  The key to getting some good 
performance from the pennant could include:


    * Antenna 50 ' (minimum) away from nearby antennas, towers, or power
      lines.
    * Support made by wood, fiberglass, or non conducting material.

    * Good impedance matching 950 ohms and with a preamp to compensate
      for the  signal loss (powered over the cable) at or near the feed
      point.  (A multi turn 5K pot to maximize the null off the
      termination could enhance performance by tuning in a BC station of
      the back and tuning for minimum signals.  When the sweet point is
      found replace the pot with the fixed value when determined.
    * Coax dress away from the feed point at one end to minimize pattern
      distortion
    * In a rotatable Pennant a double common mode rejection circuit
      might work so the horizontal support could carry the drooping feed
      line....but I think that taping them close together to the antenna
      wire should be avoided...even with a decoupler at the support pipe.
    * Common Mode Rejection  near (15-20 feet away is fine) the feed
      point with a double "T" coax toroid decoupling where the mult wrap
      RG-6, RG59, or RG-174 (in the case of 50ohm feed)  passes through
      two rings with an earth ground between the two rings. This concept
      is supposed to isolate some of the impact of the unbalanced feed
      line near the Pennant
    * Some gurus recommend a similar decoupling device near the shack
      entry.....and although I have mine out near the antenna to avoid
      common mode noise pickup I can't imagine that another one near the
      house could hurt a bit.

Good luck with the noise....but almost  every weekend I find something 
on Top Band that can be improved upon by going over the options.  I am 
just plain tired of seeing someone spot me...with comments like "deaf" 
or  "alligator no ears".  Like all of use hearing in QRN whether man 
made or atmospheric is a real challenge. 


73,

Herb Schoenbohm, KV4FZ