145 cm and 78 cm Loop Tuning Checklist

20150308_150254

May 2014


10M –  78 cm /  2.54′ diam    in closer to house position

  • feed just above center produces  1.0:1   SWR Rs = 48Ω  Xs =4Ω    BW = 169

10M –  78 cm /  2.5′ diam    in corner elevated position  — this is the best position —

  • feed 2″  above center produces  1.0:1   SWR Rs = 53Ω  Xs =0Ω    BW = 99

15M – 78 cm / 2.5′ diam   1:1  Rs = 53Ω  Xs = 2Ω )   Bandwidth  63 khz  2.45M C,  11mm radius (.011 M) = 23% eff/  FSG = -4.6 DB (15jun14)

  1. Move cap to the 15 meter mark
  2. move feeder to 15 meter position about two inches above the primary
  3. the corner location may require higher palcement of the feeder

August 2014:  Directionality – finding significant differences in reports with Hawaii contacts and DX in marginal conditions.  Quality of service is better with the distant end in the plane of the loop.

20M —  145 cm == 4.76 ft

  • move capacitor to 20M position
  • feed centered produces 1.1:1 but not 1.0:1 in dry WX
  • insert the 1/12λ matching section to bring SWR down from 1.5 to 1.1 with #4 coax.
  • Using the #3 COAX may not require the matching section
  • The #4 COAX requires the matching section
  • With matching Section: SWR 1.0:1  2.6 SWR BW == 111 khz (15aug14)  
  • With matching Section: SWR 1.0:1   1sep14  2.6 swr BW == 152 khz – could be losing efficiency.

40M – 145 cm == 4.76

  • Move cap to 40M position
  • feeder up 2.75″ above the 20M (center) position
  • remove the 1/12λ matching section (5/18/14 aloha net left it in round one and few could hear me)
  • Bandwidth  40 khz at 7.188  swr=1:1  40khz (5/26/14)  Rs=50Ω RX=2Ω  Eff 2.6%, FSG -14dB
    10aug14 32 khz @ 7.188 swr 1.0 : 1
  • 5/26/14  tuning feedpoint 1″ above primary OD
  • BW 33 khz
  • 1/31/2015  7,192  7.162  2.5 swr bandwidth == 30 khz  (1:1 SWR  feeder up 1.7″ above inside of the loop conductor 

Efficiency and FSG using Owen Duffy’s calculator:  http://owenduffy.net/calc/SmallTransmittingLoopBw2Gain.htm


Notes

  • 40m 6/7/14 – best ever setup: +5 from kh6wa, +10 miliani wg. orientation 090°,  SWR 1.2 Rs 63Ω, Rx 0 Ω- resonant- no 1/12λ,  feeder had to move up for .5 SWR shift.  In Horiz position loop tuned 1.0 swr, BW @1.2 SWR  199-168 = 31 khz.  (8/10/14 +20 wh6dxw kula – mike gain 80  proc 39)
  • The feedline length affects tuning.
    • #3 RG6 COAX used for the 78 cm loop  (may 14)
    • #4 RG6 COAX used for the 145 cm loop (may 14)
  • radio control tuning failure occurs more often than it should.
  • the capacitor set screw must not slip or the servo will slip won’t work
  • the 6V PowerPoles fail easily – tape them up
  • the RC receiver must be off or the VSWR will go bonkers when you key up!
  • Ensure there is no short in the feeder loop F connector
  • If the CAP gets wet, especially big drops of water,  the loop may not be tune and won’t work.
  • Free and clear is much better – the 78cm loop is much more sensitive to environment than the 145cm loop.
  • VSWR problems often the result of user issues.  Loop on one freq, radio on another.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

 
%d bloggers like this: