STACKING QUESTION

[bill.lumnitzer at paonline.com]

 Original message was about stacking a 20M yagi above a 10M yagi....
 
(stuff deleted)
 Fi> I noticed 1DB+ degredation in gain and
 Fi> 10db in F/B with the 20M 205CA stacked 6 feet above a 10M KLM 6
 Fi> element.
(stuff deleted)
 Fi> Both K4VX and K8CC felt that a 10m yagi stacked 6
 Fi> feet below 20m yagi will not be affected by the 20m yagi.  Other proof
 Fi> of this is in the suggestions of Hygain that a 15M antenna needs to be
 Fi> about (I think) 6 feet away from a 10m yagi.  Hygain has an antenna
 Fi> range!  I tend to believe these folks!  
 Fi> OK you antenna modelling experts... What say?

 Fi> Bill Fisher, KM9P

Bill, why did you have to get me started on antenna modelling?!!!
I ran various combinations of 10/20 stacks using MNC and reached the
same conclusion as when I went through this exercise when I put up
my yagis.

In the table below the gains and F/B ratios are compared to a 
single antenna at the same height, except for the case of 10m stacked 10'
ABOVE 20m where I also list the figures compared to a single 10m at 40'.

The data show that the 20m antenna is virtually unaffected in any of the
combinations. However, the 10m Yagi is DOWN about 1.5dB in gain and 7dB
in F/B when stacked 6' BELOW the 20m beam. As the 20m antenna is raised
higher above the 10m Yagi, both gain and F/B degradation lessen and 
are both ENHANCED at at stacking distance of 35 feet! With the 20 beam
10' ABOVE 10m, the interaction is not severe and is much better than the 
situation at 6' spacing.

The BEST combination seems to be to have the higher frequency antenna
10' ABOVE 20m, which yields virtually NO degradation on 10m with respect
to the 10m Yagi alone at 40'. I have found that the same rule holds on
other bands as well: Higher Frequency Antenna on Top, unless you can really
space them out. Sometimes mounting the booms at 90 degrees, like on 20/40,
helps but not always, depending on the boom resonances. My 20/40 are both
on 42' booms and really don't like each other much with the booms crossed!

73 de Bill, N6CQ/3  (n6cq at paonline.com)


  ANTENNA    FREQ   HEIGHT    GAIN   F/B   @ELEV  +/- Gain  +/- F/B 
            (MHz)  (10m/20m)  (dBd)  (dB)  (deg)     (dBd)*     (dB)*

                                                     *WRT a single Yagi
  Single KLM 6el 10m: 

  KLM610     28.5    40/NA    13.22  22.36  12   
  KLM610     28.5    46/NA    13.40  20.99  10
  KLM610     28.5    50/NA    13.67  23.11  10

  Single HG205CA 5el 20m:

  205CA      14.2    NA/40    10.91  25.00  22
  205CA      14.2    NA/46    11.25  31.41  20
  205CA      14.2    NA/50    11.37  39.55  18

  20m stacked over 10m:   
                              
  20/10-6    28.5    40/46    11.66  15.26  12     -1.56    -7.10
  20/10-8    28.5    40/48    12.14  17.62  12     -1.08    -4.74
  20/10-10   28.5    40/50    12.54  20.25  12     -0.68    -2.11
  20/10-12   28.5    40/52    12.90  23.98  12     -0.32    +1.62
  20/10-35   28.5    40/75    13.53  24.92  12     +0.31    +2.56

  20/10-6    14.2    40/46    11.26  30.66  20     +0.01    -0.75
  20/10-10   14.2    40/50    11.37  44.62  18      0.00    +5.07 

  10m stacked over 20m:

  10/20-6    28.5    46/40    12.24  14.80  10     -1.16    -6.19
  10/20-10   28.5    50/40    13.11  20.01  10     -0.56    -0.98
 
                              WRT KLM610 at 40':   -0.98    -7.56
                                        NOTE ****> -0.11    -2.35 <****

  10/20-6    14.2    46/40    10.94  24.49  22     +0.03    -0.51
  10/20-6    14.2    50/40    10.93  24.42  22     +0.02    -0.58