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119 Posts
Discussion Starter #1
Flat gain uhf hybrid antenna antenna is a big improvement, over
my old antenna hybrid design with flat gain.

Went back to 6 whisker & enclosed bow ties, and designed a
ff4 based on this.

Used the 4nec2 optimizer to create this.


Here is a graphic of it:




Uhf Gain:





UHF Swr:





Vhf Gain:





Vhf Swr: A bit excessive, but it's the signal to noise ratio that
counts.





Flat Gain UHF Hybrid Antenna Nec Code:

Code:
CM Uhf Flat Gain Hybrid Antenna (whisker & enclosed bow ties)
CM Auto Segmentation 7
CE
SY Rsrc=0.0036    '554 mhz SOURCE wire Radius.
'SY Rsrc=0.052    '201 mhz SOURCE wire Radius.
SY Rbow=0.0404    'Radius (in inches) of BOWTIE elements
SY Rfeed=0.0254   'FEEDLINE wire Radius (in case they're different)
SY AngleInr=14.11808    ' Angle = half of the flare Angle in degrees
SY AngleOut=20.80523    ' Angle = half of the flare Angle in degrees
SY BowLenI=11.07717     ' Bow Half-Length Inner(plus some in bend)
SY BowLenO=8.932685     ' Bow Half-Length Outer(plus some in bend)
SY MidWhisker=BowLenO   'Middle whisker Length
SY BowSepI= 2 * BowLenI * SIN(AngleInr)     ' INNER Bow Tine Separation - Assume all SAME
SY BowSepO= 2 * BowLenO * SIN(AngleOut)     ' OUTER Bow Tine Separation - Assume all SAME
SY ZBowII=17.23582      'Distance between the Centers of the two INNER bowties
SY BowSepDist=7.905161
SY ZBowOI= BowSepDist + (BowSepI + BowSepO)/2'From Center of INNER bowtie to Center of OUTER bowtie

SY VertFram=0           '1.605063
SY Horz=0'8

SY FeedSep=1.62434      'Separation (in inches) between two FEEDLINE wires
SY Hop=1.25             'Separation between Feedlines at Crossover
SY Cond=1.67e7'Conductivity (Copper=3.0e7, Alum=2.0e7, StainlessSteel=1.67e7)
' Calculated from above INPUT Values:
SY ZBowInr=ZBowII/2           'Distance from antenna center to center of INNER bowtie
SY ZBowOut=ZBowII/2+ZBowOI    'Distance from antenna center to center of OUTER bowtie
SY Z1=ZBowOut+BowSepO/2
SY Z2=ZBowOut
SY Z3=ZBowOut-BowSepO/2
SY Z4=ZBowOut                 'Very long crossover region
SY Z5=(ZBowII + ZBowOI)/2
SY Z6=ZBowInr                 'Very long crossover region
SY Z7=ZBowInr+BowSepI/2
SY Z8=ZBowInr
SY Z9=ZBowInr-BowSepI/2
SY YBowInr=FeedSep/2 + BowLenI * COS(AngleInr)     ' Ymax for Inner Bowties
SY YBowOut=FeedSep/2 + BowLenO * COS(AngleOut)     ' Ymax for Outer Bowties
SY YBowN=-FeedSep/2
SY YBowP=FeedSep/2
SY YMidWhisker = (FeedSep/2)+(MidWhisker)       'Ymax for Outer Bowties
'  #    segs    X1      Y1    Z1    X2      Y2        Z2    radius
' SIMULATED BALUN SOURCE ON GW1:
GW   1  3   0    YBowN+Horz        VertFram     0   YBowP+Horz           VertFram       Rsrc
' GW2 Not used
' GW3 Not used
' INNER BOWTIES:
GW   4  9   0    YBowInr+Horz    Z7+VertFram    0   YBowP+Horz          Z8+VertFram     Rbow
GW   5  9   0    YBowInr+Horz    Z9+VertFram    0   YBowP+Horz          Z8+VertFram     Rbow
GW  40  7   0    YBowInr+Horz    Z7+VertFram    0   YBowInr+Horz        Z9+VertFram     Rbow
GW   6  9   0    YBowN+Horz      Z8+VertFram    0  -YBowInr+Horz        Z7+VertFram     Rbow
GW   7  9   0    YBowN+Horz      Z8+VertFram    0  -YBowInr+Horz        Z9+VertFram     Rbow
GW  41  7   0   -YBowInr+Horz    Z7+VertFram    0  -YBowInr+Horz        Z9+VertFram     Rbow
GW   8  9   0    YBowInr+Horz   -Z7+VertFram    0   YBowP+Horz         -Z8+VertFram     Rbow
GW   9  9   0    YBowInr+Horz   -Z9+VertFram    0   YBowP+Horz         -Z8+VertFram     Rbow
GW  43  7   0    YBowInr+Horz   -Z7+VertFram    0   YBowInr+Horz       -Z9+VertFram     Rbow
GW  10  9   0    YBowN+Horz     -Z8+VertFram    0  -YBowInr+Horz       -Z7+VertFram     Rbow
GW  11  9   0    YBowN+Horz     -Z8+VertFram    0  -YBowInr+Horz       -Z9+VertFram     Rbow
GW  42  7   0   -YBowInr+Horz   -Z7+VertFram    0  -YBowInr+Horz       -Z9+VertFram     Rbow
' OUTER BOWTIES:
GW  12  7   0   YBowOut+Horz    Z1+VertFram     0    YBowP+Horz         Z2+VertFram     Rbow
GW  13  7   0   YBowOut+Horz    Z3+VertFram     0    YBowP+Horz         Z2+VertFram     Rbow
GW  38  7   0   YBowP+Horz      Z2+VertFram     0  YMidWhisker+Horz     Z2+VertFram     Rbow
GW  14  7   0   YBowN+Horz      Z2+VertFram     0   -YBowOut+Horz       Z1+VertFram     Rbow
GW  15  7   0   YBowN+Horz      Z2+VertFram     0   -YBowOut+Horz       Z3+VertFram     Rbow
GW  39  7   0   YBowN+Horz      Z2+VertFram     0   -YMidWhisker+Horz   Z2+VertFram     Rbow
GW  16  7   0   YBowOut+Horz   -Z1+VertFram     0    YBowP+Horz        -Z2+VertFram     Rbow
GW  17  7   0   YBowOut+Horz   -Z3+VertFram     0    YBowP+Horz        -Z2+VertFram     Rbow
GW  45  7   0   YBowP+Horz      -Z2+VertFram    0   YMidWhisker+Horz   -Z2+VertFram     Rbow
GW  18  7   0   YBowN+Horz      -Z2+VertFram    0  -YBowOut+Horz       -Z1+VertFram     Rbow
GW  19  7   0   YBowN+Horz      -Z2+VertFram    0  -YBowOut+Horz       -Z3+VertFram     Rbow
GW  44  7   0   YBowN+Horz      -Z2+VertFram    0  -YMidWhisker+Horz  -Z2+VertFram      Rbow
' CROSS-OVER FEEDLINE:
GW  24  3   0   YBowN+Horz      Z6+VertFram    Hop/2   Horz            Z5+VertFram     Rfeed
GW  25  3   0   YBowP+Horz      Z4+VertFram    Hop/2   Horz            Z5+VertFram     Rfeed
GW  26  3   0   YBowP+Horz      Z6+VertFram   -Hop/2   Horz            Z5+VertFram     Rfeed
GW  27  3   0   YBowN+Horz      Z4+VertFram   -Hop/2   Horz            Z5+VertFram     Rfeed
GW  32  3   0   YBowN+Horz     -Z6+VertFram    Hop/2    Horz          -Z5+VertFram     Rfeed
GW  33  3   0   YBowP+Horz     -Z4+VertFram    Hop/2    Horz          -Z5+VertFram     Rfeed
GW  34  3   0   YBowP+Horz     -Z6+VertFram   -Hop/2   Horz           -Z5+VertFram     Rfeed
GW  35  3   0   YBowN+Horz     -Z4+VertFram   -Hop/2   Horz           -Z5+VertFram     Rfeed
GW  36  7   0   YBowP+Horz      Z8+VertFram     0    YBowP+Horz          VertFram      Rfeed
GW  37  7   0   YBowN+Horz      Z8+VertFram     0    YBowN+Horz          VertFram      Rfeed
GW  38  7   0   YBowP+Horz     -Z8+VertFram     0    YBowP+Horz          VertFram      Rfeed
GW  39  7   0   YBowN+Horz     -Z8+VertFram     0    YBowN+Horz          VertFram      Rfeed

GS   0  0   0.0254
GE   0
LD   5  0     0   0   Cond      'Conductivity
GN  -1
EK
EX   0  1     2   0    1    0    0    0        'GW1 is SOURCE wire
FR    0    29    0    0    554    12
RP    0    1    73    1510    90    0    1    5    0    0
EN


Have fun building antennas.
 

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Vhf Swr: A bit excessive, but it's the signal to noise ratio that counts.
SWR has a direct effect on Signal to Noise. High SWR reduces Gain. Reduced Gain lowers the available Signal, so your signal to noise ratio is also reduced. Why do you believe that your design will have improved signal to noise ratio, even though it has it has less actual gain, than some other similar designs?
 

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Discussion Starter #3
Antenna signal contains not only the tv broadcast signal, but also the noise that the antenna picks up.

Thus high swr reduces not only the signal, but also the noise that comes with the signal.
 

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You also have tuner/cabling noise, that affects the signal to noise ratio. It's signal to noise ratio, inside the tuner, that is important. No antenna designs can reduce the tuner/cabling noise. Your antenna has to have enough gain, that it can overcome the noise, that comes from your system, as well as the environment. The more signal, that your antenna receives(actual gain), the more signal, that you have, to overcome the noise from the tuner/cabling, as well as environment noise. It is true that an antenna, that has more gain, may also pick up more environmental noise, but doesn't have any effect on the tuner/cabling noise, so the increased signal gain will increases the SNR. You can sometimes improve SNR by selecting an antenna design, that picks up the transmission signal that you want, and reject signals from any direction, that may have a troublesome source of noise, such as electrical transmission wires, co-channels and other sources of noise. This becomes more difficult, if you are trying to get signals from a variety of directions. It's even more important to increase the actual gain, of a non-directional antenna, because they usually pick up more environmental noise, as a result of them picking up noise from all directions. High SWR reduces your antennas actual gain, if no other factors are changed. Your antenna's actual gain affects your systems ability to overcome environmental, tuner, and cabling noise. The quality of your receiver/tuner(less tuner noise) and cabling(less noise), also affects your ability to lock in a signal. You need to understand how each factor affects reception, but gain, impedance matching reception pattern, and SWR are all important in antenna design. Since improvements of one may affect the others, it is an important balancing act, that takes some time to master. Since modeling only gives us approximate results, often building and testing of designs, is just as important. This is my personal opinion, but I also feel that how easy a design is to build, should be taken into account. The easier the design is to build, the more likely the average DIY builder will keep the dimensions accurate enough, that their build quality does not adversely affect their results. When I design an antenna, I'll gladly give up a 1/4 or 1/2 decibel, if it makes the antenna much easier to build.
 
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