 | 1.
FM Turnstile - A-C FMSS Rotated (22 Apr 2013)Antennacraft FMSS FM Turnstile, ROTATED to receive both Horizontally and Vertically Polarized signals
ALSO is a fairly good RHCP (Right Hand Circularly Polarized) antenna when signal direction along X-Axis.
Carefully check interconnections to ensure this happens in "forward" rather than "reverse" direction.
Vertical Polarization is very consistent, but Horizontal Polarization exhibits the usual Bi-Directional Pattern.
Vertical Gain remained between -1.6 and +0.7 dBi across all angles and frequencies.
However, Horizontal Gain exhibited the usual Bi-Directional pattern, with Gain in Forward Direction
between -3.1 and +0.1 dBi and Gain Nulls to either side.
When receiving a RHCP signal, Total Gain (Vert. + Horiz.) remained between -1.6 and +2.3 dBi across all angles
and frequencies, with a moderate RHCP/LHCP Cross-Polarization Ratio between 7 dB (108 MHz)and 10.4 dB (98 MHz). |
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 | 2.
FM + Hi-VHF 8-Spokes Discone (26 Aug 2012)FM + Hi-VHF 8-Spokes Discone Antenna analyzed using 4nec2.
I determined dimensions mostly via trial and error, resulting in barely acceptable (3:1) SWR on
the lowest frequency (88 MHz) and reduced Gain (0 dBi) on the highest frequency (216 MHz).
Gain=1.4 dBi in FM Band. [Somewhat larger antenna JUST for FM Band adds 0.2-0.3 dBi.]
Presumed use of AWG10 and 60-degree Complimentary Cone Angle measured from the X-Y Plane.
[Some references measure Cone Angle to the Z-Axis.]
Cone Whisker Length=36-in, Disc Radius=20-in, Feedpoint Gap=2.0-in, Inner Circle Radius=1-in.
Polarization is almost completely Vertical.
Elevation Gain charts reveal that Gain in FM Band is directed at Horizon (Elev=0-deg).
However, in Hi-VHF Band, Gain is significantly below the Horizon...hence the depicted antenna
SHOULD be mounted UPSIDE-DOWN from shown.
Ditto for commonly encountered off-the-shelf VHF Discone Antennas. |
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 | 3.
FM Monopole Whip over Groundplane (21 Dec 2011)FM Monopole Whip over a 38-in x 24-in Groundplane anallyzed using 4nec2. Length=32-in optimized for best SWR.
This antenna responds to Vertically Polarized signals, with minimal response to Horizontal Polarization.
Vert. Pol. Gain only varied from 1.54 to 1.62 dBi for all angles and frequencies, an Excellent Omni characteristic.
SWR (75-ohms) is 3.0-4.5 (just slightly worse than Optimum 71-ohms "best fit"). |
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 | 4.
FM Vertical Folded Dipole Omni (17 Dec 2011)FM Vertical Folded Dipole Omni-Directional Antenna analyzed using 4nec2.
Details on building a Horizontal Folded Dipole (rotated 90-deg) can be found here:
http://imageevent.com/holl_ands/loops/folded
This antenna responds to Vertical (ONLY) Polarization.
Vertically Polarized Raw Gain is not quite Omni-Directional, ranging from +1.7 to +2.6 dBi, depending on angle & frequency.
SWR (300-ohms) is under 2.0 across the entire FM Band. |
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 | 5.
FM Turnstile - Antennacraft FMSS (22 Dec 2011)Antennacraft FMSS FM Turnstile (two Folded Dipoles at 90-degrees to each other) analyzed using 4nec2.
[Similar to Wade CFM-FM, Wade OFM-1 and Winegard HD-6010, except non-Folded is 75-ohm output.]
Per FMSS Specs, Folded Dipole Elements = 55-in long with overall structure Height = 8-in.
Separation between Elements appears to be about 2-in, leaving about 4-in between the Crossed FD's.
Per FMSS Manual, Feedline is 9-in long and appears to be 450-ohms open ladder twinlead,
although modeling with 300-ohm twinlead revealed minimal differences, assuming it was the
same ELECTRICAL length (shorten by velocity factor).
Antenna Pattern maximums are on two diagonals, 300-deg for High Freqs and 335-deg for Low Freqs.
There are significant Gain Holes on the opposite Diagonals (40-60 & 220-240 degrees).
Across all angles and frequencies, Raw Gain ranges from -14 to +1.3 dB (Horizontally Polarized).
SWR (300-ohms) was 2.9, dropping to 1.5 at high frequencies.
FYI: FMSS Folded Dipole lengths are not quite optimum for Min SWR. Longer, 62.5-in FD Elements
minimized SWR, which was under 1.9, but decreased Raw Gain by a few tenths of a dB. |
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 | 6.
FM Turnstile Quasi-Omni - Alternate (21 Dec 2011)FM Turnstile (two Folded Dipoles at 90-degrees to each other) analyzed using 4nec2.
Separation between Folded Dipole Elements = 3-in, overall Height = 14-in.
Folded Dipole lengths were tweaked to minimize SWR, resulting in two different lengths:
51.5-in for 75-ohms and 62-in for 300-ohms, presuming 3-in FD Element Separation. Both are shown below.
Antenna Pattern maximum is on two diagonals, 300-deg for High Freqs and 335-deg for Low Freqs.
There are significant Gain Holes on the opposite Diagonals (40-60 & 220-240 degrees).
Across all angles and frequencies, Raw Gain ranges from -13 to +1.4 dB (Horizontally Polarized).
SWR (75-ohms) is 1.8-3.2 with minimum mid-band, however SWR (300-ohms) is 3.5 dropping to 1.6, so either may be used. |
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 | 7.
FM Double-Hoop Omni (17 Dec 2011)FM Double-Hoop Omni antenna analyzed using 4nec2.
Similar to Antennas Direct FM-360-HD, Antiference FM1080, Dipol A0210/A0220, Fracarro "FM Omni", Televes 1201 & Triax "FM Omni".
This antenna responds to Horizontal (ONLY) Polarization.
Horizontally Polarized Raw Gain is not quite Omni-Directional, ranging from -2.1 to +1.3 dBi, depending on angle & frequency.
SWR (300-ohms) is 6.2-11.5 |
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 | 8.
FM Double-Hoop + Vertical-Dipole Outside (17 Dec 2011)FM Double-Hoop plus Vertical Dipole Outside analyzed using 4nec2.
This antenna responds to both Horizontal and Vertical Polarization, although they are only have equal Raw Gain at about 97 MHz.
Below 97 MHz, Vertical Gain is reduced by more than 10 dB and above 97 MHz Horizontal Gain is reduced by more than 10 dB.
However, Total Gain (Vert. + Horiz.) remained between -1.9 and +2.1 dBi across all angles and frequencies.
SWR (75-ohms) was under 5. SWR (300-ohms) was excessive on the lowest frequencies.
Although Raw Gain varies quite a bit, the Omni-Directional azimuthal coverage remains very consistent across all angles.
However, users may be unhappy with performance if a station is only transmitting one Polarity. |
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 | 9.
FM Double-Hoop + Vertical-FD-Outside (23 Dec 2011)FM Double-Hoop plus Vertical-Folded-Dipole-Outside analyzed using 4nec2.
This antenna responds to Horizontal and Vertical Polarization, with a Horizontal Gain of -3.9 to +1.2 dBi.
Vertical Whip max was -1.4 dBi with a -22 dBi Gain hole on lower freqs for Vertically Polarized signals.
Total Gain (Vert. + Horiz.) remained between -2.3 and -1.4 dBi across all angles and frequencies.
However, users may be unhappy with performance if a station is only transmitting Vertical Polarity.
SWR (300-ohms) was 6.4-6.8. |
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 | 10.
FM Double-Hoop + Vert. Dipole In Center (21 Dec 2011)FM Double-Hoop plus Vertical Dipole Omni (IN CENTER OF HOOP) analyzed using 4nec2.
This antenna responds to both Horizontal and Vertical Polarization, although they are only have equal Raw Gain at about 97 MHz.
Below 97 MHz, Vertical Gain is reduced by up to 9 dB and above 97 MHz Horizontal Gain is reduced by up to 5 dB.
However, Total Gain (Vert. + Horiz.) remained between -1.2 and +2.3 dBi across all angles and frequencies.
SWR (300-ohms) was under 6.2
Although Raw Gain varies quite a bit, the Omni-Directional azimuthal coverage remains very consistent across all angles.
However, users may be unhappy with performance if a station is only transmitting one Polarity. |
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 | 11.
FM Double-Hoop + Vertical-FD-In-Center (23 Dec 2011)FM Double-Hoop + Vertical-Folded-Dipole In Center analyzed using 4nec2.
This antenna responds to Horizontal and Vertical Polarization, with a Horizontal Gain of -5.2 to +0.8 dBi.
Vertical Whip max was +1.2 dBi with a -10 dBi Gain hole on lower freqs for Vertically Polarized signals.
Total Gain (Vert. + Horiz.) remained between -1.8 and +2.3 dBi across all angles and frequencies.
However, users may be unhappy with performance if a station is only transmitting Vertical Polarity.
SWR (300-ohms) was 2.2-7.2. |
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 | 12.
FM Double-Hoop + Vertical Whip Outside (17 Dec 2011)FM Double-Hoop plus Vertical Whip Outside analyzed using 4nec2. Similar to Dipol A0221 Antenna:
http://www.dipolnet.com/estore-antennas-fm,4346.htm
This antenna responds to Horizontal and Vertical Polarization, but Raw Gain is not very consistent on all angles.
Vertical Whip has a Gain hole on lower freqs for Vertically Polarized signals.
Total Gain (Vert. + Horiz.) remained between -3.2 and +1.9 dBi across all angles and frequencies.
However, users may be unhappy with performance if a station is only transmitting Vertical Polarity.
SWR (300-ohms) was 5.1-7.1. |
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 | 13.
FM ESS Curves - Fracarro & Dipol (27 Dec 2011)FM ESS Curve Quasi-Omni Antennas analyzed using 4nec2. Although Vertical Polarization pattern was
mostly Omni-directional, the Horizontal pattern was Bi-Directional, with deep nulls to the sides.
Fracarro ANT1200A specifications list Height=38in (96-cm) and Width=30-in (77-cm) with 75-ohm Type "F" output
(e.g. 300:75-ohms Balun). Fracarro claims Max Gain=2.1 dB?, F/B Ratio="OMNI", -3 dB Beamwidth=360-deg
and Return Loss=-16 dB (SWR Under 1.38): http://www.fracarro.es/download/prodottitvsat/Aerials/FM_SERIES.pdf
A 4nec2 model was constructed, assuming two variable length (="Middle") wires at the mid-point with Z=0 (along Y-Axis).
At either end of the Middle wires are quarter-circle arcs with Radius-Of-Curvature=0.5*(Width-Middle), to which are attached
straight up-and-down wires extending to +/- Height/2.
Actual dimensions may be slightly different, e.g. Separation between ESS's may be (inconsequential) 2.5-in vice 2.0-in.
The "optimum" length for "Middle" (7.6-in) was found by running a nikiml optimization script on the 4nec2 file (mostly Min SWR).
Fracarro 4nec2 Results: For Vertically Polarized signals, the Azimuthal Pattern was close to Omni-directional,
varying from -4.4 to -1.4 dBi across all angles and frequencies. However, for Horizontally Polarized signals,
the pattern was Bi-Directional, with deep nulls to the sides, varying from -34 to +0.1 dBi.
Across all angles and frequencies, Total Raw Gain ranges from -4.4 to +2.3 dB (Horizontal + Vertical).
SWR was excellent, between 1.3 in middle and 2.7 at band edges.
=============================================================================
Dipol A0222/A0223 specifications are very sparse. Gain curve starts at -3 dBi, rising to -1 at mid-high frequencies.
Impedance is 300-ohm (no Balun) and they (erroneous) indicate that it has Horiz. and Vert. (wrong) polarization.
Size is indeterminate: http://www.dipolnet.com/estore-antennas-fm,4346.htm
Blowing up and comparing the photo of the Dipol A0222/A223 to the Fracarro ANT1200A reveals that they are
very similar, except for being mirror images about the Z-Axis. After reversing the sign of all Y-Axis coordinates
in the Fracarro 4nec2 file, it was compared to the Dipol photo, which appears to be slightly shorter, wider and smaller
Separation between the two ESS's compared to the Fracarro. 4nec2 file was adjusted to best match Dipol's photo:
Height=37in, Width=33in, Middle=6in & Separation=2-in.
Dipol 4nec2 Results: For Vertically Polarized signals, the Azimuthal Pattern was close to Omni-directional,
varying from -5.1 to -1.9 dBi across all angles and frequencies. However, for Horizontally Polarized signals,
the pattern was Bi-Directional, with deep nulls to the sides, varying from -36 to +0.4 dBi.
Across all angles and frequencies, Total Raw Gain ranges from -5.1 to +2.4 dB (Horizontal + Vertical).
SWR was excellent, between 1.3 in middle and 2.5 at band edges. |
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 | 14.
FM ZigZag - Triax FM Zigma (30 Dec 2011)FM ZigZag Antenna, similar to Triax FM Zigma, analyzed using 4nec2.
Triax FM Zigma Specs:
Gain = -1.0 dBi, F/B Ratio = 0 dB, Beamwidth = +/- 45-deg (Horizontal Polarization) and +/- 180-deg (Vertical Pol.).
Erroneously] "Length" [Width!!!] = 550-mm and "Width" [Height!!!] = 1140-mm:
http://www.triax.co.uk/upload/gb_-_triax_main_catalogue_2009.pdf
Triax FM Zigma Dimensions: Height = 44.88-in, Width = 21.65-in, Separation = 2.0-in.
Separation was a Guesstimate, based on Triax's picture. If it were 3.0-in, SWR is under 3.5 with negligible change in Gain.
Triax FM Zigma 4nec2 Results: For Vertically Polarized signals, the Azimuthal Pattern was close to Omni-directional,
varying from -1.5 to -0.7 dBi across all angles and frequencies. However, for Horizontally Polarized signals,
the pattern was Bi-Directional, with deep nulls to the sides (like a Folded Dipole), varying from -39 to -1.7 dBi.
Across all angles and frequencies, Total Raw Gain ranges from -1.5 to +2.4 dB (Horizontal + Vertical).
SWR (300-ohms) is under 3.7.
==============================================================================
A parameter search was conducted to find the dimensions for which the Vert. Pol. Gain was roughly equal to
Horiz. Pol. Gain and hence provided optimal response to Circularly Polarized signals. Results are below.
FM ZigZag Cir. Pol. Dimensions: Height = 39-in, Width = 22-in, Separation = 2.0-in.
Note that Cir. Pol. condition is only found in the Forward and Reverse directions due to Horiz. Pol. nulls on sides.
FM ZigZag 4nec2 Results: For Vertically Polarized signals, the Azimuthal Pattern was close to Omni-directional,
varying from -2.5 to -0.4 dBi across all angles and frequencies. However, for Horizontally Polarized signals,
the pattern was Bi-Directional, with deep nulls to the sides (like a Folded Dipole), varying from -37 to -1.1 dBi.
Across all angles and frequencies, Total Raw Gain ranges from -2.5 to +2.3 dB (Horizontal + Vertical).
SWR (300-ohms) is under 3.7.
FYI: There were many nikiml python script solutions with SWR under 3.0, but NONE came close to Cir. Pol. condition. |
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 | 15.
FM Right Circular Folded Dipole Pair (2 Jan2012)FM Right Circular Folded Dipole Pair analyzed using 4nec2. The Folded Dipole Pair was based on
K6STI's circdip3.nec Dipole Pair file found in C:/4nec2/models/VHFsimple.
K6STI's original file was modified to add the Elements completing two Crossed Folded Dipoles and was
Resized for the FM Band, with final adjustment so that the Circular Polarization was in the FORWARD
direction at 98 MHz (and REVERSE direction at 97 MHz).
EDIT (16Jan2012): Added Circular Polarization Azimuthal Charts. It's Right Hand Circular FORWARD and
Left Hand Circular to REVERSE, so carefully inspect antenna to verify direction. LHCP Suppression is reduced on low freqs. |
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 | 16.
FM Cycloid Dipole - Circular Polarized (29 Dec 2011)FM Cycloid Dipole Omni Antenna with Circular Polarization analyzed using 4nec2.
For more info re Cycloid, see: http://www.wa7x.com/cycloid_info.html
Although Raw Gain Vertical, Horizontal and TOTAL (Vertical + Horizontal) Polarization was fairly constant
across all angles and frequencies, the Impedance varied considerably. It was 9.2+127j ohms at 87 MHz,
rising to 37+410j ohms at 108 MHz, making it very difficult to design a wide-band matching network.
Best SWR was about 30:1 with 186-ohm load. Although Analog FM is tolerant of high SWR, Digital FM may not be.
Suppression of Left Hand Circular Polarization (LHCP) is very good across entire FM Band.
Intended for broadcast applications, this (and similar) antennas can be matched to 50-ohms (or 300-ohms)
for a NARROW RANGE OF FREQUENCIES by using a matching network (hit "F10" key, L/Pi/T Matching in 4nec2).
Matched SWR Chart (at bottom) was the SAME, with ANY of the L, Pi or T Filters - Low or High Pass. |
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 | 17.
Hi-VHF Monopole Whip Omni Antenna (8 Mar 2010)Hi-VHF Monopole Whip (14-in high) analyzed using 4nec2.
This antenna responds to Vertical (ONLY) Polarization.
TOTAL Raw Gain was calculated, which is the sum of Horizontal & Vertical Gain.
If a station transmits equal power in H and V (CP=circular polarization),
then the orientation of the antenna won't make TOO much difference.
More and more stations are firing up a second transmitter/antenna for CP
broadcast to an expected explosion (???) of Mobile TV viewers.
You can check the status of your local station here: http://www.rabbitears.info/ss/
However if a station is still only transmitting Horizontal Polarization, the
antenna needs to be tilted on it's side (tip of whip to left or right).
Otherwise the Gain will drop dramatically from what is listed below.
===================================
a) Whip (14-in high) with just a 2-inch circular disc ground plane, such as when placed on top of a stack of books/magazines on a wood table. Pretty pathetic.....
UHF: Raw Gain is 1 to -1 dBi for Ch14-30, but drops to -13 dBi on Ch51. SWR (75-ohm) is excessive (as high as 17 on low channels),
dropping below 4 on Ch42-69. Hence Net Gain is non-existent.
Hi-VHF: Raw Gain is constant 1.7 dBi, but SWR is excessive (300-90), hence Net Gain is non-existent.
Ch2-6: Raw Gain is constant 1.6 dBi, but SWR is excessive (60,000-6,000), hence Net Gain is non-existent.
==================================
Improved results with a small ground plane:
b) Whip (14-in high) with a 19-in x 12-in rectangular ground plane, such as when placed on top of some electronic gear. Better, but still not much of an antenna....
[Location near electronic equipment NOT recommended due to electronic interference pick-up.]
UHF: Raw Gain is 1 to -1 dBi for Ch14-33, but drops to -7 dBi on Ch51. SWR (75-ohm) is excessive (as high as 9 on low channels and 5 on high channels),
dropping below 4 on Ch27-53. Hence Net Gain is very low except on Ch27-53 it peaks at -3 dBi.
Hi-VHF: Raw Gain is constant 1.5 dBi, but SWR is excessive (10-4) on Ch7-9, hence Net Gain is only adequate on Ch11-13.
Ch2-6: Raw Gain is constant 1.7 dBi, but SWR is excessive (6000-660), hence Net Gain is non-existent.
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