Canadian TV, Computing and Home Theatre Forums banner

compact caravan antenna

9K views 64 replies 7 participants last post by  Yurii Pylypenko 
#1 ·
Hi from Australia
I have been reading this forum for a few days trying to build a antenna that is compact enough to store in the van that covers the Australian tv VHF UHF bands.
My current antenna is a matchmaster 01mm-de7 combined 4 element UHF and folded dipole VHF element with 25db booster.
Thinking of building holl_ands UHF 2-Bay SOLID Triangles bowtie with grid reflector (Grid more robust to store in caravan) https://imageevent.com/holl_ands/multibay/uhf2baysolidtrianglesvarrrs
I'm having trouble understanding the high SWR figures and if they are detrimental to the performance of the antenna.
My understanding is to tune SWR to under 2.5 or less.
Also i noticed the feed spacing is 4in where most of the other bowtie antenna's are 1.5in.
I assume Feeder spacing affects antenna impedance and SWR
Any suggestions would be appreciated
 
#2 ·
a.), b.), c.) UHF antennas at that link all have decent VSWR as indicated.


I don't want to speak for him, but quite often when holl_ands does an analysis of an antenna, he will Sweep the VHF Band as well as the UHF band. This doesn't mean the antenna was designed for VHF at all. So don't let that confuse you.
 
#7 ·
Hollands mentioned "SWR (300-ohms) = 86 to 38 is Excessive"
So is a decent figure for that antenna
It may help to read some wiki entries on VSWR...
https://en.wikipedia.org/wiki/Standing_wave_ratio

In a nutshell, the lower the VSWR the better. Is not critical, that vswr be great in the receive direction. Meaning, poor VSWR is not gonna shut your receiver down. However, it is a sure sign that the antenna was not designed for the band with high VSWR and probably won't work very well if at all.

In the Transmit direction VSWR is extremely critical to ensure an efficient transmitter system. Typical numbers for a Transmitter may start to limit the PA output power once it sees 2:1 VSWR, and may shut itself down entirely beyond 3:1 VSWR. Protection Circuit designs may vary depending on the type of antenna it's designed for, so on... But gives ya a rough idea..
 
#4 ·
As I said, look at what yoiu are reading about! eg "UHF 2-Bay SOLID Triangles - Var RR's"


So, since you are reading about a UHF antenna, ignore everything you see about VHF. Why??? Because the antenna yoiu are looking at is designed for UHF, not VHF. Simple as that...


You do know the difference, correct?
 
#5 ·
I do know the difference between VHF and UHF antenna's and that they are designed for particular bands.
I was considering the bowtie design because of their bandwidth and ability to receive some VHFhi channels at reduced gain.
The 2 bay bowtie seems to be more compact than a Single Bay Gray-Hoverman with NAROD's or a VHF/UHF yagi dipole or phased array antenna.
I'm looking for an antenna that has reasonable bandwidth/gain for it's physical size.
Considering antenna physical size is governed by wavelength that it is designed to receive.
I have been using this antenna https://www.matchmaster.com.au/digital-tv-antennas/01mm-de7/ but would like to build one with more gain.
Just asking what affect the SWR has on the net VHF gain and what the affect feeder spacing has on antenna matching as this enclosed bowtie has 4in feeder spacing where most of the other bowties are 1.5 to 2.5in.
 
#6 ·
You might want to take a look at the M4 without reflector. It's lighter and easier to build than the GH and has about 5dB gain on VHF. I used silver solder and #10 wire make mine which is light and durable. Adding a 30" wide reflector increases VHF gain considerably. The no reflector model won't be great for DX but it does a good job with fairly strong signals and doesn't require precision aiming.
 
#8 ·
If it was me, I would go with the UHF antenna ur planning on for UHF, and for VHF I'd use a separate antenna like a pair of Rabbit Ears. Combining them with a VHF/UHF diplexor (UVSJ). That gives you more flexibility since you can orient the UHF and VHF antennas independently for optimum reception of both bands simultaneously.
 
#9 ·
Start simple, see if that works for you, before heading to more complex antenna systems is what I am saying...


The missing 'Edit' button is really annoying...
 
#11 ·
I worked for Telecom Australia for 30yrs, back when radio telephones transmitters systems didn't have reflected power protection or PA stage limiters. Power up without load/antenna blown TX.
I was not sure on the affect of SWR on receivers.
From holl_and design result the high RX SWR seem to have some influence the net gain of the antenna.
But as Jorget says i shouldn't be too concerned about excessive receiver SWR.
For simplicity and small size I'll give the 2 bay bowtie a go. maybe solid or 6 whisker with reflector.
Still wonder why some bowtie's have 4in feed spacing and others have 1.5 to 2.5 in spacing.
I suppose it's what the design program optimises the antenna too.
And as ExDilbert said and i have read a reflector will improve VHF gain.
I have some smaller spacing mesh 25mm x25mm for my reflector.
Thanks for your input.
 
#52 ·
I built this, and it’s fantastic! It gets all the same channels as my M4. It looked like a good design, but I was pleasantly surprised. The VHF gain is a bit lower, but UHF might be a bit higher.

I used 14AWG copper for the phase lines instead of sheet metal. I cut out four aluminum triangles, screwed the copper directly into them, and put it all on a PVC frame.
 
#13 ·
It's my understanding that higher SWR numbers won't hurt your receiver, like it would with older transmitters(most modern transmitters have protection circuits, that shut them down if SWR is excessive). SWR number above 1.0 do affect the actual gain of your antenna. If you look at Yurii's Gain charts, you will see Total Gain figures in blue, and Actual Gain figures charted in red. It looks to me that an SWR of 2.0 caused a loss of about 0.5db. I know that there are formulas for figuring out this number, but I think that, for most people modeling and building antennas, the figure of 2.5 or 2.7, as a max SWR, will usually ensure that your antenna will work acceptably. Always keep in mind, that SWR closer to 1.0 will have less loss of gain, at that frequency. Excessive SWR numbers are going to indicate, that you may not get anyway near the gain listed, for that frequency or band.
 
#14 ·
that shut them down if SWR is excessive
that is important only for powerful rigs, which cannot handle doubled signal voltage. To keep price low, powerful transmitters always use as small transistors and tubes as possible. No one build 100 ton Caterpillar to handle 20 ton commodities.
In worst case scenario (no load at all or short circuit) SWR is getting endless and Voltage is doubled. If anode or collector can handle this double signal voltage - it will work fine for ages.

Also this is true only if transmitter has no antenna tuner (no variable impedance match), only fixed impedance 50 Ohm


I know that there are formulas for figuring out this number
https://docs.google.com/spreadsheet...DDekGm3OsjRqcEICleeDgIM1c/edit#gid=1398883485

this formula accounts only mismatch loss due to reflection. It will be true in case of zero-length transmission line (no cable, direct LNA mount) or lossless transmission line (short air line with good wire/pipe gauge)

Datasheet cable losses are always measured @ SWR=1
If standing waves occur in any cable - losses will go higher. This formula is more complicated and rarely used:
https://docs.google.com/spreadsheet...kV58lhk3V33WNiCL-G5nbcx0MI/edit#gid=402116968

If cable has 3 dB loss (about 20 meters of TV cable at UHF), going to SWR=2 gives extra 0.4 dB heat penalty (roughly equivalent of 2 meters extra cable length)
 
#15 ·
higher SWR numbers won't hurt your receiver
there are hardly any true 75 Ohm LNA which can have SWR=1 anywere at VHF or UHF frequencies.

Wideband LNA with SWR<1.5 in 174-862 MHz is hardly theoretically possible only with HEMT transistor specially designed for this frequencies to have channel impedance specifically close to 75 Ohm in 200...700 MHz range.

Most (if not all) actual TV LNA (not narrowband tunable) are built around conventional BJT or FET transistors. They have either very low input impedance (in 15...25 Ohm range), quite big reactance (j10...j15 range, which is in order of magnitude of real part of impedance) or very high (FET in common drain mode). There is no mode for conventional transistor with input impedance close to 50 or 75 Ohm.

Datasheet Nf for transistor are given for best-matching impedance (it's not always SWR=1, lowest possible Nf are often at a higher SWR, may be 1.3 ... 1.6 range)

LNA design with low noise figures is all about matching techniques.
There is no way to match 15-25 Ohm transistor to achieve SWR<5 in 174-862 MHz range

That's why best available TV tuners have only 4...5 dB noise figures (DVB-T2 standard imply not worse than 7 dB Noise figure).
Low-cost transistors with Nf=1 dB and less are available from 1990, and TV tuners or TV LNA built around this Nf=1 dB transistors get only 4 dB noise (best rigs)

This 3 dB loss is due to very poor SWR matching.

If your antenna simulator (or real-world SWR measurement) says antenna have SWR=2.7, actual SWR with actual LNA might be better or worse than 2.7
If your antenna have Z=25 +j0 and SWR75 is predicted to be 3.0 and you attach this antenna to Z=25 +j0 LNA - there won't by any reflection and SWR=1 (for direct mount).
If you have cable between LNA and antenna - there will be standing waves inside this cable (some extra 0.4..0.6 dB heat loss in 3.0 dB lossy cable) but not mismatch loss at the end (at cable-LNA junction)

if your antenna have Z=225 +j0 and SWR75 is predicted to be 3.0 and you attach this antenna to Z=25 +j0 LNA - SWR will be 9, not 3. And SWR=9 is 4.4 dB mismatch loss!
 
#16 ·
The reason i was looking at the SWR figures because they are a lot higher in the HiVHF band on the bowtie antenna that i was thinking of building.
I see the bowtie Yurii posted the link for has very low SWR in the UHF range but i assume a lot higher in the HiVHF range.
After looking at the huge variety of antenna designs holl_day has, i found a couple of Hi VHF UHF 2 bay bowties that have a Rectangular Loop Resonator that reduces the Hi VHF SWR to an acceptable level and are compact enough to store in the caravan.
These antenna don't have a reflector fitted. So I'm trying to learn how to use the 4nec2 software to simulate one with a grid reflector fitted.
Around Australia almost all free to air tv transmitter transmit all channels from the site, so narrow high gain antenna would suit me best

Yurii thanks for your explanation on antenna receiver matching. Been too long time since i worked with polar / J notation in active circuits,
If i have to use a masthead amplifier/LNA i will be mounting it as close as possible to the antenna.
So the standing wave may have less effect when the antenna feed is shorter than operating wavelength and terminated into the amp.
 
#17 ·
I'm sure that forcing UHF antenna to work as VHF antenna is not viable from any point of view: price, size, weight, perfomance.

SWR is not the only reason for perfomance degrade. When element width become less than lambda/2 it acts as director, not reflector.
If screen with is less than 860 mm @ 174 MHz - it acts as director and direct radiation in opposite to expected direction

Most lightweight and compact UHF+VHF combo is VHF dipole + UHF yagi + frequency diplexer (combiner)
 
#18 ·
I'm using a combo VHF dipole and UHF yagi with 15db maskhead amplifier at the moment

I think this antenna has a gain of only 3dbi VHF and 5dbi UHF.
I'm learning how to use the nec program and have modeled holl_der HiVHF+UHF RL-M2 2-Bay+Loop - NO Refl and added a reflector.
The 2x4 reflector gave me mixed results.
hi VHF SWR is around 40 with reflector 4.5 in behind.
When optimised i get good hi VHF SWR when reflector is 14in behind.
Not sure what I'm doing, so may stick with the VHF/VHF combo that i already have.
 
#19 ·
Not sure what I'm doing, so may stick with the VHF/VHF combo that i already have.
It's easy to add length to Yagi and get any directivity in range 5...13 dBi (proportional to length)

Any dipole is ~2 dBi. VHF dipole is not exception. To get any directivity at VHF (D>2 dBi) you need either reflector or director.

Dipole at the photo have poor perfomance for several reasons:
* it is shorted dipole, hence narrowband and R much lower than 300 Ohm. I expect SWR at least 6 over the band and realized gain -2...-1 dBi (less than 0 dBi)
* it uses open symmetrical transmission line, which is traced faulty. Both wires in symmetrical line have to be equally coupled to any obstacles (ground) and coupling to obstacles should be much less then coupling between wires. This is not true on photo. You can not wrap open symmetrical line over ground metal boom.
Due to this I expect huge directivity distortion (boom radiation) and impedance imbalance (feed radiation) and further mismatch.
 
#21 ·
I'm having a go at modifying one of holl_and,s antenna designs.
UHF 2-Bay SOLID Triangles - Var RR's
For Hi VHF i fitted a resonance loop and managed to get theHi VHF swr under 20
UHF gain 14db swr just over 2 and HiVHF gain 8.5db swr under 20.
Not sure how critical the impedance and F/B ratio are.
I assume the IMP should be as close to 300 ohn's as possible.
If i copied the NEC file on here, could someone check it out and tell me if it is worth building.
 
#22 ·
Hi Grey Nomad
Post your NEC file, and I'll look at it. Others will probably look at it as well. UHF numbers look good, and hopefully someone sees a way to get SWR down for HiVHF. Impedance matching, at 300ohm. is ideal, but often hard to achieve for VHF/UHF antennas.

Lawrence
 
#23 ·
I will try to attach my nec file.
Ended up copy and pasting.
Hope it worked

CM UHF Super-2-Bay, VARIABLE Solid Triangles, 11 Reflector Rods, 4nec2 by holl_ands, 4Mar2015
CM BowLength=9.25-in, BowSpacing=12.5-inl, TineSep=7.5-in, FeedSep=4.0-in, BS=0.0, ALL AWG10.
CM 11RR (QICT). PYTHONSEG(15), NO Errors or Warnings, UHF AGT=1.184 (0.74 dB). 8 VARIABLES.
CM
CM D--OPT -s(470,12,20) -t(13,15) --swr-target=2.7 --f2r-target=18 --f2b-target=18
CM D--OPT --target-function=(4*max_ml+8*max_gain_diff+4*max_f2r_diff+max_f2b_diff)/17
CM D--OPT --de-np=50 -r restart.log
CM D--OPT --auto-segmentation=15 --char-impedance=300 --num-cores=8
CM D--EVAL --auto-segmentation=0 --char-impedance=300 --num-cores=8
CM D--EVAL -s(174,6,8) -s(470,12,29) --publish
CM SOURCE Wire Radius, Adjust for AGT=1.0: UHF=0.0495 & Hi-VHF=0.0495
CM NOTE: IF Rsrc any smaller, big JUMP in AGT, HiVHF AGT=1.121 (0.5 dB)
CM
CM Bow Half-Length:
CM Distance between the Centers of the Two Bowties:
CM Bow Tine Separation:
CM Separation (in inches) between two FEEDLINE wires:
CM Bowtie Forward Sweep:
CM Indentation along Centerline:
CM
CM Calculated from above INPUT Values:
CM Z-Coord 1/3 of the Way from Bowtie
CM Z-Coord 2/3 of the Way from Bowtie
CM
CM SYMBOLS FOR REFLECTOR RODS:
CM Reflector Rod Separation behind Hourglass):
CM Reflector Rod-to-Rod Separation:
CM Reflector Rod Half-Lengths :
CM
CM # segs X1 Y1 Z1 X2 Y2 Z2 radius
CM
CM
CM
CM
CM
CM
CM
CM
CM
CM
CM CROSS-OVER FEEDLINE:
CM
CM
CM UP TO 17 EA REFLECTOR RODS:
CM GW 90 45 -RS -YRod 8*RR -RS YRod 8*RR Rrod
CM GW 91 45 -RS -YRod 7*RR -RS YRod 7*RR Rrod
CM GW 92 45 -RS -YRod 6*RR -RS YRod 6*RR Rrod
CM GW 103 45 -RS -YRod -6*RR -RS YRod -6*RR Rrod
CM GW 104 45 -RS -YRod -7*RR -RS YRod -7*RR Rrod
CM GW 105 45 -RS -YRod -8*RR -RS YRod -8*RR Rrod
CM
CM Top & Side Elements of OUTER RECTANGULAR LOOP:
CM
CM
CM
CM
CM FR Freq Sweep choices in order of increasing calculation time (fm holl_ands):
CM FR 0 0 0 0 198 0
CM FR 0 0 0 0 584 0
CM FR 0 34 0 0 410 12
CM FR 0 39 0 0 470 6
CM FR 0 77 0 0 470 3
CM FR 0 153 0 0 470 1.5
CM FR 0 71 0 0 300 10
CM FR Hi-VHF choices:
CM FR 0 15 0 0 174 3
CM FR 0 29 0 0 174 1.5
CM FR 0 43 0 0 174 1
CM FR 0 26 0 0 150 6
CM FR Lo-VHF choices:
CM FR 0 19 0 0 54 3
CM FR 0 35 0 0 54 1
CM FR 0 36 0 0 75 1
CM FR 0 28 0 0 54 6
CM FR 0 64 0 0 54 12
CM RP choices in order of increasing calculation time:
CM RP 0 1 1 1510 90 90 1 1 0 0
CM RP 0 1 1 1510 90 0 1 1 0 0
CM RP 0 1 1 1510 90 180 1 1 0 0
CM RP 0 1 1 1510 90 15 1 1 0 0
CM RP 0 1 1 1510 90 20 1 1 0 0
CM RP 0 1 1 1510 90 30 1 1 0 0
CM RP 0 1 1 1510 90 40 1 1 0 0
CM RP 0 1 1 1510 90 50 1 1 0 0
CM RP 0 1 1 1510 90 60 1 1 0 0
CM RP 0 1 1 1510 90 70 1 1 0 0
CM RP 0 1 1 1510 90 80 1 1 0 0
CM RP 0 1 37 1510 90 0 1 5 0 0
CM RP 0 73 1 1510 90 0 5 1 0 0
CM RP 0 73 73 1510 90 0 5 5 0 0
CM RP 0 285 73 1510 90 0 5 5 0 0
CE
SY Rsrc=0.0495
SY Rbow=0.051 'Radius (in inches) of BOWTIE elements
SY Rfeed=0.051 'FEEDLINE wire Radius
SY BowLen=10 'Optimizer found 9.236515' 7, 12
SY ZBowII=12.07 'Optimizer found 12.4823' 10, 16
SY TineSep=7.5 'Optimizer found 7.500408' 2, 12
SY FedSep=2.5 'Optimizer found 4.070262' 0.75, 5
SY BowSwp=0.0 '[NOT USED IN THIS MODEL]
SY Indent=0.0 '[NOT USED IN THIS MODEL]
SY Xbow=0.0 'X-Coord of Bowties [NOT USED IN THIS MODEL]
SY Cond=3.0e7 'Conductivity (Copper=3.0e7, Alum=2.0e7, StainlessSteel=1.67e7)
SY X1=BowSwp/3
SY Z7=TineSep/2
SY Z8=ZBowII/2
SY Z9=TineSep/2
SY Z1=TineSep/6
SY Z2=TineSep/3
SY YBowN=-FedSep/2
SY YBowP=FedSep/2
SY YBow=(BowLen^2-(TineSep/2)^2-BowSwp^2)^0.5
SY Ymax=FedSep/2+YBow
SY Y1=FedSep/2+YBow/3
SY Y2=FedSep/2+2*YBow/3
SY Yinr=Ymax-Indent
SY Ymid=FedSep/2+(Yinr-FedSep/2)/2
SY RS=4.0 'Optimizer found 4.008359' 2, 10
SY RR=2.25 'Optimizer found 2.216791' 1, 10
SY YRod=18.625 'Optimizer found 18.66497' 6, 25
SY Rrod=0.125 'Radius of Reflector Rods [QICT, COULD BE THINNER.....]
SY RACT=.0495
SY H=21
SY W=13
SY Off=-0.5
GW 1 5 Xbow YBowN 0 Xbow YBowP 0 Rsrc 'SRC
GW 2 4 Xbow YBowP Z8 BowSwp+Xbow Y1 Z8+Z1 Rbow
GW 3 4 Xbow Y1 Z8+Z1 2*X1+Xbow Y2 Z8+Z2 Rbow
GW 4 4 Xbow Y2 Z8+Z2 X1+Xbow Ymax Z8+Z7 Rbow
GW 5 4 Xbow YBowN Z8 X1+Xbow -Y1 Z8+Z1 Rbow
GW 6 4 Xbow -Y1 Z8+Z1 2*X1+Xbow -Y2 Z8+Z2 Rbow
GW 7 4 Xbow -Y2 Z8+Z2 BowSwp+Xbow -Ymax Z8+Z7 Rbow
GW 8 4 Xbow YBowP Z8 X1+Xbow Y1 Z8-Z1 Rbow
GW 9 4 Xbow Y1 Z8-Z1 2*X1+Xbow Y2 Z8-Z2 Rbow
GW 10 4 Xbow Y2 Z8-Z2 BowSwp+Xbow Ymax Z8-Z7 Rbow
GW 11 4 Xbow YBowN Z8 X1+Xbow -Y1 Z8-Z1 Rbow
GW 12 4 Xbow -Y1 Z8-Z1 2*X1+Xbow -Y2 Z8-Z2 Rbow
GW 13 4 Xbow -Y2 Z8-Z2 BowSwp+Xbow -Ymax Z8-Z7 Rbow
GW 14 4 BowSwp+Xbow Yinr Z8 BowSwp+Xbow Ymax Z8+Z7 Rbow
GW 15 4 BowSwp+Xbow Yinr Z8 BowSwp+Xbow Ymax Z8-Z7 Rbow
GW 16 4 BowSwp+Xbow -Yinr Z8 BowSwp+Xbow -Ymax Z8+Z7 Rbow
GW 17 4 BowSwp+Xbow -Yinr Z8 BowSwp+Xbow -Ymax Z8-Z7 Rbow
GW 18 5 Xbow YBowP Z8 BowSwp+Xbow Ymid Z8 Rbow
GW 19 5 Xbow Ymid Z8 BowSwp+Xbow Yinr Z8 Rbow
GW 20 5 Xbow -YBowP Z8 BowSwp+Xbow -Ymid Z8 Rbow
GW 21 5 Xbow -Ymid Z8 BowSwp+Xbow -Yinr Z8 Rbow
GW 22 2 BowSwp+Xbow Ymid Z8 BowSwp+Xbow Y1 Z8+Z1 Rbow
GW 23 3 BowSwp+Xbow Ymid Z8 2*X1+Xbow Y2 Z8+Z2 Rbow
GW 24 2 BowSwp+Xbow -Ymid Z8 X1+Xbow -Y1 Z8+Z1 Rbow
GW 25 3 BowSwp+Xbow -Ymid Z8 2*X1+Xbow -Y2 Z8+Z2 Rbow
GW 26 2 BowSwp+Xbow Ymid Z8 BowSwp+Xbow Y1 Z8-Z1 Rbow
GW 27 3 BowSwp+Xbow Ymid Z8 2*X1+Xbow Y2 Z8-Z2 Rbow
GW 28 2 BowSwp+Xbow -Ymid Z8 X1+Xbow -Y1 Z8-Z1 Rbow
GW 29 3 BowSwp+Xbow -Ymid Z8 2*X1+Xbow -Y2 Z8-Z2 Rbow
GW 30 4 BowSwp+Xbow Yinr Z8 2*X1+Xbow Y2 Z8+Z2 Rbow
GW 31 4 BowSwp+Xbow -Yinr Z8 2*X1+Xbow -Y2 Z8+Z2 Rbow
GW 32 4 BowSwp+Xbow Yinr Z8 2*X1+Xbow Y2 Z8-Z2 Rbow
GW 33 4 BowSwp+Xbow -Yinr Z8 2*X1+Xbow -Y2 Z8-Z2 Rbow
GW 42 4 Xbow YBowP -Z8 BowSwp+Xbow Y1 -Z8+Z1 Rbow
GW 43 4 Xbow Y1 -Z8+Z1 2*X1+Xbow Y2 -Z8+Z2 Rbow
GW 44 4 Xbow Y2 -Z8+Z2 X1+Xbow Ymax -Z8+Z7 Rbow
GW 45 4 Xbow YBowN -Z8 X1+Xbow -Y1 -Z8+Z1 Rbow
GW 46 4 Xbow -Y1 -Z8+Z1 2*X1+Xbow -Y2 -Z8+Z2 Rbow
GW 47 4 Xbow -Y2 -Z8+Z2 BowSwp+Xbow -Ymax -Z8+Z7 Rbow
GW 48 4 Xbow YBowP -Z8 X1+Xbow Y1 -Z8-Z1 Rbow
GW 49 4 Xbow Y1 -Z8-Z1 2*X1+Xbow Y2 -Z8-Z2 Rbow
GW 50 4 Xbow Y2 -Z8-Z2 BowSwp+Xbow Ymax -Z8-Z7 Rbow
GW 51 4 Xbow YBowN -Z8 X1+Xbow -Y1 -Z8-Z1 Rbow
GW 52 4 Xbow -Y1 -Z8-Z1 2*X1+Xbow -Y2 -Z8-Z2 Rbow
GW 53 4 Xbow -Y2 -Z8-Z2 BowSwp+Xbow -Ymax -Z8-Z7 Rbow
GW 54 4 BowSwp+Xbow Yinr -Z8 BowSwp+Xbow Ymax -Z8+Z7 Rbow
GW 55 4 BowSwp+Xbow Yinr -Z8 BowSwp+Xbow Ymax -Z8-Z7 Rbow
GW 56 4 BowSwp+Xbow -Yinr -Z8 BowSwp+Xbow -Ymax -Z8+Z7 Rbow
GW 57 4 BowSwp+Xbow -Yinr -Z8 BowSwp+Xbow -Ymax -Z8-Z7 Rbow
GW 58 5 Xbow YBowP -Z8 BowSwp+Xbow Ymid -Z8 Rbow
GW 59 5 Xbow Ymid -Z8 BowSwp+Xbow Yinr -Z8 Rbow
GW 60 5 Xbow -YBowP -Z8 BowSwp+Xbow -Ymid -Z8 Rbow
GW 61 5 Xbow -Ymid -Z8 BowSwp+Xbow -Yinr -Z8 Rbow
GW 62 2 BowSwp+Xbow Ymid -Z8 BowSwp+Xbow Y1 -Z8+Z1 Rbow
GW 63 3 BowSwp+Xbow Ymid -Z8 2*X1+Xbow Y2 -Z8+Z2 Rbow
GW 64 2 BowSwp+Xbow -Ymid -Z8 X1+Xbow -Y1 -Z8+Z1 Rbow
GW 65 3 BowSwp+Xbow -Ymid -Z8 2*X1+Xbow -Y2 -Z8+Z2 Rbow
GW 66 2 BowSwp+Xbow Ymid -Z8 BowSwp+Xbow Y1 -Z8-Z1 Rbow
GW 67 3 BowSwp+Xbow Ymid -Z8 2*X1+Xbow Y2 -Z8-Z2 Rbow
GW 68 2 BowSwp+Xbow -Ymid -Z8 X1+Xbow -Y1 -Z8-Z1 Rbow
GW 69 3 BowSwp+Xbow -Ymid -Z8 2*X1+Xbow -Y2 -Z8-Z2 Rbow
GW 70 4 BowSwp+Xbow Yinr -Z8 2*X1+Xbow Y2 -Z8+Z2 Rbow
GW 71 4 BowSwp+Xbow -Yinr -Z8 2*X1+Xbow -Y2 -Z8+Z2 Rbow
GW 72 4 BowSwp+Xbow Yinr -Z8 2*X1+Xbow Y2 -Z8-Z2 Rbow
GW 73 4 BowSwp+Xbow -Yinr -Z8 2*X1+Xbow -Y2 -Z8-Z2 Rbow
GW 90 7 Xbow YBowP Z8 Xbow YBowP 0 Rfeed
GW 91 7 Xbow YBowN Z8 Xbow YBowN 0 Rfeed
GW 92 7 Xbow YBowP -Z8 Xbow YBowP 0 Rfeed
GW 93 7 Xbow YBowN -Z8 Xbow YBowN 0 Rfeed
GW 93 45 -RS -YRod 5*RR -RS YRod 5*RR Rrod
GW 94 45 -RS -YRod 4*RR -RS YRod 4*RR Rrod
GW 95 45 -RS -YRod 3*RR -RS YRod 3*RR Rrod
GW 96 45 -RS -YRod 2*RR -RS YRod 2*RR Rrod
GW 97 45 -RS -YRod RR -RS YRod RR Rrod
GW 98 45 -RS -YRod -RR -RS YRod -RR Rrod
GW 99 45 -RS -YRod -2*RR -RS YRod -2*RR Rrod
GW 100 45 -RS -YRod -3*RR -RS YRod -3*RR Rrod
GW 101 45 -RS -YRod -4*RR -RS YRod -4*RR Rrod
GW 102 45 -RS -YRod -5*RR -RS YRod -5*RR Rrod
GW 14 9 Off -W/2 H/2 Off W/2 H/2 RACT 'Top
GW 15 9 Off -W/2 -H/2 Off W/2 -H/2 RACT 'Bot
GW 16 5 Off -W/2 0 Off -W/2 H/2 RACT 'LT
GW 17 5 Off -W/2 0 Off -W/2 -H/2 RACT 'LB
GW 18 5 Off W/2 0 Off W/2 H/2 RACT 'RT
GW 19 5 Off W/2 0 Off W/2 -H/2 RACT 'RB
GW 66 5 -RS -YRod 0 -RS YRod 0 Rrod
GS 0 0 0.0254
GE 0
LD 5 0 0 0 Cond 'Conductivity
GN -1
EK
EX 0 1 3 0 1 0 0 'GW1 is SOURCE wire
FR 0 29 0 0 470 12
RP 0 1 73 1510 90 0 1 5 0 0
EN
 
#24 ·
Hi Grey Caravan
I was able to download your .nec code OK. Select </> from icons below and paste in window before selecting continue will place .nec info in a code window and your post will look better. First impressions of model are that the SWR and Impedance match, for Hi-VHF still need some work. I had a hard time getting models to work with solid bowties and loops. I ended up using standard bowties.
Give us some more informations concerning your goals, and I'll see what I can do with your model. It sounds like you will always be looking at only one transmission location, at any given time. What frequencies are still being used in Australia, for Hi-VHF and UHF bands? Do you have any size constraints? What materials do you have access to? Anything else you might think will affect your design choices?

Here's a 4 bay UHF/Hi-VHF design with very simple reflector arrangement, that has pretty good numbers. I'd guess that it's a bit larger than your wanting, but it might work.

Code:
CM Based on Kosmic SuperQuad 4-Bay, NO Reflector, 4nec2 by holl_ands, 1Mar2010
CM Added Loop around antenna to improve Hi-VHF performance.
CM Modeled the Loop from 1/2" copper plumbing pipe with four 90degree elbows.
CM Added 9 equal reflectors spaced to improve Hi-VHF performance.
CM Simplified this model to use only 3 reflectors
CM Simple SOURCE Wire. Modeled without Autoseg.   Autosegment(15) can be used.
CM Source wire sized to be half way between Hi-VHF and UHF
CM Antenna can be built without reflectors.  Remove wire 42-50(Tag 51-59) and
CM set Rsrc to 0.0499    AGT=1.0  UHF(540)=0.589   &   HiVHF(198)=0.0409 - No Reflectors
CE
SY Scale=1.0
SY sc=Scale
SY Rsrc=0.0900    'SOURCE wire Radius. Adjust for AGT=1.0:           UHF(540)=0.0999   &   HiVHF(198)=0.0800
SY Rbow=0.125    'Radius (in inches) of BOWTIE elements    0.125  1/4" tubing
SY Rfeed=0.0625    'FEEDLINE wire Radius (in case they're different)
SY Rloop=0.3125    '0.3125       1/2" copper tubing (5/8"od)
SY Rrefl=0.125    '0.125         1/4" rods    SWR slightly better with 1/2" tubing
SY ZBowII=12.0    'Distance between the Centers of the two INNER bowties    12.0
SY ZBowOI=ZBowII    'From Center of INNER bowtie to Center of OUTER bowtie    12.0
SY BowLen=10.50    'Bow Half-Length - Assume all SAME (Reality +/- 0.25+ in)    10.625    11.0
SY BowSep=3.25    'Bow Tine Separation - Assume all SAME (Reality +/- 0.25 in)         3.25
SY FedSep=1.556    'Separation (in inches) between two FEEDLINE wires           2.25    1.556
SY Hop=FedSep    'Separation between Feedlines at Crossover                       Same as FedSep to work with PVC center support.
SY ZCross=5.3125    'From Center of Feedline Crossover to Center of OUTER bowtie        5.3125
SY ZClen=4.375    'From Center of Feedline Crossover to Inflection point       4.375
SY Cond=3.0e7    'Conductivity (Copper=3.0e7, Alum=2.0e7, StainlessSteel=1.67e7)
SY LoophighDelta=4.719    '5.5     7.875 better for UHF
SY LoopwideDelta=0.44215    '.4375  1/8" gap              0.5625 for 1/4" gap
SY Reflector0=36.0    'Length of center reflectors       46.3125      50.25        48" is very close and cheaper.
SY Reflector1=Reflector0    'Length of first reflectors
SY Reflector2=Reflector0    'Length of second reflectors
SY Reflector3=Reflector0    'Length of third reflectors
SY Reflector4=Reflector0    'Length of fourth reflectors
SY Rdback=16.0    '15.8125        16.0
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+BowSep/2
SY Z2=ZBowOut
SY Z3=ZBowOut-BowSep/2
SY Z4=ZBowOut-ZCross+ZClen    'Very long crossover region
SY Z5=ZBowOut-ZCross
SY Z6=ZBowOut-ZCross-ZClen    'Very long crossover region
SY Z7=ZBowInr+BowSep/2
SY Z8=ZBowInr
SY Z9=ZBowInr-BowSep/2
SY Z10=(Z2+Z8)/2
SY Z11=Z8*4
SY YBowN=-FedSep/2
SY YBowP=FedSep/2
SY YBow=(BowLen^2-(BowSep/2)^2)^0.5
SY Ymax=YBow+FedSep/2
SY Loophigh=Z1+LoophighDelta
SY Lh=Loophigh
SY Loopwide=Ymax+Loopwidedelta
SY Lw=Loopwide
SY R0Ypos=Reflector0/2
SY R1Ypos=Reflector1/2
SY R2Ypos=Reflector2/2
SY R3Ypos=Reflector3/2
SY R4Ypos=Reflector4/2
GW    1    3    0    YBowN*sc    0    0    YBowP*sc    0    Rsrc
GW    4    5    0    Ymax*sc    Z7*sc    0    YBowP*sc    Z8*sc    Rbow
GW    5    5    0    Ymax*sc    Z9*sc    0    YBowP*sc    Z8*sc    Rbow
GW    6    5    0    YBowN*sc    Z8*sc    0    -Ymax*sc    Z7*sc    Rbow
GW    7    5    0    YBowN*sc    Z8*sc    0    -Ymax*sc    Z9*sc    Rbow
GW    8    5    0    Ymax*sc    -Z7*sc    0    YBowP*sc    -Z8*sc    Rbow
GW    9    5    0    Ymax*sc    -Z9*sc    0    YBowP*sc    -Z8*sc    Rbow
GW    10    5    0    YBowN*sc    -Z8*sc    0    -Ymax*sc    -Z7*sc    Rbow
GW    11    5    0    YBowN*sc    -Z8*sc    0    -Ymax*sc    -Z9*sc    Rbow
GW    12    5    0    Ymax*sc    Z1*sc    0    YBowP*sc    Z2*sc    Rbow
GW    13    5    0    Ymax*sc    Z3*sc    0    YBowP*sc    Z2*sc    Rbow
GW    14    5    0    YBowN*sc    Z2*sc    0    -Ymax*sc    Z1*sc    Rbow
GW    15    5    0    YBowN*sc    Z2*sc    0    -Ymax*sc    Z3*sc    Rbow
GW    16    5    0    Ymax*sc    -Z1*sc    0    YBowP*sc    -Z2*sc    Rbow
GW    17    5    0    Ymax*sc    -Z3*sc    0    YBowP*sc    -Z2*sc    Rbow
GW    18    5    0    YBowN*sc    -Z2*sc    0    -Ymax*sc    -Z1*sc    Rbow
GW    19    5    0    YBowN*sc    -Z2*sc    0    -Ymax*sc    -Z3*sc    Rbow
GW    20    1    0    YBowP*sc    Z2*sc    0    YBowP*sc    Z4*sc    Rfeed
GW    21    1    0    YBowN*sc    Z2*sc    0    YBowN*sc    Z4*sc    Rfeed
GW    22    1    0    YBowP*sc    Z6*sc    0    YBowP*sc    Z8*sc    Rfeed
GW    23    1    0    YBowN*sc    Z6*sc    0    YBowN*sc    Z8*sc    Rfeed
GW    24    3    0    YBowN*sc    Z6*sc    (Hop/2)*sc    0    Z5*sc    Rfeed
GW    25    3    0    YBowP*sc    Z4*sc    (Hop/2)*sc    0    Z5*sc    Rfeed
GW    26    3    0    YBowP*sc    Z6*sc    (-Hop/2)*sc    0    Z5*sc    Rfeed
GW    27    3    0    YBowN*sc    Z4*sc    (-Hop/2)*sc    0    Z5*sc    Rfeed
GW    28    1    0    YBowP*sc    -Z2*sc    0    YBowP*sc    -Z4*sc    Rfeed
GW    29    1    0    YBowN*sc    -Z2*sc    0    YBowN*sc    -Z4*sc    Rfeed
GW    30    1    0    YBowP*sc    -Z6*sc    0    YBowP*sc    -Z8*sc    Rfeed
GW    31    1    0    YBowN*sc    -Z6*sc    0    YBowN*sc    -Z8*sc    Rfeed
GW    32    3    0    YBowN*sc    -Z6*sc    (-Hop/2)*sc    0    -Z5*sc    Rfeed
GW    33    3    0    YBowP*sc    -Z4*sc    (-Hop/2)*sc    0    -Z5*sc    Rfeed
GW    34    3    0    YBowP*sc    -Z6*sc    (Hop/2)*sc    0    -Z5*sc    Rfeed
GW    35    3    0    YBowN*sc    -Z4*sc    (Hop/2)*sc    0    -Z5*sc    Rfeed
GW    36    3    0    YBowP*sc    Z8*sc    0    YBowP*sc    0    Rfeed
GW    37    3    0    YBowN*sc    Z8*sc    0    YBowN*sc    0    Rfeed
GW    38    3    0    YBowP*sc    -Z8*sc    0    YBowP*sc    0    Rfeed
GW    39    3    0    YBowN*sc    -Z8*sc    0    YBowN*sc    0    Rfeed
GW    40    11    0    -Lw*sc    Lh*sc    0    Lw*sc    Lh*sc    Rloop
GW    41    11    0    -Lw*sc    -Lh*sc    0    Lw*sc    -Lh*sc    Rloop
GW    42    23    0    -Lw*sc    Lh*sc    0    -Lw*sc    -Lh*sc    Rloop
GW    43    23    0    Lw*sc    Lh*sc    0    Lw*sc    -Lh*sc    Rloop
GW    51    19    -Rdback*sc    -R1Ypos*sc    0    -Rdback*sc    R1Ypos*sc    0    Rrefl
GW    54    19    -Rdback*sc    -R2Ypos*sc    Z10*sc    -Rdback*sc    R2Ypos*sc    Z10*sc    Rrefl
GW    55    19    -Rdback*sc    -R2Ypos*sc    -Z10*sc    -Rdback*sc    R2Ypos*sc    -Z10*sc    Rrefl
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    'GW1 is SOURCE wire
FR    0    38    0    0    174    12
RP    0    1    73    1510    90    0    1    5    0    0
EN

Lawrence
 
#25 ·
Hi Lawrence.
I'm limited by antenna size to fit in my caravan, so trying to use a 2 bay bowtie. Most Hi UHF antenna's are bit on the big size.
In Australia we are using VHf band 3 174-230 MHZ and UHF band 4 and 5 526 to 694 MHZ.
TV channels are mostly transmitted from one site in each district, so high directional high gain would be good.
If i can't get enough gain from the antenna i am happy to use a masthead amplifier around 15-20db.
I was able to get around 8dbi HiV/HF and 13dbi UHF from my 2 bay bowtie
I have access to 2mm copper wire for elements and have 1 by 2 in mesh or 6 mm rod for reflector.
 
#26 ·
I have access to 2mm copper wire for elements and have 1 by 2 in mesh or 6 mm rod for reflector.
What material is the 6mm Rod? Can it be bent into the Loop or Bowties?

I was able to get around 8dbi HiV/HF and 13dbi UHF from my 2 bay bowtie
Your design isn't that bad in the UHF band, but the SWR is pretty high in the Hi-VHF band. The SWR of 20 will cause about a 7db reduction to the actual gain, at that frequency.
I had designed the 4 bay for another application, and used some of my discoveries, from that project, to design a 2 bay, with a loop just outside the ends of the bowties. It's getting about the same raw gain figures, as your design, but the SWR is better(SWR runs from 8.0 to 3.0 for Hi-VHF and is under 3.8 across the UHF band). This is using the 6mm material for the loop and reflector and the 2mm wire for the bowtie element. Using the 6mm for the bowties, and 16mm copper tubing for the loop will reduce the SWR. In the US 1/2" (actually 5/8" diameter) copper plumbing pipe and solder joints are common in our hardware stores(Home Depot). Is there something similar available in Australia? Some more work and it may be possible to reduce the SWR even more. Give me a day or two and I'll see what I can come up with.
 
#27 ·
Yes we have a home depot equivalent called Bunnings that has copper tubing.
I think the aluminium tubing is to brittle to bend past a few degrees.
With a SWR of 20 reduces my VHF gain to around 2db. Not very good.
Looking forward to seeing what design you can come up with.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top