A Super-quiet 12 element EME and Weak signal antenna for 144MHz
Download the EZNEC files for this antenna HERE
Many believe that an antennas G/T performance (Gain over temperature mean opinion scoring) is the most important attribute for weak signal reception within VHF Yagis. While I do not believe this to be true (I believe much lower temperature antennas will yield better receive performance in most real-world environments) I decided to produce a range of VHF Yagis with best-ever G/T performance. Additionally, at time of publishing, there are no other antennas showing as much gain over the same bandwidth of any of my 2013 Yagi per metre of boom.
If you are not sure how good this antenna is, divide the gain by boom length to achieve a gain figure per metre of boom and compare this antenna to others. Note this is wideband and thus stable in wet and icy weather too!
Each of these 2013 OWL Yagi will provide stunning 'best in class' performance, you can be assured of that!
The only place you can buy this antenna is InnovAntennas
I have proven that very low impedance Yagi antennas can be very stable and wide band too. This is a perfect example and can be fed with a normal split dipole (12.5Ω feed point) or with a folded dipole (50Ω direct feed). Take a look HERE for details on the folded dipole and HERE for DK7ZB style matching.
Note: G/T & sky temperature will drop with the split dipole therefore a folded dipole is favoured. In addition to the inherent noise reduction propoerties of a closed loop feed system, the folded dipole is fed in such a way as to 'push' most elevation distortion lobes upwards away from ground and thus improving G/T performance over split dipole versions.
Note the very fast drop off to high suppression either side of the antenna from the 45 degree line backwards. This is key in ensuring you receive no unwanted noise (from directions other than which your antenna is facing).
This super-clean antenna when placed 10m above ground is a serious performer.
A nice flat, SWR curve where it is needed to be. No need to go silly here, just give the antenna 'band pass filter' characteristics where it is needed.
Tant output showing gain (4 antennas) Sky temperature and G/T
Gain @144.1MHz: 15.86dBi
F/B @144.1MHz: 27.74dB
SWR/Performance bandwidth: better than 1:17.1 from 143.8-144.8MHz
Stacking Distances (DL6WU): 3.196m Vertically 3.480m Horizontally
4 x Sky Temperature: 226.2 Kelvin
4 x G/T: -1.76dB GT
Stacking Distances (G0KSC): No recommended changes to DL6WU calculations
VE7BQH table comparisons with other antennas of the same/similar size (bay of 4 antennas, DL6WU Stacking distances):
Antenna Length (wl) Gain single antenna (dBd) Temperature (Kelvin) G/T (dB) SWR across 1MHz
K1FO 3.26 13.36 237.8 -2.32 1.42:1
G0KSC 12 LFA 3.32 13.44 220.5 -1.92 1.07:1
G4CQM 11 3.36 13.55 232.0 -2.01 1.94:1
G0KSC 12-144-ZB 3.37 13.71 226.2 -1.76 1.17:1
DK7ZB 11 3.40 13.68 234.3 -1.94 1.94:1
UA9TC 12RS 3.40 13.55 218.2 -1.78 1.09:1
Notes: The lower the temperature figure, the better but it is. The G/T figure is the most important attribute in the above specification (more positive the G/T figure, the better the antenna is for receiving weak signals) and as you can see, this antenna is better than anything else listed in both gain and G/T. 1MHz bandwidth normalised to best 1MHz bandwidth not 144Mhz to 145Mhz. If the antenna is very narrow band, it is more likely to shift in wet weather conditions.
So here are the details for this one if you want to go build it yourself.
Boom positions (metric in mm):
DE: 113.5mm (12mm - 1/2'' DE. email for different sizes)
Element Lengths - (driven element 12mm Parasitic elements 8mm)
DE: 960mm (This is folded dipole sizing, see note below on building Folded Dipole)
Folded Dipole Notes:
- With a folded dipole this antenna is direct feed, 50Ω and needs no matching device
- While you will read elsewhere to the contrary, a choke or balun (1:1) IS required see here
- Take the above listed dipole length and remove 50mm to achieve the length required for the straight sections in the diagram below
- Bend loop ends from 10mm (if you selected 12mm loop) or 3/8'' end sections (if you have a 1/2'' loop) long enough to allow for up to 50mm of adjustment either side (50mm wider than the dipole size suggested above)
- This is required to allow for correction due to the curves in the loop-ends, the step-down in loop-end diameter and correction due to the loop being earthed opposite the feed point
- A tool to bend loop ends to exactly the right size required can be purchased here
- It is best to have absolute minimum contact with the drive element itself so use the shortest/smallest form of insulators possible. Avoid feed point enclusres where possible and only use coaxial coax joins that maintain impedance.
- Once the loop is together, measure its complete width to the above mentioned dipole length plus 30mm and adjust for best SWR from that starting point
- The overal height of the folded dipole can vary if you wish it, but the length of the folded dipole will change. For example, if you change loop height from 46mm to 40mm, the width if the FD will need to be longer then the above stated in order to acheive a perfect SWR. The opposite applies if you increase loop height. The construction of the loop allows for easy SWR adjustment be means of a Trombone type adjustment. See here for more details
Folded Dipole Recommended Construction Method
Pitfalls and Cliffs
If you want to use a folded dipole, mail me. I will help you calculate the sizes of this both width and height for your chosen boom diameter
DON'T offset a folded dipole and expect to have the nice clean pattern you have seen above, it will not happen. Any change needs to be modelled and checked. If a folded dipole is offset, the elevation plane pattern will be distorted. However, this distortion can be used to your advantage (noise reduction) especially when stacking. For out side of the square scenarios like this, mail me.
It is perfectly expectable to use the DK7ZB twin 50Ohm coax match on a split dipole version of this antenna. However, ensure you measure the coax you will use to check its exact velocity factor (VF). If this is wrong, the transformer will not work correctly. I have not found any coax that fits the specified (manufacturers) suggested VF and of course this VF will change with frequency! If you do not have an antenna analyser, borrow one!
There is NO CORRECTION added to any element lengths. If you follow my mechanical construction guidelines, nothing will need to be added at all. DO NOT use any insulators where bolts pass through the boom and element without establishing correction factors, your antenna elements will need to be lengthened should you chose to go down this route.
Any questions just ask. Within this next few weeks, I will add this antenna to as new category and will add another version.
COMMERICALLY AVAILABLE FROM INNOVANTENNAS. NO OTHER COMPANY HAS COMMERCIAL USE RIGHTS OF ANY KIND
Copyright G0KSC 2013 all rights reserved