F6ARC - FG/F6ARC - FM/F6ARC, please QSLs via bureau or direct with a SAE envelope and 1 US dollar (EU), 2 US dollars (Outside EU) or one valid IRC, to: FE11DX, Stéphane LAIGNEAU 1 Résidence François Foreau 28110 LUCE - FRANCE
View towards Long Path VK-ZL, in the heights of the village (43 ft tilt-over tower in the foreground).
Moxon Rectangle on 20m, Reflector-Radiator Yagi on 15m, Radiator-Director Yagi on 10m.
Computer simulations have shown a slight but significant improvement in both forward gain and front/back ratio on 10m due to the presence of the 15m Reflector (sometimes called "forward stagger effect"). The forward gain of a Moxon Rectangle is almost the same as a full-size two-element Yagi. So why choose the Moxon version rather than its "big sister"? Because this design offers certain avantages:
- smaller footprint (28% less width than the Yagi),
- minimal movement in high winds (well-balanced antenna),
- direct 50-ohm connection (no matching system required),
- wide bandwidth (max 1.3:1 SWR at band edges),
- wide beamwidth (no need to be pointed precisely in the right direction),
- outstanding F/B ratio (20-25 dB; particularly useful on the crowded 20m band).
In my opinion, the only potential issue (and only for those lacking sufficient mechanical knowledge) is the bending of the corner sections. Perharps that's the price to pay for getting optimal performance from such a small antenna.
"If the Moxon Rectangle didn't exist, you'd have to invent it."
I have been using this tribander since May 2013. Bear in mind that only two elements are active on each band, therefore it can't compete with multi-element monobanders. Although tests were carried out without another antenna as reference, I have made enough tests to rate its performance. I live out in the country, but soil quality is rather poor (sandy). The antenna is less than 14 meters (45.9 ft) above the ground, fed with 45 meters (147 ft) of RG-213 coaxial cable. However, the least I can say is that the results are well beyond my expectations. I hardly ever wait to break a pileup! Another feature of this tribander is that although it is not designed for 24 MHz, I am able to use it on the 12m band with 100 watts, through the ATU (high SWR) of the transceiver. There is some directivity and gain due to the presence of the other elements.
A 5 element 6m DXBeam was added, 2.10m (6.9 ft) above the tribander. No noticeable change in SWR was observed, neither on the 6m monobander nor on the tribander. That said, simulations indicate a loss of up to 0.3 dB in forward gain on the 6m Yagi when compared to the same antenna in "standalone". As such, I suggest minimum spacing of 3m (10 ft) between antennas to minimize the mutual coupling effect.
In conclusion, I would say that this multiband beam is a good compromise for those who have antenna restrictions.
A Yagi antenna can be tested at ground level, prior to installation on the tower. To do this, rest the antenna on an insulated (e.g. wooden) base at about 50cm above ground, and point it upwards (towards the sky). VSWR measurements made in this position, together with the transmission line and balun, are very similar to those obtained with the antenna in the air, in its final horizontal position.
A few years ago I was looking to get high performance from 7.0 to 7.2 MHz, on a short boom Yagi. I made my first computer simulations back in 2011, but for lack of time, it took 2 years to finally try out this new model on a tower. Initial tests were carried out by Patrick, F2DX of DX Avenue, at the end of November 2013.
Unlike a standard 3 element Yagi with reflector, driven and director elements, this antenna is based on a different concept. This significantly improves the performance of the aerial (forward gain and front-to-back ratio), and in addition, considerably increases the bandwidth, which was exactly the issue I wanted to focus on. I preferred not use log-cell driven elements, which although they improve SWR at band edges, do not maintain constant gain and front-to-back ratio throughout the entire 40m band. Note that this concept has nothing to do with a 3 element OWA-Yagi.
According to F2DX, initial on-the-air tests have shown this antenna's performance to be highly consistent with my computer simulations. Prior to marketing, this new model will be thoroughly tested this winter, especially working DX.
In the pipeline: a 4 element 40m Yagi should see the light of day within the next few months. This will be based on the same concept as the 3 element "short boom" version, i.e. without a log-cell, but on a boom length of 12.35m (40.5 ft), the same length as the existing 40m "long boom" 3-el monobander from DXBeam. I devised this computer model nearly 2 years ago. All that is required now is for it to be tested in the field.
"God gave us two ears and one mouth, so we ought to listen twice as much as we speak."
Last modified: 2013-12-09 07:40:24, 12493 bytes cached
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