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20140203 0805UTC 14017kHz F6ARC
Date : 03/Feb/2014 0805UTC
Freq : 14017kHz CW
Rig : SDR(PI4THT)
ANT : Mini-Whip(PAORDT)
PC recording
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No eQSL!
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
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-to-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 advantages:
- 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).
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.
In conclusion, I would say that this multiband beam is a good compromise for those who have antenna restrictions. The only potential issue (and only for those lacking sufficient mechanical knowledge) is the bending of the corner sections. Perhaps 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."
View towards Long Path VK-ZL, in the heights of the village (43 ft tilt-over tower in the foreground).
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.
"God gave us two ears and one mouth, so we ought to listen twice as much as we speak."
Author: ~Irish Proverb~
Last modified: 2014-01-15 15:32:47, 8031 bytes
