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Author Topic: Using a 20m Yagi for reception  (Read 1370 times)


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Using a 20m Yagi for reception
« on: January 31, 2020, 0011 UTC »
I don't currently have a tribander in the air, but I was wondering if it's a common thing to use such antennas for reception being that its just under 14mhz (20m)

Offline K3ZRT

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Re: Using a 20m Yagi for reception
« Reply #1 on: February 12, 2020, 0309 UTC »
I don't know that many do, but I don't see why it wouldn't suffice. A tuner would help a bit but it's close enough to work.

The great thing about reception is you don't risk blowing anything up, experiment! Try it out, if it works than yay, if not then back to the drawing board.

Offline Ed H

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Re: Using a 20m Yagi for reception
« Reply #2 on: February 24, 2020, 1125 UTC »
The most important thing I have found for receiving antennas and in particular for weak signal work is to guard against common mode noise. I am not sure how a Yagi will behave so far away from its design frequency, but would expect it to be rather inefficient, and with quite unknown directional response. However, if you can be sure that noise on the outside of the coax feeder doesn't add to the signals picked up by the elements (use of a good balun etc.) then the antenna could do well enough if also away from local noise. Since it is there, you might as well try it!

One of my receiving antennas is a "random wire dipole" made to fit the available space, with about 45 ft on each leg. At the centre connection to the coax I used a home made balun with separate primary and secondary windings, built on a binocular ferrite core. I think the transformer is an important part of the success of the system. Common mode noise on the coax is horrendous, but is completely absent in normal use and the system is great for 22m beacon reception. I have a long wire also connected in a similar manner, using an isolation transformer between aerial and earth points at the antenna, and the signal and shield of the coax. Similarly, this also does well in keeping the house noise out of the radios.



Offline Prairiedog

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Re: Using a 20m Yagi for reception
« Reply #3 on: March 02, 2020, 1949 UTC »
Actually, the difference between the so-called "20 meter" ham band and 22 meters is less than it might seem. The phone portion of the "20" meter band is really much closer to 21 meters wavelength, and so the dimensions of the antenna elements will only be off about 5%...only around 2% if the Yagi is cut for the CW end of "20".

That's enough to throw higher VSWR numbers than you'd want for transmitting, but as K3ZRT said, it won't blow anything up when receiving. It's not a major loss of efficiency either, so long as your receiver's input impedance is a true 50 ohms or greater. As for directionality, I wouldn't worry at all. The difference will be indistinguishable to the ear.  Such a small error in element spacing will slightly affect the depth of nulls and gain of the forward lobe, but has very little effect impact on their orientation.  At least, I've found that to be true with a 3-element Yagi; the more elements the antenna has, the more critical spacing could become, and the more bands it covers, the more chances for the traps to complicate its out-of-band impedance characteristics.

Ed makes good points about isolating the transmission line for control of common mode noise. And, reducing common mode coupling may also have beneficial effects on directional properties of more complex antennas as well.


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