144 mhz Biquad horizontal antenna

kc5uta

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Joined
Jul 18, 2011
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72
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Shiner Tx.
Building a biquad antenna for the low end of 2 meters, to try a little sideband action. So far I have used approx 13 feet +/- of #8 gauge copper grounding wire formed into the 2 squares and connected in the middle (see attached pictures I gleaned off the web) Each side was measured at 19.5 inches. What I've noticed so far, is that the antenna was wonderfully flat in the 160mhz range, and horrible at 144.2mhz., that is until you add the reflector section. Also make sure the coax is perpendicular to the plane of the antenna.:rolleyes: (This seems to be critical don't ask lol) Once I did that, the SWR dropped to 1:1 at the target frequency. So far it appears to be quite wide banded. Less than 1:4 at 148mhz. I started the temporary chicken wire reflector spacing at 1/4 wave, and moved it in or out to get lowest SWR. Turned out to be about 10-12 inches vs 19.5. (your mileage may vary) estimated gain is anywhere from 5- 12dbi depending on what site you read. Hope to update soon, with real pictures...... Kc5uta
 

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prcguy

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Jun 30, 2006
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So Cal - Richardson, TX - Tewksbury, MA
Very interesting. I have a 2.4GHz biquad that someone gave me but I never thought about making a larger one. I suspect its more than 5dBi gain as a full wave loop has slightly more gain than a dipole over a reflector. This has two full wave loops but they are probably not spaced just right to get an additional 3dB gain.

I think the impedance of the two loops in free space is higher than 50 ohms and when you get them closer to the screen its lowering the impedance close to 50 ohms. It might be better to leave the loops about .2 to .25 wavelengths away from the reflector and use some kind of matching like a small variable capacitor across the feedpoint. I would also use at least two and maybe three #43 mix or Laird 28 mix snap on ferrites on the coax at the feedpoint as it probably lights up the coax with some RF.

Building a biquad antenna for the low end of 2 meters, to try a little sideband action. So far I have used approx 13 feet +/- of #8 gauge copper grounding wire formed into the 2 squares and connected in the middle (see attached pictures I gleaned off the web) Each side was measured at 19.5 inches. What I've noticed so far, is that the antenna was wonderfully flat in the 160mhz range, and horrible at 144.2mhz., that is until you add the reflector section. Also make sure the coax is perpendicular to the plane of the antenna.:rolleyes: (This seems to be critical don't ask lol) Once I did that, the SWR dropped to 1:1 at the target frequency. So far it appears to be quite wide banded. Less than 1:4 at 148mhz. I started the temporary chicken wire reflector spacing at 1/4 wave, and moved it in or out to get lowest SWR. Turned out to be about 10-12 inches vs 19.5. (your mileage may vary) estimated gain is anywhere from 5- 12dbi depending on what site you read. Hope to update soon, with real pictures...... Kc5uta
 

kc5uta

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Joined
Jul 18, 2011
Messages
72
Location
Shiner Tx.
You are right about the impedance. In free space it was at 50 but way higher than designed frequency, on the MFJ analyzer. Impedance was all over the place, it refused to tune at 144.2, until I added the reflector.. Nice idea about the ferrites though. Was thinking of an "ugly balun" but ferrites are easier to adjust ( add or subtract more as needed) thanks..Dave Kc5uta
 

ko6jw_2

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May 18, 2008
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1,052
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Santa Ynez, CA
Once you get the antenna working the next problem will be finding anyone on 2 meter SSB. Locally we have a SSB net, but I'm over the mountains from most of the stations. I could hear them using a yagi but the other stations refused to rotate their antennas in my direction. What a bunch of lids! Waste of time. I tried from a mountain top where we have several repeaters. Zero contacts from anywhere in Southern California. Did make contacts on 146.520 from there, but nothing on sideband.
 

kc5uta

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Joined
Jul 18, 2011
Messages
72
Location
Shiner Tx.
Sadly you may be right.. I live in South Texas (Shiner) about 90-100 "southish" from either Austin or San Antonio. I think S.A. has a late night ssb net. Caught them once during a band opening on my vertical, and... Louisiana that same night. Fortunately though, the biquad, much like the Hentenna is easy to change to vertical. :)
 
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