1.6 wavelength Dipole Antenna

[KOA4705]

Plans for DYI dipole with over 9 dbi gain, feed with 50 ohm coax

[KOA4705]

Plans for DYI dipole with over 9 dbi gain, feed with 50 ohm coax files/10714/27dc02c/006fa5e/f2529150c09545ca50f7cb97502fad00.jpg[/img] [img]ext/dmzx/imageupload/img-

Radiation pattern ext/dmzx/imageupload/img-file ... ce905f.jpg

[KOA4705]

Plans for DYI dipole with over 9 dbi gain, feed with 50 ohm coax files/10714/27dc02c/006fa5e/f2529150c09545ca50f7cb97502fad00.jpg[/img] [img]ext/dmzx/imageupload/img-

Radiation pattern ext/dmzx/imageupload/img-file ... ce905f.jpg
Gainhttps://www.cbradiotalk.com/ext/dmzx/ ... 0c9207.jpg

[KOA4705]

Plans for DYI dipole with over 9 dbi gain, feed with 50 ohm coax files/10714/27dc02c/006fa5e/f2529150c09545ca50f7cb97502fad00.jpg[/img] [img]ext/dmzx/imageupload/img-

Radiation pattern ext/dmzx/imageupload/img-file ... ce905f.jpg
Gainhttps://www.cbradiotalk.com/ext/dmzx/ ... 0c9207.jpg

Matchhttps://www.cbradiotalk.com/ext/dmzx/ ... dea16f.png

[KOA4705]

Plans for DYI dipole with over 9 dbi gain, feed with 50 ohm coax files/10714/27dc02c/006fa5e/f2529150c09545ca50f7cb97502fad00.jpg[/img] [img]ext/dmzx/imageupload/img-

Radiation pattern ext/dmzx/imageupload/img-file ... ce905f.jpg
Gainhttps://www.cbradiotalk.com/ext/dmzx/ ... 0c9207.jpg

Matchhttps://www.cbradiotalk.com/ext/dmzx/ ... dea16f.png

Smith Charthttps://www.cbradiotalk.com/ext/dmzx/ ... 97634c.png

[The DB]

I did some modeling based on this data. The gain my modeling software showed for this antenna at 30 feet was 8.97 dBi, which is close enough that a change in the quality of the ground below will easily get it to the listed 9.22 dBi, or even a correction after running an AGT (average gain test).

The 3d pattern also closely matched the model I made, so all is good there.

The one thing my modeling software disagreed with was your 1.5:1 SWR bandwidth. In the modeling software, the SWR bandwidth was from channel 17 to channel 20 on the CB band. The 2:1 SWR bandwidth was from 15a (an open spot between channels 15 and 16) to channel 23. Much narrower than listed. That being said, these numbers are as measured from the coax end of the 300 ohm twin-lead, and on the other side of the coax you will see more SWR bandwidth. How much more depends on how much losses are in the coax...

I was surprised at how accurate the info on this ended up being. Typically when seeing this type of data it ends up being way off, especially with that type of gain claim. The one thing I would be concerned about would be the SWR bandwidth. I believe the author of that measured said bandwidth at the other end of the 50 ohm coax, and unfortunately I don't have the length or loss information of said coax to quantify it here, so your results may vary.

A few suggestions for this setup.

1) Choke the feed line right where it connects to the twin-lead. Better yet, put a 1:1 isolation balun between the so-239 and the twin-lead portion of the setup.

2) Start with a longer length of twin-lead and cut it to length to tune for SWR. Also, cut very small pieces out of it when tuning, especially when the SWR low point is near where you want it.

3) If its SWR bandwidth isn't wide enough to cover the bandwidth that you need/want, and I can't believe I'm actually going to say this but, add more coax. The reason is the SWR bandwidth you see at the radio with this antenna design will be heavily determined by coax losses...


The DB

[MDYoungblood]

I played with modeling (I'm a novice to these modeling programs but I do try) it to, got close to DB's figures placing the antenna 30ft in the center and 20ft on the ends. The SWR was a little but better and slightly wider bandwidth. I agree with using a balun, anytime ladderline is used s a matching network it should terminate with a balun.

3's

Greg

[The DB]

Just for a reference, my model was horizontal, so that could explain part of the difference between our results.


The DB

[KOA4705]

I did some modeling based on this data. The gain my modeling software showed for this antenna at 30 feet was 8.97 dBi, which is close enough that a change in the quality of the ground below will easily get it to the listed 9.22 dBi, or even a correction after running an AGT (average gain test).

The 3d pattern also closely matched the model I made, so all is good there.

The one thing my modeling software disagreed with was your 1.5:1 SWR bandwidth. In the modeling software, the SWR bandwidth was from channel 17 to channel 20 on the CB band. The 2:1 SWR bandwidth was from 15a (an open spot between channels 15 and 16) to channel 23. Much narrower than listed. That being said, these numbers are as measured from the coax end of the 300 ohm twin-lead, and on the other side of the coax you will see more SWR bandwidth. How much more depends on how much losses are in the coax...

I was surprised at how accurate the info on this ended up being. Typically when seeing this type of data it ends up being way off, especially with that type of gain claim. The one thing I would be concerned about would be the SWR bandwidth. I believe the author of that measured said bandwidth at the other end of the 50 ohm coax, and unfortunately I don't have the length or loss information of said coax to quantify it here, so your results may vary.

A few suggestions for this setup.

1) Choke the feed line right where it connects to the twin-lead. Better yet, put a 1:1 isolation balun between the so-239 and the twin-lead portion of the setup.

2) Start with a longer length of twin-lead and cut it to length to tune for SWR. Also, cut very small pieces out of it when tuning, especially when the SWR low point is near where you want it.

3) If its SWR bandwidth isn't wide enough to cover the bandwidth that you need/want, and I can't believe I'm actually going to say this but, add more coax. The reason is the SWR bandwidth you see at the radio with this antenna design will be heavily determined by coax losses...


The DB

Yes, the antenna was model at a height of 30 feet. Common mode choke certainly would work for this application. 300 ohm transmission line: VF =.8, insertion loss= .578 db/100ft
@ 30 Mhz. Longer length of twin-lead and cut it to length to tune for SWR. Makes sense to do this due to antenna feed point Z vs actual installation height..... etc. Lossy line will spiral to the center of the Smith chart. Antenna feed point Z:
From EZNEC
"MHz" Z
26.7 174.4967,j450.9472
26.75 177.4267,j460.8159
26.8 180.4323,j470.7146
26.85 183.5153,j480.6454
26.9 186.6769,j490.6075
26.95 189.9192,j500.6024
27.0 193.2434,j510.6306
27.05 196.6518,j520.6935
27.1 200.1455,j530.7902
27.15 203.7271,j540.9235
27.2 207.3979,j551.0924
27.25 211.1599,j561.2981
27.3 215.0151,j571.5413
27.35 218.9655,j581.8231
27.4 223.0134,j592.1438
27.45 227.1604,j602.5031
27.5 231.4091,j612.9031
27.55 235.7616,j623.3438
27.6 240.2197,j633.8241
27.65 244.7864,j644.3481
27.70 249.4638,j654.9134
Equation for transmission line Zin for lossy line, derived from load Zl

Here are the results for Zin, Antenna input Z using Matlab

"MHz" Zin
26.7 52.2,-j33.5
26.75 51.2,-j29.3
26.8 50.3,-j26.0
26.85 49.5,-j21.9
26.9 48.8,-j18.4
26.95 48.5,-j14.7
27.0 47.6,-j10.6
27.05 47.0,-j7.1
27.1 46.5,-j4.1
27.15 45.8,-j.29
27.2 45.4,j3.1
27.25 44.8,j6.2
27.3 44.6,j9.4
27.35 44.0,j13.0
27.4 43.8,j15.6
27.45 43.2,j19.4
27.5 43.0,j21.8
27.55 42.7,j24.9
27.6 42.4,j28.2
27.65 42.0,j31.2
27.7 41.5,j34.2

[KOA4705]

I did some modeling based on this data. The gain my modeling software showed for this antenna at 30 feet was 8.97 dBi, which is close enough that a change in the quality of the ground below will easily get it to the listed 9.22 dBi, or even a correction after running an AGT (average gain test).

The 3d pattern also closely matched the model I made, so all is good there.

The one thing my modeling software disagreed with was your 1.5:1 SWR bandwidth. In the modeling software, the SWR bandwidth was from channel 17 to channel 20 on the CB band. The 2:1 SWR bandwidth was from 15a (an open spot between channels 15 and 16) to channel 23. Much narrower than listed. That being said, these numbers are as measured from the coax end of the 300 ohm twin-lead, and on the other side of the coax you will see more SWR bandwidth. How much more depends on how much losses are in the coax...

I was surprised at how accurate the info on this ended up being. Typically when seeing this type of data it ends up being way off, especially with that type of gain claim. The one thing I would be concerned about would be the SWR bandwidth. I believe the author of that measured said bandwidth at the other end of the 50 ohm coax, and unfortunately I don't have the length or loss information of said coax to quantify it here, so your results may vary.

A few suggestions for this setup.

1) Choke the feed line right where it connects to the twin-lead. Better yet, put a 1:1 isolation balun between the so-239 and the twin-lead portion of the setup.

2) Start with a longer length of twin-lead and cut it to length to tune for SWR. Also, cut very small pieces out of it when tuning, especially when the SWR low point is near where you want it.

3) If its SWR bandwidth isn't wide enough to cover the bandwidth that you need/want, and I can't believe I'm actually going to say this but, add more coax. The reason is the SWR bandwidth you see at the radio with this antenna design will be heavily determined by coax losses...


The DB

Yes, the antenna was model at a height of 30 feet. Common mode choke certainly would work for this application. 300 ohm transmission line: VF =.8, insertion loss= .578 db/100ft
@ 30 Mhz. Longer length of twin-lead and cut it to length to tune for SWR. Makes sense to do this due to antenna feed point Z vs actual installation height..... etc. Lossy line will spiral to the center of the Smith chart.