Sunday, April 24, 2016

80m Dipole/Inverted V + Dimensions

OK now that I have bought all of the hardware its time to plan in detail the 80m  Inverted V or Dipole.   The antenna is going at the top of the hill because .....

1 )   Height advantage 100+ ft above the house.
2)    The Hill is steep and consist of Gravel so its a great insulator.  I expect the ground affect to be minimal and I should have no problem getting things elevated 60' or so.
3) Orientation will be more or less East / West so it will favor Europe and USA / South America with the null off the ends towards Australia and Africa.  It should give a 3db gain over the Vertical as long as I can get it up at least 1/2 Wavelength .  
4) I am going to try to possibly make this a 160/80/40 m antenna with the emphasis on 160m and 80m.  

Design considerations ....

#1 Priority is to make the antenna as efficient as possible with as low a take off angle as possible.   I am hoping the Balun will assist on achieving this goal.

Below is a VSWR chart Dipole vs Inverted V.    There is now doubt its going to be an inverted V so that should help drop the feed point impedance.

Just a little note on the Balun ....

One feature which should not be overlooked is the use of a current balun or RF choke at the feed point. This device encourages RF current to stay off of the outside of the transmission line. This unbalanced current causes the feed line to radiate, in addition to the antenna. This can create all sorts of problems. First, your antenna is now a combination of an inverted vee and a vertical running down the center of the vee. Since the transmission line is now part of the antenna, changes to its length will change the antenna length, which will change the antenna impedance, which will change the SWR on the feed line. Ideally, the SWR on a transmission line will be exclusively determined by the impedance of the antenna and the transmission line. The SWR should stay constant for different length transmisson lines. Actually, real transmission lines, due to loss, will lower the SWR (towards 1.0) with increasing length. If you have an antenna where changing the transmission line by a few feet causes a noticeable change in SWR, odds are that the feed line is part of the antenna, and that is rarely desired. Finally, the RF current on the outside of the transmission line may travel all of the way back to the radio shack, where it can cause additional trouble. 

And a cool way to do "strain relief " ...

and now the numbers ....

80 Meter CW

Center Frequency:   3.600 Mhz 10.648 Mhz 3rd Harmonic
Halfwave in space is:  136.67 feet 91.57 coax|120.27 twinlead
Quarter wave in space is: 68.33 feet 45.78 coax|60.13 twinlead

Quarter wave Vertical is: 65.00 feet 76.53 foot ground radials
Five eights wave Vertical is: 169.47 feet 65.00 foot ground plane
Three Quarter wave Vertical: 201.67 feet 32.50 foot eighthwave

Halfwave wire dipole is: 130.00 feet 65.00 one side.
Halfwave Reflector is:  136.50 feet 124.15 for Director
Low Mount Halfwave is:  127.22 feet 63.61 one side.
Halfwave folded dipole is: 128.33 feet 64.17 one side.
Halfwave inverted V is:  134.72 feet 67.36 one side.

Extended double Zepp is: 349.87 feet 174.93 one side.

Fullwave quad loop is:  283.33 feet 70.83 one side.
Reflector|Director:  297.50|270.58 74.38|67.65 one side.
Fullwave delta loop is:  283.33 feet 94.44 one side.
Reflector|Director:  297.50|270.58 99.17|90.19 one side.

Waves 1: 266.67 |1.5: 403.33 |2: 540.00 |2.5: 676.67 |3: 813.33 |4 :1086.67
Waves 5:1360.00 |6.0:1633.33 |7:1906.67 |8.0:2180.00 |9:2453.33 |10:2726.67

 I am going to design this as an inverted V so the antenna  will be .... 

Halfwave inverted V is:  134.72 feet 67.36 one side.

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