[TowerTalk] Antenna design questions please

[K4SAV]

I was so concerned with trying to match the antenna on more than one 
band that I forgot to address the basic issue of how the antenna will 
perform. 

On 160 meters for low angle signals, in its best direction it should be 
down about 5 dB from a full size vertical with a good ground system.  In 
its worst direction it should be down somewhere around 10 dB.  It is 
basically a cloud warmer antenna, so receive noise should be high.

On 80 meters it is also a cloud warmer antenna.  Compared to a full size 
vertical, for low angles it should be down 5 to 8 dB in all directions.

Jerry, K4SAV

K4SAV wrote:

>Here is a quick simulation.  This may not be exactly what you are 
>thinking because I don't know how high the ends of your vee will be off 
>the ground, but it should give you an idea of what to expect. I assumed 
>the ends were at 15 ft, and set the antenna for resonance at 1.8 MHz 
>(resonance at the antenna, not at the end of the feedline). With 65 ft 
>of 600 ohm line, and a 4 to 1 balun, the SWR at the switch box would be: 
>1.8MHz = 24.7, 3.6 MHz = 3.5, 7MHz = 7.9, 10.1MHz = 12.2, 14MHz = 4.5, 
>18.1MHz = 5, 21MHz = 3.3, 24.9MHz = 9.2, 28.1MHz = 9.6.  Probably not 
>what you are looking for.
>
>There is a basic problem with trying match a 160M inv vee to get a 
>reasonable SWR on 80M.  On 80 meters it is very high impedance. One 
>solution would be to use the feedline as a tuner.  This would require 
>that you switch feedline lengths for each band.  For example for this 
>antenna, you would need 260 ft of 600 ohm feedline for 1.8 MHz and 200 
>ft for 3.5 MHz. This can become a real switching nightmare for more than 
>about 2 bands. You would not need the 4 to 1 balun, but you would need a 
>good common mode choke balun at the end of the feedline.  If you are 
>interested in this approach see:
>http://www.qsl.net/w5dxp/notuner.htm
>
>You can also use 450 ohm ladder line instead of the 600 ohm line, but 
>the required lengths will be a little different.
>
>Probably a simpler approach is to convert your inv vee into a fan 
>dipole, with an element for 160M and another for 80M.
>
>Jerry, K4SAV
>
>
>Gary.Stone at med.va.gov wrote:
>
>  
>
>>Hi,
>>
>>
>>
>>I am thinking of putting up an antenna and would like your input please?  I
>>am thinking of putting up an inverted vee configuration and then feed it
>>with 600 ladder line so that it would be tunable on 160 thru 10 meters.   I
>>am thinking the apex would be at about 70 feet on the tower and the two legs
>>would be about long enough to allow tuning for 160 meters (about 120 feet or
>>even a little more on each leg).  I would like to take the 600 ohm feedline
>>down to the rat pak (PL259) switch box on the tower - mounted at about 5
>>feet up from the ground.  So, it would have about 65 feet of 600 ohm ladder
>>line.  From my rat pak to the shack is 50 ohm LMR400.  I would also consider
>>using twin lead (easy to buy in rural North Texas) but also want to run 600
>>watt amp if desired.   I am thinking I would need to use a 4-1 balun at the
>>bottom end of the ladder line and then connect a short coax jumper to the
>>rat pak. 
>>
>>
>>
>>I now have an alpha delta sloper (DX-A) with the apex at about 60 feet.  I
>>am hoping to improve my signal on 80 and 160 with the added plus of being
>>able to load up easily on other bands (hence the ladder line feed line).  
>>
>>
>>
>>Ideas?  And how far do I need to put the feedline away from the tower - is a
>>couple feet ok?  Thanks in advance for any tips and critique.  
>>
>>
>>
>>Gary, N5PHT
>>
>>
>>
>>
>>
>>_______________________________________________
>>
>>See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
>>
>>_______________________________________________
>>TowerTalk mailing list
>>TowerTalk at contesting.com
>>http://lists.contesting.com/mailman/listinfo/towertalk
>>
>> 
>>
>>    
>>
>_______________________________________________
>
>See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
>
>_______________________________________________
>TowerTalk mailing list
>TowerTalk at contesting.com
>http://lists.contesting.com/mailman/listinfo/towertalk
>
>  
>