[SECC] Models

[Jerry Montgomery]

Your apex-up 40 meter triangle data doesn't sound correct.  Thats a 
vertically polarized antenna, and something as simple as this should not 
have that much gain.

So I also modeled it.  I got a 7 MHz resonance point with impedance of 
160+j0.6.  Very close to what you got.  However, the max gain is only 
1.1 dB and occurs at a take-off angle of 23 degrees. This is close to 
that of a vertical, which is approximately what it is.  The only way you 
can get 6 dB of gain out of this antenna is to put it over sea water.

Jerry, K4SAV


k4sb at bellsouth.net wrote:

>>Dan/W4NTI wrote:
>>I wonder if you could take the time to model a couple antenna systems
>>I have here?
>>
>>1.  A 40 meter loop.   Apex at 40' Bottom wire about 4' .  Not quite a
>>triangle.  The bottom wire is  longer and makes the shape a bit
>>elongated.  hi.  Probably about 20 feet or so longer than it should
>>be.
>>
>>Feed is with open wire,  on the bottom wire.  About 10 feet from the
>>far corner point.   Probably not a "perfect" setup,  but does seem to
>>work.  Just wondering why.
>>    
>>
>-------------
>Dan earlier sent me the above, so perhaps the info would be useful to
>Jeff and the others.
>
>As to his "not a perfect setup", that is the understatement of the year.
>When fed as he describes, radiation is from about 60 degrees peaking at
>90. Good cloud burner.
>
>But, I did model a 40 meter triangle, and here it is.
>
>Each sloping leg is 48.375' long, with the bottom being 51.25'. At about
>7' off the ground, and fed at
>75% down from the apex, the impedance is 158.9+j.12 and a 50 ohm feed
>gives you a 3.178:1 SWR. But, feed it
>with a 4:1 balun, and the max SWR is 1.259 from 7 to 7.1 mHz. Now the
>good news, this antenna has a TO angle of 10 degrees with useful
>radiation at the -3db points of 2 degrees and 34 degrees. The Front to
>Side ratio is
>close to -13 db ( not dbi ) down at angles above 40 degrees. Definitely
>not your SS antenna. Oh, gain is
>6.24 dbi, almost equivalent to a dipole.
>
>As a note, if you run a program such as "TRLINE", you will find you can
>insert an ELECTRICAL x length of 70 ohm coax at an ELECTRICAL point y
>from the antenna feed, and you have a perfect 1:1.
>
>While I was at it, I also modeled an antenna called a "Hentenna".
>Basically, it looks like this:
>
>            X          Y 
>---------------------------
>|                    |     |
>|                   >|     | Z
>|                    |     |
>----------------------------
>           X            Y  
>Side X is 57'     Y is 13.375' and all vertical legs ( Z ) are 17'. I
>modeled this one so the top wires were at 51.25'. Impedance is
>47.86-j.09 ohms when fed in the middle of the wire marked with a ">".
>
>Pattern is beautiful. A figure 8 with max gain ALONG the axis of the
>antenna a little over 3.71 dbi.
>
>SWR at resonance (7.04) is 1.041. Less than 1.5 to 1 from 7 to 7.060.
>
>have fun.
>
>73
>Ed
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