Wait a minute!
You originally had a 281 ft OCF dipole that resonated at 2.1 MHz.
You then shortened it by 10 ft and moved the resonance to 1.95 MHz?
Kinda blew my mind there for a second.
Assuming you are giving us good data, then there are two possibilities.
1. What you are getting is not the resonant frequency of the antenna,
What you are getting is the impedance of the antenna, transformed by a
highly mismatched transmission line. This impedance can be almost
anything depending on the length of the feedline.
2. The balun is not working as a current balun, and the feedline is
acting as part of the antenna. These effects will be difficult to predict.
Jerry, K4SAV
W4ZW wrote:
>
>
>Wow!
>
>Great information from all the responses. I forgot to remark that the
>"short" leg of my OCF is short because I only have about 89' to that Rohn
>mast in the Olive tree. That ends at the road and my front property line.
>I do have well over 350' from the center support west to the ocean.
>
>Many have suggested an inverted "L" and I would have done that except I have
>no ground installed nor a transmitting variable handy for tuning it.
>
>David, N1EA, suggested using twin lead to raise the impedance of an inverted
>"L" and that sounds like a great idea.
>
>This balun is a 4:1 current balun and worked well when this antenna was a
>80M OCF dipole (nearly a flat 1:1 match at 3.6MHz . I just left the long
>leg of the 80M OCF dipole to the East in place and added the length to the
>former "short end". I'm going to raise the far end to about 30' and see if
>that won't help. BTW, it is almost a flat match 1.2:1 at 1.950 MHz in the
>present configuration with a length of about 271'.
>
>I may try an old trick I used before and make it a "traveling wave"
>transmitting antenna by feeding it like a long grounded loop and use 50 ohm
>termination at the far end. Now if I can only find those big 50 ohm
>terminators I built about 15 years ago!
>
>Thanks for all the advise fellows. This reflector is great!!
>
>
>
>Jon Hamlet, W4ZW
>
> Casey Key Island, Florida
>"A little piece of paradise in the Gulf of Mexico"
>
>
>
>_______________________________________________
>
>
>
>_______________________________________________
>TowerTalk mailing list
>TowerTalk@contesting.com
>http://lists.contesting.com/mailman/listinfo/towertalk
>
>
>
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|