On 10/20/2011 09:19 AM, béo-master wrote:
HI,

I picked up two coils that could be a trap for the CWA-840 COMET
antenna. (They have two stickers "CL-840").
The manual of the CWA-840 says : 40/80m dipole.

I found amazing that there isn't any capacitor in // of these coils...
These coils measure 76uH.
Could someone tell me how they works ?
In the manual of the CWA-840, each leg of the 7MHz section, is
11.1meters in lenght , wich, it seems to me, that it is rather longer
that 1/4 wave. (10.1m).
Why ?

Thanks a lot for your answers

CWA-840:

-----[ ]-------------ooo--//--
2.3m coil 11.1m balun

This is not a trap antenna:

1)- At 40 meters the coil works like a medium impedance insulator,76uH
represents 5300 ohms.

2)- At 80 meters, the antenna works like a vertical mobile antenna, the
coil resonates with the 2.3m section.

I made several of these antennas years ago, and the 40 meter section is
always longer than in a simple 40 meter dipole.
--
Alejandro Lieber LU1FCR
Rosario Argentina

Real-Time F2-Layer Critical Frequency Map foF2:
http://1fcr.com.ar