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use of long lead coax to 6BTV antenna

Jan 2nd 2013, 02:48


Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Because of our condo lay-out I must use about 120 feet of RG8 to reach my Hustler antenna.

If I screw the connector at my tranceiver signal is lost. If only the center of the plug is connected the signal level is normal.

How can I correct the problem.

I've checked the cable and there is nothing wrong there. The antenna resonates in all bands with an SWR less than 1.5.

Dave Ghen
Jan 2nd 2013, 14:52


Super Moderator

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0

It is common for signal strengths to be louder when the shield is disconnected, as you describe. But, if you listen carefully for on the air signals, the signal to noise ratio, which is what you really want, is usually better with the shield connected.

The reason is a little complex so most folks can't figure it out on their own--low noise HF preamps often have a high input impedance, yet work best with low impedance 50 ohm sources. Thus, with a high Z antenna, such as an end fed wire, you have a better power match, hence more signal. But, when you feed the preamp with a low Z source, you lose more noise than signal, so you are ahead in the final result. You can read more about this in the Introduction to RF Design by Wes Hayward.

Zack Lau W1VT

ARRL Senior Lab Engineer
Jan 2nd 2013, 15:53


Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
In addition to Zack's explanation, there is another effect. When you use only the inner conductor, your whole feed line plus your antenna becomes the effective antenna. That can raise the signal voltage, but it also can bring in a lot more noise from your household and shack noise generators - computers, TVs, switching supplies, etc.

A shielded feed line with a balun and a well-balanced antenna is a good defense against such noise sources.

73 Martin AA6E

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