Topband: Excessive noise on beverages

[Wes Stewart]

Dave,

First I see by my log that we've had two QSOs---35 years apart--- one on 2-meter 
EME and one on TB.

I'm no Beverage expert---antenna Beverage that is--- but it seems to me that 
shortening the west antenna just decreased its sensitivity.  If you're pointing 
at one or more noise sources, there isn't much antenna improvements can do.

I can't recommend a tower detuning mode, however, you might at least consider 
terminating the feedpoint on receive rather than leaving it open.  My system is 
quite modest on TB, a 55' vertical with an ~85' loading wire.  The separation 
between the vertical and a tower is 90'.  The 85' loading wire is attached (via 
an insulating rope) to the tower.  The tower supports a triband Yagi and a 
dual-band inverted-vee for 40-80. In doing some feedpoint measurements on the 
vertical v. number of radials with a vector network analyzer I saw a little 
anomaly on the Smith Chart.  To make a long investigation short, I discovered 
that either lowering the inverted-vee or terminating the coax at the shack end, 
rather than having it open, corrected the anomaly.  I have no clue as to what 
this might have been doing to the pattern.

Wes  N7WS


On 3/6/2018 10:30 AM, David Olean wrote:
> I have been putzing around trying to improve my 160 meter setup, and have run 
> into a real problem. Most of the USA is covered by two directions from here in 
> Maine.  SW and W.  My problem is that I have an excessively high noise level 
> on both of the beverages that run in these directions.  In the last six months 
> it has gotten worse, and so bad that I cannot use either beverage.  The wires 
> terminate at the side of my barn where I have ground rods and the RG-6 goes 
> through PVC conduit up to the shack on the second floor of the barn.  During 
> the day I see noise levels at -133 or -132 on the two wires, but at night the 
> noise had climbed to levels around -100  or to -110 on a good night.  I 
> suspected that I was getting noise coupled in from my vertical which is rather 
> close and on the other side of my barn all of 55 ft away.
>
> Yesterday, I modified the west beverage and shortened it so that it terminated 
> about 150 feet away from the barn and I ran new coax back across the field.  I 
> kept the SW beverage as is to compare noise levels at night. Lo and behold, 
> but the noise went to -110 on the SW beverage, but only about -120 dBm on the 
> modified beverage.  This is a 10 dB improvement.  Other directions at night 
> run at about -130, so I am now seeing a 10 dB extra hit in noise to the west.
>
> The vertical is a shunt fed Rohn 25 with a total height just over 90 ft with 
> top loading from a 5 element long boom 10 Meter yagi. I am not sure if it is 
> possible to simply un resonate this tower. Does anyone have experience with 
> simple ways to decouple a shunt fed tower from the rx antennas?
>
> The extra 10 dB of noise that I get to the west and SW  is mostly due to the 
> location of a town about 7 or 8 miles away in NH. It is ripe with all sorts of 
> power line noise.  I still can't rule out re radiation from the vertical 
> though! I spent many years fighting with the electric utility to quell the 
> noise. I involved Riley Hollingsworth and later on, Laura Smith, his 
> replacement.  The effort was futile and I lost heart as the problem was just 
> too big for one person to fight.  I was hoping that the noise would not affect 
> 160 meters as it had messed up my VHF exploits, and so far I only have this 
> ten dB swath of noise that bothers me in two directions.
>
> Any help with un resonating a shunt fed tower would be appreciated.
>
> Dave K1WHS
>
>
> _________________
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