Topband: Beverage Antenna Tuning

[Nick Hall-Patch]

Hi Ash,

I see that you are evaluating your Beverage antenna by using 
SWR.   Have you actually adjusted the termination resistance to null 
medium-wave broadcasters located off the back end of the 
antenna?   If so, what was the value of that termination resistance?

If not, it might be worthwhile to make that adjustment in order to 
understand better your antenna.   As others have pointed out however, 
the Beverage will work well without optimizing its termination, but 
it sounds as if you would like to understand its operation more clearly.

If your ground conductivity is very poor, much of your termination 
resistance will be made up of the resistance between the ground 
rod(s) and the earth, and that resistance can be substantial when 
using short ground rods in poorly conductive ground.   Perhaps only a 
small value of termination resistor will actually be needed, even 
though the impedance of the antenna is around 500 ohms.  And, that 
termination resistance will possibly vary with the season of the year.

I have had to use zero ohms termination at one site, as that provided 
the best null for a medium-wave broadcast signal off the back end of 
the Beverage antenna.  Perhaps the resistance to earth at that site 
was even in excess of 500 ohms, so I would have needed to create a 
better system of ground rods to improve the null further.   I imagine 
the SWR of that antenna varied quite a lot with frequency.

The Saudi and Egyptian broadcasters that you will use for nulling are 
quite powerful I believe, so I hope that they do not suffer from 
short term fading at night that can make a null difficult to find.

best of luck with this project,

Nick
VE7DXR



At 14:33 2018-07-06, Ashraf Chaabane wrote:
>Hi Mark, Peter,
>
>The BC station to be used to minimize the back lobe would be in 
>Egypt or Saoudi Arabia right on the back of my beverage antenna. 
>That should offer signals coming well above 10deg (I presume!). 
>Comment noted regarding how efficient that will be on 1820 kHz. I 
>know Egypt has BC station on Medium Wave which isn't that far from 160m.
>
>Frank,
>
>I have two 3-feets rods at each end so far with two buried radials 
>at the feed end. I will add radials at the termination side as well 
>as you recommend.
>
>For the sake of experimentation, I  will play a bit with the 
>termination resistor trying to flatten the SWR curve as much as 
>possible, although, as many said, I shouldn't expect a noticeable 
>improvement in reception.
>
>Thank you all and those who wrote me in private. This generous 
>technical support is needed for developing experience on 160 among 
>3V hams (mostly youngsters). I hope we will be ready with strong 
>100W signals this winter!
>
>73 from Tunisia
>
>Ash 3V8SS/KF5EYY
>www.kf5eyy.info
>
>
>
>------ Original Message ------
>From: donovanf at starpower.net
>To: topband at contesting.com
>Cc: "Ashraf Chaabane" <ash.kf5eyy at gmail.com>
>Sent: 04/07/2018 19:00:33
>Subject: Re: Topband: Beverage Antenna Tuning
>
>>Hello Ash,
>>
>>Your results are normal for a typical Beverage. Receiving performance
>>is not significantly degraded by imperfect matching of the coaxial feedline
>>to the Beverage feed point or by non-optimum termination resistance.
>>You could optimize your matching transformer and termination resistor
>>but the improvement in receiving performance will be very minor.
>>
>>On the other hand, Beverage antenna receiving performance can be
>>significantly degraded by:
>>     - nearby antennas, power lines and other long conductors, and
>>     - common mode signals coupled into the feedline
>>
>>You could optimize your matching transformer to reduce the VSWR to
>>closer to 1:1 on the frequencies you care about most, but you won't
>>notice any improvement in receiving performance.
>>
>>You could optimize your Beverage termination by:
>>    - adding extra ground rods and/or short radials to improve 
>> ground resistance
>>       stability at the connection to termination resistor.
>>    - adjusting the termination resistance to minimize the VSWR excursion
>>       as you sweep from 1.5 to about 10 MHz
>>
>>73
>>Frank
>>W3LPL
>>
>>--------------------------------------------------------------------------------
>>From: "Ashraf Chaabane" <ash.kf5eyy at gmail.com>
>>To: topband at contesting.com
>>Sent: Wednesday, July 4, 2018 2:13:27 PM
>>Subject: Topband: Beverage Antenna Tuning
>>
>>Hi All
>>
>>I measured the SWR in my beverage antenna; the SWR fluctuates between 1.5
>>and 3 in a range of 1.8 to 7 MHz. (See:
>>https://drive.google.com/drive/folders/0B9AtNpPfAOUMRDNsaXROMG1VUTg?usp=sharing
>>)
>>I know SWR should not vary too much. However, some people are suggesting
>>adjusting the termination resistor. Others suggest checking the transformer
>>number of windings for a good match. What shall I do?
>>
>>73 Ash 3V8SS/KF5EYY
>>_________________
>>Topband Reflector Archives - http://www.contesting.com/_topband
>_________________
>Topband Reflector Archives - http://www.contesting.com/_topband

Nick Hall-Patch
Victoria, BC
Canada