In my experience, a 50% VF is associated with a wire lying on the
ground and is in the lower end of measured VF's for wires laying on
the ground. 45% is the lowest I have seen personally. A regular
beverage up six to eight feet above ground will usually be 95% or
better.
A BOG cut to certain lengths certainly WILL reverse pattern.
Regular beverages will lose a good degree of front-to-back with
unfortunate lengths which might render it useless with a given source
of noise. Beverages closely parallel to long conductors, or with a
blown termination/transformer, or dysfunctional grounding at either
end can also develop unpredictable patterns.
Slinky's have their own private discipline :>)
73, Guy K2AV
On Mon, Jul 28, 2014 at 1:54 PM, Carl <km1h@jeremy.mv.com> wrote:
> There is really nothing new to explain. It has been established since the
> mid 1920's that the Beverage is a slow wave antenna, ie: it has a velocity
> factor, and at an electrical 50% VF it will reverse direction.
>
> It doesnt take much effort or math to compute the electrical length
> shortening of a Slinky and I believe I stated that mine was around 60% on
> this reflector in the late 90's and I was supplying Slinkys to others in the
> US and international. This was also picked up by ON4UN who published the
> Slinky Beverage in one of the earlier revisions of his book with incomplete
> data to easily reproduce.
>
> Using a 1590 BC station directly to the rear I determined the proper
> termination resistance to be 1200 Ohms for the final version. This was
> around 1987-88 and years before I even knew about any reflectors and
> discussions were only on 160 SSB just above the DX window when the band was
> dead. K1ZM gets the credit for planting the idea during one of those chats
> and it didnt take me long to work out the details. Those 1987-88 experiments
> took many forms and the number of Slinkys used and running 100-300'. Other
> lengths required different terminations and transformers. After a certain
> person started in with belittling comments I stopped posting and just shared
> later data via direct emails or phone calls.
>
> Doing a Google on "KM1H Slinky Beverage" will give loads of hits and also
> refreshed my memory...disregard the 18 month useful life...that was after
> they were no longer cadmium plated.
>
> Carl
> KM1H
>
>
>
> ----- Original Message ----- From: "Mike Waters" <mikewate@gmail.com>
> To: "topband" <topband@contesting.com>
> Sent: Monday, July 28, 2014 12:42 PM
>
> Subject: Re: Topband: Length of Beverages
>
>
>> Hi Jim,
>>
>> As we move the turns closer, we increase the velocity factor too much. At
>> some point, the Slinky will receive off the opposite (feed) end. Tom
>> explains it at
>> www.w8ji.com/slinky_and_loaded_beverages.htm .
>>
>> And I just found this, where K5UO seems to say that his Slinky was about
>> 12
>> turns per foot.
>> lists.contesting.com/_towertalk/2006-12/msg00510.html
>>
>> 73, Mike
>> www.w0btu.com
>>
>>
>>
>> Mike, what do you mean when you say "fires backwards".
>>>
>>>
>>>
>>>
>>> On 7/28/2014 8:59 AM, Mike Waters wrote:
>>>
>>>> Carl,
>>>>
>>>> On Sun, Jul 27, 2014 at 6:53 PM, Carl <km1h@jeremy.mv.com> wrote:
>>>>
>>>> I knew that answer 20 years ago Mike. Perhaps someone has a large
>>>> Slinky,
>>>>>
>>>>> can count the turns and then give it back to his grandson (-:
>>>>>
>>>>> Ok. I think the thing to do is just experiment with the length/pitch.
>>>>
>>>> Stretch it out along the rope, past the point where it fires backwards
>>>> (and
>>>> then some), maybe.
>>>>
>>> ...
>>
>> _________________
>> Topband Reflector Archives - http://www.contesting.com/_topband
>>
>>
>> -----
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>>
>
> _________________
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