In the case of the Centaur 411, the input is simply a 25 Ohm resistor in
parallel with the cathodes of the 4 811s (which are also in parallel).
The input load impedance of the Centaur is always less than 25 Ohms and thus
the length of input coaxial cable plays a significant role in transforming
the SWR for the driving solid state transmitter.
73,
Gary - AB9M
(NOT an E.E.)
--------------------------------------------------
From: <wow_chf@hotmail.com>
Sent: Monday, May 31, 2010 8:32 PM
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Subject: Re: [TenTec] Ten-Tec 411 Centaur Amp Problem
> Yes indeed. In fact, there were two different lengths in the Collins 30S1
> manual, one for their transceiver and one for their transmitter.
>
> In my article the explanation as to why this works is as follows:
>
> "In cases involving RF signals, some time will pass during the 'round trip
> of the reflected energy and the phase of the reflection will also depend
> upon this length of time. Imagine that a resistor in a black box is at the
> end of a length of cable. From the outside world this length of cable will
> give the reflection from the resistor a phase shift since the signal must
> make a round trip through the length. If a 100 ohm resistor has an SWR of
> 2,
> a cable long enough to invert the signal after the round trip will make it
> look like a 25 ohm resistor, also with an SWR of 2 but with inversion (a
> cable with a multiple of 1/4 wavelength would do the trick). Since the
> impedance looking into this black box is a function of the SWR and the
> cable
> length, it can be seen that intentionally mismatched lines can be used to
> transform one impedance into another. Notice that the 1/4 wave cable
> inverts
> the impedance and preserves the SWR. This impedance inversion may be used
> to
> match two impedances at a particular frequency by connecting them with a
> 1/4
> wave cable with an impedance equal to the geometric mean of the two
> impedances. (The geometric mean is the square-root of their product.) A 50
> ohm, 1/4 wave cable will match a 25 ohm source to a 100 ohm load : sqrt(25
> x
> 100) = 50. Of course, it is not always easy to find the desired impedance
> cable!
>
> Multiples of 1/2 wavelength will give enough delay that the reflection is
> not inverted and the impedance will be the same as the load. Such cables
> may
> be used to transfer the load impedance to a remote location without
> changing
> its value (at one frequency).
>
> Other cable lengths will transform an impedance which differs from the
> cable's impedance with a reactive component. If the load is a lower
> impedance than the cable, a length below 1/4 wave will have an inductive
> component and above 1/4 (but below 1/2) wave a capacitive component. If
> the
> load is a higher impedance than the cable, the reverse is true. Above 1/2
> wavelength, the reactance will alternately look capacitive and inductive
> in
> 1/4 wave multiples. This reactance will combine with the load's reactance
> and offers the possibility of resonating the reactive component of the
> load.
> Therefore, a cable with the "right" length and impedance can match a
> source
> and load with different resistance and reactance values. Obviously, these
> calculations can become quite involved and most engineers resort to a
> Smith
> chart, a computer program or perhaps the most common method, trial and
> error
> with a SWR meter or return loss bridge!"
>
> Sorry for so much bandwidth.
>
> 73 and Happy DXing,
>
> Mike
> W2AJI
>
>
>
> -------------------------------------------------
> From: "James Duffer" <dufferjames@hotmail.com>
> Sent: Monday, May 31, 2010 8:15 PM
> To: "Ten Tec" <tentec@contesting.com>
> Subject: Re: [TenTec] Ten-Tec 411 Centaur Amp Problem
>
>>
>> I recall from some Collins manual for their amp 30S1 they specified a
>> length for the coaxial cable between the KWM-2 and the amp. In that case
>> that was their fix.
>>
>> Jim de wd4air
>>
>>> From: k9yc@audiosystemsgroup.com
>>> To: tentec@contesting.com
>>> Date: Mon, 31 May 2010 13:19:38 -0700
>>> Subject: Re: [TenTec] Ten-Tec 411 Centaur Amp Problem
>>>
>>> On Mon, 31 May 2010 15:55:31 -0400, wow_chf@hotmail.com wrote:
>>>
>>> >I submitted the article draft to QST, and it was questioned by the
>>> >Technical
>>> >Review folks, and although I have been published in QST before, they
>>> >could
>>> >not see how this would "transform" the apparent input SWR.
>>>
>>> Because it's a POOR fix for the fundamental problem, which is something
>>> wrong
>>> in the input circuit of the power amp causing a mismatch. The proper fix
>>> is
>>> to find and correct the problem in the input circuit. Adding coax is a
>>> band-
>>> aid.
>>>
>>> 73,
>>>
>>> Jim K9YC
>>>
>>>
>>>
>>> _______________________________________________
>>> TenTec mailing list
>>> TenTec@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/tentec
>>
>> _______________________________________________
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