You will often find the input SWR higher on one or more bands. This is
especially true with amplifiers with torroidal input.
But as I have said before, one test is worth a thousand expert opinions.
Why not just go ahead and replace that 8" jumper with the longest one you
have around the shack, or couple a few jumpers together, and see what the
results are?
73,
Mike
W2AJI
--------------------------------------------------
From: "Kris Merschrod" <Kris@merschrod.net>
Sent: Monday, May 31, 2010 10:32 PM
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Subject: Re: [TenTec] Ten-Tec 411 Centaur Amp Problem
> I should have asked. Does anyone have this exact problem on their 411
> with
> a TT solidstate exciter? If not, then I have a problem that is unique
> and
> not "standard."
>
> Kris KM2KM
> Merschrod
> 123 Warren Road
> Ithaca, NY 14850
> www.merschrod.net
> ----- Original Message -----
> From: "CSM(r) Gary Huber" <glhuber@msn.com>
> To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
> Sent: Monday, May 31, 2010 10:16 PM
> Subject: Re: [TenTec] Ten-Tec 411 Centaur Amp Problem
>
>
>> 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
>>>>
>>>> _______________________________________________
>>>> TenTec mailing list
>>>> TenTec@contesting.com
>>>> http://lists.contesting.com/mailman/listinfo/tentec
>>>>
>>> _______________________________________________
>>> TenTec mailing list
>>> TenTec@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/tentec
>>>
>> _______________________________________________
>> TenTec mailing list
>> TenTec@contesting.com
>> http://lists.contesting.com/mailman/listinfo/tentec
>>
>
> _______________________________________________
> TenTec mailing list
> TenTec@contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
>
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|