Gary's observation means that no matter the band the input impedance is the
same except for the "intervention" of the coax between the exciter and the AMP.
No, that's not quiet the case... the input resistor's impedance remains the
same but impedance/reactance of the tubes will change with the operating
frequency, the load (antenna and feedline) and the tune and load controls of
the amplifier (and the quality of the amplifier's chassis to RF ground
connection). So you can get a different input impedance as well as a different
reactance which may require a different length of coax between the exciter and
amplifier.
>From http://www.wa3key.com/collins.html
INPUT CIRCUITS
Pi-network broad-tuned circuits and the interconnecting r-f feed line match the
50-ohm input impedance to the cathode impedance, which is approximately 100
ohms. The 20.5-foot length of cable (furnished) is necessary between the 32S-1
(or KWM-2) driver and the 30S-1 input circuits. This is due to the necessity of
having an even multiple of 180-degree phase shifts between driver plate and
power amplifier grid. The cable length and the 30S-1 input circuits together
accomplish this. An even multiple of 180-degree phase shifts is necessary
because modulation components cause a change in the resistive PA cathode
impedance which is translated to a shift in reactive impedance at the driver
plate. The shift in reactive impedance, at the driver plate, results in phase
modulation of the driver and increases the total over-all distortion of the
system. A 2.5-foot additional length of cable is furnished to bring the total
interconnecting cable length to 23.0 feet for use with the KWM-1 a
s a driver. Drive power required for maximum legal input on SSB is 80 watts
PEP.
I'd build a two section cable (RG-8) as above and try loading the amplifier
into a good dummy load just to see if it'd solve the problem.
Best regards,
CSM(r) Gary Huber - AB9M
9679 Heron Bay Rd
Bloomington, IL 61705
(309-662-0604)
www.csm-gh.com
glhuber@msn.com
gary.huber@us.army.mil
--------------------------------------------------
From: "Rick - NJ0IP / DJ0IP" <Rick@DJ0IP.de>
Sent: Wednesday, June 02, 2010 11:43 AM
To: "'Discussion of Ten-Tec Equipment'" <tentec@contesting.com>
Subject: Re: [TenTec] Ten-Tec 411 Centaur Amp Problem
> Did you try an RF choke on the coax yet?
>
>
> -----Original Message-----
> From: tentec-bounces@contesting.com [mailto:tentec-bounces@contesting.com]
> On Behalf Of Kris Merschrod
> Sent: Monday, May 31, 2010 9:31 PM
> To: Discussion of Ten-Tec Equipment
> Subject: Re: [TenTec] Ten-Tec 411 Centaur Amp Problem
>
> Good evening, I am still fiddling and pondering the observations on this
> problem. Gary's observation means that no matter the band the input
> impedance is the same except for the "intervention" of the coax between the
> exciter and the AMP. That is hard to believe, b/c my 8"jumper cable seems
> to keep the 160, 80 and 20 meter input "happy" (No SWR) but on 40 it all
> goes to "pot."
>
> I can't believe that TT built non-matching rigs in the 1990s. Something
> else has to be wrong.
>
> 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
>>>>
>>>> _______________________________________________
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