Tony, I think your understanding of the tuned input pro's and con's is
better than most of the comments posted to date. A look at my 2001 ARRL HB
(p 13.19)gives a good explanation of the multiple benefits of a tuned input.
While the HB material is copyrighted, I doubt if they will object to me
quoting their exact explanation rather than paraphrasing it.
"The input impedance of a grounded-grid 8877 is typically on the order of
50-55 ohms shunted by input capacitance of about 38pf. While this average
impedance is close enough to 50 ohms to provide negligible input swr, the
instantaneous value varies greatly over the drive cycle- that is, it is non
linear. This nonlinear impedance is reflected back as a non linear load
impedance at the exciter output, resulting in increased intermodulation
distortion, reduced power output, and often meaningless exciter swr meter
indications. In addition, the tubes parallel input capacitance, as well as
parasitic circuit reactances often are significant enough at 28mhz to create
significant swr. A tank circuit at the amplifier input can solve both of
these problems"
There is more but I think this may answer your question. 73, Dan, N5AR
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]On
Behalf Of Tony King - W4ZT
Sent: Tuesday, March 29, 2005 8:47 AM
To: amps@contesting.com
Subject: Re: [Amps] MLA-2500B Question
Agreed, cost is an issue for the manufacturing world as it is for
individuals but this isn't about the cost.
Once again, back to Tomm's question: I believe it is not a good idea to
depend on a rig's inboard tuner to match the input of the amp through
some length of coax. I don't think there is any flywheeling going on
through that length of coax and as a result there is poor IMD
performance and poor efficiency. Of course no one else has expressed an
opinion on that question so I may be the lone soul that feels this way.
73, Tony W4ZT
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