[TenTec] Re: Al Gavenas' position on Front-End atenuation

[eugene gerber]

No, you sound like someone who knowa what he is talking about, and has been
aroung the block a few times!  Keep it up..w2gcx
----- Original Message -----
From: "George, W5YR" <w5yr@att.net>
To: <tentec@mailman.qth.net>
Sent: Thursday, April 10, 2003 1:10 PM
Subject: Re: [TenTec] Re: Al Gavenas' position on Front-End atenuation


> The quoted statements at the start of your posting are still, I claim,
> correct as stated. Your point that a tuner is advisable is a good one, but
> the presence or absence or a tuner does not alter the validity of either
> statement. Sound like a lawyer, don't I?
>
> <:}
>
> Actually, Heinz, the power reflected from the mismatched antenna will
> encounter another mismatch when it reaches the transmitter output
terminals
> and be re-reflected and so on. Very little of the reflected power will
> actually be conveyed to the final amp, depending upon the reflection
> coefficient of the feedline/transmitter mismatch.
>
> A tuner allows the mismatch to be better and more conveniently controlled
> and ensures (a) total re-reflection of the reflected wave and (b) a 50 ohm
> resistive load for the transmitter. But, even without the tuner,
> re-reflection still occurs  . . .
>
> The reason an amp overheats when improperly loaded is because it *is*
> improperly loaded, that is it is not seeing its design load resistance,
> usually 50 ohms resistive. Thus it cannot put out all of the power it is
> being fed, less internal losses.
>
> Under those conditions, unless the drive power or the d-c input power is
> reduced, the amplifier is unable to deliver all its available output power
> and the difference shows up as a heat rise.
>
> It is an urban myth that "reflected power heats up the final amp." It
> "looks" that way, but the actual mechanics are quite different.  The fact
> that there *is* reflected power is involved but the heat rise in the amp
is
> not a result of the actual reflected power appearing at the amplifier
> devices.
>
> Good discussion of this in "Reflections II" by Walt Maxwell, W2DU. Also
his
> QST articles are on the ARRL website.
>
> Thanks for the interest and the comment!
>
> 73/72, George
> Amateur Radio W5YR -  the Yellow Rose of Texas
> Fairview, TX 30 mi NE of Dallas in Collin county EM13QE
> "In the 57th year and it just keeps getting better!"
> <mailto:w5yr@att.net>
>
>
>
>
>
> ----- Original Message -----
> From: "Heinz und Hannelore Breuer" <hbreuer@debitel.net>
> To: <tentec@mailman.qth.net>
> Sent: Thursday, April 10, 2003 2:04 PM
> Subject: Re: [TenTec] Re: Al Gavenas' position on Front-End atenuation
>
>
> > "George, W5YR" wrote:
> > >
> > > Of course, it is all nonsense since there is no correlation between
> feedline
> > > SWR and antenna effectiveness. Any antenna will radiate all the power
it
> > > receives in whatever pattern its dimensions and location dictate.
> >
> >
> > Hi George,
> >
> > not exactly. If the SWR is high and you don't use a tuner to match the
> > antenna a considerable amount of rf is reflected back to your
> > transmitter and might even damage your final.
> >
> > 73
> > Heinz DH2FA, KM5VT
> > _______________________________________________
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> > Tentec@mailman.qth.net
> > http://mailman.qth.net/mailman/listinfo/tentec
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