[Elecraft] Feedline loss w/wo tuner

[Ken K6MR]

“One thing that is often overlooked in these discussions is that older
tube type transmitters had an adjustable output network which had a
sizable range for matching antennas.”

I remember my DX-20: that thing could load anything!

But I’m not going back. Being able to change bands instantly and completely hands free is a big advantage. I continue to make sacrifices to the Amplifier Gods asking for the KPA-1500  :^)

Ken K6MR



From: Don Wilhelm<mailto:donwilh at embarqmail.com>
Sent: Wednesday, April 27, 2016 12:23
To: elecraft at mailman.qth.net<mailto:elecraft at mailman.qth.net>
Subject: Re: [Elecraft] Feedline loss w/wo tuner

True, the reasons for an ATU are not all associated with feedline loss.

One thing that is often overlooked in these discussions is that older
tube type transmitters had an adjustable output network which had a
sizable range for matching antennas.  You would 'dip the plate' and
adjust the 'loading' until you could feed the antenna efficiently.  With
that, one did not have to pay much attention to SWR or the feedpoint
impedance.  The PA output network did the job of matching the plate load
resistance to whatever was connected to the network output (the antenna).

Today's transmitters need to see a low SWR because they were designed to
operate into a 50 ohm load.  The adjustable elements of the transmitter
output have been moved from the transmitter into the ATU because there
is nothing to adjust in the transmitter other than the band and VFO.

If all your antennas present a 50 ohm load on each band - and across the
span of those bands, no ATU is needed at all, but that requires many
tuned antennas.  Not everyone has that luxury.

73,
Don W3FPR

On 4/27/2016 2:52 PM, Ken K6MR wrote:
> Somewhere in the past hams have become obsessed with SWR.  With a 2:1 SWR on a feedline with a matched loss of 3.0 dB (which is a bit extreme) there is an additional 0.35 dB of loss. It’s just not big enough to worry about.
>
> Of course now that we all have solid state finals 2:1 can be a problem. But a tuner in the shack is a completely reasonable and efficient way to deal with it.
>

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