[Elecraft] Feedline loss w/wo tuner

Wed Apr 27 17:30:55 EDT 2016

The modern combination of a fixed-tune filter plus that ATU means much better harmonic suppression than we got with the old pi or pi-L networks. That's not just "nice", it's generally needed here in the USA to meet modern FCC specs. 

And with digital logic flipping the knobs (or, rather the relays to do the same thing) the operator is completely isolated from the much more complex adjustments being made beyond the initial buzz of the relays before the tuning solution is stored. 

73, Ron AC7AC

-----Original Message-----
From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Ken K6MR
Sent: Wednesday, April 27, 2016 12:30 PM
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] Feedline loss w/wo tuner

“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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