On Mon, 06 Jun 2005 07:40:49 GMT, "nick smith"
wrote:

...

"Cecil Moore" says -

There's no such thing as a 100% efficient tuner.
====================================

Cecil, not a very surprising statement.
There's nothing which is 100% efficient.

What is the typical efficiency of a typical tuner with a typical
antenna.
Does it differ significantly from 100% ?
Yes or no?
----
Reg.


Well, at the risk of David going into conflict with the Goliaths of the
newsgroups, I would reckon that a tuner (matcher ?) must be a pretty efficient
device as it doesn't get very warm from wasting energy as heat - or perhaps my
aerials are a reasonably good match and the tuner isn't doing any / much work.

Let me refer to you to this link:

http://users.triconet.org/wesandlinda/ladder.htm

and suggest that you also follow the imbedded link to my letter to
Dean.

There you will find an analysis if what tuner losses can be.

But let's also answer this issue of "It doesn't get hot, so it must
not be lossy."

First let's say that, unless the op is a real blabbermouth, the
transmit duty cycle will be 50%. Transmit half the time, listen half
the time.

If the op is on CW then the duty cycle of the transmit cycle is ~44%.
(The standard word "PARIS" sent repeatedly with 1:3:7 spacing. So for
CW operation, the overall duty cycle is .5 * .44 = 22%.

On SSB it's more complicated. Without speech processing, the peak to
average ratio is variously given, but 14:1 (11.5 dB) is typical. Most
rigs have some form of speech compression or clipping these days (most
used to excess). Really effective clippers, (ahem)

http://users.triconet.org/wesandlinda/s_proc.pdf

can improve this quite a bit so let's say that it's 6 dB. So the
average power is 6 dB below the peak or 25% of the peak. Our overall
duty cycle is .5 * .25 = 12.5%

Of course the digital modes and FM are full carrier so the duty cycle
is 50%. Not many using FM on hf where tuners are the norm, the PSK
guys pride themselves on QRP, which leaves only the special case RTTY
contesters running full power.

So back to the guy running 100 W CW through a tuner driving a ladder
line fed antenna. If his tuner burns up half of the power will it get
hot? Are 11 W (22% of 50) going to smoke most components? What if
the tuner loss is 6 dB? The average power dissipation climbs to a
whopping 16.5 W. (22% of 75) Is this a big thermal management issue?

Certainly, KW rigs running RTTY are going to be a bigger concern, but
the tuners (and component parts) are commensurately bigger and can
dissipate more power without "getting hot".