[Elecraft] high-power tuner

[Fred Townsend]

Ron, Rick, Erik: There are many reasons why temperature measurements are a
poor way of evaluating a tuner. There is a method of power measure based on
temperature rise. It's called a bolometer.  It only works well if the mass
involved is small. Wiki bolometers if you want the details.

I think there is an even more important reason not to use this approach.
Let's consider the case where the transmitter has a very strong second
harmonic say -10db. If the tuner is doing its job, tuning, not just
matching, the 2nd harmonic will be tuned or filtered out. 10% of the energy
will be lost. What becomes of that energy? In an ideal world that energy
would be reflected into a dummy load, like when you use a circulator. Since
most tuners don't have circulators, part of the energy will be dissipated in
the tuner and part will be reflected back to the transmitter. That energy
that is dissipated in the tuner is a measure of how well, not how poorly,
the tuner is working. BTW in this case measuring SWR at the transmitter will
also suggest the tuner is not doing its job well when it is. 

Now we know good rigs don't have strong harmonics but I think I have
illustrated why measuring heat is not a good measure of performance.

73, Fred, AE6QL

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Erik Basilier
Sent: Saturday, March 10, 2012 12:31 PM
To: 'Ron D'Eau Claire'; 'Rick Stealey'; elecraft at mailman.qth.net
Subject: Re: [Elecraft] high-power tuner

As has been clearly demonstrated in this thread, there are multiple methods
of measurement. The one that gets my vote for elegance is the one with two
tuners back-to-back. With respect to the method that measures temperature
rise, taking into account the mass of the tuner, one also needs to take into
account the specific heat capacity of the tuner. One kilo of material x
doesn't heat up at the same rate as one kilo of material y when the same
heating power is applied. The tuner will of course be a mix of materials, so
one would have to measure the rate at which the tuner heats up when heat is
applied through a know heating source rather than TX power. If it is done
that way, one needs to know neither the mass nor the specific heat capacity,
since what one is measuring is essentially the mass times the specific heat
capacity.

73, Erik K7TV

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Ron D'Eau Claire
Sent: Saturday, March 10, 2012 11:47 AM
To: 'Rick Stealey'; elecraft at mailman.qth.net
Subject: Re: [Elecraft] high-power tuner

I was investigating tuner losses a few years ago and ran into many of these
same questions. 

A physicist buddy pointed out to me that the normal approach to measure loss
in something like a tuner is to put it in a well-insulated chamber and
measure the rise in temperature over time while transmitting. From there on
can calculate the energy required to cause the temperature rise which can be
used to calculate the number of watts of RF that never make it through the
box. 

73, Ron AC7AC

-----Original Message-----

There seems to have been no answer as to how to accurately measure the loss
in a tuner.  
Here is a solution but requires two tuners or at least one calibrated one
that could be used to measure others.
Take first tuner and tune it into the mismatch, say 600 ohms.  Use an
antenna analyzer.
Then remove the load, and connect another tuner to the output of the first
(back- to-back - antenna port on first to antenna port on second tuner.)
Then put a 50 ohm load on the second tuner where the transceiver would be
connected, and tune the second tuner to a match.  It will have the same
settings as the first tuner, complete symmetry.
Then measure the power in the 50 ohm load  to get the loss.

Since both tuners are matching the same load, and the system is symmetrical
the loss contribution by each tuner is half.  Repeat for other types of
loads, and now you have a calibrated tuner to use with any tuner you want to
test.

Rick  K2XT

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