steveeh131047 wrote in
:

On Oct 5, 10:14*am, Owen Duffy wrote:


Non-ideal transformation ratio is not a big issue for an unun used
with an ATU, voltage withstand and loss are higher priority.

Owen,

Agreed. But the "non-ideal transformation" will result in changed
feedline losses and tuner losses. May be better, may be worse

Almost always, but probably more often for the better.

BTW, I gave a brief description of the FT240 #61 12t unun, but didn't
mention the winding details, they are 0.8mm wire spaced (centre to
centre) 3.2mm and permittivity 1.2 which describes a winding with 0.8mm
PTFE insulation for high voltage withstand, an 'ATU unun' in commercial
talk.


I enjoyed reading your balun loss article. "66% of the transmitter
power converted to heat inside the ATU" will be a surprise to many
folk. I can replicate almost the exact set-up you describe: G5RV
half-wave of ladderline4:1 voltage baluntuner; so If I can find
the time I'll try to measure the rate of temperature rise inside the
tuner case when it's handling 100W CW, and then stick a 60W light bulb
in the case and measure the rate of temperature rise again.

Keep in mind that ferrite cores heat (and cool) very slowly. One could
easily be fooled into thinking that there isn't much heat dissipated in
a short test, but after an hour of operation, the core is still heating
at a substantial rate. This is one of the things that saves the bacon of
manufacturers of 5kW and 10kW continuous rated baluns, they are not
usually called upon to operate at high duty cycle for long enough to
reach the Curie point.

Calorimetric measurments are problematic, they sound simple enough, but
latency my mean it takes hours to reach close to maximum operating
temperature.

The greater worry is that this manufacturer, and probably some others,
use thermoplastic insulation to support the coil, which could result in
damage if you operate the ATU long enough to reach operating
temperature. Do so entirely at your own risk.

At one time, I had two identical ATUs, and I attached one with a 600+j0
load to the tx on 1.8Mhz and adjusted for VSWR=1 on the input. I
replaced the load with another ATU backwards and with a 50+j0 load and
adjusted the second ATU for VSWR=1 on the input to the first ATU. I then
read the power into the 50 ohms load and out of the tx using a Bird 43
and calculated the loss. The loss in the first ATU under those
conditions can be approximated by allocating half the total loss. This
test indicated quite high loss, and the case was quite warm near the
balun after just minutes of testing. BTW, this was the same type of ATU
as in the article you mentioned earlier.

In the example article, about 26% of the tx power is radiated on 80m.
That sounds pretty awful, but it should be seen relative to say 80% as a
reasonable system efficiency for a multiband antenna.

Owen