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

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.

73,
Steve G3TXQ

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

On Mon, 05 Oct 2009 21:30:06 GMT, Owen Duffy wrote:

Calorimetric measurments are problematic, they sound simple enough, but
latency my mean it takes hours to reach close to maximum operating
temperature. ...
and the case was quite warm near the balun after just minutes of testing.

Sounds like the BalUn was doing a superlative job.

Hi Owen,

What you describe (sans the problematic word latent) is specific heat
capacity. And just like any capacitor, charge/heat does not increase
after a source is removed. If it is not removed (which I presume was
the intent of both your statements), then the specific heat capacity
you describe is a design boon.

73's
Richard Clark, KB7QHC

Richard Clark wrote in
:

....
What you describe (sans the problematic word latent) is specific heat
capacity.

I used the term latency in the context of time, there is a delay between
commencement of application of steady power to reaching substantially full
operating temperature. Yes, the effect can be predicted using the material
specific heat capacity, subject to the temperature variability of the
ferrite characteristics.

....
the intent of both your statements), then the specific heat capacity
you describe is a design boon.

Yes, but a trap if long term use is envisaged but tested only in the short
term.

Owen

To put some numbers around the problem, if one had a FT240 core which has
a mass of around 0.2kg, and specific heat capacity around 800J/kgK, the
energy to raise the core to a Curie point of 130°C to 300°C would be 17kJ
to 44kJ. If the core was well insulated (no heat loss) and dissipating
say 20W, that would take 15 to 40 minutes.

Of course, one would hope that the transformers do lose heat to the
environment, and that would substantially slow the rate of rise of
temperature.

Experience shows that a 5 minute test of a ferrite transformer does not
indicate continuous power handling capability.

Digressing slightly, but on this ferrite heat thing...

Martin questioned my article "A review of the Guanella 4:1 balun on a
shared magnetic circuit" at http://www.vk1od.net/balun/gsc/index.htm . In
particular, his issue was with my proposition that the extent to which
these things "work" is due to flux leakage on low µ cores, the lower the
µ, the more they resemble Guanella's balun.

Martin's inital experiments indicated that the thing did work, but on my
advice he tried prototypes on high and low µ cores and took thermal
pictures of the things after operation. The images showed non-uniform
distribution of heat in the cores which is either due to the main heat
source being the conductor losses, or that magnetic flux is a significant
contribution and not evenly distributed in the toroid. The flux
distribution is a credible explanation for the different patterns for
same winding on the different µ cores.

Again, this is one of those things that lots of hams have QSLs to prove
that they "work real good".

Owen

On Tue, 06 Oct 2009 06:25:53 GMT, Owen Duffy wrote:

Of course, one would hope that the transformers do lose heat to the
environment, and that would substantially slow the rate of rise of
temperature.

Hi Owen,

This opens another topic of my study with Thermal Resistance. One
paper that I have filed away that may aid you is W.E. Hord's "Recent
Developments In The Average Power Capacity Of Rotary-Field Ferrite
Phase Shifters." It may lack the specific application discussed here,
but it covers the math and interface relationships. Sorry, but I
don't have any publication details except for author/title.

Hord's work is with ferrites capable of sustaining RF power levels in
multiple KW. My first experience with ferrites (ca. 1972) was with RF
transmission line source/load isolation in the microwaves (the paper
is S-Band), a field that is wholly alien to discussion here.

73's
Richard Clark, KB7QHC

Owen Duffy wrote in
:

....
Martin questioned my article "A review of the Guanella 4:1 balun on a
shared magnetic circuit" at http://www.vk1od.net/balun/gsc/index.htm .

Ian (GM3SEK) kindly drew my attention to incorrect reference to two of the
figures in the above article. The error was misleading, it is fixed now. My
apologies to anyone who was confused by the error.

Thanks Ian.

Owen