Why are power limits specified so low for dual-band and tri-band HT
rubber duck antennas? The conductors in the couple I saw surgerized
looked like they could handle lots more.

I am considering a mobile magnetic base that accepts SMA antennas,
but am deterred by the low limits for the duckies I would want to use.

The concept is that you transfer your ducky from the HT to the roof
when you get into your car. No problem with just the HT but not so
good with a QRP amp that outputs 30 watts.

Ken KC2JDY

Ken
(to reply via email
remove "zz" from address)

Some of it has to do with the rather wildly variable impedance that an HT
antenna will present, but in general, HT's aren't high power devices, pretty
much by definition.

try pumping a kw into a 6" ducky on 2m and see how long it takes to be a
roast ducky... but it surely won't smell as good while cooking. oh, and
since most ducky's are not very far from the people using them you may get a
bit warm also.

"Ken" wrote in message
...
Why are power limits specified so low for dual-band and tri-band HT
rubber duck antennas? The conductors in the couple I saw surgerized
looked like they could handle lots more.

I am considering a mobile magnetic base that accepts SMA antennas,
but am deterred by the low limits for the duckies I would want to use.

The concept is that you transfer your ducky from the HT to the roof
when you get into your car. No problem with just the HT but not so
good with a QRP amp that outputs 30 watts.

Ken KC2JDY

Ken
(to reply via email
remove "zz" from address)

Not to mention safty concerns- like those FCC rules for hams in the KW
class- minimum safty standards - and those at 100 FEET, not in front of
your face ! Also, those have rarely had great swr readings when
measured. Most likely a combonation of these concerns-- Jim NN7K


Richard Clark wrote:

The reasons may be manifold, but I would figure issues of
loss would be found in the soft tissues of the antenna mast (a
hand/arm) or nearby obstructions (skull/torso).

The dual banders would undoubtedly contain components
that were designed to feed or present a Hi-Z antenna, and would thus
face a rather stiff voltage - hence the limits on power.

73's
Richard Clark, KB7QHC

"Jim - NN7K" wrote in message
m...
Not to mention safty concerns- like those FCC rules for hams in the KW
class- minimum safty standards - and those at 100 FEET, not in front of
your face ! Also, those have rarely had great swr readings when
measured. Most likely a combonation of these concerns-- Jim NN7K


Years ago there was a very interesting letter from a real old timer who put
a telephone element across the output of his transmitter .. He was having a
voice QSO with another ham for the first time.. He does not remember what
happened but woke up on the floor. The RF had caused some intercranial
changes and this fellow was fortunate enough to make it alive. I remember
years ago giving SW diathermy transcranial for Alzheimer's with capacity
plates at either ear. I would not want to do that again but it was standard
practice. It is really amazing what tissue heating feels like with those RF
fields ...... adds a new meaning to the phrase ..."a warm feeling within".

73 Tom Popovic KI3R Belle Vernon Pa

"garigue" wrote in message
news:jSjCd.19888$wu4.13273@attbi_s52...

"Jim - NN7K" wrote in message
m...
Not to mention safty concerns- like those FCC rules for hams in the KW
class- minimum safty standards - and those at 100 FEET, not in front of
your face ! Also, those have rarely had great swr readings when
measured. Most likely a combonation of these concerns-- Jim NN7K


Years ago there was a very interesting letter from a real old timer who
put
a telephone element across the output of his transmitter .. He was having
a
voice QSO with another ham for the first time.. He does not remember
what
happened but woke up on the floor. The RF had caused some intercranial
changes and this fellow was fortunate enough to make it alive. I remember
years ago giving SW diathermy transcranial for Alzheimer's with capacity
plates at either ear. I would not want to do that again but it was
standard
practice. It is really amazing what tissue heating feels like with those
RF
fields ...... adds a new meaning to the phrase ..."a warm feeling within".

73 Tom Popovic KI3R Belle Vernon Pa



A couple of anecdotal experiences.

Back about 15 years ago, I was doing some high-power RF exposure testing on
a cruise missile. I had a 300 watt TWT amplifier feeding an X-band pyramidal
horn antenna through waveguide. I went into the chamber to rotate the
antenna polarization, and put my left hand across the antenna aperture. I
immediately thought it was strange, as warm air was blowing out of the horn.
But that was impossible, since the horn had a mica window across the throat!
Duh, I had left the amplifier turned on! So I can report that tissue heating
is an almost pleasant experience (very short term!), quite akin to the
warm-air hand dryers found in some washrooms.

I also recall reading a letter to an RF trade journal, where an experimenter
was relating his experience on a WWII research project. His team of four was
working on waveguide hardware design, observing high-altitude, high-power
breakdown problems. He related that the team had set up a horn antenna
within a large glass bell-jar (so that they could pump it down to altitude).
The horn faced horizontally out of the jar, and the team set up a small
telescope just outside the jar so that they could look down into the horn
throat and feed to observe arcing. He said that they would change observers
when their face got too hot!

Ed
wb6wsn

A few years back I opened the highish-level kitchen microwave oven door and
felt what seemed to be a warm breeze of air on my face and especially round
my eyes.

I immediately recognised the sensation felt when standing in the beam from
the non-rotating dish of a 3 GHz, 50 Kwatt radar equipment during WW2, some
50 years before.

I very fast switched all power OFF. The safely mechanism must have been
defective. It may have been a good thing my XYL had not opened it.

There were no after-effects except on my bank balance for a new oven of
different make.
----
Reg.

Reg Edwards wrote:
There were no after-effects ...
.... that you are aware of. :-)
--
73, Cecil http:www.qsl.net/w5dxp

I looked into the hazards of microwave energy quite a while back
(mid-60s), when I was a radar technician. Some of the old-timers in
Alaska had routinely warmed their hands by putting them in front of the
feedhorn, but enlightenment had taken place by the time I was involved,
and systems were interlocked to prevent accidental exposure. (I worked
on heavy ground radar, with peak output power of about 5 MW, and average
power of several kW.)

As far as I could determine, plain heating was the only bad effect that
had been found. The main potential for damage was the eyes, where there
are apparently not enough blood vessels to carry away the heat very
fast. Internal organs were vulnerable to very high rate doses, because
of the relative lack of nerves to communicate the problem before it got
serious. They hadn't found any cases of permanent sterility, in spite of
the pervasive fear. Heat can kill any sperm present at the time of the
exposure, leading to temporary sterility, which is likely the source of
the belief. Otherwise, all it was found to do is warm you up. As long as
the heat doesn't build up too much, there was no lasting harm.

I'm sure there's been a great deal of research since then -- both
microwave ovens and cell phones have become ubiquitous in the
intervening years. I believe some research has shown potential harm in
long-term cell phone use with the antenna very close to the head, but
don't know if anyone knows the mechanism -- or how good the research is.

So my view of microwave energy is that it's something to take care with,
but not to irrationally fear.

Roy Lewallen, W7EL

Reg Edwards wrote:
A few years back I opened the highish-level kitchen microwave oven door and
felt what seemed to be a warm breeze of air on my face and especially round
my eyes.

I immediately recognised the sensation felt when standing in the beam from
the non-rotating dish of a 3 GHz, 50 Kwatt radar equipment during WW2, some
50 years before.

I very fast switched all power OFF. The safely mechanism must have been
defective. It may have been a good thing my XYL had not opened it.

There were no after-effects except on my bank balance for a new oven of
different make.
----
Reg.

Reg, G4FGQ wrote:
"A few years back I opened the highish-level kitchen microwave oven door
and felt what seemed to be a warm breeze of air on my face and
especially around my eyes."

I coincidentally happened across a couple of related stories. First,
Louis N.Ridenour wrote in "Radar System Engineering":
"A British Technical Mission arrived in Washington in September 1940 and
mutual disclosures were made of British and American accomplishments in
radar up to that time." Seems the British had invented a magnetron.
America thought it important. On board my ship during WW-2, we kept the
spare for our Raytheon SO radar in the ship`s safe!

Second is from IEEE`s June 2003 edition of "The Institute":
"In 1946, Percy Spencer, an engineer and inventor who held more than 120
patents, was conducting radar-related research for Raytheon Corp. While
testing a new type of vacuum tube - the magnetron - he noticed that the
chocolate bar he had been carrying in his pocket had melted. Intrigued,
Spencer began conducting more experiments. He watched popcorn "pop" and
bounce around the room when he held a bag of uncooked kernals up to the
tube. Next, Spencer observed a raw egg placed next to the magnetron
explode from the pressiure that had built up inside.

Spencer concluded that each of the items had "cooked" when exposed to
low density microwave energy emitted by the magnetron. Raytheon
engineers quickly adapted his discovery, and the first commercial
microwave oven, the "Radarange" began to move into household kutchens
the following year.

Best regards, Richard Harrison, KB5WZI