On Sun, 3 Aug 2003 10:19:55 -0700, "Richard Henry"
wrote:


Besides, they're not really robots. All of them are just RC toys. I'll
be more impressed when they are autonomous.

That's not entirely true these days. Autonomy in certain areas of
control is becoming increasingly prevalent. It'll be interesting to
see how this particular aspect of design develops over the coming
years...
--

"I believe history will be kind to me, since I intend
to write it." - Winston Churchill

In article ,
says...
On Sun, 3 Aug 2003 11:40:55 -0400, "Bob Lewis \(AA4PB\)"
wrote:

Stainless steel is awful at conducting electricity - so it won't
make a
very efficient antenna.

I doubt that the difference in resistance between stainless and copper
is going to cause any significant additional losses in a whip antenna.
That difference will be small compared to the other losses. Stainless
is often used for whip antennas because of its mechanical properties.

Yes, I've several proprietory s/steel whip antennas that give
excellent results. But a question springs to mind. If a s/steel
antenna has slightly higher resistance, does that appreciably lower
its Q?


--

"I believe history will be kind to me, since I intend
to write it." - Winston Churchill


you mean it's bandwidth? probably, but why worry? it's not cut to
resonance, anyway. it's a resistor in an E field. Tx units can be run
with the telescoping verticle collapsed and still control the toy at
short ranges. i think the biggest prob would be front end overload
regardless of the antenna, which i'd try to deal with in an active
antenna setup which is well suited to short verticles, you just can't
let it blast the front end of one of those little RC Rxs.

i've used all kinds of different scraps of wire to get FM RXs going to
see if they work. how about those little pieces of scrap wire on RC
cars? they're no better than yours.

BR,
mike

In article ,
says...
On Sun, 3 Aug 2003 11:40:55 -0400, "Bob Lewis \(AA4PB\)"
wrote:

Stainless steel is awful at conducting electricity - so it won't
make a
very efficient antenna.

I doubt that the difference in resistance between stainless and copper
is going to cause any significant additional losses in a whip antenna.
That difference will be small compared to the other losses. Stainless
is often used for whip antennas because of its mechanical properties.

Yes, I've several proprietory s/steel whip antennas that give
excellent results. But a question springs to mind. If a s/steel
antenna has slightly higher resistance, does that appreciably lower
its Q?


--

"I believe history will be kind to me, since I intend
to write it." - Winston Churchill


you mean it's bandwidth? probably, but why worry? it's not cut to
resonance, anyway. it's a resistor in an E field. Tx units can be run
with the telescoping verticle collapsed and still control the toy at
short ranges. i think the biggest prob would be front end overload
regardless of the antenna, which i'd try to deal with in an active
antenna setup which is well suited to short verticles, you just can't
let it blast the front end of one of those little RC Rxs.

i've used all kinds of different scraps of wire to get FM RXs going to
see if they work. how about those little pieces of scrap wire on RC
cars? they're no better than yours.

BR,
mike

If a s/steel antenna has slightly higher resistance, does that
appreciably lower its Q?

I don't have any figures available but I wouldn't think so. The
difference between the resistance of a 2-foot piece of copper and a
2-foot piece of stainless is going to be pretty small.

If a s/steel antenna has slightly higher resistance, does that
appreciably lower its Q?

I don't have any figures available but I wouldn't think so. The
difference between the resistance of a 2-foot piece of copper and a
2-foot piece of stainless is going to be pretty small.

The short answer is that stainless probably won't make a noticeable
difference in loss, and therefore won't make a significant difference in Q.

The conductor loss of an antenna of a given wavelength size gets less as
the frequency gets higher. That's because the antenna length decreases
in inverse proportion to the frequency, while the loss per unit length
increases only as the square root of the frequency. So for a given wire
diameter, a half wavelength dipole at, say, 10 MHz has half the loss of
a half wavelength dipole at 2.5 MHz. Stainless steel whips are fine at 2
meters. But an 80 meter dipole made from small or moderate gauge
stainless wire could be pretty lossy -- almost certainly so, if the
stainless is a magnetic alloy. (Being magnetic greatly increases the RF
loss -- by a factor of the square root of the permeability.)

Loss becomes very important when a whip is a lot shorter than a quarter
wavelength. However, in many or most cases (like an HF mobile whip), the
whip typically has a fairly large diameter where the current is high,
and the whip loss is swamped by other losses, so the whip loss isn't
objectionable.

It's always possible to come up with a combination of whip diameter,
length, and frequency where stainless could be a poor choice -- but it's
uncommon in typical applications.

Roy Lewallen, W7EL

Paul Burridge wrote:
On Sun, 3 Aug 2003 11:40:55 -0400, "Bob Lewis \(AA4PB\)"
wrote:


Stainless steel is awful at conducting electricity - so it won't

make a

very efficient antenna.

I doubt that the difference in resistance between stainless and copper
is going to cause any significant additional losses in a whip antenna.
That difference will be small compared to the other losses. Stainless
is often used for whip antennas because of its mechanical properties.


Yes, I've several proprietory s/steel whip antennas that give
excellent results. But a question springs to mind. If a s/steel
antenna has slightly higher resistance, does that appreciably lower
its Q?


--

"I believe history will be kind to me, since I intend
to write it." - Winston Churchill

The short answer is that stainless probably won't make a noticeable
difference in loss, and therefore won't make a significant difference in Q.

The conductor loss of an antenna of a given wavelength size gets less as
the frequency gets higher. That's because the antenna length decreases
in inverse proportion to the frequency, while the loss per unit length
increases only as the square root of the frequency. So for a given wire
diameter, a half wavelength dipole at, say, 10 MHz has half the loss of
a half wavelength dipole at 2.5 MHz. Stainless steel whips are fine at 2
meters. But an 80 meter dipole made from small or moderate gauge
stainless wire could be pretty lossy -- almost certainly so, if the
stainless is a magnetic alloy. (Being magnetic greatly increases the RF
loss -- by a factor of the square root of the permeability.)

Loss becomes very important when a whip is a lot shorter than a quarter
wavelength. However, in many or most cases (like an HF mobile whip), the
whip typically has a fairly large diameter where the current is high,
and the whip loss is swamped by other losses, so the whip loss isn't
objectionable.

It's always possible to come up with a combination of whip diameter,
length, and frequency where stainless could be a poor choice -- but it's
uncommon in typical applications.

Roy Lewallen, W7EL

Paul Burridge wrote:
On Sun, 3 Aug 2003 11:40:55 -0400, "Bob Lewis \(AA4PB\)"
wrote:


Stainless steel is awful at conducting electricity - so it won't

make a

very efficient antenna.

I doubt that the difference in resistance between stainless and copper
is going to cause any significant additional losses in a whip antenna.
That difference will be small compared to the other losses. Stainless
is often used for whip antennas because of its mechanical properties.


Yes, I've several proprietory s/steel whip antennas that give
excellent results. But a question springs to mind. If a s/steel
antenna has slightly higher resistance, does that appreciably lower
its Q?


--

"I believe history will be kind to me, since I intend
to write it." - Winston Churchill

surface armor, there's a hulking great metal framework. Consequently,
sandwiching the antenna between the armour and the frame is going to
lead to unacceptable loss of radiated energy, I'd have thought. Unless
anyone knows differently..
I do not know the frequencies, but if they are high enough, one could think
of a slot or a patch antenna

Is there anything in the rules forbidding your installing a jammer
If jamming would be allowed, it would be a totally different sport (but
interesting as well). In that case you may as well omit the robots See all
the military history about ECM, ECCM, ECCCM (Electronic Counter(*n)
Measures) etc.

Wim

surface armor, there's a hulking great metal framework. Consequently,
sandwiching the antenna between the armour and the frame is going to
lead to unacceptable loss of radiated energy, I'd have thought. Unless
anyone knows differently..
I do not know the frequencies, but if they are high enough, one could think
of a slot or a patch antenna

Is there anything in the rules forbidding your installing a jammer
If jamming would be allowed, it would be a totally different sport (but
interesting as well). In that case you may as well omit the robots See all
the military history about ECM, ECCM, ECCCM (Electronic Counter(*n)
Measures) etc.

Wim

Stainless steel is awful at conducting electricity - so it won't make a
very efficient antenna. But how much it really matters, I don't know.
You can coat it with silver or copper, only the outer few microns conduct HF
(skin-effect)

Wim