news wrote:

Hi:
There are some problems with using stainless steel for elements in a beam.
1) Stainless Steel has much higher loss than aluminum. Remember because of
skin effect the RF current flows only in the outer few thousand of an inch
of the metal. The depth of conduction gets less as the frequency goes higher
so 2m antenna made of stainless would have higher loss than a 6m and 440
antenna would have even more. . . .

If you do the actual calculations, you'll find that even the greater
loss of stainless is insignificant for typical VHF and higher frequency
antennas, even when made with wire of moderate diameter. When made with
tubing, loss is even less.

And, it's not necessarily true that antenna loss increases with
frequency. The skin depth decreases only as the square root of
frequency, while for a given antenna length in wavelengths, the element
length is inversely proportional to frequency. For example, if you
increase the frequency by a factor of two, the skin depth decreases by a
factor of about 1.4 while the length shortens by a factor of 2. The net
result is *lower* total resistance as the frequency increases -- a
factor of about 0.71 each time you double the frequency. (This is
assuming that you maintain the same absolute conductor diameter and keep
the length constant in terms of wavelength.) That's why stainless steel
isn't a problem for higher frequency antennas.

Roy Lewallen, W7EL

How do I determine the length of elements for a stainless steel element
beam antenna?

What about the length of using stainless steel in a j pole?

In making a beam, if I wanted to use a metal boom, how could I insulate
the elements from the boom?
Please forgive me if these are elementary questions.

On 6 Jan 2005 06:14:21 -0800, wrote:
Please forgive me if these are elementary questions.

Hi OM,

We can forgive the questions, but they are far from elementary. In
fact, there are so many variables to consider, that it often makes
such questions hard to answer without going into a considerable length
of constraints.

One simple response, however, is that for VHF/UHF, stainless steel is
hardly the most complex issue - this has already been noted here in
discussion. The remaining characteristics of length, size, and
distribution of elements has as many answers as answerers³.

To put it bluntly, you should put some effort into coming to terms
with modeling software to appreciate the variety of answers and their
ramifications. Getting this same education through single one-off
questions could take many, many years.

Another way is to simply pick a design, and build it. When you
discover what's good or bad about it, THEN discussion could more
easily respond to what you have and what you need to do. Experience
is the great leveler against "what-if." One notable aspect of this
past time is you are NOT going to do this once! So you may as well do
something and expect you will do some more (and more...).

73's
Richard Clark, KB7QHC