On Sep 7, 12:22*pm, Roy Lewallen wrote:
On 9/6/2010 5:06 PM, Frank wrote:



On 7 MHz a dipole constructed of salt water: Er = 81,
* conductivity 5 S/m, and 0.5" diameter has a free
space efficiency of 0.08%. *i.e. with 100 W input
the total radiated power = 80 mW.

Frank
(VE6CB)

That looked so bad I had to run an analysis to see for myself. Sure
enough, it's that bad. And even with a 0.25 inch diameter column at 146
MHz, the efficiency is only on the order of 1%. A foot and a half of
wire vs. a pump, power source, and ferrite transformer? No contest.

Roy Lewallen, W7EL

I know Dan Tam, the SPAWAR engineer in the video. He's a pretty sharp
guy. I hesitate to throw him into the Lions' Den but I will if you
let me watch. :-)

"Sal"

On 9/8/2010 8:06 PM, Sal M. Onella wrote:
On Sep 7, 12:22 pm, Roy wrote:

That looked so bad I had to run an analysis to see for myself. Sure
enough, it's that bad. And even with a 0.25 inch diameter column at 146
MHz, the efficiency is only on the order of 1%. A foot and a half of
wire vs. a pump, power source, and ferrite transformer? No contest.

Roy Lewallen, W7EL

I know Dan Tam, the SPAWAR engineer in the video. He's a pretty sharp
guy. I hesitate to throw him into the Lions' Den but I will if you
let me watch. :-)

"Sal"

It's a sad comment on the state of this newsgroup that an objective
statement of what are believed to be facts is taken as "throwing [the
engineer] into the lions' den". It's not my intent at all to impugn the
engineer. Surely he's aware of the efficiency of the "antennas" he's
creating, so either my (and Frank's) calculations are grossly incorrect
or SPAWAR thinks there's a market for such inefficient antennas. It
would be educational to know which of these is the case. It was
interesting that there was no mention in the video of very low
efficiency, but I guess that's to be expected for a promotional piece
produced by a marketing department looking for investors.

Roy Lewallen, W7EL

On 9/8/2010 9:35 PM, Roy Lewallen wrote:

...
It's a sad comment on the state of this newsgroup that an objective
statement of what are believed to be facts is taken as "throwing [the
engineer] into the lions' den". It's not my intent at all to impugn the
engineer. Surely he's aware of the efficiency of the "antennas" he's
creating, so either my (and Frank's) calculations are grossly incorrect
or SPAWAR thinks there's a market for such inefficient antennas. It
would be educational to know which of these is the case. It was
interesting that there was no mention in the video of very low
efficiency, but I guess that's to be expected for a promotional piece
produced by a marketing department looking for investors.

Roy Lewallen, W7EL


Gesus! If it walks like a duck, quacks like a duck, swims like a duck,
smells like a duck, sounds like a duck ... well, you know that one.

Never thought I would hear you say that ... ya' never had a hard time
calling a duck a duck before.

Regards,
JS

On Wed, 08 Sep 2010 21:35:19 -0700, Roy Lewallen
wrote:

so either my (and Frank's) calculations are grossly incorrect
or SPAWAR thinks there's a market for such inefficient antennas.

The point I caught, and apparently was not modeled, was the discussion
of antenna height for any particular band. Albeit, such mention was
fleeting, but it sounded suspiciously like half wave, not quarter wave
dimensions.

Aside from that speculation, power specs for military usage are
appropriate for theater operations, not global communications. When I
taught UHF/VHF in the Navy, 10% efficiency was considered perfectly
acceptable as point-to-point communications was the only expectation
and that was rarely as much as 20 miles at best. Experience teaches
that even that only takes 100s of milliwatts.

73's
Richard Clark, KB7QHC

On 9/8/2010 10:50 PM, Richard Clark wrote:
On Wed, 08 Sep 2010 21:35:19 -0700, Roy
wrote:

so either my (and Frank's) calculations are grossly incorrect
or SPAWAR thinks there's a market for such inefficient antennas.

The point I caught, and apparently was not modeled, was the discussion
of antenna height for any particular band. Albeit, such mention was
fleeting, but it sounded suspiciously like half wave, not quarter wave
dimensions.

Aside from that speculation, power specs for military usage are
appropriate for theater operations, not global communications. When I
taught UHF/VHF in the Navy, 10% efficiency was considered perfectly
acceptable as point-to-point communications was the only expectation
and that was rarely as much as 20 miles at best. Experience teaches
that even that only takes 100s of milliwatts.

73's
Richard Clark, KB7QHC

That's still an order of magnitude better than what this antenna seems
able to do at VHF, although the demonstration clearly showed it to be
adequate for working a local repeater with an HT.

But what about HF, which the video clearly mentions? Is a fraction of a
percent efficiency adequate for typical communication needs? I know that
some military HF use is NVIS, for which a vertical antenna is poorly
suited to begin with, so that probably wouldn't be an application. Are
milliwatts of radiated HF used and useful for theater communications?

Roy Lewallen, W7EL

On 9 sep, 03:21, Roy Lewallen wrote:
On 9/8/2010 10:50 PM, Richard Clark wrote:





On Wed, 08 Sep 2010 21:35:19 -0700, Roy
wrote:

so either my (and Frank's) calculations are grossly incorrect
or SPAWAR thinks there's a market for such inefficient antennas.

The point I caught, and apparently was not modeled, was the discussion
of antenna height for any particular band. *Albeit, such mention was
fleeting, but it sounded suspiciously like half wave, not quarter wave
dimensions.

Aside from that speculation, power specs for military usage are
appropriate for theater operations, not global communications. *When I
taught UHF/VHF in the Navy, 10% efficiency was considered perfectly
acceptable as point-to-point communications was the only expectation
and that was rarely as much as 20 miles at best. *Experience teaches
that even that only takes 100s of milliwatts.

73's
Richard Clark, KB7QHC

That's still an order of magnitude better than what this antenna seems
able to do at VHF, although the demonstration clearly showed it to be
adequate for working a local repeater with an HT.

But what about HF, which the video clearly mentions? Is a fraction of a
percent efficiency adequate for typical communication needs? I know that
some military HF use is NVIS, for which a vertical antenna is poorly
suited to begin with, so that probably wouldn't be an application. Are
milliwatts of radiated HF used and useful for theater communications?

Roy Lewallen, W7EL- Ocultar texto de la cita -

- Mostrar texto de la cita -

What about if you are a whale?

What if you are a firefighter?, you can got a good 160 m portable
antenna in your fire engine! Do you remember the pretty nice
"Frequency" film with Dennis Quaid as W2QYV, an ideal antenna for
him :D

Greetings to all - Miguel Ghezzi - LU6ETJ

On 9/9/2010 7:03 AM, lu6etj wrote:

...
What about if you are a whale?

What if you are a firefighter?, you can got a good 160 m portable
antenna in your fire engine! Do you remember the pretty nice
"Frequency" film with Dennis Quaid as W2QYV, an ideal antenna for
him :D

Greetings to all - Miguel Ghezzi - LU6ETJ

ROFLOL! Good sense of humor man!

And, you are totally correct, firemen expending BIG tax dollars for a
dollar conversation is about right.

Regards,
JS

Having dealt with water streams for a while, I wonder how the stream
is measured, because all streams break up into droplets at some point
well before they appear to do so.
- 'Doc

On 9/11/2010 7:46 PM, 'Doc wrote:
Having dealt with water streams for a while, I wonder how the stream
is measured, because all streams break up into droplets at some point
well before they appear to do so.
- 'Doc

You are absolutely correct. Would be interesting to have real time
monitoring of the match, field strength in relation to a standard 1/4
wave and real power delivered to the water stream. I am thinking this
is the dummies, dummy load. Or, the dummy load of the century ... could
sure use a 5KW ferrite core like he has, just sink the signal into a
"barrel of sal****er dummy load" ... would be nice to be have this
dis-proven and start discussing why.

Who knows, when the stream goes "live" perhaps the feedline "lights up"
as a radiator. As someone already pointed out, the repeater makes one
highly suspicious. I mean, is he line of sight from the repeater? How
far is he from the repeater? Why didn't he just choose direct contact?
Etc., etc. He certainly could have supplied us with better.

I just might write him and ask him for a new youtube video and different
test parameters.

Regards,
JS

On Sep 12, 3:13*am, John Smith wrote:
On 9/11/2010 7:46 PM, 'Doc wrote:

Having dealt with water streams for a while, I wonder how the stream
is measured, because all streams break up into droplets at some point
well before they appear to do so.
* - 'Doc

You are absolutely correct. *Would be interesting to have real time
monitoring of the match, field strength in relation to a standard 1/4
wave and real power delivered to the water stream. *I am thinking this
is the dummies, dummy load. *Or, the dummy load of the century ... could
sure use a 5KW ferrite core like he has, just sink the signal into a
"barrel of sal****er dummy load" ... would be nice to be have this
dis-proven and start discussing why.

Who knows, when the stream goes "live" perhaps the feedline "lights up"
as a radiator. *As someone already pointed out, the repeater makes one
highly suspicious. I mean, is he line of sight from the repeater? *How
far is he from the repeater? *Why didn't he just choose direct contact?
* Etc., etc. *He certainly could have supplied us with better.

I just might write him and ask him for a new youtube video and different
test parameters.

Regards,
JS

yeah, like compare the signal to one of those rubber coated dummy load
antennas.