OK, let's discuss dipoles vs length
 

On 10/13/2014 4:56 PM, Lostgallifreyan wrote:
Jerry Stuckle wrote in news:m1h7sm$9bc$1@dont-
email.me:

I did see a video about a couple of guys free climbing an television
antenna about 2K feet in the air. I lost count how many safety
practices they violated. If OSHA had seen them doing that, they would
have been grounded big time. The fines would have probably put the
company out of business.


I can't find it to check, but I do remember it being very up-front about who
and where they were, and it was connected to soem company. The one I had was
probably kosher enough, if was effectively a promotional video, because
other, as you say, the effect would have been dramatically unwanted for them.
I could be wrong, but I won't know till I find it, and I have no idea where I
stowed it yet..


I don't know where it is, either - I never saved it. But AFAIK, OSHA
won't take action based on a youtube video - they want to see it
occurring.

I could be wrong, though. However, since I don't know what the company
was, there is no reasonable way to check the OSHA records (they are public).


--
==================
Remove the "x" from my email address
Jerry, AI0K

==================

OK, let's discuss dipoles vs length
 

"Ralph Mowery" wrote in
:

Most I have climbed was 100 ft of Rohn 25. I did climb some silos at
work that were about 130 feet up. Just a ladder up the side, but they
did have a stepoff offset platform about every 30 feet.



Axtually that I could cope with. I know what I said before about vertigo, but
I have crewed on a tall ship, and I got by despite hanging over the Irish Sea
in awkward coircumstances at about 60 foot up for a while, watching the sheet
I'd managed to drop as it swept through the racing water below.. I just tend
to freeze for a moment if overwhelmed by the insecurity of it. At moments
like those I think the best thing is being able to trust the other people
you're with. I'll never forget Charlie the cook on the Jean de la Lune.

OK, let's discuss dipoles vs length
 

On 10/13/2014 4:02 PM, wrote:
Jerry Stuckle wrote:

snip

You didn't say "optimum". You said it was "crap". What part of "crap"
don't you understand?

I will not engage in a ****ing contest with you.


You're the one who said it, not me.

You think an NEC analysis is the slickest thing since snot on a
doorknob. But what about HAAT or ground conductivity, for instance?

What about it?


Both have effects on the radiation pattern of an antenna.

Feel free to include all the above in your analysis.

You have considered neither when telling me my antenna was "crap" -
which it provably was not.

Where is the data that proves that?



Easy. The QSL card from Alaska and Hawaii on 75 meters.

--
==================
Remove the "x" from my email address
Jerry, AI0K

==================

OK, let's discuss dipoles vs length
 

Ian Jackson wrote in
:

Are you confusing the internet being carried (like cable TV) over coax
at RF, and via ADSL on twisted-pair phone lines? The coax drop cables
are usually RG6, which has a copper-plated steel inner.


I was likely confused enough to not know what I was confusing, but I do
remember it was about 40MHz or so (actually I think 36 to 39) which fits what
you said below.

If it's anything like some coax I worked with in the 60s, there might be
a small 'kink' in the frequency response* at around 40MHz, which is
probably the frequency at which all the RF has moved out of the steel
core, and into the copper plating.

OK, let's discuss dipoles vs length
 

On 10/13/2014 4:37 PM, Jeff Liebermann wrote:
On Mon, 13 Oct 2014 12:26:23 -0500, Lostgallifreyan
wrote:

If any given directional antenna can radiate at its best to one particular
direction, is it safe to assume that it will be at its best similarly aimed
when receiving?

Yes. For purposes of calculations and under most conditions, the
pattern is the same for transmit and receive for most antennas.

However, there are plenty of confusing exceptions. A common exception
is putting a 2.4GHz USB Wi-Fi dongle at the focus of a dish or corner
reflector. The USB dongle is almost an isotropic radiator, which
spews RF in all directions. If you transmit from the USB dongle, most
of the RF will never hit the dish antenna and wander off to parts
unknown. Only the part that hits the dish eventually ends up going
towards the other end of the wireless link. However, in receive,
almost all of the signal that hits the dish, gets reflected to the USB
dongle. Therefore the gain is higher in receive, than in transmit.


A common misconception. The radiation pattern is the same for both
transmit and receive.

True that most of the received signal is reflected back to the antenna.
But the antenna still receives in an almost isotropic pattern, also.
It has the same amount of gain in the direction of the dish in both cases.

If the USB dongle were replaced with a proper dish feed, where the
bulk of the transmit RF hits the dish, the dish becomes more
"efficient". About 50% to 70% efficiencies are typical. However, it
is also possible to mess that up in the opposite direction. Instead
of a very non-directional feed, suppose I use as a feed, a high gain
directional antenna with a very narrow beamwidth. Instead of spraying
RF outside of the dish edge (over-spray), It puts all of it into a
narrow diameter spot somewhere on the dish surface. This time, the
symmetry is in the opposite direction. Transmit is fine, because all
of the power produced by the feed hits the spot and is radiated in the
direction of the other end of the link. However, receive is now a
problem because none of the RF seen by the dish OUTSIDE the area of
the spot is "seen" by the spot. Therefore, the gain is higher in
transmit, than in receive.

Gone to move some firewood...


The same is true on receive. The dish feed also has gain, and more of
the signal will be received by a proper dish feed than by an isotropic
antenna.

Look at it this way. The antenna is a strictly passive component. It
doesn't know or care whether it is transmitting or receiving. And it
doesn't care.

--
==================
Remove the "x" from my email address
Jerry, AI0K

==================

OK, let's discuss dipoles vs length
 

Jeff Liebermann wrote in
:

Yes. For purposes of calculations and under most conditions, the
pattern is the same for transmit and receive for most antennas.



Works for me. :) Thanks. Point taken about the other examples though, your
descriptions remind me of problems with badly mismatched laser optics. Also,
though I'm not sure how close this metaphor is regarding coupling
efficiencies, a loudspeaker and microphone have reciprocality, as John S
names it, but they have a hard time doing each other's job. (Though as a kid
I preferred two small speakers and a long mains flex cable to the tin cans
and string I'd read of in some book).

OK, let's discuss dipoles vs length
 

Jerry Stuckle wrote in news:m1hemc$34d$2@dont-
email.me:

On 10/13/2014 4:02 PM, wrote:
Jerry Stuckle wrote:

snip

You didn't say "optimum". You said it was "crap". What part of "crap"
don't you understand?

I will not engage in a ****ing contest with you.


You're the one who said it, not me.

You think an NEC analysis is the slickest thing since snot on a
doorknob. But what about HAAT or ground conductivity, for instance?

What about it?


Both have effects on the radiation pattern of an antenna.

Feel free to include all the above in your analysis.

You have considered neither when telling me my antenna was "crap" -
which it provably was not.

Where is the data that proves that?



Easy. The QSL card from Alaska and Hawaii on 75 meters.


I'm out of my depth and maybe shouldn't be posting this one, but there is a
way that 'optimal' can be different in some system given a tiny modification,
by example some loudspeaker tuned so it rolls off at somewhere around 80 Hz
for efficiency aboive that point, then someone decides they can block the
port, reduce the total drive, and lose power but gain a low of 40Hz, enough
for a flat response for every string on a bass guitar. They're not the same
'optimal', but it can depend what you're after. The way I understand it, the
word 'optimal' usually involves some technical tradeoff, somewhere, and
there may be multiple cases that all make respectable use of calculated
values..

OK, let's discuss dipoles vs length
 

Jerry Stuckle wrote:
On 10/13/2014 4:02 PM, wrote:
Jerry Stuckle wrote:

snip

You didn't say "optimum". You said it was "crap". What part of "crap"
don't you understand?

I will not engage in a ****ing contest with you.


You're the one who said it, not me.

I will not engage in a ****ing contest with you.

You think an NEC analysis is the slickest thing since snot on a
doorknob. But what about HAAT or ground conductivity, for instance?

What about it?


Both have effects on the radiation pattern of an antenna.

Yes, they do, so feel free to include all the above in your analysis.

Feel free to include all the above in your analysis.

You have considered neither when telling me my antenna was "crap" -
which it provably was not.

Where is the data that proves that?



Easy. The QSL card from Alaska and Hawaii on 75 meters.

ROFL.


--
Jim Pennino

OK, let's discuss dipoles vs length
 

On Mon, 13 Oct 2014 17:01:10 -0400, Jerry Stuckle wrote:


I don't know where it is, either - I never saved it. But AFAIK, OSHA
won't take action based on a youtube video - they want to see it
occurring.

I could be wrong, though. However, since I don't know what the company
was, there is no reasonable way to check the OSHA records (they are
public).

Was it this one?

http://www.youtube.com/watch?v=jbEqnLjHyf8

OK, let's discuss dipoles vs length
 

Lostgallifreyan wrote:
Jerry Stuckle wrote in news:m1hemc$34d$2@dont-
email.me:

On 10/13/2014 4:02 PM, wrote:
Jerry Stuckle wrote:

snip

You didn't say "optimum". You said it was "crap". What part of "crap"
don't you understand?

I will not engage in a ****ing contest with you.


You're the one who said it, not me.

You think an NEC analysis is the slickest thing since snot on a
doorknob. But what about HAAT or ground conductivity, for instance?

What about it?


Both have effects on the radiation pattern of an antenna.

Feel free to include all the above in your analysis.

You have considered neither when telling me my antenna was "crap" -
which it provably was not.

Where is the data that proves that?



Easy. The QSL card from Alaska and Hawaii on 75 meters.


I'm out of my depth and maybe shouldn't be posting this one, but there is a
way that 'optimal' can be different in some system given a tiny modification,
by example some loudspeaker tuned so it rolls off at somewhere around 80 Hz
for efficiency aboive that point, then someone decides they can block the
port, reduce the total drive, and lose power but gain a low of 40Hz, enough
for a flat response for every string on a bass guitar. They're not the same
'optimal', but it can depend what you're after. The way I understand it, the
word 'optimal' usually involves some technical tradeoff, somewhere, and
there may be multiple cases that all make respectable use of calculated
values..

When I talk about an optimum antenna, I am talking about putting the
maximum power in some desired direction, which may be omnidirectional
or may be in some particular direction.

While there are other things that can influence an antenna pattern, in
reality I can not raze the houses of all the neighbors and sow the ground
with salt, nor can I move my house to the top of the highest hill around.

The things that are in my control are the antenna design and the
height of the antenna above ground, and even that has limits.



--
Jim Pennino