OK, let's discuss dipoles vs length
 

"Ralph Mowery" wrote in
:

The type of wire does not
matter, just the weight and how much tension you can put on it before it
breaks.

Well, the type of material kind of defines that. :) But I take your point.
Thanks for the extra detail.

OK, let's discuss dipoles vs length
 

Ian Jackson wrote:
In message ,
writes




60 feet is good for 30M, marginal for 40M, and crap for 80M and below
for a dipole.

It is also too high for 15M and up.

For best results, a diple should be at .5 labda.

Then again, a marginal 40M dipole is better than no antenna at all.

Regardless of the theory, in real life (with real-life ground
conductivity/reflectivity, and the prevalence of nearby clutter and
obstruction), I can't help feeling in my water that 'higher generally
works better'!!

Depends on what you mean by "higher".

As you start getting higher than 1/2 lambda, that one big lobe starts
becoming a lot of smaller lobes pointing into the sky.

Even the free demo version of EZNEC can show this.


--
Jim Pennino

OK, let's discuss dipoles vs length
 

On 10/13/2014 11:21 AM, Jeff Liebermann wrote:
On Mon, 13 Oct 2014 03:48:29 -0500, Lostgallifreyan
wrote:

when I see a Smith chart or other diagram indicating relative
signal transmission strength at some distance and direction,

A Smith Chart is a transmission line matching tool and has nothing to
do with distance, range, direction, and strength of an RF signal.
Reading between the lines, you might be referring to an antenna
pattern polar graph, which sorta looks like a Smith Chart while one is
under the influence of controlled substances.

does this follow
the rule of many 'simple' transducers, in that the same chart exactly models
the sensitivity of the same antenna for reception?

Antennas do not have a sensitivity spec. That's in the receiver. All
antennas do is direct the RF in some particular direction, sometimes
concentrating it, which is called gain. Antennas do not produce,
amplify, or "strengthen" RF. The only re-direct it.

I think you might need some help in basic RF buzzwords. It's helpful
when we're both using the same terms to discuss the same phenomenon.
Google finds several RF glossary lists online. Start with "A" and
work your way to "Z" trying to absorb and understand as many buzzwords
as possible. I do that when I initially approach a new technology and
recently had to do it for optical terminology, of which I know little.
If successful, we might then be able to decode what you're asking.
http://micro.apitech.com/glossary.aspx
http://e-meca.com/tech_papers/glossary.php
http://www.amphenolconnex.com/support/glossary

I'm hoping it does,
otherwise life might get complicated. :)

Hope is a poor substitute for understanding.
Hit the books and enlightenment will hopefully follow.


Jeff, maybe he is kind of asking about reciprocity in his own way?

OK, let's discuss dipoles vs length
 

Jerry Stuckle wrote:
On 10/12/2014 4:29 PM, wrote:
Ralph Mowery wrote:

"Ian Jackson" wrote in message
...
In message ,
writes
Like I said, there is no difference in free space between a V and an
inverted V.

There are slight differences when close to ground.

Assuming it's a halfwave dipole, I would have thought it was better to
concentrate on getting the centre (where the current is) as high as
possible, rather than the ends. [Obviously this depends on whether you
have a suitable sky-hook available for and at the centre.] However, I
believe that there is at least one commercial loaded dipole (essentially
for portable use, I think) that has a short mast, and the ends of the V
are up in the air.



In free space I would not think there would be much of any differance.

Near the ground where most of us are is what we have to live with. In my
back yard I have enough room to string wire dipoles for 80 meters and
shorter. I don't have a way to support the antennas in the middle. I can
go up about 60 feet or so at the ends.

60 feet is good for 30M, marginal for 40M, and crap for 80M and below
for a dipole.


I'll argue with that. I got WAS on 75 meters with an inverted vee with
an apex of 50'. I was in Iowa at the time - but had a pretty good
signal across the continental U.S. late at night.

There are many things to consider, and blanket statements like yours are
pretty much worth what people pay for them.

The only "blanket statements" in there is that 1/2 lambda is the OPTIMUM
height for an antenna. Above and below that height a good deal of the
patten goes to warming clouds.

Note the word "optimum"; that means that antennas at other heights do work,
just not as well as they could.

--
Jim Pennino

OK, let's discuss dipoles vs length
 

Jerry Stuckle wrote in news:m1gumv$73s$1@dont-
email.me:

I enjoyed the work - you can't imagine the view from 1800' up a TV
tower. But I'm glad I'm not doing it any more.


I doubt I could cope with that much risk of vertigo (occasionally I sufer the
real, medical thing, just waking up in the morning, but it's still rare enouh
that I prefer not to know more about why). I did see a video once though, I
saved it somewhere. Extremely interesting, as well as having a chance to see
so much of the climb in detail. I suspect you or someone here might even know
who made it.

OK, let's discuss dipoles vs length
 

Jerry Stuckle wrote in news:m1gvg0$9v8$1@dont-
email.me:

One side note. Copper clad anything is not certified for any ethernet
cables. Even though ethernet runs at very high frequencies, only solid
or stranded copper is acceptable.


Telewest, who became Blueyonder, then after merging with ATL got bought by
Vitgin Media here in Britain, used copper clad steel cores. I don't know
enough to comment on their reasons, but it's definitely true, I just waved a
magnet at a few cables of theirs to prove it. My guess is that because the
lines were ostensibly for cable TV, they just coerced them into internet
wiring later. ADSL on the phone lines later beat them for speed, presumably
because the phones were using solid copper, but I'm not sure they used in the
external cables because I can't reach one right now.

OK, let's discuss dipoles vs length
 

Jeff Liebermann wrote in
:

you might be referring to an antenna
pattern polar graph

That's the one. :) I'm too new to them to name them right, is all.

OK, let's discuss dipoles vs length
 

Jeff Liebermann wrote in
:

Antennas do not produce,
amplify, or "strengthen" RF. The only re-direct it.


Point taken, and I agree because they're passive constructions in metal. Even
before reading more, I'll have one quick retry..

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?

OK, let's discuss dipoles vs length
 

In message ,
Lostgallifreyan writes
Jerry Stuckle wrote in news:m1gvg0$9v8$1@dont-
email.me:

One side note. Copper clad anything is not certified for any ethernet
cables. Even though ethernet runs at very high frequencies, only solid
or stranded copper is acceptable.


Telewest, who became Blueyonder, then after merging with ATL got bought by
Vitgin Media here in Britain, used copper clad steel cores. I don't know
enough to comment on their reasons, but it's definitely true, I just waved a
magnet at a few cables of theirs to prove it. My guess is that because the
lines were ostensibly for cable TV, they just coerced them into internet
wiring later. ADSL on the phone lines later beat them for speed, presumably
because the phones were using solid copper, but I'm not sure they used in the
external cables because I can't reach one right now.

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.

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.
*Above 40MHz, the attenuation might become somewhat lower than you would
expect from extrapolating loss figures obtained below 40MHz. While I
have to say that I've never noticed this with RG6, this may be because
I've never looked for it. In any case, it often has been in the
guardband where the crossover between the cable TV forward and reverse
RF paths occur.
--
Ian

OK, let's discuss dipoles vs length
 

On 10/13/2014 1:06 PM, Lostgallifreyan wrote:
Jerry Stuckle wrote in news:m1gumv$73s$1@dont-
email.me:

I enjoyed the work - you can't imagine the view from 1800' up a TV
tower. But I'm glad I'm not doing it any more.


I doubt I could cope with that much risk of vertigo (occasionally I sufer the
real, medical thing, just waking up in the morning, but it's still rare enouh
that I prefer not to know more about why). I did see a video once though, I
saved it somewhere. Extremely interesting, as well as having a chance to see
so much of the climb in detail. I suspect you or someone here might even know
who made it.


It was not I, and almost assuredly no on I know. The ones I knew back
then got out of the business - one way or the other.

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.

--
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Jerry, AI0K

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