Here is the 'T" antenna I referred to. It is totally plastic.

http://www.happywanderer.net.au/page...9&parent2id=24

If link doesnt work the website is www.happywanderer.net.au and the image
is on first screen. The totally plastic covered yagi I saw was somewhere in
ebay. I,ll see if I can find it again.
Regards
John



"John" wrote in message
. au...
Whilst trying to source a "digital" TV antenna I came across some with all
external surfaces plastic. One was a small yagi with all external surfaces
plastic, hopefully with metal elements embedded. Another a "T" shape made
out of plastic conduit with elements inside conduit.
My question is how do they work?. If they are detecting electrical fields
how does increasing source impedance by 100,s of megohms improve things?.
Capacitive coupling, I suppose at the frequencies involved there would be
some.
If it works as well as all metal why doesn,t every one use it and stop
corrosion?
Hope this is not too off topic.
Many thanks
John

And the yagi,

http://www.ebay.com.au/itm/Caravan-R...e m2ebd055150

The argument I seemed to have inadvertently triggered reminds me of
disgreement
I had about 40 years ago describing Op Amp inputs as virtual earths.
Odd how equally intelligent and educated people can look at things
differently.
Cheeers
John

"John" wrote in message
news
Here is the 'T" antenna I referred to. It is totally plastic.

http://www.happywanderer.net.au/page...9&parent2id=24

If link doesnt work the website is www.happywanderer.net.au and the image
is on first screen. The totally plastic covered yagi I saw was somewhere
in ebay. I,ll see if I can find it again.
Regards
John



"John" wrote in message
. au...
Whilst trying to source a "digital" TV antenna I came across some with
all external surfaces plastic. One was a small yagi with all external
surfaces plastic, hopefully with metal elements embedded. Another a "T"
shape made out of plastic conduit with elements inside conduit.
My question is how do they work?. If they are detecting electrical fields
how does increasing source impedance by 100,s of megohms improve things?.
Capacitive coupling, I suppose at the frequencies involved there would be
some.
If it works as well as all metal why doesn,t every one use it and stop
corrosion?
Hope this is not too off topic.
Many thanks
John

On 5/30/2012 10:21 PM, John wrote:
Here is the 'T" antenna I referred to. It is totally plastic.

http://www.happywanderer.net.au/page...9&parent2id=24

If link doesnt work the website is www.happywanderer.net.au and the image
is on first screen. The totally plastic covered yagi I saw was somewhere in
ebay. I,ll see if I can find it again.
Regards
John

I liked the reflector screen on the HW-DT8. It's appears just a bit
sparse for the frequencies it's supposed to cover.

Other than that the driven part is kind of interesting. If it's
reasonably priced enough and shipping isn't out of line I may order one
just to see what mischief they are up to.

tom
K0TAR

Link to the antenna I referenced.

http://www.happywanderer.net.au/page...9&parent2id=71

And of course it will give me a nice new antenna to perform weight and
charge measurements on.

Can't use an old one. See, when the antenna gets used more and more it
gets tired because of electron loss. You have to watch your transmit
and receive balance. If you don't you will end up with too few
electrons around, which makes for an increase in transmit resistance.
Some people think it's impedance, but they don't know it's just because
you haven't got the right length coax.

And the other way around, if you receive all the time you eventually
fill the electron sump, and the antenna must be discarded unless you can
get a good electron sump pump for cheap. Funny thing, that's why the
old AM and FM radios wore out - they were full.

Its why you should never leave a powerpoint switched on. You end up with a
heap of electrons on the floor.
And a hole under the neutral hole.


"tom" wrote in message
. net...
On 5/30/2012 10:21 PM, John wrote:
Here is the 'T" antenna I referred to. It is totally plastic.

http://www.happywanderer.net.au/page...9&parent2id=24

If link doesnt work the website is www.happywanderer.net.au and the
image
is on first screen. The totally plastic covered yagi I saw was somewhere
in
ebay. I,ll see if I can find it again.
Regards
John

I liked the reflector screen on the HW-DT8. It's appears just a bit
sparse for the frequencies it's supposed to cover.

Other than that the driven part is kind of interesting. If it's
reasonably priced enough and shipping isn't out of line I may order one
just to see what mischief they are up to.

tom
K0TAR

Link to the antenna I referenced.

http://www.happywanderer.net.au/page...9&parent2id=71

And of course it will give me a nice new antenna to perform weight and
charge measurements on.

Can't use an old one. See, when the antenna gets used more and more it
gets tired because of electron loss. You have to watch your transmit and
receive balance. If you don't you will end up with too few electrons
around, which makes for an increase in transmit resistance. Some people
think it's impedance, but they don't know it's just because you haven't
got the right length coax.

And the other way around, if you receive all the time you eventually fill
the electron sump, and the antenna must be discarded unless you can get a
good electron sump pump for cheap. Funny thing, that's why the old AM and
FM radios wore out - they were full.

"John" wrote in message
. au...
Its why you should never leave a powerpoint switched on. You end up with a
heap of electrons on the floor.
And a hole under the neutral hole.

Not if you leave a plug in the socket. That'll stop the electrons.
What about the neutrons, protons and croutons?

Regards, Ian.

Ian wrote:
"John" wrote in message
. au...
Its why you should never leave a powerpoint switched on. You end up with a
heap of electrons on the floor.
And a hole under the neutral hole.

Not if you leave a plug in the socket. That'll stop the electrons.
What about the neutrons, protons and croutons?

Croutons are especially nasty when they end up on the floor...

"Rob" wrote in message
...
Ian wrote:
"John" wrote in message
. au...
Its why you should never leave a powerpoint switched on. You end up with
a
heap of electrons on the floor.
And a hole under the neutral hole.

Not if you leave a plug in the socket. That'll stop the electrons.
What about the neutrons, protons and croutons?

Croutons are especially nasty when they end up on the floor...

But you can weight them and they are easy to detect :-)

"Rob" wrote in message
...
Ian wrote:
"John" wrote in message
. au...
Its why you should never leave a powerpoint switched on. You end up with
a
heap of electrons on the floor.
And a hole under the neutral hole.

Not if you leave a plug in the socket. That'll stop the electrons.
What about the neutrons, protons and croutons?

Croutons are especially nasty when they end up on the floor...

The commercial power in my neighborhood has an asymmetric waveform. Some of
us have been saving the extra electrons on one-half-cycle. We had a power
outage in October of last year and what we're saving now will be used if we
ever suffer another outage.

"Sal M. O'Nella" napisa³ w wiadomo¶ci
...

"Rob" wrote in message
...
Ian wrote:
"John" wrote in message
. au...
Its why you should never leave a powerpoint switched on. You end up
with a
heap of electrons on the floor.
And a hole under the neutral hole.

Not if you leave a plug in the socket. That'll stop the electrons.
What about the neutrons, protons and croutons?

Croutons are especially nasty when they end up on the floor...

The commercial power in my neighborhood has an asymmetric waveform. Some
of us have been saving the extra electrons on one-half-cycle.

The extra electrons flow into the ground. Like in your radios.
S*

"John" wrote in message
news
Here is the 'T" antenna I referred to. It is totally plastic.

http://www.happywanderer.net.au/page...9&parent2id=24

If link doesnt work the website is www.happywanderer.net.au and the image
is on first screen. The totally plastic covered yagi I saw was somewhere
in ebay. I,ll see if I can find it again.
Regards
John



"John" wrote in message
. au...
Whilst trying to source a "digital" TV antenna I came across some with
all external surfaces plastic. One was a small yagi with all external
surfaces plastic, hopefully with metal elements embedded. Another a "T"
shape made out of plastic conduit with elements inside conduit.
My question is how do they work?. If they are detecting electrical fields
how does increasing source impedance by 100,s of megohms improve things?.
Capacitive coupling, I suppose at the frequencies involved there would be
some.
If it works as well as all metal why doesn,t every one use it and stop
corrosion?
Hope this is not too off topic.
Many thanks
John

It is probably what is called a "folded dipole."

We used to make them out of common TV twinlead. They have a characterisstic
impedance around 300 ohms, same as the twinlead, so the black block at the
hub is likely to be a 300-75-ohm balun (trannsformer) to match the coaxial
cable lead-in.

You determine the frequency of interest and cut it to size, accordingly.
They're not too great for wide-band coverage, but you might get lucky. (The
wide-band issue is why big, expensive antennas always have elements of many
different sizes. "One Size Fits All" definitely does NOT apply to antennas.

"Sal"