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'[OT] Connecting a TV aerial'
2008\07\17@005727 by Jinx

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I need to put up another aerial. The one in these pictures

http://home.clear.net.nz/pages/joecolquitt/aerial1.jpg

http://home.clear.net.nz/pages/joecolquitt/aerial2.jpg

I brought it from a previous house, and it's been stored under this
one unused for a while. I've forgotten how it was connected. Can't
see anywhere obvious that the cable connected to before

The elements marked with a red circle are insulated from the central
beam. Opposite elements of that group are connected by the criss-
crossing strips. All other elements are screwed to the centre beam

Do I assume correctly that co-ax shield would go to one criss-cross
and signal to the other ? Or shield to centre beam and signal to one
criss-cross ?

Looked around the web but wiring is all about the TV end

TIA

2008\07\17@022828 by W. Jacobs

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The antenna is designed to be fed with 300 ohm twin lead to the cris
cross, not coax.  You should put one of the 300 ohm to 75 ohm
transformers to the cris cross and then use co-ax.  I would assume that
there were 2 wing nuts somewhere that would make connections easy.
bill


Jinx wrote:
> Do I assume correctly that co-ax shield would go to one criss-cross
> and signal to the other ? Or shield to centre beam and signal to one
> criss-cross ?
>
>  

2008\07\17@030050 by Jinx

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Bill,

> The antenna is designed to be fed with 300 ohm twin lead to the cris
> cross, not coax

300 ohm ? Oh. Didn't expect that

> You should put one of the 300 ohm to 75 ohm transformers to the
> criss-cross and then use co-ax

Okey-doke. Now, could I take a 300-75 balun that you'd find on
rabbit ears and turn it around ?

eg http://www.dse.co.nz  L4456 (indoor type, socket + spades)

or http://www.dse.co.nz   L4465

"TV Balun Indoor/Outdoor- For matching 75 Ohm coaxial cable to
300 ohm ribbon terminals on your TV tuner or antenna. It's weather-
resistant so can be used indoors or out"

I have an exterior VHF/UHF mixer too. Would that help ?

> I would assume that there were 2 wing nuts somewhere that would
> make connections easy

Wing nuts all over the place

2008\07\17@034939 by Richard Prosser

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2008/7/17 Jinx <spam_OUTjoecolquittTakeThisOuTspamclear.net.nz>:
> Bill,
>
>> The antenna is designed to be fed with 300 ohm twin lead to the cris
>> cross, not coax
>
> 300 ohm ? Oh. Didn't expect that
>
>> You should put one of the 300 ohm to 75 ohm transformers to the
>> criss-cross and then use co-ax
>
> Okey-doke. Now, could I take a 300-75 balun that you'd find on
> rabbit ears and turn it around ?


Should be OK until the water gets in. If it's weather resistant or
properly sealed, it should be electrically OK.

Depending on what sort of signal strength you get or need you'd
probably get away with connecting a coax directly to the  aerial as -
is. It will be a bit more susceptable to interference however.

RP


{Quote hidden}

> -

2008\07\17@064612 by Jinx

face picon face
> 300-75 balun that you'd find on rabbit ears and turn it around ?
>
> Should be OK until the water gets in. If it's weather resistant or
> properly sealed, it should be electrically OK.

So would a short length of 300 ohm ribbon be OK ? Say 2m from
the aerial to under the eave, then a transformer and then the co-ax
run to inside the house

2008\07\17@065725 by Lee Jones

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> home.clear.net.nz/pages/joecolquitt/aerial1.jpg
>
> home.clear.net.nz/pages/joecolquitt/aerial2.jpg
>
> I brought it from a previous house, and it's been stored under this
> one unused for a while. I've forgotten how it was connected. Can't
> see anywhere obvious that the cable connected to before

As previously mentioned on PIC list, 300 ohm twinlead should
go to one pair of wing nuts.  Ahhh, but which pair...  Are you
willing to try hooking the 300 ohm (either twinlead or balon) to
various wingnut pairs and see what effect it has on performance?


> The elements marked with a red circle are insulated from the central
> beam. Opposite elements of that group are connected by the criss-
> crossing strips. All other elements are screwed to the centre beam

Insulated are the driven elements; non-insulated are directors.

Wow, I've never seen an antenna with this many criss-cross pairs
and this many attachment points (i.e. wingnuts).  Higher resolution
photo would be really nice (I'd like to inspect center section in
more detail).

It almost appears that you can use the wingnuts to remove some of
the criss-cross pairs and thus adjust the antenna.

Is it possible that the antenna has a manufacturer & model number
on it?  That might allow a datasheet to be found.

How interesting.
                                               Lee Jones

2008\07\17@071505 by Richard Prosser

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2008/7/17 Jinx <.....joecolquittKILLspamspam@spam@clear.net.nz>:
>> 300-75 balun that you'd find on rabbit ears and turn it around ?
>>
>> Should be OK until the water gets in. If it's weather resistant or
>> properly sealed, it should be electrically OK.
>
> So would a short length of 300 ohm ribbon be OK ? Say 2m from
> the aerial to under the eave, then a transformer and then the co-ax
> run to inside the house
>
> --

That would work fine. You could run the 300ohm ribbon right to the TV
if required.

>From memory, the balun is connected to the second longest pair of
insulated dipoles in the array. But I may be wrong. If you get stuck,
let me know & I'll climb into my roofspace & photgraph my antennae
which is similar. The problem I have is that the signal strength is
too much & overloads the sky decoder vhf/uhf input so I have had to
add an attenuator.

RP

2008\07\17@072209 by Lee Jones

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>>> 300-75 balun that you'd find on rabbit ears and turn it around ?

Yes.  If rated for outdoor use, it may last an acceptably long
period of time.  If rated for indoor use, it still may last a
longish period of time -- but less likely.

>> Should be OK until the water gets in. If it's weather resistant
>> or properly sealed, it should be electrically OK.

> So would a short length of 300 ohm ribbon be OK ? Say 2m from
> the aerial to under the eave, then a transformer and then the
> co-ax run to inside the house

I'd put the balun right up at the antenna.  Cheap twinlead does
not last well in direct sunlight; you need the better grade.
In the US, good grade outdoor twinlead is no longer common.

Also, twinlead has no shield, so signal field extends outside
the insulation (coax sheild contains signal within the cable).
If you tiewrap or electrical tape twinlead to the metal pole
which is supporting the antenna, it will effect the signal.
You need to buy standoffs that strap to the pole and hold the
twinlead ~6" (150mm) away.  Such standoffs were common -- 30+
years ago.  They're probably still available but I haven't seen
them in a long while.  Downlead is now almost always coax.

I'd either get a 300 ohm to 75 ohm balun that is weatherproof
or use an inexpensive balun plus some weatherproofing (either
designed for the purposse sealing tape _or_ judicious use of
silicone seal plus electrical tape plus tiewraps [it doesn't
have to be pretty, it just has to keep water out]).  I seal
both ends of the balun -- where the twinlead comes out and
over the entire F connector (from balun body over connector
to coax insulation).

                                               Lee Jones

2008\07\17@072907 by Jinx

face picon face
> Are you willing to try hooking the 300 ohm (either twinlead or
> balon) to various wingnut pairs and see what effect it has on
> performance ?

I guess, but I don't fancy running up and down a ladder all day
like a flipping budgie ;-)

In a pretty strong signal area so might not have too many problems

> Wow, I've never seen an antenna with this many criss-cross pairs
> and this many attachment points (i.e. wingnuts).  Higher resolution
> photo would be really nice (I'd like to inspect center section in
> more detail).

As happens on a regular basis, at this time of night, in these here
parts, it's very dark outside. I'll sort that out for you in the morning

Thanks for the insights

2008\07\17@080647 by cdb

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:: but I don't fancy running up and down a ladder all day
:: like a flipping budgie ;-)

Hmm wouldn't that be more like a Galaah or one of those windscreen
wiper destructive birds that NZ has. Perhaps you could train them to
fly the cable up to the aerial.

Colin
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Baltasar Gracian





2008\07\17@085129 by Dave Lagzdin

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Check the plastic insulators on the driven elementsThere may be some faded
marks or moulded arrows on the
correct attaching element?
D

2008\07\17@090214 by Jinx

face picon face
> :: but I don't fancy running up and down a ladder all day
> :: like a flipping budgie ;-)
>
> :: Hmm wouldn't that be more like a Galaah

A galah is a cockatoo from Australia

> :: or one of those windscreen wiper destructive birds that NZ has.
> :: Perhaps you could train them to fly the cable up to the aerial

Keas. Yes, smuggling protected birds from 1000 miles away and
training them to wire up what they don't chew to bits certainly sounds
like a quicker way to do it ;-)

We have lorikeets around here but I haven't seen one yet with a
toolbelt on. But maybe I just don't look hard enough

2008\07\17@092559 by Jinx

face picon face
> Check the plastic insulators on the driven elements. There may be
> some faded marks or moulded arrows on the correct attaching element?

Good idea

2008\07\17@093035 by cdb

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:: A galah is a cockatoo from Australia

Indeed, along with Lorikeets, Rosellas and Kookaburras they annoy me
with their shreaking in my trees and perching on my washing line. Now
where is my slingshot?

As for Keas, couldn't you pop down to that nice Swedish furniture
store and pick them up there?

Alternatively, why not just wire it up and bung it on top of a hedge
or car, see if it works and then bung it up on the roof?

Colin

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2008\07\17@095427 by Jinx

face picon face
> As for Keas, couldn't you pop down to that nice Swedish furniture
> store and pick them up there?

Or get an Apple brand one. An iKea

> Alternatively, why not just wire it up and bung it on top of a hedge
> or car, see if it works and then bung it up on the roof ?

Yeah, probably do something like that first instead of messing about
on high



2008\07\17@113214 by Michael Rigby-Jones

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> -----Original Message-----
> From: EraseMEpiclist-bouncesspam_OUTspamTakeThisOuTmit.edu [piclist-bouncesspamspam_OUTmit.edu] On
Behalf
{Quote hidden}

Is it not also an Oz insult?

Mike

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2008\07\17@120758 by Alan B. Pearce

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>> A galah is a cockatoo from Australia
>
>Is it not also an Oz insult?

Sort of an insult implying one is acting silly or stupid.

Also used a little bit in NZ as it has filtered across the Tasman through TV
programs and physical visitation ...

2008\07\17@171415 by W. Jacobs

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face
Jinx
The balum for outdoor use would be the one to use.  Connect it to the
cris-cross wires somewhere near the mast just so it is easy to fasten
the wire so it will not flop around in the wind.
I do not think the mixer will do a lot of good.  (personal opinion)
The antenna should be good to about 100 -125 miles
bill


Jinx wrote:
{Quote hidden}

2008\07\17@173813 by Jinx

face picon face
> The balum for outdoor use would be the one to use
>
> bill

Cheers

And of course, in accordance with Sod's Law, it's raining ;-)

2008\07\17@174454 by PAUL James

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Bill,

Trivial correction here.  The correct term is "BALUN" not "BALUM"  It is
a contraction for the
words "BALanced-UNbalanced.  It transforms a transmission line from (or
to) one of where one terminal
Is referenced to ground or unbalanced like Coax) to (or from) one where
the terminals are symetrical
and not referenced to ground or balanced like twin lead .  

Just an FYI.  


       
Regards,

       
Jim

{Original Message removed}

2008\07\17@190253 by cdb

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I have just looked up my copy of 'secrets of RF design' by Joseph J
Carr, on page 274, he has a Balun made from shorted co-ax cable, so if
you've some co-ax lying around assuming a 4:1 impedance transfer the
length of the U shaped co-ax is  Length = 492 x V / F where,

L is in feet
V velocity factor of the co-ax cable
F the frequency

It then goes on for umpteen pages on transmission line matching
tangents and such like.

Colin
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2008\07\18@040313 by Alan B. Pearce

face picon face
>I have just looked up my copy of 'secrets of RF design' by Joseph J
>Carr, on page 274, he has a Balun made from shorted co-ax cable,

However while these are fine for narrow band use, like a Ham band, they are
next to useless for a wideband TV aerial, unless receiving only one channel.
Even then there may be problems like smearing or loss of colour due to the
narrow band nature of a coax balun.

I would expect a balun out of a rabbits ear aerial to be suitable, after
all, before the days of coax connectors on the back of the TV set, such
aerials were always connected with 300 ohm ribbon. Many still use ribbon (I
believe it is cheaper than coax) down to the plug, which has the balun in it
to convert to the unbalanced connector. Just a case of encapsulating the
balun in some waterproof coating at the top of the aerial, I would be
tempted to use a great glop of contact cement or something similar. Should
last a winter at least.

2008\07\18@055535 by Jinx

face picon face
> I would expect a balun out of a rabbits ear aerial to be suitable

I picked up an external 300-75 balun and will try it out tomorrow.
Pretty much same price as an internal. Difference not worth getting
messed up with silicone for

Dennis Crawley sent me this picture

http://home.clear.net.nz/pages/joecolquitt/pict0777.gif

Thanks again Dennis

Lee, couldn't really get a better picture of the criss-crosses. The
aerial is made by The Multichannel Antenna Co Ltd. I remember
asking for a good aerial when it was installed, as the house was
in a valley and reception of most channels was very poor. Even
with that aerial only one channel was really any good. TV2. And
I don't watch TV2. The suburb, Remuera, where all the hoity-
toities live (lived) now has much better reception via a repeater

In the summertime of the mid-80s it was not unusual to pick up
Australian channels as ghosts


2008\07\18@064613 by Lee Jones

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face
> I picked up an external 300-75 balun and will try it out tomorrow.
> Pretty much same price as an internal. Difference not worth getting
> messed up with silicone for

Still watch for possible water intrusion where the F connector
screws onto the end of balun.  You want to seal it so water is
kept out of the balun and the coax cable.  Receiving isn't a
big deal; low power levels, so nothing gets hurt (except picture
quality) if connection corrodes.  It's another story if you were
using it with a transmitter.

> Dennis Crawley sent me this picture
>
> http://home.clear.net.nz/pages/joecolquitt/pict0777.gif

That figure looks like the picture you posted, so hooking the
balun up as shown seems quite reasonable ... and "feels" right. :-)

> Lee, couldn't really get a better picture of the criss-crosses.

Thanks.  Just curious why they used all the wingnuts.  Normally,
I have only seen 1 pair of wingnuts -- point where the twinlead is
expected to be connected.  If the mechanical construction demands
it, there are usually regular hex nuts at other points.  But the
vast majority of attachments seem to be made with rivits (cheaper
to produce).

                                               Lee

2008\07\18@161422 by Robert Rolf

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Lee Jones wrote:
> Thanks.  Just curious why they used all the wingnuts.  Normally,
> I have only seen 1 pair of wingnuts -- point where the twinlead is
> expected to be connected.  If the mechanical construction demands
> it, there are usually regular hex nuts at other points.  But the
> vast majority of attachments seem to be made with rivits (cheaper
> to produce).

Perhaps so it can be readily folded up for shipping?
R

2008\07\18@195456 by Jinx

face picon face
> > Thanks.  Just curious why they used all the wingnuts

> Perhaps so it can be readily folded up for shipping?

It does collapse quite easily and has been stored in a tube. Rivets
would not have been a good choice for this design because the
cross members have plates with slight indentations that align them
to the square-profile centre beam. From memory this particular
one was at the upper end of the price range (because of reception
difficulties) and therefore I probably paid for the convenience of
wing nuts rather than hex nuts

2008\07\19@235728 by cdb

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:: In the summertime of the mid-80s it was not unusual to pick up
:: Australian channels as ghosts

Thats just plain spooky.

When I lived in Ipswich (Queensland) during winter, the commercial
stations could be picked up from Victoria (3 hours flight away) - not
well, but it was annoying looking at two stations showing two
different programs superimposed upon each other.

Colin
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2008\07\20@094402 by Dennis Crawley

picon face

I'd like to see a photograph from the side.
There is a model of logaritmic antenna which can be "feeded" by 50-75Ohm
coax line directly.

Regards,
Dennis.


2008\07\20@185236 by Jinx

face picon face
> I'd like to see a photograph from the side.
> There is a model of logaritmic antenna which can be "feeded" by
> 50-75Ohm coax line directly

With connection points so far apart (100mm), and the exterior balun
having 300 ohm spades that can be spread to a Y to get to those points,
would you not expect this aerial to be 300 ohms ?

Anyway, it is working well with a balun

2008\07\21@124650 by Martin

face
flavicon
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Jinx wrote:

>
> Wing nuts all over the place
>

This IS the piclist, after all.

-
Martin

2008\07\21@155351 by Carl Denk

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Yea, but how many have  a pilot's license?  :)

Martin wrote:
> Jinx wrote:
>
>  
>> Wing nuts all over the place
>>
>>    
>
> This IS the piclist, after all.
>
> -
> Martin
>  

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