Re: Coax vs flat twin?
- From: RickH <passport@xxxxxxxxxxxxxxxxxxxxx>
- Date: Thu, 16 Aug 2007 08:17:42 -0700
On Aug 16, 9:11 am, "PVR" <peterv666@.adelphia.com> wrote:
Many thanks for your very informative answer. My focus is on FM radio
reception from local stations. We live in a condo (stand alone residence)
which is supplied with cable TV/telephone/Internet, etc.
My reason for running the exterior cable under the vinyl siding is that,
being a condo, there shall be no change to the external appearance of the
unit. As a result standoffs are not an option. I am hoping that the space
beneath the vinyl siding will remain dry so perhaps the flat feeder may not
be unacceptably lossy. I think I shall try the twin feeder before buying
coax.
One thing that surprises me is that I have heard or read several times that
flat feeder is OK where the signal is below 30 MHz. Also I have been advised
that flat feeder is OK to use for FM radio reception. Now, as I recall, FM
broadcasts, are between 88 and 108 MHz. I guess I am confused.
Peter.
"mm" <NOPSAMmm2...@xxxxxxxxxxx> wrote in message
news:2555c3p7c20prjsaocnru4ae45cfrhid92@xxxxxxxxxx
On Tue, 14 Aug 2007 07:08:22 -0700, RickH
<passp...@xxxxxxxxxxxxxxxxxxxxx> wrote:
On Aug 14, 7:19 am, "PVR" <peterv666@.adelphia.com> wrote:
I want to run about 50ft of antenna feeder cable for FM radio. The
feeder
cable will be attached to an exterior wall beneath vinyl siding.
Which cable should I use, coax or flat twin feeder?
Just so I start off annoying, flat lead is not cable. I guess because
it is not round, but I don't thin I was alive when these things were
named.
I suspect the answer is
coax but I would like to use flat wire because I have 50ft of that. Also
flat feeder would be easier to hide inside the house.
You can use flat wire, but like cable, it has to match the imepedance
of what it is connected to. at each end. Your tv and your antenna may
have two screws the right distance apart for flat wire**, they may
have a coaxial connector, and they may have both. Whether you use
cable or flat line, if the connector on the tv or antenna doesn't
match physcially, you have to use an "impedance matching transformer".
You see one kind of these all the time, with a female cable connection
at one end of usually white cylinder about 2 inches long, with a
shortpiece of flat lead coming out the other end, with some metal
forks on the end for mounting under the screws.
The inverse is available too, but less common, with a male cable
connection, a cylinder with the transformer inside, and two screws to
attach the flat lead too. This kind is less commmon because all new
tvs for the last 20 years or more have cable connections on them, and
probably all new antennas.
If you have one kind of connector at the tv, or splitter, or vcr, or
dvr, and the other kind at the antenna, that tends to give you the
easy ability to use either flat lead or cable, but you should know
that there is a small amount of signal loss whenever a impedance
matching transformer is used, so using one at both ends, when you
could use a different "wire" and use none at either end, seems like a
mistake.
Although another factor would be where you live. If you're close to
the antennas you want to receive from, your signal strength might be
so high that losses don't matter. In my case, I want Baltimore
stations, but I also want DC stations. DC is 40 miles away and some
antennas might be farther than that. But to add another factor, I had
to buy an amplified antenna (or one could buy a signal amplifier
designed for antenna signals) because some of the DC stations were so
weak I wouldn't be able to get them at all otherwise.
When I lived right in Brooklyn, all the NYC stations were strong, and
Connecticut and Philadelphia stations there was no chance of getting
or I just didn't want them.
BTW, if you use flat lead, you have to twist it a little, so that it
rotates on its axis a half turn every two feet or so (I forget if
there is a distance suggested). If you;re a neat freak like I can be,
and run the wire so it has no twists, you'll end up picking up static
from nearby cars, lawnmowers, transmitters if any, lightning, and all
kinds of sources of electronic radiation. By twisting the wire,
whatever is picked up at one section of wire is counteracted and
neutralized by the opposite signal induced in the part of the wire
that is flipped.
You also have to use stand-offs to keep the wire away from your house.
You can find "antenna stand-offs" for "flat lead" (probably called
flat lead or flatlead, on Google, to see what I mean. I don't know
the details about this, but I'm pretty sure if there is rain sticking
between the wire and the house, you'll have plenty of signal loss.
Probalby other reasons too.
Looking back at your original plan: I don't know if one can be
succssful putting it *beneath* vinyl siding. Never heard of that and
never heard the question asked. Ask on sci.electronics.repair . Make
your question simple and don't be too distracted by answers you can't
understand. I don't understand a lot of their answers either, but you
can either reread what they say until you do, or wait until someone
replies in English, or ask again.
They make special tubes for putting flat-lead through a wall, but I
don't know if they are needed or not. They have an insulating support
at each end and are empty in the middle. I guess this is all about
avoiding signal loss. Although we had an outdoor antenna with flat
lead when I was little. My father had enough money and would have
hired a pro and done things right, and I don't remember ever seeing a
tube like that. When I lived in a 6-story Brooklyn apartment, I found
a flat lead hanging down from a roof-top antenna and saw that it
wasn't being used at the other end, so I just spliced in and ran my
flatlead between the window and the sill, and everything was fine.
Like I say, the signals were strong, so any loss there was in excess
signal strength (the tv has amplifiers in it. It's only when the
signal strengh for a given station is near or below a minimum that a
little more signal loss will cause a probelm
I don't think the flat lead was twisted either, but it was only 21
feet from the antenna to my window sill. I was 40 feet up and 40 feet
back from the traffic, and maybe lightning did cause static.
That's to be expected, even if it can be avoided. :)
Another variable is that coax has more impedance (bad) per foot than
flat lead, but it is more isolated from interferance. I don't know if
that is still true if the flat lead is twisted as recommended. BTW,
the wires to burglar alarm sensors, like door and window switches,
should also be twisted. You can buy twisted pair, already twisted, and
you should use it here, because lightning will induce voltages in the
wires to the sensors and burn out your alarm control panel if the wire
isn't twisted. When twisted, each half turn neutralizes the unturned
part.
The price for ignoring the rules is varying amounts of signal loss for
each one. They all add up.
By not violating them, I get all 6 TV stations in DC, and maybe with a
2nd amplifer I could get Lancaster Pa.
You could start off by putting flat lead under the siding, and if it
isn't great, comparing it with flat lead just handging away from the
wall (don't put in standoffs unless it is better and you want it to be
permanent, and maybe only have to put in one standoff at the edge of
the roof, and one at the bottom. Or comparing with cable, which has
the center wire shielded by a saparate metal braid, and isn't fussy
where it is put.
**BTW, if you see teeth pointing down on the washers for the flatlead,
it is designed so you don't have to strip the wire, and the teeth will
cut into the insulation. However, I always imagine that the wire I
have has new super-duper insulation that the teeth can't penetrate,
and end up stripping the wire. Does anyone know if these teeth are
reliable or not? Flat lead does come in lots of different qualities,
indoor and outdoor for example.
Peter.
For a quickie FM feed, flat twin should be fine, but not for analog
TV,
Why do you say not analog? All TV has been analog since the 1940's
until recently, and flat twin has been used all these years. For 25
years, plus or minus, there was no cable, and it wasn't common for
another decade or two.
P&Mailed to OP. Please reply by post.
but... Since over the air analog TV will be phased out in a few
short years you wont have to worry about that anyway. That is unless
you want to one day receive over the air high definition digital
signals which will be available. In that case you may want to just
get yourself set up with a digital HDTV antenna and proper coax
downfeed, rotator, mast, and preamp. But if you are just looking to
get a better FM signal then twin should be fine for that. If you go
whole hog and want a proper digital exterior TV antenna then Frys
electronics has them, unfortunately Radio Shack seems to have turned
into a cell phone store (what a shame), Best Buy I think sells digital
antenna parts too. If you go with coax then I like RG6 quad shield
the best, but you have to get good at terminating them with the Thomas
Betts (sp?) waterproof F connectors and their snap crimping tool.- Hide quoted text -
- Show quoted text -
If the cable TV feed is analog then there might be FM available there
too, older analog cable systems did not brickwall filter out the lower
FM frequencies, (but they would never advertise that fact). I used my
old analog cable TV feed as my FM antenna for years. Its worth a try,
may need a small splitter and xformer.
.
- References:
- Coax vs flat twin?
- From: PVR
- Re: Coax vs flat twin?
- From: RickH
- Re: Coax vs flat twin?
- From: mm
- Re: Coax vs flat twin?
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