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Guest Message by DevFuse

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"borrowing" an antenna?


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12 replies to this topic

#1 OFFLINE   lwdaniel

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Posted 09 November 2009 - 05:45 PM

I am in a downtown Building in Houston, Tx. We have a UHF/VHF TV antenna outside our office building. It was okay for analog, when digital hit, reception went to crap. On the fence where our antenna is, someone across the hall put up one of those DIY HDTV antenna and a person who works over there said they are pulling in many channels.
Question, If we took our antenna coax and also connect to his antenna, will it screw up his reception? It is difficult to get to antenna, just want to do this once, not have to go back to disconnect it if possible.

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#2 OFFLINE   Stewart Vernon

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Posted 09 November 2009 - 06:08 PM

That would amount to splitting the signal... which means you'd be going from no TV to half-power signal... and the other guy would be going from whatever signal he has now to half that.

If there are marginal signals, he'll notice immediately.

-- Respect the S.H.I.E.L.D.


#3 OFFLINE   lwdaniel

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Posted 09 November 2009 - 06:34 PM

That's my thinking also, Thanks.

#4 OFFLINE   Stuart Sweet

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Posted 09 November 2009 - 07:03 PM

Seems to me, the polite thing to do would be ask, and commit to removing your line if his signal is affected.
Opinions expressed by me are my own and do not necessarily reflect
those of DBSTalk.com, DIRECTV, DISH, The Signal Group, or any other company.

#5 OFFLINE   kenglish

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Posted 10 November 2009 - 01:46 PM

Could it be that your antenna is OK, but the problem is in your cabling?
If so, you wouldn't see any improvement.

#6 OFFLINE   INSIDERINFO

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Posted 10 November 2009 - 01:54 PM

get a convert box to hook to your UHF/VHF ant

#7 OFFLINE   sum_random_dork

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Posted 10 November 2009 - 02:31 PM

Maybe your antenna needs to be reaimed or your local channels changed from UHF back to VHF? As was mentioned check your connections, it could be something came loose. Rats and mice love to eat the cables....

#8 OFFLINE   lwdaniel

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Posted 10 November 2009 - 08:46 PM

thanks to all,

Yes, we were going to ask, but I figured it would lessen his signal and I wanted a 2nd opinion. The antenna is somewhat difficult to get to, esp. if one has acrophobia. and I wanted to keep from having too many return visits.

I am going to make one similar to his and place it next to his.
The setup will be temporary, though. This building is going to be leveled later next year.

Don't think it is the cable, the analog was okay until the cutoff.

Night shift tried re-aiming recently. no good.

#9 OFFLINE   Jerry Springer

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Posted 25 November 2009 - 09:36 PM

Reception 101

Basically the only experience you have with reception is analog and not digital.

Digital is broadcast at a much lower power level, compared to the VHF - with line loss, you are loosing about 5 to 6 Db of signal in 100 feet of good wire at channel 51 - which is the highest digital signal which is being transmitted.

Depending on where you are situated and what your reception situation is - you may or may not get any reception.

Most times it takes a pre amplifier to over come long runs of wire and splitters.

There may or may not be anything wrong with your antenna physically, but if it is in the wrong location - it still might not work, even with a pre amplifier.

Trees with leaves on them will block your signal, a building 3 or more stories high will block your signals, rain will block your signals, even migrating birds and swarms of bugs can block your signal - momentarily. If you live too close to a airport, the airplanes can temporarily block your signals.

If the transmitter is behind a hill or mountain - the mountain or hill can block your signal.

Even a reflection of the original signal coming back at a different time then the original signal will cause multipath - which will corrupt the information inside of the signal - which will be even worse then a fringe signal.

PS - if the neighbor has a pre amplifier on his antenna and you try to connect your wire to his without a voltage block, you will mess up both his reception and yours.

Here is a site where you can get coordinates for your address.

http://www.tvfool.co...apper&Itemid=90

Enter in your address and then ask it to make a plot for your reception.

The coordinates will come up on the first screen it comes to.
Right next to the box that asks what your antenna height is.

Edited by Jerry Springer, 26 November 2009 - 06:49 PM.


#10 OFFLINE   olguy

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Posted 26 November 2009 - 08:20 AM

I am in a downtown Building in Houston, Tx. We have a UHF/VHF TV antenna outside our office building. It was okay for analog, when digital hit, reception went to crap. On the fence where our antenna is, someone across the hall put up one of those DIY HDTV antenna and a person who works over there said they are pulling in many channels.
Question, If we took our antenna coax and also connect to his antenna, will it screw up his reception? It is difficult to get to antenna, just want to do this once, not have to go back to disconnect it if possible.

You might want to post this question at Houston, TX - OTA - Page 182 - AVS Forum. A couple of the folks who follow that thread are broadcast engineers in Houston. One works at Channel 8 and the other used to be at 39. And you can get a decent antenna pretty cheap on line. I got the one in my attic from Antennas Direct | Your TV and HDTV Antenna Source. I called the 800 number and spoke to a tech rep who checked all the numbers and made a recommendation. Works great in Kingwood.

Edited by olguy, 26 November 2009 - 10:39 AM.

Just another old geezer killin' time till time kills me.

#11 OFFLINE   harsh

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Posted 26 November 2009 - 09:20 AM

Listen close - because I am only going to tell you this once.
...
The audio was broadcast in AM - Amplitude Modulation - which had to be transmitted at a very high amount of power to compensate for noise - which anyone who has ever listened to a AM radio would know - you have a lot of noise to over come with a AM radio.

Your post started out sounding very authoritative but went south with this false statement that was immediately contradicted in the following paragraph.

There are some truths in there, but it certainly wasn't the schooling that it presented itself to be. There is quite a lot of misinformation contained throughout the post.

#12 OFFLINE   Jerry Springer

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Posted 26 November 2009 - 06:43 PM

Well Harsh,

Let me put it to you like this, a flower has to bloom where it is planted.

I tried to put it into terms that anyone could understand in explain it in a way that anyone could understand. I made a mistake and got my words mixed up. Sorry everybody, I apologize to everyone.

Again, if there is a building between you and the signal, you will have no signal if the building is opaque to the signal.

Even having your antenna on the wrong side of a building will give you problems.

I have had people ask me for advice for a indoors antenna for a steel building and when I tried to explain to them that the Steel or aluminum can and will block your signal, it all went in one ear and out the other - due to the fact that people do not understand how television is transmitted and what it takes to receive it.

In the analog days there were two effective transmitters for the TV
station.
A transmitter for the video and a transmitter for the audio.
The video transmitter was Amplitude Modulation.
The audio was FM at a much lower power.

The reason that the video was a higher power is that AM is more susceptible to noise requiring a stronger signal at the receive and a higher power output of the video transmitter

"In North America, full-power stations on band 1 (channels 2 to 6) are
generally limited to 20 kW digital (8VSB) ERP.
Stations on band III (channels 7 to 13) can go
up by 5dB(W) to 63.2 kW digital.
Low-VHF stations are often subject to long-distance reception just as with FM.

UHF, by comparison, has a much shorter wavelength, and thus requires a
shorter antenna, but also higher power. North American stations can go up
1000 kW digital.
Low channels travel further than high ones at the same power, but UHF does not suffer from as much electromagnetic interference and background "noise" as VHF, making it much more desirable for TV.

UHF communications are more "line of sight" communications than lower
frequency VHF.
It is sort a like having a sound vs a light. If you make sound it radiates
in all directions, around buildings, through walls, down into holes (valley).
Shining a light does not go around corners or through walls and if it is a
pinpoint light it doesn't go down into the valleys.

The earth is round and eventually the beam of light, UHF TV the beam will
no longer touch the earth but go up into the sky.

The height of the transmitting antenna is factored into the power output of
the TV station.
The power output for TV & FM is rated in ERP (Effective Radiated Power)
There are a number of factors the go into this calculation.
Several Key items are:
Height of Antenna. listed both as HAAT (Height Above Average Terrain) and
AMSL (Height Above Mean Sea Level).

Gain of antenna:
Just like your receiving antenna has gain in db so does the transmitter.
Remember 3db gain is equivalent to doubling the output power, or 1/2 the
electric consumption expense.

20 dB = gain factor of 100

10 dB = gain factor of 10

3 dB = gain factor of 2 (actually 1.995)

0 dB = no gain or loss

-1 dB = a 20% loss of signal

-3 dB = a 50% loss of signal

-10 dB = a 90% loss of signal

All radio frequencies reduce at the ratio of the square of the distance, that is if the distance is doubled the level is reduced to 1/4 if its level, if the distance is tripled is it reduced to 1/9. If the distance is 5 times it is reduced 1/25. So eventually the level is so low that it seemingly disappears in the noise.

Like a flashlight it is only good for a certain distance and then the light goes no further.

Edited by Jerry Springer, 26 November 2009 - 11:52 PM.


#13 OFFLINE   narrod

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Posted 26 November 2009 - 08:16 PM

He is correct that your original statement that audio was broadcast on AM is wrong.




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