Attic Antenna, a fools errand?

[CanadianOTA]

Hi,

I live in a subdivision in Canada where a large TV antenna would be an unwelcome addition.
Unfortunately I live at least 60 miles from the closest tv tower.

As a compromise I installed a Winegard FL6550a on the roof (30 feet high) and aimed it to the southwest (between
110 degrees and 150 degrees).


http://www.tvfool.com/?option=com_wr...d243810d24d748

I think due to the height of the antenna (30 feet), the elevation of the home (I can see over 20 miles to the south), the fact
that the FL6550A is amplified, and the straight cable run from my antenna to my TV I am able to consistently receive:

CKWS-DT (11.1) CBC
WWNY-TV (7.1) CBS
WPBS-DT (16.1) PBS
WWTI-DT (50.1) ABC

During periods of Tropospheric Ducting I am able to also receive:
WSTM-DT (3.1) NBC
WCNY-DT (24.1) PBS
WSYR-TV (9.1) ABC (and METV on 9.2!)
WSYT-DT (68.1) FOX

I very much would like to pick up
WSTM-DT (3.1) NBC and WSYR-TV (9.1) on a consistent basis but I am 99 and 101 miles away from them AND cannot place a large antenna on the outside
of my home.

Question 1) Would a large antenna in my attic provide me with any improvement in receiving WSTM and WSYR? Or would it just be a fools errand?

Question 2) If a large antenna would provide me any improvement in receiving WSTM and WSYR. What would be the best antenna for receiving
the UHF channels of 17 and 24?

Many thanks!

[timgr]

This article may be of interest to you - http://www.kyes.com/antenna/stackluge.html

Looking ath the NM (noise margin) column in your report, channel 17 is at -13.9 dB and 24 is at -10.2. Translating from dB into percentages, that's 20% and 31% of the signal needed to resolve those channels under ideal conditions. Let's say you stacked two Antennas Direct 91XG antennas https://www.antennasdirect.com/store...V-Antenna.html ... these would have a 3 dB gain (ideally) from stacking and roughly 16 dB at 533 MHz (WSMT) and 15 dB at 481 Mhz (WSYR). So even with this formidable stacked array, you are still in the 2-3 dB NM neighborhood (25% to 70% more signal than minimum), under ideal conditions.

What's the gain of your Winegard antenna? A quick view of the Winegard site shows nothing ... I would guess between 6 and 10 dB. If we knew the Winegard antenna gain, you might guess at what noise margin will work in that location. If we guess 6 dB, then you are receiving WWTI at -0.2 NM plus 6 dB is 5.8 dB signal. 6 dB is 200% of what you minimally need, compared to maybe 2-3 dB from the stacked array. Hypothetically.

What direction are you pointing the antenna? It has a front and a back, and most sensitive pointing directly at the station you want.

No personal experience with this, but you might have a chance of getting those stations if you used the vertically stacked array or if you went higher with a high-gain antenna.

Regarding amplification, the amplifier actually degrades the signal from the antenna. It contributes its own noise to the signal. However, amplifiers can be useful when the cable losses between the antenna and the receiver degrade the signal more than the cost of putting the amplifier in the circuit. If you have a short cable run, the amplifier is doing very little for you.

JMO - I'm not an antenna engineer, or part of the industry, though I am an engineer. Forget the attic installation - you are dreaming. These only work for strong local stations, and they are always operating at a substantial handicap to a clear air installation. Plus you are thinking of combining dissimilar antennas widely separated? It will be worse, maybe a lot worse.

[Tower Guy]

Originally Posted by CanadianOTA

Question 1) Would a large antenna in my attic provide me with any improvement in receiving WSTM and WSYR? Or would it just be a fools errand?

A large antenna on the ROOF with a low noise preamp is barely possible to pick up WSTM or WSYR. The attic....uh uh.

When determining how much antenna is necessary to pick up a station you must also subtract the system noise figure from the NM value. The system noise figure is determined by a preamp, which is roughly 2 db; and would be necessary in your case. Without a preamp the system noise figure is the noise figure of the TV set plus the loss of the coax downlead, plus losses for mismatches. In the most favorable situation this would total 5 db.

WSTM NM = -10.2
factor in system noise with 2 db NF preamp = -12.2
gain of DB 8e = 15.4 db (at the low end of the UHF band)

net margin for WSTM = + 3.2 db
net margin for WSYR = + 0.4 db

I would expect both those stations to be somewhat unreliable at the net margin values shown.

[CanadianOTA]

Thank you both for your insight. I think now I will leave it.

[CanadianOTA]

A couple more questions:
1) How do you go from the db to Percentages? I would like to learn more about calculating.
2) I am now seriously thinking of going to a Clearstream 4 outside. I sincerely appreciate your suggestion to go with a 91XG. I was looking at that antenna for the attic. But I do not think I can get away with it outside. But I may be able to get away with the Clearstream 4.

[Tower Guy]

Engineers don't use percentages, only decibels, abbreviated db. The formula for DB is 10 times the logarithm of the ratio of the power difference.

[timgr]

Maybe this is clearer - depending on your math savvy.

The actual unit is the bel, named for Alexander Graham Bell. The decibel is one tenth of a bel.

All calculations are done in base 10, thus log10(10) = 1 and 10^log10(10) = 10.

Decibels from voltage, dB = 20 log10(V1/V2)

Decibels from power, db = 10 log10(P1/P2)

Recall that P = V^2/R, so power goes like the square of the voltage. That's where the extra factor of 2 comes from.

So to get percentages from dB, find V1/V2 or P1/P2.

V1/V2 = 10^(dB/20), then (V1/V2 - 1) * 100 = voltage change in percent.

hth!

Note that your calculator likely has a "log" button (base 10) and a "ln" button (base e, the natural log), and a corresponding 10^x and e^x button respectively.