Newb

[Larry]

I'm new to OTA TV, just installed a digital antenea, but the reception is in and out. Sometimes crystal clear and minutes later digitized. First question is should it be grounded. Didnt see that on manufacturers instructions, wondered how to do that for best results.

I've got the antenna wired to the in line amp that comes with it and then directly into the digital tv. Its omni directional, so i'm assuming there's no sweet spot?

Heres my report

http://www.tvfool.com/?option=com_wr...d243e390ca25a3

[Larry]

Heres the antenna specs

Lava OmniPro HD-8008 omni-directional HDTV Antenna

Specifications
Frequency(VHF)
40-230MHz
Frequency(UHF)
470-862MHz
Gain(VHF)
28+/-3dB
Gain(UHF)
30+/-3dB
Impedance
75Ω
Working Voltage
110V/60Hz
DC Input
12 V

[timgr]

Hi Larry - yes, your antenna should be grounded for safety. Here is a thread that discusses grounding, which may help you. http://forum.tvfool.com/showthread.php?t=901

No personal experience with the Lava antenna, but the gain numbers you posted seem absurdly high. They may be reporting the actual antenna gain (sensitivity) plus the amplifier gain. If so, this strikes me as a) intentionally deceptive and b) hiding the real number of interest, which is the antenna gain. An amplifier does not improve the signal; it simply takes what ever signal and noise is there and amplifies both, adding a little more noise of its own. An amplifier can be helpful if the loss of signal due to a long cable run is large compared to the signal quality, or if you have a splitter downstream which will also attenuate the signal.

Here are some old posts about the Lava - https://www.google.com/search?q=site...m+lava+antenna - I'm not an antenna engineer (though I a am an engineer), and have no personal experience with the Lava.

You should have no trouble receiving the green majors on your plot. If anything, your amplifier is overloading your TV tuner and it's occasionally breaking up. A NM of 60 is more than 1000 times more signal than you ideally need. Just point the antenna north, even indoors unless you live in a cave ... you should have plenty of signal. Can the amp come out of the circuit? It has to come completely out for this test - you can't just unplug it. Connect your antenna's downlead to directly to the TV, if you can.

Also, you say you installed; where, on the roof? Pointed how? What are the surroundings? Your antenna has a front and a back, and you'll need to point the front toward the stations you want.

[No static at all]

Yes, you may need to spin the antenna around to find a more favorable aim to the north. No antenna is 100% directional, so this might do the trick.

If you still can't achieve reliable reception, I suggest a new (old school) antenna aimed due north. Something like this small antenna should be all you need to receive all the major networks from the north.

[ADTech]

A NM of 60 is more than 1000 times more signal than you ideally need.

Actually, it's a million times more than is required. 60 dB = 6 x 10^6th power when converted from log to linear numbers.

If anything, your amplifier is overloading your TV tuner and it's occasionally breaking up.

Probably. With signals that strong, an amplifier should be avoided.

All you should need is a small UHF-only antenna aimed to the north to catch your local stations.

[timgr]

I don't think so. Tell me what I'm doing wrong.

60 dB = 20 log10(x)

60/20 = 3

10^3 = x = 1000.

Maybe you are thinking of power. My reading of the literature says NM is like SNR, ie voltage. Noise is voltage, by definition, different from noise power.

60 dB power is a million times, 10^6.

[ADTech]

This is power, not voltage. Have to use the correct units.

Everything in the TVFool math is based on the 'dBm' where 0 dBm= 1 mW across 75 ohms. Differential numbers such as the noise margin are simply in 'dB' as they represent a ratio rather than absolute values.

Noise is voltage, by definition,

Voltage has to be across a load (75 ohms for our calculations), therefore there is current and Ohm's law applies, including the extensions for power calculations (W=V*A).

[timgr]

Offered in a friendly collegial tone...

I'm not doubting your expertise, but I am sure noise margin is widely defined in terms of voltage: http://encyclopedia2.thefreedictionary.com/noise+margin - it's just implicit in the name.

Noise increases like the root of the bandwidth and is measured in volts. There is a another unit noise power, that is proportional to the bandwidth and is measured in watts. Signal is defined as volts. So when I say "signal" I mean in volts. dBm is only relevant to the power measurements column, where you need a baseline to compare to. For noise margin, there is no need for a baseline, since you are comparing the signal to the noise.

Basically, it does not matter really ... as long as you understand whether you are comparing voltage or power. You can get the NM in dB by comparing the noise to the signal (in volts/volts) or by comparing the signal power to the noise power (watts/watts). You will get the same value in dB, as long as you use the proper multiplier (10 or 20) appropriate to the inputs.

[ADTech]

No worries, I struggled with this at one time in the past...

The reference you gave isn't applicable to RF communications, it's for digital logic.

Pop over to the FAQs (https://www.tvfool.com/index.php?opt...d=57&Itemid=78) where Andy describes the various calculated items and see if they clear things up.

Some basic assumptions upon which the TVFool calculations are based:

1) Assumed noise floor in a 6 MHz bandwidth is -106.2 dBm
2) ATSC specification is 15.2 dB SNR in channel.

Therefore, a signal power calculated to at -91 dBm will have a noise margin of 0.

However, the NM values calculated do not yet take into account the tuner noise figure and any insertion or mismatch losses in the system which must additionally be accounted for. Since tuner noise figures may vary widely (4-10 dB), a value of 6 dB is a common assumption for system operating calculations. Add in 50 ' of RG6 (2.5-3 dB) and you're at a requirement for almost 10 dB of extra margin required for a basic antenna, coax, tuner system.

If time permits, there's a very long thread over at AVS that covers much of the development period for this website's tools. It's an interesting read. http://www.avsforum.com/forum/25-hdt...on-thread.html

[rabbit73]

timgr:

If you look at Larry's tvfool report you will see that NM is dB (power, or more exactly power ratio), not voltage:



This is my take on NM:



Andy Lee (who created this forum) did an interesting post with diagrams about NM in the long thread that ADTech mentioned above:

http://www.avsforum.com/forum/25-hdt...l#post15700679

Click on the second set of diagrams (they were attachments before AVS changed the software) for a larger image. If your cursor has a plus sign, click again for an even larger image.

And while I'm at it, there is a lot of confusion about dBmV vs dBm. The dBm scale is used by RF engineers and TV Fool. The dBmV scale is used by antenna installers and cable guys. Both are power, but some people think that dBmV is a voltage scale. It's not; the only thing voltage about it is the 0 dBmV reference level for the scale which is defined in terms of voltage across 75 ohms.
http://www.avsforum.com/forum/25-hdt...l#post16837993