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The Official AVS Antenna and Related Hardware Topic! - Page 377

post #11281 of 16086
Quote:
Originally Posted by rbarbier View Post

I am 57 miles away also.

I sent it back a few days later and picked up the AntennaCraft Y5-7-13 and get 0 signal with that one (looks like the C5 might be better then the Y5-7-13).

I just hate High VHF. That is all I have to say. UHF at 57 miles away with a small C4 antenna and I get perfect UHF reception. High VHF with a 5' antenna and still no signal.

You might think about a deep fringe antenna at your distance out. I get rock solid VHF from 50 miles over mountainous terrain with a Winegard HD8200. Signal levels 90 - 100 %.
post #11282 of 16086
Quote:
Originally Posted by Davird_Jr View Post

You might think about a deep fringe antenna at your distance out. I get rock solid VHF from 50 miles over mountainous terrain with a Winegard HD8200. Signal levels 90 - 100 %.

Unfortunately, he has to keep it on his balcony. The 8200 is probably bigger than the whole balcony.
post #11283 of 16086
Quote:
Originally Posted by ProjectSHO89 View Post

Unfortunately, he has to keep it on his balcony. The 8200 is probably bigger than the whole balcony.

Yeah. Even the current 5' antenna is taking up a good amount of my space. I want something like the C5 for High VHF with a little more gain or something.
post #11284 of 16086
How about make your own 16" loop with 1" or 1/2" copper tubing and put a screen behind it about 15" back?
post #11285 of 16086
Quote:
Originally Posted by EscapeVelocity View Post

How about make your own 16" loop with 1" or 1/2" copper tubing and put a screen behind it about 15" back?

PLEASE explain this. Would this work for 7-13 in my area?

Thanks in advance.

(I really only care about 7 (ABC) and 11 (FOX)) if that helps.
post #11286 of 16086
Well, people make 16" loops for the ham band 144Mhz. I was just thinking out loud.

Maybe a 15" loop and 15" Reflector Screen.
post #11287 of 16086
Yesterday, I attempted to increase my signal strength by reaiming my Yagi antenna to point directly at the station that I'd like to peak. It was a few degrees different. I wound up loosing a couple of points of signal strength versus aiming it to peak out the signal. Is it possible that I was getting a higher number before due to some cumulative reflection effect where I'm still better off aiming it dead on at their tower? I haven't watched enough since then to know how it affected the signal.
post #11288 of 16086
Quote:
Originally Posted by JimP View Post

Yesterday, I attempted to increase my signal strength by reaiming my Yagi antenna to point directly at the station that I'd like to peak . . . . . . I wound up loosing a couple of points of signal strength versus aiming it to peak out the signal. Is it possible that I was getting a higher number before due to some cumulative reflection effect where I'm still better off aiming it dead on at their tower?

Yes, it could be many things(trees, buildings, hills, system overload). It may only affect certain channels even though they are coming from the same direction. I have 17 channels coming from the same direction. All come in fine except 2, which both require re-aiming 30 degrees off axis.
post #11289 of 16086
Quote:
Originally Posted by EscapeVelocity View Post

How about make your own 16" loop with 1" or 1/2" copper tubing and put a screen behind it about 15" back?


That would be even lower gain than either antenna already tried out....
post #11290 of 16086
Quote:
Originally Posted by rbarbier View Post

...I just hate High VHF. That is all I have to say. UHF at 57 miles away with a small C4 antenna and I get perfect UHF reception. High VHF with a 5' antenna and still no signal.

Same scenario for many many people in certain parts of the country.
post #11291 of 16086
Quote:
Originally Posted by ProjectSHO89 View Post

That would be even lower gain than either antenna already tried out....


Is there something similar to the V21 without channels 2-6 and without the UHF channel? Would this antenna work in my situation? Or if I just cut off the Low VHF part and use this as a UHF/High VHF antenna?

Or...how about paying somebody to make me a custom antenna for 7-13 with the highest gain and small form factor. I am willing to do this also.

Thanks.
post #11292 of 16086
Great info, all. Test equipment is only as reliable as the knowledge of the operator. I am lucky to have a modern instrument that makes it much easier. It gives the voltage level of digital signals in center value or average value, depending on mode. And seeing the waveform explains exactly why these two values might be much different.
Sencore has great tech info. Their "Seeing is Believing" on spectrum analyzers a few years ago convinced me to get a signal level meter with a spectrum display as well as the spectrum analyzer feature.
post #11293 of 16086
Quote:
Originally Posted by arxaw View Post

Same scenario for many many people in certain parts of the country.

Not here. AT 50 miles VHF near perfect. On UHF half the stations come in intermittently on a single UHF antenna, the rest not at all.
John
post #11294 of 16086
Quote:
Originally Posted by ctdish View Post

Not here. AT 50 miles VHF near perfect. On UHF half the stations come in intermittently on a single UHF antenna, the rest not at all.
John

What antennas are you using for UHF/VHF?
post #11295 of 16086
Could I be overloading my TV? According to TVfool, my High VHF signals are 18.5, 16.6, 15.5 and 12.7 NM(dB). My UHF signals start at 7.0 dB down to 1.7 dB.

I am using the CM7777 with a short cable run (like 10 feet split to 4 tuners). What is weird is that my strongest UHF channel (43..CBS 2.1) is actually one of my lowest dB signal on TVfool.

http://www.tvfool.com/?option=com_wr...74fa52fb44c917
post #11296 of 16086
One way to tell. Bypass the 7777 and see if your signal quality improves.

You can't just unplug the power supply, you have to temporarily bypass the preamp.

But if your tvfool results are correct, overload is not likely. The 7777 might be defective, though.
post #11297 of 16086
Is the power supply warm or cool to the touch? It should be warm.
post #11298 of 16086
Quote:
Originally Posted by JimP View Post

Is the power supply warm or cool to the touch? It should be warm.

Not sure. Not at home right now. I know the 7777 works for the UHF because I do get a higher signal with UHF through the 7777. I never really had to use the 7777 for VHF until now. I know the switch inside the Amp is correct (seperate instead of combined) and FM Trap is on.

I will try running VHF antenna directly to my TV (about 15' cable run) and see if I get any signal.
post #11299 of 16086
Quote:
Originally Posted by rbarbier View Post

Could I be overloading my TV? According to TVfool, my High VHF signals are 18.5, 16.6, 15.5 and 12.7 NM(dB). My UHF signals start at 7.0 dB down to 1.7 dB.

I am using the CM7777 with a short cable run (like 10 feet split to 4 tuners). What is weird is that my strongest UHF channel (43..CBS 2.1) is actually one of my lowest dB signal on TVfool.

http://www.tvfool.com/?option=com_wr...74fa52fb44c917



Pretty much zero chance of overload from the actual signals. Usually don't have to worry about that until the TVFool Rx level is more positive than -20 dBm or so. You might try an FM trap (check FMfool.com for any nearby FM stations.)

Try also running straight from the VHF > 7777> to a single set.
post #11300 of 16086
Quote:
Originally Posted by EscapeVelocity View Post

Well, people make 16" loops for the ham band 144Mhz. I was just thinking out loud.

Maybe a 15" loop and 15" Reflector Screen.

Optimum Circular Loop diameter for the Hi-VHF Band is 24-inches using 1/2-in pipe,
23-inches for QuarterInchCopperTubing, 21.5-inches for AWG12 and 21-inches for
AWG26 (tiny wire taped to window):
http://imageevent.com/holl_ands/loops/vhfloop
So Loop Reflector would probably be about 5-percent larger....next on my list...

Other antenna analyzes can also be found here:
http://imageevent.com/holl_ands/
post #11301 of 16086
Thanks Holl_ands!
post #11302 of 16086
Quote:
Originally Posted by holl_ands View Post

So Loop Reflector would probably be about 5-percent larger....next on my list...

...optimal spacing between the loop and reflector?
post #11303 of 16086
Quote:
Originally Posted by ProjectSHO89 View Post

Pretty much zero chance of overload from the actual signals. Usually don't have to worry about that until the TVFool Rx level is more positive than -20 dBm or so. You might try an FM trap (check FMfool.com for any nearby FM stations.)

Try also running straight from the VHF > 7777> to a single set.


Tried both ways (directly to my TV and directly from my 7777), same thing. No signal. Tried scanning without antenna then rescanning. UHF still 80% on my TV. Guess I am in a dead zone for VHF.

Guess I will dream about the days I got all my local channels in HD when they were all UHF. Maybe if I move, I will get the biggest High VHF antenna I can find. That might work.
post #11304 of 16086

dBmV vs dBm

 

Quote:

Originally Posted by ProjectSHO89 View Post

Since no one here is likely to be working on optical front ends and signal measurements there-in, this app-note is afar more relevant to this audience: http://www.sencore.com/uploads/files...RF_Signals.pdf

Here's another one that's pretty conservative with recommended signal levels: http://www.sencore.com/uploads/files...veGoodHDTV.pdf

Those articles are two of my favorites. But I also like this one because I have found that old signal level meters designed for analog signals are still useful for digital signals:

Quote:
Originally Posted by holl_ands View Post

Meters and Spectrum Analyzers will give different results, depending on the
bandwidth of the measurement filter, which is usually much less than 6 MHz:
http://www.pi-usa.com/pdf/dtva.pdf

--------------------------------------------------------------------------------------------------

Quote:
Originally Posted by ProjectSHO89 View Post

Also, keep in mind that TVfool and the FCC mapping tool provide estimates of signal POWER, not voltage. To convert from the projected power value to voltage (as measured with a dB voltmeter), add 48.8 to the dBm value to convert to dBmV (into a 75 ohm load).

As an example, if the forecast signal strength were -48.8 dBm, a unity gain (0 dB) antenna were used, and the circuit were perfect (no losses or mismatches), the dB voltmeter should read 0 dBmV, a -58.8 dBm forecast should read -10 dBmV, a -38.8 dBm forecast should read +10 dBmv, etc

Your conversion factor of 48.8 is correct when going from dBm to dBmV, but there is no such thing as a dB voltmeter. Decibels express a difference in power levels. If not, how could you use the constant conversion factor when going from dBm to dBmV?

Signal level meters that are calibrated in dBm and dBmV both measure signal power, not voltage. Each uses a different reference level to compare with the signal to be measured, but the difference between these two reference levels is constant. That is what makes it possible to use the conversion factor:

The 0 dBm reference level = 1 mW

Converting the 0 dBmV reference level also to power (E squared divided by R):
0 dBmV reference level = 1.33333E-05 mW

This could also be stated as 0.0000133333 mW, but using the powers-of-ten engineering notation as above makes it possible to retain more significant figures on the average handheld scientific calculator. (You can also say it as "1.33333 times ten to the minus five milliwatts.")
 

Code:
dB ratio  =  10 log (P1/P2)

          =  10 log (1/1.33333E-05)

          =  48.7506 dB

The dB ratio could have also been calculated using the voltages from each reference level and the formula dB = 20 log (E1/E2), but the reference level for dBm is by definition 1 mW of power. If we convert the reference level for dBm to voltage the impedance must also be 75 ohms. The reference level voltage for 0 dBm for 75 ohms is 0.274 Vrms, but it is 0.224 Vrms for 50 ohms.

To quote the ARRL Handbook:

Quote:


Sometimes there is confusion about whether the decibel was calculated using power, voltage or current. Since the current and voltage equations use 20 instead of 10 times the log term, some hams believe the "voltage" or "current" decibel is different than one calculated using power. This is not true, however. There is ony one decibel definition, and that is ten times the log of a power ratio.

I like to use these sites when making conversions:
http://www.soontai.com/cal_exunit.html
http://www.jneuhaus.com/volts_to_dBm.html

http://www.cabletronix.com/pdf/dB%20Conversion%20Chart.pdf

Signals that are stronger than the reference level are assigned a positive value. Signals that are weaker than the reference level are assigned a negative value. Signals that are equal to the reference level are assigned a zero value (which doesn't mean no signal). The accuracy of the meter depends upon its calibration and the standards used for calibration.

Fortunately, we don't need to know the absolute value of the power measurement to a high degree of accuracy because most of our measurements are comparisons to find the strongest signal when aiming an antenna, finding the best location for an antenna, comparing antennas, and measuring loss in a distribution system. When making comparisons, meter linearity is important. This is easily checked with a built-in or external fixed attenuator.

A signal level meter (SLM) that uses a dB scale with a reference level of 1mV across 75 ohms for 0 dBmV is a relative power meter, not a voltmeter. It allows us to measure signal levels in dBmV, cable loss in dB, amplifier gain in dB, and make dB comparisons of antennas---all differences in power, not voltage. It's very convenient, because you can easily add or subtract decibel values. The "V" in dBmV is only to tell us what reference level is being used.

The older field strength meters (FSM) that came before the SLMs calibrated in dBmV used microvolts. They WERE signal voltmeters, and used the same reference level of 1000 microvolts (equals 1mV), but the scale was calibrated in microvolts. The later field strength meters included a dB scale along with the microvolt scale, which was the transition instrument between the early field strength meters and the present SLMs:



Notice that 10 times the voltage gives a 20 dB difference in power. This explains why some of the early field strength meters, calibrated in microvolts, had 20 dB attenuators marked with the label "10," for ten times the voltage.

A meter scale can be calibrated in any units that are appropriate for the application. Which scale you use determines what you name the meter. If you use the microvolts scale you can call it a voltmeter. If you use the dB scale, it becomes a relative power meter.

So, your meter to measure signals can be calibrated in microvolts, dB, dBmV, or as in the photo above with two scales: one for microvolts and one for dB (but not "dB microvolts"). I don't think there is such a thing as a "dB voltmeter" because I'm not aware of a measurement unit called "dB volt."

Many years ago I attended a seminar led by Gordon Gow, longtime president of McIntosh Laboratory (mfg of high-end high-fi equipment). Whenever he hired a new EE as an employee, he had to sit him down to talk about decibels and invariably had to tell him that "there is no such thing as a voltage decibel. Decibels indicate a POWER ratio."

A measurement unit cannot be an expression of power and voltage at the same time; it is not consistent with Ohm's Law. Given enough information, one can be calculated from the other, but they are not synonymous. Please look at the screen shot below of digital channel 31 from my Sadelco DisplayMax 800 and note that the reading of +13.4 dBmV is labeled PWR:



Q.E.D.


Edited by rabbit73 - 6/14/12 at 12:45pm
post #11305 of 16086
Quote:
Originally Posted by rbarbier View Post

Tried both ways (directly to my TV and directly from my 7777), same thing. No signal. Tried scanning without antenna then rescanning. UHF still 80% on my TV. Guess I am in a dead zone for VHF.

Guess I will dream about the days I got all my local channels in HD when they were all UHF. Maybe if I move, I will get the biggest High VHF antenna I can find. That might work.

I did not realize you only had a balcony to mount the antenna. You might try looking around your neighborhood to see what antennas other people are using.
post #11306 of 16086
Quote:
Originally Posted by Davird_Jr View Post

I did not realize you only had a balcony to mount the antenna. You might try looking around your neighborhood to see what antennas other people are using.

Not too many people have antennas around here and the ones that I do see are old. I really don't see huge antennas out here but I don't know what kind of reception they have either. The balcony worked/works perfect for me with my C4 UHF antenna. I even had perfect UHF digital with my Squareshooter 1000 at 57 miles away. I think my location might be optimized for UHF signals or something. Just can't get the High VHF stations at my location.
post #11307 of 16086
Quote:
Originally Posted by rbarbier View Post

Just can't get the High VHF stations at my location.

Your TVFool results show almost all of your VHF signals as 1Edge which indicates that there is some sort of obstruction between you and the transmitters. That probably explains why you're having such a hard time finding an antenna that works well for VHF.

I assume that your balcony faces toward the transmitters. Have you tried aiming the antenna at various angles? Sometimes aiming the antenna in a slightly different direction will allow you to pickup a reflected signal.
post #11308 of 16086
Quote:
Originally Posted by Rick313 View Post

Your TVFool results show almost all of your VHF signals as 1Edge which indicates that there is some sort of obstruction between you and the transmitters. That probably explains why you're having such a hard time finding an antenna that works well for VHF.

I assume that your balcony faces toward the transmitters. Have you tried aiming the antenna at various angles? Sometimes aiming the antenna in a slightly different direction will allow you to pickup a reflected signal.

Yeah. My balcony faces the correct direction. I tried all directions but still nothing.

I thought VHF was supposed to be better with obstructions. All my UHF stations are 1Edge and from the same degrees and I don't have any issues. I can even have my C4 antenna inside my apartment and I still get a usable signal for most of my UHF stations. I can even lay my C4 on the floor of the balcony and I still get a reception (I live on the second floor).

I will keep playing around with the VHF antenna and see what happens. I might just get a second UHF antenna and face it towards San Diego and at least have Fox5 from San Diego (about 77 miles away). I am able to get that station most of the time even though my antenna is facing the LA towers.
post #11309 of 16086
Quote:
Originally Posted by rbarbier View Post

I thought VHF was supposed to be better with obstructions.

I know it's supposed to propagate better through trees, but I'm not sure about other obstructions.

Quote:
Originally Posted by rbarbier View Post

I will keep playing around with the VHF antenna and see what happens.

You might try angling it up a just a bit if you can. Sometimes that helps too. Good luck.
post #11310 of 16086
Quote:
Originally Posted by rbarbier View Post

Yeah. My balcony faces the correct direction. I tried all directions but still nothing.

I thought VHF was supposed to be better with obstructions. All my UHF stations are 1Edge and from the same degrees and I don't have any issues. I can even have my C4 antenna inside my apartment and I still get a usable signal for most of my UHF stations. I can even lay my C4 on the floor of the balcony and I still get a reception (I live on the second floor).

I will keep playing around with the VHF antenna and see what happens. I might just get a second UHF antenna and face it towards San Diego and at least have Fox5 from San Diego (about 77 miles away). I am able to get that station most of the time even though my antenna is facing the LA towers.

I'm new at this, so I'm throwing this out there for others to comment on.

The AntennaCraft Y5-7-13 VHF antenna you used specifications read "Mileage VHF:60 Miles" which I believe presumes that you have perfect conditions and no line loss. Even with an amplifier, you don't have enough signal at 57 miles to amplify for it to matter.

If you're looking for a dual antenna solution, then the VHF antenna should be something like the Antennacraft Y10-7-13 rated up to 100 miles for high band VHF. Note that its 10' long. Here's a comparison of antennacraft's 3 Yagi style antennas. http://www.antennacraft.net/Yagi.html
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