NEXXTECH in-line VHF/UHF signal amplifier life cycle? - AVS Forum
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post #1 of 10 Old 03-14-2013, 07:28 AM - Thread Starter
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Hi all,

I recently got a CM4228 installed without a pre-amp to feed a Samsung UNxxES7100 LED TV. I am from Ottawa, ON Canada, with this great antenna I got 10 solid English channels and 4 French.

In the scanning process, I found 3 US weak, snowy channels:

18.1 23.1 WNPI-DT PBS-SD Norwood, NY
18.2 23.2 WNPI-DT THINK Norwood, NY
18.3 23.3 WNPI-DT PBS-HD Norwood, NY

Then, I picked up a Rat/Shack or now The Source (in Canada) this TV/VCR/FM Signal amplifier, which is a 9 dB in-line signal booster. Plugged this in, connected the In and Out, then voila, all 3 US NY channel appeared nice and clean.

http://www.thesource.ca/estore/Product.aspx?language=en-CA&catalog=Online&category=VideoAmplifiers&product=1501118

Note that at first when the TV was on, it was on another good channel, the picture appearred blurred at first, apparently good channel signal was saturated by the 9 dB gain introduced. Then, when I flipped to the NY channels, and back to the known good channels, it looks normal (and still good) now. My guess is there is a AGC circuit inside the Samsung digital tuner, that compensated for the 9 dB unecessary gain.

But then, I need to go to the gym for Wed night. When I got back, those 3 additional NY channels are gone. I checked and changed the coax cable, re-scanned the TV, still no joy. It appeared the signal amplifier is DEAD frown.gif!

I don't think this brand is reliable, will return it, and look for another choice. At Cdn Tire there is a 25 dB gain in-line amp:
http://www.canadiantire.ca/AST/browse/3/HouseHome/HomeElectronics/VideoAccessories/PRDOVR~0452364P/In-Line+Amplifier%2C+25dB.jsp?locale=en

My concern is, not knowing how much the Samsung TV tuner can take, would I damage the tuner by pumping a 25 dB gain signal to its input?

I intend to cut my SAT TV services, only use OTA HDTV, would not want to risk $30 for the TV digital tuning circuit, just to get 3 more channels that I may not watch that often?

Any thoughts?
Thanks!
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post #2 of 10 Old 03-14-2013, 06:28 PM
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The noise figure is probably rather high on those amps. Consider a dist amp from PCT/Channel Master or Motorola for better results. Also Viewsonics. Now Walmart does sell an RCA inline amp for $15.99 here in the U.S. that claims to be extremely low noise. And you may want to look at the new Mohu Jolt amp or the Winegard LNA-100 amp. All of these amps are 10-15db gain with lower noise figures. These should be better choices to consider.
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post #3 of 10 Old 03-14-2013, 06:36 PM
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Quote:
My concern is, not knowing how much the Samsung TV tuner can take, would I damage the tuner by pumping a 25 dB gain signal to its input?

There are three types of preamp or tuner overload, in order of increasing signal strength:

1. The strong signals cause enough IM distortion to interfere with the reception of weak desired signals. This is the point that holl_ands uses in his preamp charts to obtain max SFDR (Spurious Free Dynamic Range). No damage will happen.

2. The strong signals cause overload to the preamp or tuner that makes it impossible to receive any signals. No damage will happen.

3. The signals are so strong that the input transistor is toast. You are not likely to encounter OTA signals that strong.

I looked at the tvfool report for Ottawa (an exact address report for your location would be more accurate):

http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id%3d1dda3cfb7e89e9

Based on that report, it doesn't seem likely that preamp or tuner overload would cause damage. However, WNPI is a 2Edge signal 76 miles away with a signal power of -96 dBm, which is not likely to give you reliable reception. Transmitters that are more than about 70 miles away have their signal blocked by the curvature of the earth, and most tuners need a stronger signal that is at least -84 dBm.

Since your strongest signal is about -30 dBm, a preamp might make it so strong that the IM distortion created could mask the very weak WNPI signal, which is the type 1. overload mentioned above.

I notice another problem: you have a very strong adjacent channel signal on CH24 that can cause a problem for reception of WNPI on CH23.



CICO-DT on CH24 has a signal power of -32 dBm; WNPI on CH23 has a signal power of -96 dBm. The difference is about 64 dB, which is more than the threshold value of 33 dB.

Chart from:
ATSC Recommended Practice:
Receiver Performance Guidelines
Document A/74:2010, 7 April 2010
page 15

http://www.atsc.org/cms/standards/a_74-2010.pdf

If you can not measure it, you can not improve it.
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post #4 of 10 Old 03-14-2013, 08:40 PM - Thread Starter
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Wow, I am really impressed with the two replies above, that show not just common knowledge (on in-line distribution amp selection) but also professional advice on tuner overload! When I have a chance, I'll upload the tvfool report of my location for further discussions. Thank you all!
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post #5 of 10 Old 03-14-2013, 09:27 PM
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Glad that you found our answers helpful.

Besides your exact address (or coordinates) tvfool report, you might tell us a little more about your setup, like where your antenna is located and do you have a rotator?

If you wanted to throw money at the problem, one possible solution that MIGHT work:

A separate high gain UHF antenna just for WNPI, followed by a single channel custom bandpass filter by Tin Lee in Toronto for CH23 that would attenuate adjacent CH24, followed by a low noise preamp and then an A/B switch for WNPI or the rest of your channels.
http://www.tinlee.com/index.php

2Edge signals often act like Tropo signals, in that they are affected by weather conditions.

If you can not measure it, you can not improve it.
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post #6 of 10 Old 03-15-2013, 06:55 AM - Thread Starter
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Quote:
Originally Posted by rabbit73 View Post

Glad that you found our answers helpful.

Besides your exact address (or coordinates) tvfool report, you might tell us a little more about your setup, like where your antenna is located and do you have a rotator?

The antenna is mounted on the roof facing south-east, particularly aiming at the Manotick transmitter. There is no rotor, but fixed at 177 deg ( vs 324 deg of the Camp Fortune's). It was first fixed at 324 deg. but I miss channel 43-1 CHRO Ottawa; by turning the antenna south east, I got it:
http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id%3d1dda35812f60a5%26t%3dALLTV%26n%3d10

As can be seen from this Tvfool report (hopes it works), my location can "tune in" either Camp Fortune or Manotick transmitter:
http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id%3d1dda35812f60a5

Quote:
If you wanted to throw money at the problem, one possible solution that MIGHT work:

A separate high gain UHF antenna just for WNPI, followed by a single channel custom bandpass filter by Tin Lee in Toronto for CH23 that would attenuate adjacent CH24, followed by a low noise preamp and then an A/B switch for WNPI or the rest of your channels.
http://www.tinlee.com/index.php

2Edge signals often act like Tropo signals, in that they are affected by weather conditions.

No I probably don't have more $ to throw at this problem, as it may not be a real problem for me. It is rather a desire, nice to have -not sure if it is an absolute need smile.gif.

As for the WNPI-DT signal:
WNPI-DT (Digital)
Channel: 23 (18.1)
Network: PBS
Maximum ERP: 40.000 kW
Coordinates: 44.491453 -74.857138
Distance: 71.5 miles Azimuth: 148 degrees Compass: 161 degrees
http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id%3d1dda35812f60a5%26t%3dALLTV%26n%3d16

Your observation of 2Edge =>Tropo signals is bang on, when I checked early in this morning before going to work, I actually have good reception of these 3 channels (18-1, 18-2 &18-3) without any amplification at all. The picture was nice and clean as if my antenna is within range (60 miles). Thus I would guess adding a 3dB gain would suffice.

That said, my installer offers a 2-port CM-3412 at a reasonable price, throwing in a 75-ohm F type terminator (for the unused port) if that makes me happy. I'll say I throw money at this now smile.gif
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post #7 of 10 Old 03-15-2013, 04:59 PM - Thread Starter
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I may have confused many of you because of the claim, out of my ignorance that I could have been able to receive those PBS channels from Norwood NY. In reviewing the Tvtool report, that PBS transmitter is about 71 miles away, completely out of range of the CM 4228 (60 miles) limit. I have not tried the CM 3412 distribution amp because what I saw early this morning, and reading up on the Tropo-scattering effects of VHF/UHF signals, I now understand the random, sporadic receptions of the NY PBS channels: when they are on, they are on, otherwise there is no signal, period. Unless I change the outdoor antenna to something of longer range, say 80 or 90 miles (if there are such antennas), this current setup won't work.

My apologies for such a waste of bandwidth, however an interesting lesson on VHF/UHF propagation and those Tropo effects smile.gif!
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post #8 of 10 Old 03-15-2013, 05:23 PM
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Quote:
Your observation of 2Edge =>Tropo signals is bang on
Thank you for the feedback that confirms my evaluation. Thank you also for a more accurate tvfool report for your location; I wasn't too far off with my guess.
Quote:
That said, my installer offers a 2-port CM-3412 at a reasonable price
I have a 3412 and a 3410 that I like very much; they seem to be well made.
Quote:
In reviewing the Tvtool report, that PBS transmitter is about 71 miles away, completely out of range of the CM 4228 (60 miles) limit.
Don't take those mileage claims for antennas too seriously; they are merely estimates used for marketing purposes.
Quote:
Unless I change the outdoor antenna to something of longer range, say 80 or 90 miles (if there are such antennas), this current setup won't work.
The only antenna that might beat the 4228 is a 91XG. Why not just enjoy the signal when it is available. Sometimes it can scatter over the terrain obstructions and make it to your location and sometimes it can't.
Quote:
I may have confused many of you because of the claim, out of my ignorance that I could have been able to receive those PBS channels from Norwood NY.
You are learning by experience just like I had to learn, and you DID receive it at times.



You can see in the coverage map above that you are on the fringe.
Quote:
My apologies for such a waste of bandwidth, however an interesting lesson on VHF/UHF propagation and those Tropo effects
Your apology isn't necessary. Every reception problem is unique, we learn from your experience, and it adds to the knowledge bank of the forum.

Good luck with your antenna experiments.

Best regards,
rabbit

If you can not measure it, you can not improve it.
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post #9 of 10 Old 03-16-2013, 04:46 PM
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quote from dta721 msg:
Quote:
I am just curious if it means anything to first boost the signal from the CM 4228 antenna, then split it into 2, one for TV and one for the FM Antenna input?

That way I expect to have strong FM signals, perhaps even more FM stations? But then, do I need to care about the FM radio input in the receiver, if there is any protection for overpower?
Your FM signals are very strong:



That might work; try it. There is a possibility of the strong FM signals causing interference to your VHF TV signals. If that happens, then you would need to have separate FM and TV antenna systems. If you still have the interference to your TV signals from the FM signals, then you will need to use an FM trap in the TV antenna system.

CIII-DT on CH6 might very well have interference from FM signals because it is just below the FM band. Your CH13 TV signal might have interference from FM signal harmonics. Ask roger1818 on the Canadian forum below.

It is a mystery to me why CH6 is used for TV signals in your area with such strong FM signals. IF there was a ham on the frequency allocation board, that probably wouldn't happen.

Have you asked about TV reception on your local Ottawa forum?

ON - Ottawa, Vanier, Gloucester, Orleans - OTA
http://www.digitalhome.ca/forum/showthread.php?t=126059

The FM tuner is probably not any more sensitive to overload damage than the TV tuner or preamp.

If you can not measure it, you can not improve it.
Lord Kelvin, 1883
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post #10 of 10 Old 03-16-2013, 05:41 PM
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The 4228 is a very good UHF antenna and can receive UHF signals up to 75 miles if signals are strong and you have a decent line of sight with no obstructions. And using a good low noise preamp. Mileage claims will vary from location. And it can also receive HiVHF signals if signals are strong, and maybe FM radio. The newer 4228HD is supposed to perform a bit better on HiVHF than the original, which was a top of the line UHF antenna.
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