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Old 21-Oct-2013, 7:29 PM   #1
MetHerb
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Signal loss questions

I've put up a new antenna array and I'm happy with the improved performance but in setting up and playing around under different conditions, I think there are a couple of areas where I could improve and I'm trying to understand signal loss a little more. I have about as much gain as a person can have.

First, I have separate UHF & VHF antenna's and my understanding was that all splitters/combiners suffer from the same signal loss (about 3.5db). However, after some reading, I'm wondering if there is a TV specific diplexer that would give me a lower signal loss.

Next loss question - When I originally ran my coax I had to combine two lengths of RG6 to equal to about 100'. I'm wondering how much signal loss I have (if any) in combining cables and if I would prevent some by shielding the connection. I will be upgrading to RG11 at some point once I settle on a location for the antenna.

Last, I happen to be in the middle of 4 separate television markets and can receive signals from all 4. However, one of the markets is blocked by a large pine tree and I can only get VHF channels from that market. How much does vegetation lower the signal strength? All of the channels in the 290 to 320 range from me are very strong but only come in on the clearest of signal days. Just how much affect does vegetation have!? The tree is about 50' from the antenna.

Thanks for the info...

Dave
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Old 21-Oct-2013, 10:03 PM   #2
GroundUrMast
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There is some variation between loss calculators. However, a conservative estimate of loss at the top of the UHF band would be about 6 dB / 100' of RG-6. RG-11 would come in at about 4 dB / 100'. As the frequency gets lower, so does the loss. By the time you're down to the H-VHF range, the losses are about half that of the upper UHF band.

There's going to be some minor amount of loss associated with a splice, but if you use quality parts and good technique during assembly, there's no advantage or need to provide additional shielding. The estimated losses cited would account for the connectors. Good practice would include protecting connections from water intrusion when they may be exposed.

The best 2-way split is going to come in at about 3.5 dB of insertion loss. 3 dB is the theoretical perfect split of power (no losses in the components). For example, if you put 1 milli-watt of power into a splitter and got 0.5 milli-watts of power out each of the two output ports, the loss inside the splitter would be zero, the sum of the power output would equal the input. But the difference between the input and either output would be 3 dB (a factor of 2 or 1/2 depending on the direction you view it from). 0.5 dB of loss in real world components is doing very well. If your system can't tolerate 3.5 dB of loss, you'll need to add an amplifier ahead of the loss.

Trees are 'wild things'. If the loss was fixed and stable, trees and other vegetation would not pose the problem they do. The signal path fluctuation/variation caused by the movement of the foliage causes the dynamic equalizers in the tuner to have to frequently readjust to the changing conditions, this often results in data errors and loss of signal lock. Bottom line, there isn't a single answer to your question.
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Last edited by GroundUrMast; 21-Oct-2013 at 10:20 PM. Reason: punc.
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Old 21-Oct-2013, 10:35 PM   #3
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What did you use to combine the UHF and the VHF antennas? It should have been a UVSJ, not a reversed splitter.
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Old 22-Oct-2013, 12:49 AM   #4
MetHerb
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Originally Posted by GroundUrMast View Post
There is some variation between loss calculators. However, a conservative estimate of loss at the top of the UHF band would be about 6 dB / 100' of RG-6. RG-11 would come in at about 4 dB / 100'. As the frequency gets lower, so does the loss. By the time you're down to the H-VHF range, the losses are about half that of the upper UHF band.

There's going to be some minor amount of loss associated with a splice, but if you use quality parts and good technique during assembly, there's no advantage or need to provide additional shielding. The estimated losses cited would account for the connectors. Good practice would include protecting connections from water intrusion when they may be exposed.

The best 2-way split is going to come in at about 3.5 dB of insertion loss. 3 dB is the theoretical perfect split of power (no losses in the components). For example, if you put 1 milli-watt of power into a splitter and got 0.5 milli-watts of power out each of the two output ports, the loss inside the splitter would be zero, the sum of the power output would equal the input. But the difference between the input and either output would be 3 dB (a factor of 2 or 1/2 depending on the direction you view it from). 0.5 dB of loss in real world components is doing very well. If your system can't tolerate 3.5 dB of loss, you'll need to add an amplifier ahead of the loss.

....
Thanks for the info all around. What I was considering using to combine the antenna signals was something like a diplexer this that has a low signal loss.

http://www.hollandelectronics.com/ca...-Diplexers.pdf

If I'm understanding the specs properly, I would only be loosing about 0.5 to 0.7db by combining the two antenna's. Is that correct? So if a standard splitter looses 3.5db, would that leave a stronger signal to be amplified by the preamp? I already have a Kitztech Preamp which I've connected directly after combining the signals.

I'd have to evaluate if it would be worth the effort to swap out the cable but by combining that with a lower signal loss in combining the antennas I could add an extra 5db to signal reaching my tuner...is that correct?

I'm also curious what you meant by good technique during assembly. Anything I should know? I'm not a pro...just someone trying to maximize my signal strength and minimize my signal loss.
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Old 22-Oct-2013, 12:52 AM   #5
MetHerb
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Originally Posted by ADTech View Post
What did you use to combine the UHF and the VHF antennas? It should have been a UVSJ, not a reversed splitter.
I'm not exactly sure what that is but it does combine the signals from the VHF and UHF antenna. I get all the UHF channels I had (and a little more stable thanks to new preamp) plus VHF channels that I could not get before. I don't have an issue with what I have - just wondering if some combiners/diplexers have less signal loss.
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Old 22-Oct-2013, 4:41 AM   #6
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The Holland UVSJ would be appropriate as a combiner when you have one antenna serving only UHF reception and another serving only VHF. None of the satellite diplexers would be useful as OTA antenna combiners. Regardless, I can't see any point in worrying about tenths of a dB of difference between different vendors' UHF/VHF combiners.

If you need to overcome the loss of the UHF/VHF combiner, equip each antenna with a preamplifier of it's own (this would be an extreme situation). The gain of the preamplifier will overcome the noise margin 'hit' of the combiner provided the preamplifier is upstream of the combiner. The same is true of cable and splitter losses. If the preamplifier is upstream of the loss, you can ignore the loss and subsequent cost in NM.

Another way of saying this is, The noise figure of the first amplifier in the system is the most important NF. Even if you have long cable runs with many splits, you can overcome all that loss with properly selected amplifiers placed in appropriate locations in your network.

Example: http://forum.tvfool.com/showthread.php?t=13659
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Old 22-Oct-2013, 1:01 PM   #7
MetHerb
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Originally Posted by GroundUrMast View Post
The Holland UVSJ would be appropriate as a combiner when you have one antenna serving only UHF reception and another serving only VHF. None of the satellite diplexers would be useful as OTA antenna combiners. Regardless, I can't see any point in worrying about tenths of a dB of difference between different vendors' UHF/VHF combiners.

If you need to overcome the loss of the UHF/VHF combiner, equip each antenna with a preamplifier of it's own (this would be an extreme situation). The gain of the preamplifier will overcome the noise margin 'hit' of the combiner provided the preamplifier is upstream of the combiner. The same is true of cable and splitter losses. If the preamplifier is upstream of the loss, you can ignore the loss and subsequent cost in NM.
...
Technically I don't need to do anything but I'm trying to learn more about noise and signal loss to have a better setup. I'm thinking that I could possibly gain some additional channels with a little more gain, particularly the channels that are closer to me with strong signals and get a couple of channels more regularly that are farther away and only partially come in.

You are correct in that I have one VHF antenna (AntennaCraft Y10-7-13) and UHF antenna (Winegard HD-9032). I have them stacked appropriately and one coax run to my tuner. What I'm trying to understand is that I know I'm loosing about 3.5db by joining the two antennas - will using the UVSJ joiner from Holland reduce that to just 0.7db? In essence, isn't that a 2.8db gain?

If I combine that with a 2db gain by upgrading the coax cable, wouldn't that be a net 4.8db gain to my setup? That might be enough for me to get some less reliable channels that I receive and perhaps the more local channels that are currently blocked by that one pine tree. I know the signal is there, it's just not strong enough for me to get it regularly. Currently, the weakest stations I can get regularly are -5.5db and I can sometimes get one at -8.6 so just a little gain would give me those channels more regularly. I might also be able get the channels channels in the -12.5db range occasionally so any any little bit helps.

Thanks again....Dave
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Old 22-Oct-2013, 3:40 PM   #8
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Great questions...

Yes, if you are using a common 2-way splitter as a UHF/VHF signal combiner, replacing it with a UVSJ or similar product from another manufacturer will eliminate some needless loss and provide a net improvement to your system noise margin. You also reduce the interference between antennas. This is due to the filters in the UVSJ which are intended to block UHF signals entering the VHF port and VHF signals entering the UHF port. A single band antenna will receive some out of band energy and if allowed to mix with the primary signal from the correct antenna, can be enough interference to cause difficulty.

You're on the right track, trying to improve your system by eliminating unneeded losses, particularly near the antenna, is more effective than throwing active amplification at the problem. Very minute amounts of noise are generated by every atom in the universe. This is due to the fact that they all have moving electrons and each atom moves about even when it's a part of a larger mass. The result is that there is a low level of noise present, sort of like 'sea-level'. Even if there was no signal transmitted, an antenna will produce noise all by itself. That noise can never be eliminated, the desired signal must be stronger than the 'background noise' in order for successful reception to occur. Losses in cable and splitters will lower the level of the antenna noise power before it arrives at the tuner, but the cable and splitters also produce similar amounts of noise, so at the tuner, the background noise level can never drop below the minimum amount produced by the atoms of the cable or splitters. Meanwhile, if the desired signal has been attenuated enough, ratio between desired signal and noise may be too low for the tuner to use.

Again, trees and other vegetation present more trouble than a simple fixed loss. They produce a rapidly fluctuating amount of loss when moving in the wind, that can vary depending on the frequency. Adding passive gain (higher performance antenna, not amplifier gain) or removing loss may help, but there is not a guaranty that added fixed gain will overcome the variable component of the problem.
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Old 22-Oct-2013, 7:38 PM   #9
MetHerb
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Thanks a lot GroundUrMast. That info is really helpful and I do understand about vegetation.

In a situation where you have two different antenna's like a VHF antenna and a UHF antenna, would it be practical to have two pre-amps, one for VHF and one for UHF and have them before the joiner? Or am I doing it correctly in joining the antenna's and then sending them through the preamp and to the tuner?

Outside of what I'm doing, I don't think I can improve on my gain/losses. One change I might make next year is swap out my Winegard HD-9032 for an Antennas Direct 91XG for a slight increase in gain but I think that is about it. I don't see how I could improve on loss prevention unless there is something I'm doing wrong with hooking everything up.

Thanks again!
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Old 22-Oct-2013, 9:49 PM   #10
GroundUrMast
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Quote:
Originally Posted by MetHerb View Post
...

In a situation where you have two different antenna's like a VHF antenna and a UHF antenna, would it be practical to have two pre-amps, one for VHF and one for UHF and have them before the joiner? Or am I doing it correctly in joining the antenna's and then sending them through the preamp and to the tuner?

...

Thanks again!
I would only consider separate preamps to be "practical" if they produced results. If you are already close to reliable reception of a weak signal with one preamp at the output of the UVSJ combiner and are trying to squeeze the last bit of performance from the system (having exhausted all other options of improving net noise margin), then consider the use of separate preamps on each antenna.


Quote:
I'm also curious what you meant by good technique during assembly. Anything I should know? I'm not a pro...just someone trying to maximize my signal strength and minimize my signal loss.
Older crimp type connectors are prone to both 'under-crimping' & 'over-crimping'. If not crimped tightly enough, you get a poor shield connection or even a loose fit the separates from the cable. If over-crimped, you get an impedance change in the cable at that point which can cause loss and signal reflection in the cable. Even with commercial grade crimp tools, variations in connector dimensions would make for trouble. (In my past career in the telecom industry, we used some very expensive Belden crimp tools. We had to be careful to spec the Belden F connector to be sure we got reliable results. I've never been satisfied with the consumer grade crimping options.

The newer compression type connectors are very consistent if you use the correct stripping dimensions and make sure there are no scraps of wire or foil left to short the center conductor to the shield. The connector should not need a great amount of force to slide onto the prepared cable end. If you have to use lots of force, you may be snagging the shield or core insulation. You can look down the barrel of the connector to align the axis of the connector ant the cable as you push the two together.
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Last edited by GroundUrMast; 22-Oct-2013 at 10:13 PM. Reason: connector assembly, sp.
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Old 7-May-2014, 2:00 AM   #11
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Originally Posted by MetHerb View Post

You are correct in that I have one VHF antenna (AntennaCraft Y10-7-13) and UHF antenna (Winegard HD-9032). I have them stacked appropriately and one coax run to my tuner. What I'm trying to understand is that I know I'm loosing about 3.5db by joining the two antennas - will using the UVSJ joiner from Holland reduce that to just 0.7db? In essence, isn't that a 2.8db gain?

Thanks again....Dave
when you use a splitter, you do not loose 3.5 DB, in fact you loose .5DB. the 3DB difference comes from the fact that the splitter split the signal in 2, each output has half the power or -3DB.

You can even use splitter to combine 2 identical antennas, this in theory double the power or +3DB minus losses equal +2.5DB.

Bur when you combine a VHF and a UHF antenna you have to use a VHF/UHF combiner to prevent one antenna influencing the other
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