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Old 6-Aug-2016, 10:22 PM   #1
crashHD
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How much preamplification do I need here?

TV Fool report: http://www.tvfool.com/?option=com_wr...e2cbce2acb6e02

I have a brand new db8e I'm planning on pointing due west. All the stations I'm concerned with picking up are either in a direction between 270 and 279 except KMOS, which is so damned powerful I don't need to worry about it, it will come regardless of where I point the antenna.

I need a preamp. I will have roughly 50 or 60 feet of cable from the antenna to the main splitter. From there split off to 4 different locations. There may possibly be a second split at some of the TV's to feed a DVR, and also the TV's own tuner.

My current setup is what the house was equipped with when I bought it. It works well enough, most of the time, but suffers in wind and inclement weather. It's a very old uhf/vhf yagi type antenna, a very old winegard preamp, a recently (4 yrs ago) HDA-200 distribution amp.

I'm pointing at the KC tv market. They are all UHF since the end of analog. What I've got to work with is a roughly 30 foot antenna tower, a brand new DB8e, a roll of new rg6quad cable, and good compression type ends (running new cable everywhere). To the best of my knowledge, the only thing my plan is lacking is the selection of a good preamp. Within reason, price is not an object, as I'd rather pay for the best one now, than do this again.

I'm leaning toward one of the kitztech preamps. There's one that is a straight 24 dB gain, and one adjustable 0-36dB gain. I don't want to do much adjusting, as I intend to climb the tower as few times as possible, but if I can dial it to the max and 36 dB isn't too much, I'm ok with that. I just don't know if there's a way to tell from a tvfool report how much amplification will be overamplification.

Also, confirm if I'm correct on this, but if possible, I would do better with a preamp strong enough that I don't need to use a distribution amp, right?

Thanks!

Last edited by crashHD; 6-Aug-2016 at 11:24 PM.
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Old 7-Aug-2016, 4:20 AM   #2
GroundUrMast
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I'd lean towards the Antennas Direct 'Juice' or an RCA TV1PRAMP. Remember, preamplifier gain does not add to the gain of the antenna, it only deals with loss and noise sources on the output side of the amp.

The DB8e is an excellent choice based on the report you've posted, so focus on making the most of it by locating it in a spot that has the least obstructions and be willing to experiment with height as well.

Using the single best tuner you've got and a coax run that is just enough to connect the antenna to the tuner, verify your results with no amplifier first... Then, once you know you have a usable signal at the antenna, add the amplifier to push that hard won signal to each TV in the house.
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Old 7-Aug-2016, 11:25 AM   #3
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Quote:
It works well enough, most of the time, but suffers in wind and inclement weather.
That symptom suggests that trees are your problem, not the antenna. If you do not or cannot address this issue replacing the antenna may turn out to be a disappointing adventure... or not. It is impossible to guess accurately when trees are in the signal path.

Quote:
I'm leaning toward one of the kitztech preamps.
Don't. The single stage ones overload too easily and the adjustable gain one, as I commented elsewhere last year after running one through my lab, appeared to have no reason for even existing.

Quote:
I would do better with a preamp strong enough that I don't need to use a distribution amp, right?
Not necessarily. Sometimes, it's better to use separate amps, sometimes it's better to use a single amp, sometimes it doesn't matter. Your reports suggests that it likely won't matter.

Quote:
How much preamplification do I need here?
Most consumers use the wrong factors in selecting an amp, they simply get the one with the highest gain number they can find assuming the bigger is better so the highest gain amp has to be the best one. This selection logic is usually wrong about 90% of the time. The easiest method of selecting the gain of a preamp is to account for the total insertion loss in the distribution system and just round up to the next closest available amp. Since most consumer installs have less than a 100' of coax (~5.5 dB/100') and a 4 (or less) port splitter (~8 dB), that usually means that a 15-20 dB amp is almost always the most appropriate choice, again, for probably 90% of folks. Higher gain amps should be reserved for those situations where there a larger distribution systems and weaker signals or some combination thereof. Higher gain amps tend to be more susceptible to overloading so they must be used with caution in locations where there are strong local signals, including those outside the TV broadcast band.

Save yourself some hassle and mount the preamp down lower on the tower where you can reach it from a ladder or even the ground. You'll sacrifice just a bit of your system noise figure, but you'll make it simple to service or experiment.

We've been out of stock on the Juice for several weeks, but we have a replenishment shipment due to hit the warehouse any day now. It should be available shortly.
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Old 7-Aug-2016, 12:14 PM   #4
crashHD
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Quote:
Originally Posted by ADTech View Post
That symptom suggests that trees are your problem, not the antenna. If you do not or cannot address this issue replacing the antenna may turn out to be a disappointing adventure... or not. It is impossible to guess accurately when trees are in the signal path.
Trees could be an issue with wind, but I'm not so convinced about weather. Dropouts due to weather could be clear skies locally at my house, but heavy thunderstorms 20 miles west of me, between my antenna and the transmitter.
The current old antenna sits atop a broken rotator and tends to swing it's aim by 15 degrees when the wind is just wrong. Also when it's not windy, it tends to set at an aim that is about 20 degrees (visual estimation) from what tvfool signal maps would suggest is optimal.
I'm not thrilled about having to pull through the trees, but I'm not able to clear them with what I have, so I'm going for as high as possible. I'm hoping the DB8e might be better at rejecting some of the multipath I think I'm getting from tree limbs.
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Originally Posted by ADTech View Post
Don't. The single stage ones overload too easily and the adjustable gain one, as I commented elsewhere last year after running one through my lab, appeared to have no reason for even existing.
Thanks for the heads up. The AD juice unit looks good. First glance at it's webpage didn't show any gain or noise figures. It looks like a good tough weathertight enclosure. It looks to me like it's made to mount to the mast, and maybe even heatsink through that mounting, which I like a lot better than what with the kitztech ones looked like they simply furnished a PVC box to mount it in.
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Originally Posted by ADTech View Post
Not necessarily. Sometimes, it's better to use separate amps, sometimes it's better to use a single amp, sometimes it doesn't matter. Your reports suggests that it likely won't matter.

Most consumers use the wrong factors in selecting an amp, they simply get the one with the highest gain number they can find assuming the bigger is better so the highest gain amp has to be the best one.
I don't disagree with that, but that's not the direction I was going, although upon further consideration I may still have not been on the best track. I was looking for the preamp with the lowest noise figure, as much like the fact you can't amplify into existence a signal that isn't there, noise introduction is also not removable once introduced. If I can get a low noise preamp with enough strength to cover my distribution strength needs as well, that should eliminate the noise introduction of a distribution amp, should it not?

Quote:
Originally Posted by ADTech View Post
This selection logic is usually wrong about 90% of the time. The easiest method of selecting the gain of a preamp is to account for the total insertion loss in the distribution system and just round up to the next closest available amp. Since most consumer installs have less than a 100' of coax (~5.5 dB/100') and a 4 (or less) port splitter (~8 dB), that usually means that a 15-20 dB amp is almost always the most appropriate choice, again, for probably 90% of folks. Higher gain amps should be reserved for those situations where there a larger distribution systems and weaker signals or some combination thereof. Higher gain amps tend to be more susceptible to overloading so they must be used with caution in locations where there are strong local signals, including those outside the TV broadcast band.
I'll be about 60 feet from the antenna to the 4 port splitter, then each TV will have at most another 40 feet run to the wall, probably (undecided yet) one more split in two to feed both the Tivo and the TV's tuner (does a dual tuner DVR count as a split?)

That makes roughly 100 feet total of cable(~5.5dB), one 4 way split (~8dB), and one two way split (~3.5dB?) That gives me 17dB, right? Plus a little extra because I think I have room then without hitting overload, so a good preamp here would be something in say 20-24dB, with the lowest noise figure I can find?
Quote:
Originally Posted by ADTech View Post
Save yourself some hassle and mount the preamp down lower on the tower where you can reach it from a ladder or even the ground. You'll sacrifice just a bit of your system noise figure, but you'll make it simple to service or experiment.
I like that idea. I'm willing to climb the tower, but not looking forward to it. Just 10 feet down from the antenna would make a lot of difference, without adding enough cable to induce a meaningful quantity of signal loss.
Quote:
Originally Posted by ADTech View Post
We've been out of stock on the Juice for several weeks, but we have a replenishment shipment due to hit the warehouse any day now. It should be available shortly.
Thanks!

Last edited by crashHD; 7-Aug-2016 at 5:30 PM.
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Old 7-Aug-2016, 12:23 PM   #5
crashHD
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I'm not sure what to call it, but my antenna tower is just that common three-pole truss type structure, set in concrete at the base. Is there any reason I need some sort of J-mount, or if I can hit the aim I'm looking for, while doing so, can I just clamp it to one of the tower tubes? I know nearby metal can affect things, but with a bowtie such as this DB8e, don't the screens on the backside block anything from affecting it from the rear?
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Old 8-Aug-2016, 12:18 PM   #6
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Well, I got an AD Juice preamp ordered today. Hopefully I can get this wrapped up by the weekend.

Initially I'm going to point both panels west for best signal on the KC stations. If that works well, with signal margin to spare, I may try pointing the second panel at Columbia. It has one VHF Hi station that I don't expect to pull in, but all the rest are UHF. It would be neat to get the stations from both cities.
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Old 8-Aug-2016, 2:44 PM   #7
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I was looking for the preamp with the lowest noise figure, as much like the fact you can't amplify into existence a signal that isn't there, noise introduction is also not removable once introduced.
That is correct, the preamp noise reduces the SNR of the signal coming from the antenna. But it is more than made up for by the reduction in the system noise figure which makes it possible to receive signals with a lower NM. Otherwise, there would be no point in using a preamp.
Quote:
If I can get a low noise preamp with enough strength to cover my distribution strength needs as well, that should eliminate the noise introduction of a distribution amp, should it not?
Yes, when you are using a preamp AND a distribution amp, the noise from the distribution amp (IF you really need it) will be buried in the amplified noise floor as is the tuner noise.



Quote:
Initially I'm going to point both panels west for best signal on the KC stations. If that works well, with signal margin to spare, I may try pointing the second panel at Columbia. It has one VHF Hi station that I don't expect to pull in, but all the rest are UHF. It would be neat to get the stations from both cities.


That might not work too well; you will just have to try it. There are 3 problems with that:

1. You will lose about 3 dB of antenna gain for signals from the west, because there will only be one panel aimed in that direction.
2. You will lose the front-to -back ratio of the DB8e that protects the preamp from partial overload. Partial overload can produce distortion products that might mask your weakest signals because they raise the noise floor.
3. In spite of what marketing departments say, aiming the two panels in different directions doesn't always work. The same signals from each antenna can interfere with each other if they don't arrive at the combining point in phase (at the same instant). According to ADTech, it has the best chance of working if the two directions are at a right angles (90 degree apart).

It might not be as neat as you think it will be.
Attached Images
File Type: png NMdiagOutdoorRev.png (62.2 KB, 1432 views)
File Type: jpg crashHDTVFmap.JPG (72.9 KB, 927 views)
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Last edited by rabbit73; 8-Aug-2016 at 3:39 PM.
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Old 8-Aug-2016, 3:13 PM   #8
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When UHF stations are nearly opposite each other, one is usually better off simply removing the reflector screens off bowtie antennas rather than trying to aim one panel or antenna in each direction. That makes the antenna bi-directional and eliminates combiner, reflection, and re-radiation losses.
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Old 9-Aug-2016, 2:55 PM   #9
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Originally Posted by ADTech View Post
When UHF stations are nearly opposite each other, one is usually better off simply removing the reflector screens off bowtie antennas rather than trying to aim one panel or antenna in each direction. That makes the antenna bi-directional and eliminates combiner, reflection, and re-radiation losses.
I was going to suggest that. I have a similar tower distribution and get reception from channels up to 50 miles from both sides of a 4 bay bow tie antenna with no reflector.
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Old 9-Aug-2016, 5:23 PM   #10
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Yeah, that strategy usually works well as long as there is no severe multi-path situation.
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Old 10-Aug-2016, 12:47 AM   #11
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I've considered removing the reflectors. I thought that made a bowtie bidirectional, but wasn't sure until it was confirmed here.

I'm hesitant to do that for a few reasons.
The antenna has a lifetime warranty I'd kind of like to be able to collect on if it ever has a problem (wouldn't be the first antenna around here that failed to stand up to wind on top of a tower). I think modifying it in such a manner might void the warranty.
The backside stations aren't that important. Most of them are duplicates of networks already received. My interest in trying to pull them in is...I don't really know how to explain it, but just because I think I can.
Lastly, this antenna isn't going to the top of the tower, so removing the reflectors would mean the backside reception has the antenna tower in the way. I'm not certain what effects this will have, but I'm going to assume it would not be helpful. If I wanted to attempt reception in this manner, would it be worth the effort to make an offset mount, such that the antenna is either to the north or to the south of the tower, and thus the tower is not in either the east or west signal direction? Or would the tower's effect be negligible (not what I would guess, but admittedly beyond my experience at this point).
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Old 10-Aug-2016, 1:21 AM   #12
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I think modifying it in such a manner might void the warranty.
We're not sticklers on such details. I frequently make that specific recommendation.

It's hard to say how much of an effect the tower's structure might have. FWIW, it's normal to install most antennas on the TOP of a tower if it's the only thing up there.
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Old 10-Aug-2016, 9:53 AM   #13
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The current antenna is on a rotor, at the top. If this DB8e gets solid reception of the west stations, I'm toying with the idea of fixing/replacing the rotor and putting a good UHF/VHF long range antenna back up there. I would leave it usually pointed to the east. There are two stations in the VHF Hi range to the east, the weakest one being about -8.3dB NM according to tvfool. I'm not trying to pull them in right now, but I think I would enjoy trying to see if I can pull them in after I've managed reliable reception of the UHF stations in the west.
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Old 10-Aug-2016, 5:40 PM   #14
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Originally Posted by crashHD View Post
The current antenna is on a rotor, at the top. If this DB8e gets solid reception of the west stations, I'm toying with the idea of fixing/replacing the rotor and putting a good UHF/VHF long range antenna back up there. I would leave it usually pointed to the east. There are two stations in the VHF Hi range to the east, the weakest one being about -8.3dB NM according to tvfool. I'm not trying to pull them in right now, but I think I would enjoy trying to see if I can pull them in after I've managed reliable reception of the UHF stations in the west.
The DB8e, (with reflector), has about the longest range, (gain) of almost all the other UHF antennas out there.

If you only want UHF from the west and VHF from the east, I'd put the DB8e on top aimed at your westerly stations and a VHF 4 feet below it aimed at your easterly stations then combine them with a UVSJ, or a pre-amp with a separate VHF/UHF inputs.
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Old 12-Aug-2016, 10:35 AM   #15
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Well, I got the antenna up last night. It's not all the way up, it's about halfway up the tower. I'm a little squeamish about heights, and it's temporary. Amazon screwed up delivery on my order of a juice preamp and rg6 compression fittings, so I'm delayed anyway.

At "half-mast", when plugged into a single device using the shorted possible coax, it is almost as powerful as my current antenna, which is preamplified, distribution amplified, and connected to every TV in the house. I think when I get this antenna up to it's final mounting spot, and get it preamped, it should do pretty good.

To see if I really needed an amp, I connected it to the distribution cabling, instead of the single tuner. Signal quality dropped to unusable. I then added back in the distribution amp, and then signal throughout the house was comparable to the unampliefied signal on a single tv.

I don't have any further questions or need anything else, I just like to provide followup when I have been helped. I'll update again as this project nears completion. Thanks everyone, you have been so helpful.
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Old 14-Aug-2016, 2:05 AM   #16
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So I'm working this in steps. More progress tonight. Antenna is further up the tower.



I'm a little squeamish about heights, but it's getting easier to climb the tower each time I go up. I'll have to go a few more times before all is said and done.

It's about 10 feet taller than before. I was able to watch the signal strength during some weather (before raising it further to the pictured height). wdaf and kctv cut out in rain, and stayed out until after the tree leaves were dry (antenna was not clear of the trees in the front yard).

Currently, the antenna is nearly above the tops of the nearest trees. The absolute peak of the tower would be almost level with the tops.

Still no preamp installed. It came in the mail the other day, but I want to watch my signal for a few days first, with a single tuner installed.

Signal strength on this DB8e (unamplified, connected to single device) is equal, to slightly better than the old antenna on the top (preamped, distribution amped, and connected to whole house (3 tvs, 3 dvrs).

How close can it get to the top antenna before they affect each other? Ultimately, once the DB8e proves reliable, it will get connected to all the tv's in the house, and I will experiment with turning the top antenna east and seeing what comes in. Does the direction they are pointed have any connection to how close they can be?
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Old 14-Aug-2016, 11:32 AM   #17
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Thank you for the tower photo; it's always interesting to see how others do it.

Please try to keep the width of a photo to 800 pixels or less; Any wider and the posts get so wide that the type gets too small.
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Old 14-Aug-2016, 11:39 AM   #18
crashHD
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I don't know if it was right, but I just clamped the antenna directly to the leg of the tower.

It's been discussed, that removing a bowtie's reflectors makes it bidirectional. I am considering that, but does anyone know if removing reflectors has ramifications on signal strength, or mulitpath rejection? I'm not willing to give up much signal, and my signal path is unfortunately skimming a few treetops, so any reduction in mulitipath resistance may be a heavy penalty.
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Old 14-Aug-2016, 12:58 PM   #19
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Thank you for resizing the photo; much easier to read the posts.
Quote:
How close can it get to the top antenna before they affect each other?
The general rule is 1/2 wavelength for the lowest frequency used. See the attachment.
Quote:
Does the direction they are pointed have any connection to how close they can be?
Yes, when the elements are parallel to each other the interaction is greatest because the coupling is the greatest. When the elements are at right angles, the interaction is minimum.
Quote:
I am considering that, but does anyone know if removing reflectors has ramifications on signal strength, or multipath rejection?
Removing the reflectors makes the antenna bi-directional. but costs you about 3 dB in gain; there is no free lunch.

Removing the reflectors probably will not change the multipath caused by the scattering of the signal as it passes through the trees, but the antenna will be less able to reject multipath reflections from other directions.
Quote:
I don't know if it was right, but I just clamped the antenna directly to the leg of the tower.
For minimum interaction, the tower should be behind the reflector; IOW
incoming signal > bowtie elements > reflector > tower
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File Type: jpg Antenna Spacing Chart2.JPG (112.3 KB, 322 views)
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Last edited by rabbit73; 14-Aug-2016 at 1:05 PM.
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