Confused: Televison Pre-Amplifier or Distribution Amplifier Needed?

Thread Starter

PGB1

Joined Jan 15, 2013
110
Hello All!
I apologize if All About Circuits is not appropriate for this question, but I thought this would be the group from which to get the most educated answers. Also, I hope this is in the correct section of the forum.

In our home, we use antenna for television. Many stations will pixelate when the weather is windy or rainy. Those are usually the stations where the signal meter on the TV shows few bars (Such as these type of meters are...). Sometimes even the strong statins go wonky. The weak stations are about 18 miles north-east, as the crow flies and the strong ones 2 miles south-west. On occasion, it is backwards. The close stations are goofed up and the far ones work well.

I searched on line and found conflicting advice whether a pre-amplifier or a distribution amplifier is the proper device to help with the problem.

The Set Up:
Antenna is indoors - 3 Feet to a 15 dB distribution amplifier - 35 Feet to a 3-way splitter with (-) 3.5 dB loss - 30 Feet to a TV. From the same splitter, 40 feet to a splitter (-) 3.5 dB. Then 20 feet to another splitter (-0 3.5 dB & to a TV - Same splitter goes 20 feet to a (-3.5) splitter, then 6 feet to a TV and same splitter 18 feet to a TV.

The amplifier is one the cable company left behind. The frequency range marked on it covers the UHF & VHF frequencies.
All wiring is RG-6

As you can see, there are many splitters and lots of connectors. I wish all were home runs, but re-wiring is not an option (per SWMBO).
But still I am confused if a pre-amplifier at the antenna or a larger distribution amplifier at the antenna (or elsewhere) is proper.

Thank You for your advice and for sharing knowledge. It is much appreciated.
Enjoy This Day!
Paul
 

crutschow

Joined Mar 14, 2008
24,066
What kind of antenna?
Where is it located in the house?
An attic location is best.

Do all the TVs act up at the same time or only those going through the most splitters?

You many need to add another amp at/near the antenna.
 

nsaspook

Joined Aug 27, 2009
6,704
If this is about US DTV then the problem is usually multi-path (rapidly changing signal phase-shift interference) with strong stations. A pre-amplifier or a distribution amplifier won't help with this problem because it will only amplify the reflections. What you usually need is a high gain directional antenna to reduce the reflected RF energy to a point the TV receiver can filter (blind equalization) out multi-path and provide a strong selective signal for weak stations. Sometimes for strong signal multi-path a variable attenuator works. In your case I would first see how the stations look without the distribution amplifier during picture pixelation.

https://blog.solidsignal.com/tutorials/what-is-multipath-and-what-can-i-do-about-it/
 
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Thread Starter

PGB1

Joined Jan 15, 2013
110
Thanks Crutschow & Nsaspook for taking time to reply & educate!

It is US DTV.
The current antenna is a home made vee-arm type. As an alternate, a home made fractal type is sometimes swapped in place of the vee-arm. (Photos attached. The fractal's back piece in the photo is plastic, not metal.) Regarding reception, there does not seem to be much difference between the two home made units. They both work better than the store bought units that we've tried.

The antenna is in a second floor (attic level) bedroom, near a window. That window faces the far away stations. Unfortunately the adjacent attic and other 2nd floor room have radiant barrier in the walls and ceilings. Antennas don't work well at all in those rooms.

It's interesting that usually all act up at the same time- even the one that is closest to the antenna with only one splitter between it and the antenna.
Just to confuse things, three TV sets are TCL brand and one is a discount store brand.
Once in a great while, the discount store TV will have a good signal, but the other three will mess up. It is about midway, cable feet & splitter wise, between the other sets. (In normal use, at most two sets are on at one time. Turning more on or off does not change the problem.)

Your explanation, Nsaspook, about multi-path is excellent & quite interesting- as is the linked article. It kind of reminds me of the old days when the analog TV would have two pictures of the same program at the same time, but offset by a fraction.

I'll test your suggestion of removing the amplifier during pixelation. If I understood your explanation correctly, this will help me determine if the problem is multi-path or weak signal.

Failing success without an amp, I'll try what you suggested Crutschow and add an amp near the antenna. At first I thought about trying a second amp after a down-stream splitter, but remembered that even the closest TV will mess up.

I wonder if I have two things going on at once: Multi path for the stronger stations and weak signal for the weak ones.Current Antenna.JPGAlternate Antenna.JPG
 

nsaspook

Joined Aug 27, 2009
6,704
There are times when old school antennas are best. I had bad multi-path problem with the 2nd-generation ATSC 1.0 receivers during the analog changeover.
https://forum.allaboutcircuits.com/threads/retiring-the-radioshack-vu-190-tv-antenna.161631/

These types of reception problems were discovered at the beginning on ATSC transmissions so receiver chip manufacturers used various DSP methods to reduce the sensitivity of US DTV to signal phase changes. Some were at lot better than the original generation receivers.

The future ATSC 3.0 standard will switch to ODFM (this was one of the original recommendations instead of 8-VSB), this should help to eliminate most of the multi-path issues.
https://www.edn.com/design/communications-networking/4359108/8-VSB-versus-OFDM-morethan-a-tempest-in-a-TV-
Nevertheless, OFDM advocates offer a plausible explanation for their system's claimed advantages—at least in densely populated urban areas. A key consideration in designing OFDM, but not 8-VSB,was immunity to multipath interference—particularly dynamic multipath, such as that which occurs when signals bounce off airplanes and moving vehicles.
There are a few hacks you can try.
https://www.instructables.com/id/HDTV-Multipath-Shield/
 

ronsimpson

Joined Oct 7, 2019
400
A directional antenna helps but you need more information. Here is a map of the TV stations at my house. There are antenna clusters on mountains at SSSW and NNW. In my case pointing the antenna South and slightly West increased the signal for many stations and I lost two from the SSE. Good trade.

I am thinking about adding a antenna for NNW but most of those stations are repeats or are delayed one hour.
I stood outside with this map and moved the antenna around. Found that East there is a movie channel that is really nice but I loose almost all other stations.

Click on the link and add your address. I think it only works in the US.
tvfool link
1572633852346.png
 

Thread Starter

PGB1

Joined Jan 15, 2013
110
Thank You All Very Much for your help and also for the education I received from this thread. I appreciate your time & effort.

After studying the articles that NSASpook linked, I got very interested in multi path problems. Even if I figure out how to get good reception, I certainly plan to experiment with Farady cages (for fun & knowledge).

Since the signal indicator (of dubious accuracy) on the TVs shows lower-than-when-good signals when the stations pixelate, I'll try an amplifier at the antenna. Failing success, I'll try moving it to various post-splitter locations. Perhaps an FM trap will be beneficial, as there are FM transmitters where the closer set of broadcast towers are located.

Plan B will be to make a second, identical antenna and put a reflector between them. Hopefully it will reflect lost signal back to the antenna. Right now if I slip in a piece of aluminum behind the antenna when it faces a station the signal bars improve a bit, but not by much. One bar on a five-bar scale gets added, but it flickers on & off.
As expected, the signal bars on the opposite compass facing stations went to zero. (The groups of stations' transmitters are almost 180 degrees opposite, with one we don't watch at 90 degrees to both.)

If I end up with a good, strong signal, but pixelation, I'll attack from the multi-path thought. Perhaps that is time to introduce a variable attenuator. (Or Faraday cage)

I suppose the worst case scenario is a roof top antenna, perhaps a rotating one. Where my wife's parents lived in the middle of nowhere Michigan I installed a rotating roof top unit because they had one station facing north and one facing south. That was great until both stations ended up being on the same network. (Next came satellite.)

All in all, at least we're watching TV for free!

Thank You All again for helping. If I am able to do the experiments and have tenable results soon, I'll post my findings with the hope that it will be of benefit to someone, someday.

Enjoy This Day!
Paul
 

bertus

Joined Apr 5, 2008
20,227

drc_567

Joined Dec 29, 2008
757
... One possible low cost modification to try to eliminate higher frequency channel reflections is to construct a 3 turn coil, maybe 6 or 7 inches in diameter out of excess RG-6 cable, placed between the antenna and the digital converter box. I'm not certain, but that particular coil element in the antenna feed line may serve to attenuate the multiple reflections that are a problem. Wire ties are useful to hold the 3 coil loops together. The coil assembly possibly serves as a series inductor and reduces the reflection interference.
... This is a subjective recommendation since no numerical signal strength readings were taken. However, the full scale channel reception here is now of acceptable quality.
It was necessary to place the antenna outside on a porch, at a distance of 10 or 12 feet, since walls reduced the overall signal strength.
 

MisterBill2

Joined Jan 23, 2018
4,846
Here is an approach from a different direction: How many TVs do you really have? That was a whole long list of splitters and I am wondering if you could replace splitters with just couplers and abandon the unused coax sections. But since it seems that al sets fail at once, probably either a preamplifier or a better antenna is needed. Multipath problems are mostly constant, except for the rare refelections from aircraft and such. The fact that rain and wet seem to cause the problem certainly points to a poor signal. A better antenna with a rotator would be an ultimate fix,
And one more suggestion is revisiting all of the connections and making certain that they are snug and in good condition. One poor connection with a failed shield can ruin it all.
 
I don;t think there is much to do about penalization. Satellite TV is prone to it. Rain between you and the antenna does it all the time.

You always want o amplify a signal when it's the best (at the antenna).

Line lengths should be kept the same and symetric. That 6' line might need an attenuator.

Taps are way different than splitters.
 

nsaspook

Joined Aug 27, 2009
6,704
I don;t think there is much to do about penalization. Satellite TV is prone to it. Rain between you and the antenna does it all the time.

You always want o amplify a signal when it's the best (at the antenna).

Line lengths should be kept the same and symetric. That 6' line might need an attenuator.

Taps are way different than splitters.
Satellite TV (C, KU, KA band) goes down in rain because of increased link losses as do terrestrial radio links (I ran lots of microwave links in the tropics). If a DTV reception problem is just a case of low signal strength, gain based solutions would be easy but unfortunately multipath is a very real problem in many cases where signal strength is good. Modern DTV receiver systems use an Adaptive_equalizer to reduce the level of none gain related intersymbol interference problems.
https://www.vocal.com/video/equalizer-for-atsc-digital-terrestrial-tv-receiver/
https://transition.fcc.gov/oet/info/documents/reports/TR-05-1017-ATSC-reception-testing.pdf
The tested receivers fall into two distinct tiers of multipath-handling capability—the upper tier representing a significant performance improvement associated with at least two companies’ newest generation of demodulator chips. While the difference in ability to handle difficult multipath conditions between the two tiers is large, linkage of the current results with earlier field test results (Chapter 7) suggests that the observed performance differences are of no consequence in the vast majority of reception locations, if an outdoor, mast-mounted antenna is used. When an indoor antenna is used, the linkage suggests that the observed performance differences would be significant in many, but probably not most, locations. Given that both tiers of performance appeared in all three price ranges of DTVs, there appears to be no price dependence of multipath performance; however, there was a complete absence of upper-tier performers among the tested set-top boxes. This absence is attributed to the older designs of the set-top box products—all of which were introduced in the year 2004 or earlier. Among the tested DTV receivers, none that were introduced before March 2005 were found to exhibit upper-tier performance, whereas 48 percent of those introduced in or after that month performed at the upper tier
 

SteveSh

Joined Nov 5, 2019
104
If you're going to use a pre-amp, it's best to place it as close to the antenna as possible (as someone else stated). There's a figure of merit used by RF/microwave folks called noise figure, and the lower this is for a given system, the better. A good way to minimize the noise figure, all other things such as the amplifier being the same, is to minimize the losses between the antenna element and the first amplifier. Therefore the recommendation to mount the pre-amp at the antenna.

Also, the original poster said that some of his stations (the stronger ones, I believe) are only 2 miles away. If these stations are pixelating/blocking, I would not think lack of signal strength is the problem.
 

Thread Starter

PGB1

Joined Jan 15, 2013
110
Thank You All Again for helping & teaching.

When the close stations pixelate, the signal strength meter on the TV (of questionable accuracy) drops. The far stations do likewise. That makes me believe the problem is temporary low signal caused by rain or wind, etc.

Confusing me is that one television of a different brand than the others suffers less from pixelating. Is that a stronger tuner or a tuner better able to reject multi path signals?

Perhaps we have both low signal AND a multi path problem. After studying all the linked articles you all posted, I can see how both can occur at the same time and by the same weather events. I think I have to consider both possibilities. I'll attack the far away station problem first (from the standpoint of low signal strength).

It's time to experiment!
Today, I'll take a better look to see if I can ditch some splitters in favor of couplers, as MrBill2 suggested, shunting around splitters with cable. I'd love to ditch all the loss that I can.

I think the following step will be to make a second antenna and put them back-to-back with a plane between. Perhaps I'll try to mimic the antenna that Bertus linked. It's is lucky that the stations' towers are 180 degrees apart.

Then, I'll consider assembling a MAR-3, using the helpful link Bertus posted as my guide. (Or buy one, but building is more fun.) Thanks SteveSH for the reminder of placement.

I sure am learning a lot from you all- and appreciating it!
 
There is an attenuation based on frequency too. See: https://www.multicominc.com/wp-content/uploads/Attenuation.pdf Your antenna has gains at different frequencies too. The gains are quoted relative to a simple dipole antenna.

The signal path like LOS (line of sight) that you get from TV-fool could also come into play.

That's why you would like to keeps the lengths about the same. Too much signal usually means no signal.
You also want to terminate unconnected ports. This minimizes reflections. An unterminated port could generate multi-path type interference. This is less likely with a system designed using taps. Here https://www.cisco.com/c/dam/en/us/products/collateral/video/traditional-size-taps/product_data_sheet0900aecd806c7ab0.pdf is an example of a tap.

There are two methods of distribution. Taps and splitters.

Some amplifiers have 'tilt compensators" and variable gains. You have attenuators that can adjust line lengths. There can be possible cell phone interference.

I had a decent distribution for 8-12 locations and then something happened. It wasn't characterized until recently, so I don't know what exactly I had.

Before a frequency re-assignment, I was able to measure ATSC gain (dbmV) at various frequences at 3 points in my system. A lot of channels moved to VHF.

1. Antenna = Winegard HD 8200U
2. About 30' from antenna in attic after before power injection to a mast mounted Channel Master CM-7777
3. Then probably 40' to distribution. I have a TV tat's easy to connect at this point.

1 & 2 were not done at the same time, but were done the same day. 3 was done on a different day.

Not sure if I had an amp at point (2).

Gain from 1 to 2 done by subtraction. They were not consistant, so I want to replace that amp. I bought one with a very low noise figure, but it is not installed. It has a little lower gain.

A tV at point (3) performed fairly well, but when about 30-40' of lead was added to the most used TV, it's not enough gain. Need about 5db.

I haven't checked the other locations. All but 2 TV's use a DTV converter box.
e.g.
1. Liv room (main TV)
2. Kitchen
3. bedroom
4. Basement kitchen
5. Shop1 (for aiming antenna primarily)
(these I would like to work)

6. Slingbox (not used presently) An ATSC/IPTV modulator would replace it.
7. VCR/TV (Not used presently) Monitor is broken
(Was able to broadcast NTSC on channel 4 throughout the house)
8. Porch (never hooked up for ATSC)
9. Rec room (Never hooked up for ATSC)
10. Bedroom2 (Low voltage ports exist - not wired) Old TV exists in room.
11. Bedroom 3 (Nothing) This would have to be a wall mounted TV
12. (blank) --> probably to IPTV and modulator

I have an Internet controlled TV tuner and IPTV receiver.

Life has changed.

Distribution was then a 30-45 db amplifier (Commercial) connected to four 4-way 24 db taps.

Something happened with the ground on the amplifier and, I think, the gain control went south.
What did happen is that the 120 V power wiring to the main distribution amplifier had a poor ground. The wires were twisted in an outlet box, but never wire-nutted. That ground oxidized. It was really tough to find.

Plans (concurrent):

A
1) Put a pre-amp and attenuator in the attic (initially set for 5db)
2) replace mast mounted amplifier

B)
Check out each location and re-scan

C)
Check each port and use terminators for unused locations.

D)
Check out/repair or replace 30-45 db amplifier (Not cheap)

E)
Possibly add a signal combiner for a single channel antenna

F)
Not related
Mount an active antenna for an AM/FM internet controlled dual tuner

G)
FM only antenna on the other side of the house. There is a separate UHF and VHF antenna there with a broken rotator (wiring) and a wire is off of the VHF antenna.

H)
very long term plans: Be able to read antenna position via an accelerometer for a web browser.
Be able to read antenna rotator display in a web browser. Control from an IR repeater which I have now.

I)
Complain to FCC and Samsung that the FCC needs to define what I TV has to do.
The 55" Samsung TV doesn't know how to handle Daylight Savings Time automatically. It does not know how to handle a rotator. Only clobber all and re-scan is available. Not sure it knows how to handle an audio only channel.

J
I need to calibrate antenna orientation with Rotator compass.

h
Need to be able to do signal injection from the modulator.

i)
Add a tripp-lite surge supressor to the main antenna pre-amp.

==

So, each 4-way tap should suck off 1.5-2 db from the main line and the shorter path lengths should be the last taps. Each port sucks off 24 db, so that's why you need the high gain pre-amp.

Before didtribution, I should need up to about 80-100 dbmV of signal for injection and also at each TV.

I thought about RG-11 from the attic to the point of distribution, but I don;t think it will buy much.

I got 1000' of RG-6 for free but I did not realize it was copper clad wire. This is extensively used for Satellite TV.

The rotator is an Eagle Aspen Rotr 100 which is really cool. It sends power and DiseqC positioning signals on coax. I have 2 Coax feeds: power and positioning signals and TV. A short section of the Coax is for power to the pre-amp. A dual coax siamese cable connects to the antenna. There is a Tripp Lite ISOBAR surge supressor in the attic. That's where the antenna ground is.
 

SteveSh

Joined Nov 5, 2019
104
You said "So, each 4-way tap should suck off 1.5-2 db from the main line and the shorter path lengths should be the last taps. Each port sucks off 24 db, so that's why you need the high gain pre-amp. "

"suck off 24 dB" is not the right description. A 24 dB tap provides a signal level to the tap output that's down 24 dB from the input, or -24 dB relative to the input. That's 1/250 of the input power. With a 4-port output 24 dB tap (plus the single through port), the power "loss" to the 4 ports is only about about 4*(1/250), or 1/60th of the input power. Most of the power goes out the main (inline) output port.
 
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