Lowest Insertion Loss 2-Way Splitter? / Attic or Roof mount? - AVS Forum
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post #1 of 67 Old 06-07-2009, 09:18 AM - Thread Starter
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In searching this forum, I found numerous recommendations for the the Winegard CA8800 FM Band Separator that has an insertion loss of only -0.4 dB.

However, a similar search for a low insertion loss splitter did not yield similar results.

Which two-way splitter (VHF/UHF/FM) provides an exceptionally low insertion loss? I need to split the output of our CM Quantum 1162 antenna & CM 0100DSB preamp. Thanks!

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post #2 of 67 Old 06-07-2009, 09:38 AM
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There's no such thing. They all lose about 3.5 dB at VHF frequencies and closer to 4 dB at UHF frequencies. You can ignore any decimal differences in published loss figures, as those figures are not guaranteed and furnished just for system loss estimates. You shouldn't need to worry about post amplification losses unless your system serves multiple TVs in a big house.
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post #3 of 67 Old 06-07-2009, 03:47 PM - Thread Starter
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Thanks for the reply Mike.
Quote:
Originally Posted by AntAltMike View Post

There's no such thing.

If Winegard can offer a FM Band Separator with a very low insertion loss, isn't it possible for a company to offer a 2-way splitter that also offers a very low insertion loss?
Quote:
Originally Posted by AntAltMike View Post

You shouldn't need to worry about post amplification losses unless your system serves multiple TVs in a big house.

Or, unless one has borderline reception (DTV cliff effect) on one or more channels - e.g. channels shifting to the UHF band due to the DTV transition.

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post #4 of 67 Old 06-07-2009, 04:01 PM
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Quote:
Originally Posted by ota.dt.man View Post

Thanks for the reply Mike.
If Winegard can offer a FM Band Separator with a very low insertion loss, isn't possible for company offer a 2-way splitter that also offers a very low insertion loss?

Splitting and separating are two very different things. With a separator, you send all of one group of signals one way and the remaining whole group of signals another way. With a splitter, you send all of the signals equally both ways.

CIAO!

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post #5 of 67 Old 06-07-2009, 08:57 PM - Thread Starter
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Good explanation egnlsn - thanks!

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post #6 of 67 Old 06-07-2009, 09:11 PM - Thread Starter
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Quote:
Originally Posted by AntAltMike View Post

They all lose about 3.5 dB at VHF frequencies and closer to 4 dB at UHF frequencies.

Understood, no significant differences among splitters for insertion loss.

Is there any significant advantage of one brand of splitter over its competitors for some other aspect (other than insertion loss)? - For example:
  • Bandwidth
  • Return loss
  • Isolation
  • RFI shielding effectiveness
  • Minimizing intermodulation distortions and spurious signals
Thanks

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post #7 of 67 Old 06-08-2009, 06:23 AM
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Look for splitters that have specs such as these.

There's not that much different between most major manufacturers.

CIAO!

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post #8 of 67 Old 06-08-2009, 09:43 AM
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Bandwidth: Any splitter rated to work with frequencies from 50 MHz to 1,000 MHz (or 1 GHz) is fine. A splitter sporting a bandwidth wider than this will also be suitable for your system, but won't work "better."

Return loss: This spec has to do with Internet service provided by a cable company, so you can safely ignore it.

Isolation: The higher the better; -20 dB is minimal. Bear in mind that 20 dB represents a factor-of-100 difference between two values. This info isn't commonly provided.

The rest: Good luck finding this info from sources other than Cencom. In general, though, a splitter with a fully soldered case is somewhat better than one with a glued-on back at resisting signal ingress and IM distortion.
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post #9 of 67 Old 06-08-2009, 09:57 AM
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Quote:
Originally Posted by Don_M View Post

...Return loss: This spec has to do with Internet service provided by a cable company, so you can safely ignore it.

The internet service must have a minimal "return path loss" for the modem to communicate upstream. Return loss has to do with the small amount of signal reflection that can take place in an inductive circuit. It is more of a concern to those who operate transmitters or who are managing signals at higher frequencies than we are using here. I wouldn't spend any money to buy a product with a lower claimed return loss.

Quote:
Isolation: The higher the better; -20 dB is minimal. Bear in mind that 20 dB represents a factor-of-100 difference between two values. This info isn't commonly provided.

Isolation is determined largely by how many ports there are. It matters a little in complex headends where the system designer is trying to minimize backfeed in multichannel systems, but is unimportant in this application

Quote:
The rest: Good luck finding this info from sources other than Cencom. In general, though, a splitter with a fully soldered case is somewhat better than one with a glued-on back at resisting signal ingress and IM distortion.

The main purpose behind strongly shielding a splitter case is to prevent egress. Cable companies are responsible for the "cumulative leakage" of their systems, and so they are willing to pay a few cents more for solder-backed splitters with 130dB of shielding, whereas the cheap, glue sealed ones may claim shielding of only 70 to 80dB. Even if you are under a tower, it is unlikely that you would benefit from the higher shielding factor of solder backed splitters.
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post #10 of 67 Old 06-08-2009, 09:59 AM - Thread Starter
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Thanks for the additional info Don & Mike - very helpful!

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post #11 of 67 Old 06-08-2009, 10:30 AM - Thread Starter
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Per the Cencom web page - They offer three 2-way splitters, all of which are marketed for cable modem applications:
  1. Holland 2-Way Splitter (GHS-2FC LI) - "The GHS-FCLI Series splitters are premium digital splitters featuring low intermod distortion and non-magnetizing circuit design (patents pending). The low intermod distortion allows high level return path signals (cable modems, STB's, etc.) while maintaining product integrity and eliminating the possibility of harmonics due to magnetization. " Specs
  2. PCT 2-Way Splitter (NGNII-2S) - "PCT's Genesys II drop passives offer exceptional performance and long-term reliability for drop installations, particularly in systems with cable modem applications." Specs
  3. Holland 2-Way Splitter, Power Passive One Port - "The GHS Series 1 GHz Splitters are state-of-the-art product lines designed and tested using the most current procedures. New performance features have been incorporated to make both series compatible with the latest digital and return path requirements. Low intermodulation design and optimized return band prevents high cable modem signals from affecting forward band transmission."
Which splitter is most appropriate for OTA DTV/HDTV? Thanks

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post #12 of 67 Old 06-08-2009, 11:44 AM
 
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Quote:


Return loss: This spec has to do with Internet service provided by a cable company, so you can safely ignore it.

return loss is the signal that is reflected back to the source by an impedance mismatch...nothing to do with internet service.
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post #13 of 67 Old 06-08-2009, 01:51 PM
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Quote:
Originally Posted by ota.dt.man View Post

Which splitter is most appropriate for OTA DTV/HDTV? Thanks

The one that costs the least. I build $30,000 headends. I've done headend work for ESPN, CNN, ABC News, USA Today, National Captioning Institute, Media General and Cox Communications. I never pay more than $.39 for two way, 5-900 MHz splitters.
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post #14 of 67 Old 06-08-2009, 02:15 PM - Thread Starter
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Thanks Mike. Knowing your background adds significant weight to your recommendation. A 2-way splitter is a commodity item.

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post #15 of 67 Old 06-08-2009, 02:37 PM - Thread Starter
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Quote:
Originally Posted by AntAltMike View Post

They all lose about 3.5 dB at VHF frequencies and closer to 4 dB at UHF frequencies.

I was hoping that technology had progressed to the point where someone had figured out how to design a low-loss splitter.

A 3.5 - 4 dB loss might make the difference in being able to receive a station that is on the edge of the DTV cliff effect. Swapping out a splitter would obviously much simpler than moving an antenna from the attic to the roof or adding a rotor.

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Quote:


I was hoping that technology had progressed to the point where someone had figured out how to design a low-loss splitter.

A splitter is a power divider, a two way splitter divides the available power by 2. Half power can be represented as a loss of about 3dB. This is dictated by the laws of physics, no amout of development will over come that.
BTW, the 3dB loss can be overcome with an amplifier.
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Quote:
Originally Posted by duvetyne View Post

A splitter is a power divider, a two way splitter divides the available power by 2. Half power can be represented as a loss of about 3dB. This is dictated by the laws of physics, no amout of development will over come that.
BTW, the 3dB loss can be overcome with an amplifier.

A splitter that is (theoretically) 100% efficient is a -3 dB loss of power. Since no splitter is anywhere near that efficient due to inductive, capacitive, and resistive losses, you'll typically see insertion loss specifications of around 3.5 dB for the good ones and about 4 dB loss for the ones further down the scale.
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post #18 of 67 Old 06-09-2009, 04:50 AM - Thread Starter
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Quote:
Originally Posted by duvetyne View Post

A splitter is a power divider, a two way splitter divides the available power by 2. Half power can be represented as a loss of about 3dB. This is dictated by the laws of physics, no amout of development will over come that.
BTW, the 3dB loss can be overcome with an amplifier.

Ah yes, those pesky laws of physics.

Our CM Quantum 1162 antenna already has a CM 0100DSB preamp. Results: All local stations are received with more than enough signal strength for DTV reception except one UHF channel whose signal strength is borderline with the DTV cliff effect - rather annoying. I was hoping to simply replace the splitter rather than moving the antenna from the attic to the roof with a rotor and having to add lightning protection. Hopefully, after 6/12 their transmit power will increase.

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post #19 of 67 Old 06-09-2009, 06:29 AM
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Quote:
Originally Posted by ota.dt.man View Post

Ah yes, those pesky laws of physics.

Our CM Quantum 1162 antenna already has a CM 0100DSB preamp. Results: All local stations are received with more than enough signal strength for DTV reception except one UHF channel whose signal strength is borderline with the DTV cliff effect - rather annoying. I was hoping to simply replace the splitter rather than moving the antenna from the attic to the roof with a rotor and having to add lightning protection. Hopefully, after 6/12 their transmit power will increase.

What is the callsign of the borderline station? Have you checked using tvfool.com to see if the power will change after transition? Clicking on the call in the tvfool report brings up the ERP.

Would you be willing to give us your zip code so that we can look at the signals? Or, better yet, you can enter your exact address at tvfool (the address will not show in the results) and give us the url near the top of the page in bold type so that we can see the signals now and post transition.

To counter the cliff-effect with your weak uhf signal, you might consider a separate uhf antenna (like the 4221) for more uhf gain joined with your present antenna with a uvsj (which has less loss than a splitter). I had to do that for a friend's attic installation because his all-channel RS antenna didn't have enough gain for uhf.

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post #20 of 67 Old 06-09-2009, 09:14 AM
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The CM QUANTUMs look like this:



Quote:


...one UHF channel whose signal strength is borderline with the DTV cliff effect - rather annoying.

I think you just let us know what was bothering you the most.

What are you using for reception, a digital tv or a CECB?

Does it have some kind of signal strength or signal quality indicator to tell you if you are making any progress (other than the cliff-effect) with antenna gain, aim, and antenna location in the attic for your borderline channel ?

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post #21 of 67 Old 06-09-2009, 10:42 PM - Thread Starter
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Hi rabbit73,

Thanks for all your suggestions.

WETA 27 (26.1) PBS is our least reliable DTV station. Signal strength is highly variable.
Maximum ERP: Now - 90.000 kW, 6/12 - 90.000 kW
Now: 10.1 NM(dB), -80.8(dBm), 2Edge, 39.6 miles, adjacent and co-channel warnings
6/12: 10.1 NM(dB), -80.8(dBm), 2Edge, adjacent-channel warning

WTTG 36 (5.1) FOX is usually not as much of an issue. However, tonight it was.
Max ERP: Now - 675.000 kW, 6/12 - 1000.000 kW
Now: 19.1 NM(dB), -71.8(dBm), 2Edge, 39.2 miles, co-channel warning
6/12: 20.6 NM(dB), -70.2(dBm), 2Edge, co-channel warning
  • CM-7000 D2A converter, (1st floor) which is highly rated by CR and has an easy to use signal strength meter.
  • Samsung DTB-H260F tuner (2nd floor), also highly rated by CR and has signal strength meter.
There are no significant reception differences for these channels with these two tuners, which are both connected to the attic antenna: CM-1162 with CM-0100DSB pre-amp.

Our antenna is aimed to optimize channels: 4 -NBC, 7-ABC, 9-CBS. However, WETA & WTTG are also in the same direction.

I look forward to your thoughts & ideas.

Thanks again!

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post #22 of 67 Old 06-10-2009, 04:12 AM
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Quote:
Originally Posted by ota.dt.man View Post

Hi rabbit73,

Thanks for all your suggestions.

WETA 27 (26.1) PBS is our least reliable DTV station. Signal strength is highly variable.
Maximum ERP: Now - 90.000 kW, 6/12 - 90.000 kW
Now: 10.1 NM(dB), -80.8(dBm), 2Edge, 39.6 miles, adjacent and co-channel warnings
6/12: 10.1 NM(dB), -80.8(dBm), 2Edge, adjacent-channel warning

WTTG 36 (5.1) FOX is usually not as much of an issue. However, tonight it was.
Max ERP: Now - 675.000 kW, 6/12 - 1000.000 kW
Now: 19.1 NM(dB), -71.8(dBm), 2Edge, 39.2 miles, co-channel warning
6/12: 20.6 NM(dB), -70.2(dBm), 2Edge, co-channel warning
  • CM-7000 D2A converter, (1st floor) which is highly rated by CR and has an easy to use signal strength meter.
  • Samsung DTB-H260F tuner (2nd floor), also highly rated by CR. Also has signal strength meter.
There are no significant reception differences for these channels with these two tuners, which are both connected to the attic antenna: CM-1162 with CM-0100DSB pre-amp.

Our antenna is aimed to optimize channels: 4 -NBC, 7-ABC, 9-CBS. However, WETA & WTTG are also in the same direction.

I look forward to your thoughts & ideas.

Thanks again!

Your forecasts make an attic installation ill-advised. An attic install could cost you anywhere from 3 to 20 dB of signal loss (almost impossible to accurately predict).

You'll need to get outdoors to improve those signals in a reliable and predictable manner.
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post #23 of 67 Old 06-10-2009, 10:49 AM - Thread Starter
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We opted for an attic install years ago during the "analog era" and were able to successfully transition to DTV by adding the CM-0100DSB pre-amp and by fine tuning the aim of the antenna. However, WETA & WTTG are still sub-optimal.

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post #24 of 67 Old 06-10-2009, 05:18 PM
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Quote:


Your forecasts make an attic installation ill-advised. An attic install could cost you anywhere from 3 to 20 dB of signal loss (almost impossible to accurately predict).

You'll need to get outdoors to improve those signals in a reliable and predictable manner.

I agree. If you lived closer to DC those two signals would be stronger.

Your only hope, if you must stay in the attic, is to install the best UHF antenna you can find in the best location in the attic. A slight change in antenna aim can often improve the signal QUALITY (to reduce dropouts) of a weak signal even if the signal STRENGTH doesn't change much, when you have multpath problems.

If you can not measure it, you can not improve it.
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post #25 of 67 Old 06-10-2009, 06:12 PM
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Quote:
Originally Posted by ota.dt.man View Post

Results: All local stations are received with more than enough signal strength for DTV reception except one UHF channel whose signal strength is borderline with the DTV cliff effect - rather annoying.

Your antenna is probably in a dead spot for WETA. Have you ever tried moving it around? The signal strength is more than adequate at your location for reliable reception of WETA-DT.

I just installed my small Winegard Ghost Killer antenna at a location with a very similar signal strength of WETA. The reception was surprisingly good, even before adding a pre-amp.

Your issue with WTTG was due to the abnormal atmospheric conditions here last night.(Tropo)

http://www.tvfool.com/?option=com_wr...c5347d02d523de
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post #26 of 67 Old 06-10-2009, 08:41 PM
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Quote:
Originally Posted by ota.dt.man View Post

We opted for an attic install years ago during the "analog era" and were able to successfully transition to DTV by adding the CM-0100DSB pre-amp and by fine tuning the aim of the antenna. However, WETA & WTTG are still sub-optimal.

I read about a homeowner who also wanted his antenna in the attic. His solution was to install a dormer window in the attic roof with his antenna just inside. So, his antenna WAS inside but the reception was almost as good as outside. An expensive solution, but he was determined to make it work.

It is also possible to install a translucent plastic bubble (transparent to RF) skylight in a roof with the antenna just inside. The point is, attic construction can be modified in a visually acceptable manner to improve reception. I don't know if your antenna is aimed thru the roof or thru the end of the attic.

In my case, I wanted to be able to receive DTV during a power failure, when the cable was out, and during weather emergencies. We had been using a 5" B&W analog TV inside which was good enough, but an indoor antenna doesn't work for digital because we have an aluminum foil vapor barrier on the insulation in the outer walls (can you say Faraday Cage?).

To solve the problem I mounted a 4-bay UHF antenna outside behind a decorative block wall. The signals pass thru the holes in the 12" blocks with only a 2 dB loss for UHF; I have the equipment to measure signals in dBmV.

If you are determined to improve your reception of WETA, you might try setting up a good UHF antenna and preamp outside as a test to see if it might be possible.

Another possibility would be to have a UHF antenna hidden outside, with your VHF antenna still in the attic.

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post #27 of 67 Old 06-10-2009, 09:57 PM - Thread Starter
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Quote:
Originally Posted by rabbit73 View Post

I agree. If you lived closer to DC those two signals would be stronger.

Your only hope, if you must stay in the attic, is to install the best UHF antenna you can find in the best location in the attic. A slight change in antenna aim can often improve the signal QUALITY (to reduce dropouts) of a weak signal even if the signal STRENGTH doesn't change much, when you have multpath problems.

Our antenna doesn't have to stay in the attic. We decided on the attic location for aesthetics and to not have to contend with lighting protection.

Antenna aiming: I have made several attempts at manually aiming the antenna - not convenient (must climb ladder) & somewhat frustrating trying to find one position that gives the best results for the majority of stations. Additionally, a CM 1162 has a long boom, which severely limits the amount it can be turned inside an attic before one end of it hits a roof truss.

Multipath: With analog it was easy to determine if multipath interference was the issue. All one had to do was to see if "ghosting" was present in the picture. How does one make that determination with DTV?

It sounds like I need to add a UHF antenna in the attic (Which one?) or move the 1162 to the roof on a rotor.

Does the AVS Forum have an article or an FAQ on how to properly install adequate lightning protection?

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post #28 of 67 Old 06-10-2009, 10:13 PM - Thread Starter
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Originally Posted by Digital Rules View Post

Your antenna is probably in a dead spot for WETA. Have you ever tried moving it around?

See previous post.

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I just installed my small Winegard Ghost Killer antenna at a location with a very similar signal strength of WETA. The reception was surprisingly good, even before adding a pre-amp.

Thanks, I'll look into the Winegard Ghost Killer.

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Your issue with WTTG was due to the abnormal atmospheric conditions here last night.(Tropo)

http://www.tvfool.com/?option=com_wr...c5347d02d523de

Thanks, I'll need to read about Tropo interference of DTV. Does one simply have to do without a particular station under such conditions with DTV or is there a solution for this issue?

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post #29 of 67 Old 06-10-2009, 10:48 PM - Thread Starter
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His solution was to install a dormer window in the attic roof with his antenna just inside. .... An expensive solution, but he was determined to make it work.

It is also possible to install a translucent plastic bubble (transparent to RF) skylight in a roof with the antenna just inside. ...

Novel solution. However, I don't think we'll go to that much expense just to keep the antenna in the attic.

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I don't know if your antenna is aimed thru the roof or thru the end of the attic.

It is aimed through the roof.

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To solve the problem I mounted a 4-bay UHF antenna outside behind a decorative block wall. The signals pass thru the holes in the 12" blocks with only a 2 dB loss for UHF; I have the equipment to measure signals in dBmV.

Good job! How high off the gorund is your UHF antenna?

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If you are determined to improve your reception of WETA, you might try setting up a good UHF antenna and preamp outside as a test to see if it might be possible.

I suspect we would have to buy the antenna & preamp to test if this idea will work for us.

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Another possibility would be to have a UHF antenna hidden outside, with your VHF antenna still in the attic.

From a wiring perspective, either an attic or roof-top solution may be best for us. Our house was pre-wired for an antenna either in the attic or on the roof.

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post #30 of 67 Old 06-11-2009, 03:59 AM
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Multipath: With analog it was easy to determine if multipath interference was the issue. All one had to do was to see if "ghosting" was present in the picture. How does one make that determination with DTV?

With DTV a signal strength meter that bounces up & down a lot, indicates that multipath is present.
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