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Multipath, Multipath

Started by Talos4, Thursday Mar 19, 2009, 12:31:20 pm

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Talos4

Here's the situation:

I'm reconfiguring our conference room A/V. Projector, Audio, and TV.

I'm good on the projector, A/V-PC integration.

My problem is the TV reception.

Our office is approximately 1/2 mile S-SW of the Lincoln park towers for 12-58.
and about 2 miles west of the Blue hole and the rest.

Building is 2 stories typical steel and concrete construction, steel deck and low slope roof.

The conference room is in the middle of the building. (of course)  

Experiments have been conducted with an old D* DBS/digital OTA tuner and rabbit ears.

Reception is spotty as anticipated.

My questions:

Given our proximity to all of the towers would a small rooftop antenna without a rotor improve the situation? (no rotor simplifies the situation in multi user environment)(KISS)  

Would I need the rotor?  

Or just better rabbit ears?

Penetrating the roof, routing conduit through it and flashing in that and the tripod mount is NOT an issue.  

I lived in Riverwest for about 18 years and am familiar with the reception issues being that close to the towers. 10 years later however, with the digital signals I don't know if the issue changes all that much.

Back then I put a small OTA antenna with an adjustable attenuator on the roof and it helped but was not the cure all.

Thanks!
If I can\'t be a good example - I\'ll just have to be a horrible warning!

Mits WS-48413
Samsung SP-R4232 in the Rec room
Yamaha RX-V657
Atlantis ATL-10 mains
Boston Acoustics VRC
Def Tech BP 1.2x surrounds
Def Tech Supercube II
Sony DVP-CX995V DVD Jukebox
TWC 8300 HDC :(
XBOX 360
Universal Remote MX-850


The wallet is now empty, and I couldn\'t be happier. :D

Talos4

If I can\'t be a good example - I\'ll just have to be a horrible warning!

Mits WS-48413
Samsung SP-R4232 in the Rec room
Yamaha RX-V657
Atlantis ATL-10 mains
Boston Acoustics VRC
Def Tech BP 1.2x surrounds
Def Tech Supercube II
Sony DVP-CX995V DVD Jukebox
TWC 8300 HDC :(
XBOX 360
Universal Remote MX-850


The wallet is now empty, and I couldn\'t be happier. :D

John L

I don't understand why people living closer to Milwaukee or even practically living directly under the towers of the TV station/s have trouble with reception.  Here in Muskego it doesn't seem to matter which way I turn the antenna or what direction it is at I get ALL Milwaukee stations except ch. 52 Mayville.  I have no problem getting 4, 6, 10, 12, 18, 24, 30, 36, 41, 49, 55, 58 and 63 all in Digital because the tuner I have strictly receives Digital no analog. Yes the rotor on the antenna works because it has to be directed to the SSE to get some Chicago stations like WLS-DT and WFLD-DT, and WPWR-DT.

:huh?:

-John L.

WPXE ION

Being that close to the towers, 0.7 miles, could over-modulate the input on the receiver. Attenuating the signal might work or just tweaking the antenna to find the sweet spot.

If Radio Shack doesnt have Type F attenuators try Ness Electronics on 51st and Good Hope.

techboy

"Blue Hole"?   You have been around a long long time.  I live with the same situation, but to the north east of the towers. ( North of Eastbrook park )  I used two small UHF bow tie antennas outside into a combiner.  The antennas are aimed at 90 degree right angles.  The combiner is the type used for satellite TV as it covers the UHF specturm with less attenuation.   Modern ( so called 5th generation ) DTV tuners have very good adaptive equalizers to deal with multipath and front ends with high dynamic range to deal with intermod from adjacent channels used by DTV.  Remember in the "old" days when UHF channels had to be spaced every 6th channel?
Retired Broadcast TV / Radio Engineer WTMJ. ( 35 Yrs )

Talos4

Friday Mar 20, 2009, 03:43:25 pm #5 Last Edit: Friday Mar 20, 2009, 03:46:14 pm by Talos4
They do still call it the blue hole don't they?

and yes I do remember the old days. especially when my dad had to buy a tuner to put on the TV to watch channel 18. (sound familiar?)

I'm going to try some attenuators that I have squirreled away in one of my "you never know" drawers.

I used them when I lived in Riverwest. At that time I was 4 blocks SE of the WCGV tower.

Unfortunately with my current workload, this is a project I have to work on "when I find the time"    

I'm still waiting for parts like projector mount cables etc to arrive.

I was going to play around with it today for the Marquette game but I got called away to attend a pre-bid at the last minute.

keep the suggestions coming, I'm liable to need them.

Thanks.
If I can\'t be a good example - I\'ll just have to be a horrible warning!

Mits WS-48413
Samsung SP-R4232 in the Rec room
Yamaha RX-V657
Atlantis ATL-10 mains
Boston Acoustics VRC
Def Tech BP 1.2x surrounds
Def Tech Supercube II
Sony DVP-CX995V DVD Jukebox
TWC 8300 HDC :(
XBOX 360
Universal Remote MX-850


The wallet is now empty, and I couldn\'t be happier. :D

Nels Harvey

Your location is pretty much still in the "dead zone" under the umbrella effect from the tall towers.  I would try an exterior omni antenna with a variable attenuator.  This would clear you from the structure steel and may be all you need.  Interior walls in commercial buildings are made with steel studs now, and that would cause serious reflections inside the building.

Good luck!

Nels....
Nels....
Retired TV Engineer
Resident, State of Mequon
Sharp 70" LCD, E* VIP 612 HD DVR,
40" Sony LCD, E* VIP 722K HD DVR.

mhz40

Quote from: techboy;51301I used two small UHF bow tie antennas outside into a combiner.  The antennas are aimed at 90 degree right angles.  The combiner is the type used for satellite TV as it covers the UHF specturm with less attenuation.

Combining antennas are a bad idea.  Without any design experience doing so, it's impossible to get it right.  Even in a very narrow bandwidth (6-12 MHz), antennas must be properly spaced and aimed to get good results.  IMO, You'd be better off with an omni directional UHF if that is your intent.

Also, being so close to the sources, splitter loss should be near the bottom of the list in terms of performance factors.  In this case, port-to-port isolation is more important.

techboy

I do have the design experience and I did get it right.  The antenna system that I built is what I, as a professional TV engineer would recommend.  I needed this antenna arrangement for analog "ghost free" reception.  With adaptive equalizers in DTV tuners, almost any antenna will most likely be adaquate in this fellows situation.
Retired Broadcast TV / Radio Engineer WTMJ. ( 35 Yrs )

Talos4

Quote from: Nels Harvey;51306Your location is pretty much still in the "dead zone" under the umbrella effect from the tall towers.  I would try an exterior omni antenna with a variable attenuator.  This would clear you from the structure steel and may be all you need.  Interior walls in commercial buildings are made with steel studs now, and that would cause serious reflections inside the building.

Good luck!

Nels....

The "dead zone" is something I'm familiar with. As well as the effects of the steel building.  

I set up our office "mom" with a converter box and rabbit ears on the TV on her desk. Fortunately all of our offices have windows and I put the ears at the window. Works just fine.

Unfortunately the Conference room is in the middle of the building.

I'm going to check out different "omni" antennas and when I get to that point I'll experiment. I'm still going to play with the rabbit ears I have and maybe get it into the plenum and try that first.
If I can\'t be a good example - I\'ll just have to be a horrible warning!

Mits WS-48413
Samsung SP-R4232 in the Rec room
Yamaha RX-V657
Atlantis ATL-10 mains
Boston Acoustics VRC
Def Tech BP 1.2x surrounds
Def Tech Supercube II
Sony DVP-CX995V DVD Jukebox
TWC 8300 HDC :(
XBOX 360
Universal Remote MX-850


The wallet is now empty, and I couldn\'t be happier. :D

mhz40

Quote from: techboy;51353I do have the design experience and I did get it right.  The antenna system that I built is what I, as a professional TV engineer would recommend.  I needed this antenna arrangement for analog "ghost free" reception.  With adaptive equalizers in DTV tuners, almost any antenna will most likely be adaquate in this fellows situation.

Then you know multi-path (ghost) cancellation is only one aspect in an antenna system design.  Overall frequency response across the RF spectrum of interest, RF gain, effective beam width are also factors.  You'd also agree that antenna type and spacing are very important factors when attempting to lessen the effects of multi-path AND minimize the undesirable effects in the other areas of performance I've mentioned.

I'll stand by my assertion that this approach is not for anyone without design experience, which is likely 99.6% of the users in any online group.  You say you got it, which is good news for you!  Still, I expect you'd agree that any design is specific to a particular reception location.  Others implementing your design at their reception locations would likely have very different results.

By the way, was RF even a reality 35 years ago?? JUST KIDDING!! :D