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Discussion Starter #21
You need to be a rocket scientist to understand GBPVR, which is one of those "Guide First, Then (maybe) Reception" overblown wonders. And Euro-centric.
 

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Discussion Starter #22
Further thoughts re tropo

The antenna is sitting on the side balustrade (not really a balustrade, as that would require balusters, but it's not a railing either - it's a six-inch thick slab of concrete and I can't think of the right word).

As situated, the apartment building blocks the direct-line signals from Buffalo. "Direct" tropo (reflection point in-line somewhere between Buffalo and the antenna) would also be blocked by the building's roof edge some six or seven levels up. Not to mention that it would then have to navigate down the narrow vertical channel between the balconies to hit the antenna almost on edge.

I suspect that for there to be tropo, the reflection point would have to be somewhat to the east of the antenna and fairly low on the horizon. Does horizontally polarized tropo reflect 'sideways'?
 

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Tropo is generally a bounce from the sky, so its likely coming in from the top.
 

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Tropo is a strange phenomenon that I can't explain. Recently I received a channel that was 171 miles away from me and on the opposite side of the building I live in.

http://www.digitalhome.ca/forum/showpost.php?p=1131963&postcount=521

As well I regularily receive 26.1 on tropo nights. As well as 4.1 and 7.1 which the building blocks, but 29.1 is harder to receive on tropo even though the building doesn't block it. I'm more likely to get 51.1 and 49.1 than 29.1.

Orientation of my building to the tv towers -

http://www.digitalhome.ca/forum/showpost.php?p=1117456&postcount=34
 

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Discussion Starter #25
Things that hit you in the middle of the night...

A "knife edge" is a "knife edge"! That is, it has only one dimension, length.

Thus, there is no "angle of incidence" for a signal which will undergo diffraction. It matters not whether the source is just "around the corner" or "way beyond the bend and over the hill".

One of the few remaining synapses fired and I realized why there was the unexpected appearance of CH18 - the old crap clone was incapable of receiving it. It actually said so on the box that CH20 was its lower limit. At the time I had no belief that I could get CH18 so I simply put it out of mind.

What does matter is the distance between that "knife edge" and your antenna, with more being better. Here I am fortunate in that my apartment building is long and I am at some distance from that edge.

The other factor is the frequency of the channel. Higher frequencies diffract less.

It seems that the result of this is that one aims not at the "knife edge" but slightly away from it (and the station) which seems (to me) to be counter-intuitive. In essence, the diffraction creates a "virtual source" with its angle away from the edge dependent upon the frequency and your antenna's distance to the edge. (I had to point over 15 degrees away from the edge to get CH43 to scan in.)
 

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Discussion Starter #26
Image of the challenge

I'm trying to overcome:



The balconies on the building exist only in the centre section and are inset so that the front edge of the balcony is in line with the wall line marked EDGE 1 and EDGE 2. But the balconies are actually only "half" inset as the wall of the centre section is itself inset. This leaves the side balustrade of the balcony to be less than half the actual depth.

Thus, signals from Buffalo must diffract around EDGE 1 and if the antenna is not positioned at the very front of the balcony (or beyond which will really upset the landlord), further diffract around EDGE 2.
 

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Just wondering where exactly are you in Mississauga? (nearest major intersection) Looks like you're quite north of me.

I'm down in Clarkson and the situation is much worse. The issue here isn't signal strength, it's that everything is spread out. Basically it's your image, except the green lines of Hamilton and Toronto are basically 180 degrees apart.

I might consider your design amongst others (Stealth Hawk). How has it worked for you? Like you, I don't necessarily need gain. Just directionality.
 

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Discussion Starter #28
Dunno

It's too soon to tell. At present, it's just a somewhat curved mesh (mess?) dangling in the breeze. How much detriment that curl is imposing is unknown. I've got to push on to getting the frame built to get a reasonable flat plane.

Tropo effects do seem to be in play to some degree, but I cannot ascribe tropo to all the results.

Why is CH18 so successful? Tropo implies reflecting from altitude, but that then implies it striking a rather directional (UHF) antenna way off-axis. Granted it's a powerful signal so "paperclip" rules might apply.

Why is CH39 clear and CH38 a disaster? Simply power?

CH32 is solid as expected. Why is CH43 non-existent? Power doesn't seem to be the answer. Frequency?

And if power is the question, why is CH23 solid? (But then, even the old crap clone could occasionally get it.)

Dixie/Burnhamthorpe.
 

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Why is CH18 so successful?
That signal will go through your building and reach your antenna.

Channel 13 here at 62NM will go through my building easily. I can pick this up with my portable tv without extending the antenna. I can even pick it up in my parking garage under ground. TV signals will travel through buildings. However one the big problems is multipath, which can be solved with a very directional antenna or a very inefficient antenna that only picks up the strongest of the multipath signals.



After much experimentationn, I receive this channel best with a small antenna made with coax. I looped the coax to create a balun and put it into a UVSJ. Channel comes in great, even though the antenna is behind my couch and has to go through several concrete walls of my my building.

 

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CH32 is solid as expected. Why is CH43 non-existent?
Best guess is the cliff effect of digital reception. At a certain point the signal is too weak and just disappears. From your diagram you have about 7db of difference in power which is quite a lot.

I'm chasing my last channel WUTV which has a difference of 2db between that channel and the last one I can receive reliably. That 2db of difference is quite a bit. Every improvement I make to my antenna and setup results in me getting just a bit closer to receiving it better. But I think I'm at the cliff's edge and it just seems so hard to get there. :D
 

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Discussion Starter #31 (Edited)
Paperclip rules..

That signal will go through your building and reach your antenna.
Even if it penetrates through the building, it still then strikes the antenna at a very oblique angle.

So, you're invoking the 'paperclip' rule - the signal is so powerful even a paperclip can receive it. ;)

Ch43 is not that less powerful and if direct, would strike the antenna far more on-axis.

Contradictions, contradictions, contradictions....:confused:
 

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Discussion Starter #32
Best guess is the cliff effect of digital reception. At a certain point the signal is too weak and just disappears. From your diagram you have about 7db of difference in power which is quite a lot.
Somewhat pales in comparison to CH23 (-16.1NM) yet that one is solid... :confused:
 

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At -16NM either you are getting tropo reception or tvfool is incorrect. There is no commercially available antenna with 16db gain at that frequency-

http://www.hdtvprimer.com/ANTENNAS/comparing.html

And there are some really good antennas in that gain chart.

From the tvfool info -

http://www.tvfool.com/index.php?option=com_content&task=view&id=57#how_to_read

The most important number to pay attention to is the Noise Margin, in the "NM(dB)" column, for each of your local channels. These values tell you if you are above or below the detection threshold for each station and by how much. Since these values represent the amount of signal "in the air" at your location, you need to have enough margin to account for building penetration, cable loss, splitters, tuner sensitivity, and other factors specific to your setup. If you take the initial NM value for a given channel, add your antenna gain, subtract all the other system losses, and still end up with a value above 0, then you should be able to detect that channel.

Continue reading for more info on the NM readings
 

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Discussion Starter #34 (Edited)
Continue reading for more info on the NM readings
Tx, been there.

Actually, my understanding (which is likely wrong) is that there are three factors:

a) Carrier strength / receiver sensitivity. The actual NM of the carrier isn't the question here, but rather can the receiver detect (i.e. recognize) it. The value of the carrier (NM(db)) can be below zero if the receiver is sufficiently sensitive; zero is simply an arbitrary threshold.

b) Receiver selectivity (the ability of the receiver to discern between two carriers of the same frequency (co-channels) or nearly the same frequency (adjacent channels)).

c) Signal extraction (the ability of the receiver to discern and process the information impressed upon the carrier). I believe that the requirement is extraction if the S/N ratio is 15 or greater. (My Hauppauge cards don't drop to zero unrecoverable errors until about a SNR of 18.)
 

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Discussion Starter #36
Not likely.....

Ignore everything I've said.
No way! Did confirm that CH18 is indeed driving through the width of the apartment building. (One feels really silly aiming the antenna at the wall.) The Buffalo stations being weaker have no chance trying to penetrate the length. Either they diffract or the tropo gods must intervene.

Did finally get a handle on Windows Media Center. It actually does identify what cards produce which signals. Unfortunately, it then adds in what its guide 'thinks' the cards should get and muddies it all together. You have to get in and separate the wheat from the chaff. Very, very tedious.
 

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The Buffalo stations being weaker have no chance trying to penetrate the length. Either they diffract or the tropo gods must intervene.
Probably won't go through the length, too many concrete walls to pass through.

Diffraction probably would cause about 25-30db loss in signal. This is my best guess based on this online diffraction loss calculator-

http://www.wirelesscommunication.nl/reference/chaptr03/diffrac.htm

So taking your strongest Buffalo signals from tvfool - WNLO & WNED and subtract the loss and you signal starts getting down to 0 to 10 NM, which is doable with a good antenna.

Of course this is assuming that there are no other losses from other obstacles.

Once you get below -10db NM reception gets harder. I'm just basing this on personal experience and the posts I have read here from others posting their reception results here. Getting reception below -15db NM is really hard and usually I'm reading about antennas like XG91 or channel cut yagis on masts with low noise amps to bring in these signals.

I'm not trying to discourage you, but tropo can really make you chase your tail when trying out new antenna designs. You can take readings one minute, change something and the readings the next minute will make your head scratch. From what I've read here some people will lose channels at night, while others will gain them.

I'm trying out something new with my antenna setup. Personally I'm running with this change for about 1-2 weeks to see if I have improvements. Tropo is scratching my head at times right now.

Also, I'm not entirely convinced that tvfool is 100% accurate and has a margin of error. Afterall, it's just a mathematical model based on the best available information tvfool has.
 

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Discussion Starter #39
'Tis done.

Well, finished the supporting frame and have mounted the "straightened" "Sieve".

Does it work as advertised (i.e. match the 4nec2 predictions)? Indeed it would so appear and I am seeing SNR's that I have never seen before. I'm even getting the audio from Barrie (analogue CH3) which is surprising considering the model stated a SWR somewhere in the 50's.

Did it perform the miracle I had hoped? Sadly no. The Buffalo stations "around the corner" of my apartment building remain the elusive property of the tropo gods, although their SNRs have improved into the 9 to 11 area.

Still, I now have an antenna which is far better than the crap clone vandalized by Rogers/landlord.

Comparing apples to apples, it competes well with a REFLECTORLESS GH:

a) Covers entire UHF and VHF-HIGH smoothly.
b) Excellent net gain in UHF.
c) Good net gain in VHF-HIGH.
d) Good smooth VSWR, but must defer to the GH at its peak lows.
e) Easily constructed (no wire bending - just snip away the 'slots'; simple support frame or just hang on a wall).

but like any design, there are tradeoffs:

a) Large size horizontally and vertically may not justify lack of depth feature.
b) Large amount of 'ancillary' hardware (5 baluns, 5 runs of co-ax with 4 needing to be of equal length, 4-way splitter, UHF-VHF combiner/joiner, plus a handful of connecting elbows to get the whole mess reasonably flat).
c) Somewhat costly. Although the problem is the same as any 'mesh' reflector, it is difficult to avoid purchasing far more material than is required. And the 'ancillary' hardware does add up.

Of course, one must learn to be adept with the 21st century "duct tape" - plastic wire ties (Red Green would be proud).

For me, the main feature is that it validated the idea of separately 'tapping' and 'combining' multiple slots sized for multiple frequency ranges cut in a single plane.
 
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