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@goforit, that scenario is made perfectly for the quarter wave stub...
https://www.digitalhome.ca/forum/81-over-air-ota-digital-television/42428-splitters-attenuators-filters-diplexers-other-signal-gear-117.html#post3055811
Could easily knock down the signal strength of the local Hamilton stations by
20 dB or so, with very little impact to channel 16, or any other channel in the new
UHF band. A quarter wave stub cut for a quarter wavelength at ~ 68MHz would be a little
over 3 feet long. The 7th harmonic of that would land nearly perfect at ch 14/15 with a 3 dB bandwidth
of around 13 MHz.. While higher order harmonics would have no impact at all in the new UHF band, and in fact
at the same time might help take a decent chunk out of the future 600 MHz and 700 MHz currently being used for Wireless.
I would give that a try if I were you. works really well for me to tone down the strong Grand Island Signals over here.

Is very simple...Just get yourself some of these 3 port adapters (no affiliation with this ebay link), https://www.*********/itm/VCE-5-Pack-F-Type-RG6-Female-to-2-Female-3-Way-Coax-Cable-Splitter-Adapter-F/133304960456

Cut a piece of RG-6 coax to like 38 " long for starter kit, connect it to one port and leave the far end open circuit. Keep in mind that
some of that connector length is gonna be added to your 1/4 wave stub length measurement. So maybe ur lookin at starting out at 37.5 " of coax + 1/2" or so of connector.
place that assembly inline between the antenna and preamp input. Then trim the open circuit stub little by little in like 1/8" increments,
the 20 dB + null will start out much lower than the frequency of ch 14 but will be gradually creeping up on ch 14 little by little with each trim,
when you start to see some attenuation at ch 14, start trimming by like 1/16" at a time...
then stop trimming when you hit the sweet spot where both ch14 and ch15 are attenuated. Dress it up, weatherize and leave it in place when ur happy.


 

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i just wondering if people in toronto will be screwed in a couple of months when global moves to rf 17 won't that interfear with channel 49 being at rf 16.
 

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WNYO on 49 is now dead. Rescan for new WNYO - RF16, Samsung Series 6 can't lock it - no picture.

CHCH on RF15 undoubtedly the culprit with adjacent channel interference.

When WUTV used to be on RF14, the Series 6 could lock it in; back then, WUTV on 14 probably much better signal than WNYO on 16.

We'll see what happens in September when permanent WNYO 16 gets going...
 

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1/4 Wave Stub for RF 15

I tried using a stub to knock down the signal of RF 15 (about 35 db) so that WNYO on RF 16 would come in.

I used a 3-port tap, cut a piece of coax about 38", attached it to the bottom port, attached the antenna line to the left port; right port went to amp/TV.

At 38" first thing I noticed was that many signals got knocked out, VHF (RF 8, 13) and some UHF ones; only the stronger ones came in.

I tried cutting the coax from 38" to 36", about 1/8" each time, but no difference; RF 14 and RF 15 remained very strong, and no difference on RF 16 - it did not show.
 

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I don't know what your antenna plumbing looks like, but it should only be in the UHF path. Here I use separate VHf and UHF antennas, and a diplexer, so my stub is only in the UHF path, thus no VHF impact. what are you using as an indicator when ur trimming? Here I use a tuner that indicates strength in dBm and it's very obvious when your getting close to tuning it properly. I have it adjusted to knock down rf 31/32
 

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My set up is an AD-dB4e with VHF attachment on tower about 40' up; 4-way distribution amp inside house.

I tired (see previous post) to use a stub (cutting 38 to 36") on a 3 port tap, lost VHF channels and weaker UHF channels; no change to RF 15 or 16.

To check, I'm using the signal meter on the TV.

To stop the loss of the VHF channels I used a VHF/UHF splitter and used the stub and tap only on the UHF line, which brought back the VHF channels, but no change to 15 and 16.

Maybe I need to put the stub outside?

Does the stub have to be perfectly straight? I'm using an old piece of coax approx. 3', but curls up...
 

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good ya got ur VHF worked around now.
The coax I reference in the table assumes a velocity factor of 83% (0.83), as that
was the spec for the coax I was using.

Is important to know the exact make / part number of the coax you intend to use, so that we can lookup the velocity factor for the coax ur gonna use. The Velocity factor is what will determine the electrical length of the stub. So if you have a new piece of coax to try, let me know what the part number is. If it's Velocity Factor is significantly different than mine, that will effect the calculation for the electrical quarter wavelength.

Also keep in mind that the indicator on your TV probably isn't indicating 'Strength', is more likely to indicate 'Quality'.
And quality can be affected things other than 'Strength'. I have to think about how ya might get a real strength indication.
Do you have any computer based tuners available?
 

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WIVB channel 4 and its sister channel 23 are missing in action today. Other buffalo stations are fine. Channel 4 live feed on their website is also down so they must be having some problems or working on the tower.
 

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I received a reply from WIVB late this afternoon:

"We are currently in the process of having our main broadcast antenna replaced; this project started last week. We are occasionally reducing our transmitting power and have also switched to an auxiliary antenna to protect the tower crew. I am expecting that we will be operating at full power on the new antenna within 2 weeks"

The station came back early this afternoon but it sounds like reception could be up and down for a little while longer.
 

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@goforit, that scenario is made perfectly for the quarter wave stub...
https://www.digitalhome.ca/forum/81-over-air-ota-digital-television/42428-splitters-attenuators-filters-diplexers-other-signal-gear-117.html#post3055811
Could easily knock down the signal strength of the local Hamilton stations by
20 dB or so, with very little impact to channel 16, or any other channel in the new
UHF band.
Several years ago (2013) holl_ands went through some nec simulations of a cm-4221 antenna
modeled with a 1/4 wave stub tuned for 496 MHz... with pretty bad results (his comments not mine).
Anyway his notes and model are here:
https://imageevent.com/holl_ands/multibay/4bayrefl/uhfnewcm4221hdstubfilter

I was looking at this last night and realized what went wrong. Simulated was a 1/4 wave stub tuned
for 496 MHz. The bandwidth of these is approximately 20% of the center frequency (20% of 496 MHz is
like 100 MHz), and repeats every odd multiple of a quarter wavelength. Obviously we don't want to chop 100 MHz out of UHF,
so guessing he was looking at some other scenario at the time, or just playing around experimenting. I Love reading his models:)

However, what you really want to do for this Hamilton Scenario is tune the fundamental of the stub for the center of CH 14 and ch 15 476 MHz,
DIVIDED by 7 = 68 MHz . This way the bandwidth is only .2 * 68 MHz = 13.6 MHz, and that same 13.6 MHz Bandwidth null will repeat every
odd multiple of a quarter wavelength. So, considering N =1,3,5,7,9,11 multiples, we will see a null at
68, 204, 340, 476, 612, 748 MHz.
Note 204 MHz is in the middle of CH 11 and CH 12 in VHF Hi, so if you desire those VHF Hi, use a VHF/UHF diplexer (UVSJ)
to isolate your VHF and UHF antennas. Meanwhile 612 MHz is in the new 600 MHz band being farmed out for wireless and 748 MHz
was already farmed out to wireless, so it's OK to kill those a little (Bonus = LTE / 5G filter). Might be shaving a hair off the top end of
the new UHF as a result, but may be OK if you trim to be closer to CH 15 than 14.

I modified holl_ands nec file to simulate the longer length stub tuned to 68 MHz, and there ya have it, 3 nice nulls.
Exactly where calculated ahead of time, without disturbing much else in the new UHF Band. I also made some
corrections to the segment #s for the stub wires to improve the AGT result, and swept it every 1 MHz with nikiml's eval script which takes a little longer to run, but lets ya really see where the nulls will land. 4NEC2 Pic below is in 2 MHz increments, as 4NEC2 won't let ya sweep that many points. If you use coax for the stub like I did, you will have to adjust the length in the model, by the Velocity Factor of the Coax Cable you plan on using.
My coax VF was 0.84, which would have made that change from 43.3 Inches in the NEC model to 36.4 inches (84% of 43.3).
And here is the modified NEC model in case anyone wants to take a peek.
https://pastebin.com/JznuQ7gC

Model Link

470 - 607 MHz Chart Link

470 - 806 MHz Chart Link

 

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3 Separate pieces of cable. Some interesting labelling...

1) RG5967BU-W CSA/UL CMG/FT4 E238024 (white)
2) Tyger Wire RG6 60% BR Coaxial Cable 3GHz 18 AWG (UL) OR C(UL) E230635 CM CSA/FT4 220255 0678FT 2011041001 397 345 (black)
3) RG-6U COAXIAL CABLE 75 Ohms NICE FOUNTAIN (black)
 

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Another good option would be to select a fundamental freq in the FM Broadcast Band,
say 95 MHz, and use N=5th quarter wavelength. Won't disturb anything else in the UHF Band, but may help to squelch some strong local FM Radio Signals. Might be a little too wide of a null though. But that is what testing is for to verify the theory...
 
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