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Discussion Starter · #1 ·
Evening,

I have helped a friend out with letting him borrow an old Stealth Hawk antenna from a previous build to use in his attic. It works well but limited on channels for him really.

The issue seems to be that he is so close to the CHCH tower in Hamilton, only 1.6 miles away. I believe this is hindering him in getting some of the channels around the area for Buffalo. Is there a design anyone would suggest that he try to build with my help? Holl_ands I know you might have an idea.

If possible I thought that maybe with the build of an antenna it might need to have some kind of signal trap to lower the dbi for the certain station.

His TVFool is as follows:
Hamilton Home - 1.6 miles to tower

Thanks in advance for the info.
 

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An attic reduces the signal strength of an antenna by up to half, a stealth hawk in the attic would be about as powerful as a paperclip in the back of the tv. The problem is NOT channel interference or proximity to the CHCH transmitter, it's antenna choice and location.

Tell him to put the stealthawk in an upstairs window and see how he fares.
 

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Depending on the location of CHCH relative to the desired stations, a more directional antenna might help. Something like a Gray-Hoverman is a good bet. The extra gain on desire channels would also help.

Tin Lee filters will eliminate reception issues caused by strong local channels. They are not cheap though and can cost more than an antenna.

The gain of the Stealth Hawk may be an issue. Seemingly small changes in location can cause a big change in reception results. In this situation I wouldn't count on a preamp to rectify the reception issue. It may cause more problems due to CHCH overloading the preamp. If a preamp is added, I would place a bandstop filter tuned to CHCH ahead of the preamp.
 

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Discussion Starter · #5 ·
Depending on the location of CHCH relative to the desired stations, a more directional antenna might help. Something like a Gray-Hoverman is a good bet. The extra gain on desire channels would also help.

Tin Lee filters will eliminate reception issues caused by strong local channels. They are not cheap though and can cost more than an antenna.

The gain of the Stealth Hawk may be an issue. Seemingly small changes in location can cause a big change in reception results. In this situation I wouldn't count on a preamp to rectify the reception issue. It may cause more problems due to CHCH overloading the preamp. If a preamp is added, I would place a bandstop filter tuned to CHCH ahead of the preamp.
A Bandstop was exactly what I was thinking he might need for the job.

Thanks for the suggestions.

Sent from my OnePlusOne
 

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I have never had an issue with it at my location ever
Like real estate agents say, location, location, location!

Your friends location, while it might be "on the mountain", is trying to pull Buffalo through zillions of tons of escarpment. To make matters worse he's got the antenna inside an attic and it's NOT above the height of the homes in his neighbourhood (multipath).

The stealthhawk antenna is easy to build but it's LOW GAIN.

Just because it works for you doesn't mean it's a "great antenna".

I'd suggest studying the antenna designs here:

http://imageevent.com/holl_ands

http://clients.teksavvy.com/~nickm/index.html
 

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Derek has 3 very strong signals. CITS and CHCH are from the same direction, so he would need at least 2 bandstop filters from Tin Lee. CHCJ is from a different direction, so maybe the F/B ratio of the Buffalo antenna would tame it enough.

PAR Electronics also makes filters, but I have no experience with them.
http://www.parelectronics.com/single-channel-tv.php

There is the possibility of using the "two antenna trick" to place a null a 85° magnetic. The hdtvprimer site is down now, so maybe holl_ands can advise you on that approach.
http://imageevent.com/holl_ands/stacked/horizontallystackeduhfantennas/hstacked2xcm4221hdhackednullbeam

As ExDilbert said:
Depending on the location of CHCH relative to the desired stations, a more directional antenna might help.
True.
Another possibility would be using a separate very directional yagi for the Buffalo area, and make it even more directional by surrounding it with a metal screen enclosure open at the front. It would still pick up some reflections from the strongest signals, but it might work.

Winegard PR-9014 UHF antenna



OR



CITS has a NM of 73.0 dB; WGRZ has a NM of -3.9 dB. That's a difference of 76.9 dB, a very large dynamic range to deal with.

 

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The stealthhawk antenna is easy to build but it's LOW GAIN.
Just because it works for you doesn't mean it's a "great antenna".
It's also pseudo omni, nowhere near directional enough to do what your trying to do. Do take Frankzappa's advice and look at other designs. Agree, in most cases it's best to get the antenna outside, as the roofing, plywood, and god knows what else will attenuate the signals dramatically and signals are bouncing around all over up there. BTW, half is only 3 dB. I would guess there is much more than 3 dB loss in a typical attic. But yeah, it depends on the construction.
You could also try to install a directional antenna outside, but mount it lower such that the house shadows CHCH, but has a clear view toward Buffalo. I would tell your friend to play around experimenting and have fun, that's what it is all about. There really is no one size fits all solution for everyone. Every situation is different and has it's own challenges.
 

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Nearly all of the US Networks (ABC, CBS, NBC, FOX, CW) are on Channel assignments that are ADJACENT or NEXT Adjacent (aka "TABOO") to strong, nearby Canadian Stations. Although there are no MANDATORY DTV Tuner Specs, the Low-Rez CECB (U.S. Coupon Eligible Converter Boxes) were REQUIRED to meet the ADJACENT (Table 2) and TABOO (Table 3) Requirements found in the fol. document, which were derived from ATSC A/74 Receiver Implementation "Guidelines":
http://www.ntia.doc.gov/legacy/dtvcoupon/DTVmanufacturers.pdf

Hence, Tuners manufactured after 2007 "should" tolerate Adjacent Channel Interference that is about 33 dB STRONGER than the Desired Signal and 44+ dB for Next Adjacent (aka Taboo) Channels. HOWEVER, we should also bear in mind that these were BENCH Tests with NON-FADING signals, so in practice we should try to keep Adjacent Interference no higher than about 20 dB Stronger than the Desired (probably Fading) Signal and NEXT-Adjacent Interference no higher than about 30 dB Stronger than the Desired Signal.

FOX (Ch14) is Adjacent to 65.3 dB Stronger Ch15.
ABC (Ch38) is NEXT Adjacent to 71.5 dB Stronger Ch36.
NBC (Ch33) is NEXT Adjacent to 71.5 dB Stronger Ch35.

I would NOT rely on Antenna Nulling and/or Front/Rear Ratio ONLY to provide the required 40-45+ dB of local signal suppression....strong local signals can reflect off of nearby objects, readily circumventing an Antenna-Only suppression strategy.

A TWO Channel Filter is needed to suppress CDh35/36 by AT LEAST 40 dB, with minimal attenuation on Ch33 and Ch38.....talk to Tin-Lee about your specific requirements.

One Single Channel Filter is needed to suppress Ch15 by AT LEAST 45 dB Attenuation with minimal attenuation on Ch14...which would ONLY be provided by a VERY EXPENSIVE Adjacent Channel Notch Filter....but due to the need to have minimal impact on Group Delay...which is important for Digital waveforms....I don't think they exist at any sort of reasonable price....so receiving FOX may require the use of a Dual Antenna Nulling Trick (which should be used in Addition to the Ch35/36 Filter):
http://www.hdtvprimer.com/antennas/ganging.html

Fol. example presumed the use of two CM4221HD 4-Bay Antennas...but a pair of DIY M4's or FF4's could also be used:
H-Stacked 2xCM4221HD Hacked - NULL BEAM
The NULL would be directed towards strong local stations at 75-deg (re True North), with the Antenna Separation Distance chosen so that ONE of the Two BEAMS is directed towards 105-deg for best FOX (Ch14 on 473 MHz) reception. UNFORTUNATELY, for 30-deg difference between the NULL and the BEAM, the SECONDARY BEAM must be used, with much lower Gain than the PRIMARY BEAMS.....so don't be surprised if this technique is underpowered for weak FOX signals.

Note that the Angle of the Two Beams VARIES with Frequency for a given Antenna Separation distance....ideally, I would insert an RF DPDT Switch (under DC Voltage Control) to reverse the polarity on one of the 300-ohm connections to change between NULLING and normal SUMMING mode:

 

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Discussion Starter · #15 ·
I have messaged Tin Lee about the option of the notch/trap filters.

Just wondering as another option:
From conversations with my friend, I believe he had said before that if we can block them out altogether. So instead of nulling like you had suggested above to lessen the station - maybe Faraday cage it out of the signal selection altogether as rabbit73 suggested.

Would this be done with similar to the option of stacking FF4's separated by your 51" so we can articulate them to the degrees around the 85 degree Magnetic?

Update: Sorry I think what I described here is what you were saying above. I really am out of it today: been a long day already.
 

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Since the very strong local stations are ONLY 30-deg away from the weak Desired stations, I don't think a "Faraday Cage" (i.e. Antenna in a Box) solution is going to be of much use...they just can't restrict the Beamwidth enough to make much of a difference. They would be much more useful when strong interference is coming from the Sides or the Rear....

A (very few) High Gain Antennas can be used so that the Undesired signal is attenuated by perhaps 20-30 dB when oriented so that it is well down on the SIDELOBE of the Antenna, with whatever significant Gain is still available directed toward the Desired signal. Most antennas, such as Yagi's (e.g. 91XG), 8-Bay Bowties and most 4-Bay Bowties do NOT provide the requisite Deep Sidelobe Null capability near 470 MHz...and very rarely on higher frequencies.

My DIY H4 (2x2-Bay) just happens to have a Deep Sidelobe NULL near 30-deg away from the Main Beam on 470 MHz (Ch14)...and above:
UHF H4 2x2-Bay Bowtie - 10 Refl Rods

A pair of Horizontally Stacked CM4221HD's also provide a Deep Sidelobe Null near 30-deg on 470 MHz and above:
Horiz-Stacked CM4221HD's - RF Combiner

My FF4 4-Bay Bowtie provides a Deep Sidelobe Null....except NOT on 470 MHz....if requested I could Re-Optimize (or simply Re-Scale) to "find" a solution with a Deep Sidelobe Null on 470 MHz:
UHF Free-Form 4-Bay + DblAnglRefl - OPT

I could also run a Re-Optimization to "find" a higher Gain Horizontally Stacked DIY FF4 solution with a DEEPER NULL near 30-deg at 470 MHz:
http://imageevent.com/holl_ands/stacked/horizontallystackeduhfantennas/horizstackff4dblanglereflhhh

But as I mentioned earlier, Multipath Reflections entering at Angles OTHER than in the Deep Null can circumvent these techniques....so YMMV....
 

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Discussion Starter · #17 · (Edited)
My FF4 4-Bay Bowtie provides a Deep Sidelobe Null....except NOT on 470 MHz....if requested I could Re-Optimize (or simply Re-Scale) to "find" a solution with a Deep Sidelobe Null on 470 MHz:
UHF Free-Form 4-Bay + DblAnglRefl - OPT

I could also run a Re-Optimization to "find" a higher Gain Horizontally Stacked DIY FF4 solution with a DEEPER NULL near 30-deg at 470 MHz:
http://imageevent.com/holl_ands/stac...blanglereflhhh
Could you please try and optimize for those options? I will work with him on creating them and likely modify them if need be and the YMMV doesn't work out. Would they be used horizontally stacked correct? I have the 2x2x48" grid.

As for the cage I knew it would not be ideal, but could it work similar in a V-wall between the antenna's?

Sent from my OnePlusOne
 

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OK....can I concentrate on the Horiz. FF4's for now and when (if?) it works out w can call it quits....or is there some actual interest in a shorter, lower Gain H4....and if so, I would also want to model a Double Angled Reflector Screen Grid version....

Explain a bit more what you had in mind with your proposed "V-Wall".....
 

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Discussion Starter · #19 · (Edited)
Sorry for the late response back.

The 'V' wall I was meaning was to hopefully block out that compass area to then pull in the others around it. Would this be feasible?
My crude drawing of what I was thinking about for the blocking of it.



I would assume you would be able to help with the horizontal stacking spacing and possibly with the degree of 'V' I would need. Also knowing that as you stated above we cannot predict about rebounds from other objects and it still coming in strong.

If this is to be outside, i guess it might have to be the reflector that make up the 'V'.

As the signals are low for him for the US signals I think a preamp would be needed, but know that he would have to have the Left antenna not put through as to not overload the signals from Toronto.


=====

As for the notch filter from Tin Lee it seems that would be a huge cost that my friend is not willing to spend:

Adjacent friendly and deep next to adjacent Notch Filters can range from US$575. To US$725.00 + shipping.
For example:
Filter to notch CH.15 and keep CH.14 would cost approx. US$625.00 + shipping
Filter to Notch >50dB at CH.,35 and CH.36 and to pass CH.38 and CH.33 would also cost approx. US$625.00 + shipping
 

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FF4 + SINGLE-ANGLE-REFLECTOR = DEEP SIDELOBES ON LOWER FREQS:

I haven't (yet) figured how to use nikiml's Optimizer to minimize Gain on one Azimuthal Angle while ALSO maximizing Gain in the Forward direction, (if it is even possible), so the fol. might not be an "Optimum" solution.

I MANUALLY tried a bunch of things for FF4 with Double and Single Angle Reflectors. I ended up with the fol. design which has VERY DEEP SIDELOBES on 470 MHz (at 45-deg away from Forward), which decreases in depth on the higher frequencies. Raw Gain also drops off on the higher frequencies. The key was to decrease the Reflector Sweep to only 2-inches.

Gain in the Null is -16.9 dB and 30-deg away from the Null the Gain is 12.6 dB, for a TOTAL Suppression of 29.8 dB:
UHF FF4 SingleAngleRefl - DeepSidelobes







 
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