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Discussion Starter · #1 ·
Hi all,
I live in Montreal, QC and I am trying to find a suitable 4 bay antenna for outdoor reception. The distance between the TV and the antenna would be around 10 m (30').
In my location, according to tvfool report, the worst case would be channel 13 HI-VHF and 43 UHF with an NM (db)= -3.
I have been looking at the new 4 bay antenna DB4e's (antenna direct) report and it seems that this antenna has a gain of 11.68 dbi (9.53dbd)on channel 14 which is good for my situation. But there is no mention of HI-VHF gain.
I tried to model this antenna with 4nec2 to see its HI-VHF gain, but I don't have all the dimensions of it (bowtie length and spacing...).
I am looking at two options:
1) - Make an antenna. I had modeled a 4 bay antenna and the results are:
CH7-CH13 the gain is between: 9-9.26dbi and SWR is <13.6
CH14-CH51 the gain is between: 14.35-15.09 and SWR is <2.8

This antenna required a reflector that can be made with welded wire mesh 2''Vx4''H, 36'' large and 40'' long but I can't find in my location this kind of material with a good price (less than 20$). I would need also to buy some tools to make the antenna, so I am leaning towards the second option.

2)- My second option is to find a commercial antenna that has a good HI-VHF capability and good low-UHF gain that would be suitable to my situation explained above.

Thanks to anyone can help me find cheap and good materials to make my antenna, model the antenna direct DB4e to see its HI-VHF capability or to suggest any other 4 bay-panel antenna.

MZ
 

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The Antennas Direct DB4e is UHF only;no vhf capability.I own one which I haven't put up yet,but I tried it upstairs.

I discovered:

1)Very poor VHF-Hi reception on my local ch. 12(now 12.1)
2)very directional
39good forward gain
 

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DB4e and DB8e use PCB (Printed Circuit Board) Baluns, which are VERY lossy in Hi-VHF Band, which is something NOT modeled by 4nec2:
http://www.hdtvprimer.com/antennas/temporarypage.html

mclapp M4 Super-4-Bay (9.5x9.0) is an easy DIY (from scratch or a kit) with exceptional UHF performance with better than 9 dBi in FORWARD direction on Hi-VHF and SWR between 4 and 14:
http://imageevent.com/holl_ands/multibay/4bayrefl

You can buy an inexpensive 5, 6 or 10-Element Hi-VHF Yagi or Log-Yagi Antenna....or using dimensions below, build a simple DIY Hi-VHF Antenna that can be combined with a UHF antenna using VHF/UHF Combiner (aka UVSJ) including Circular Loop with Loop Reflector (or Screen Reflector like A-D C2), 2-Bay Bowtie with Reflector Rods, Hi-VHF Bi-Quads with Reflector Rods, Hi-VHF Yagi's and others:
http://imageevent.com/holl_ands/loops/looprefl
http://imageevent.com/holl_ands/loops/hivhfhourglassloop
http://imageevent.com/holl_ands/multibay/hivhf2bayreflrods
http://imageevent.com/holl_ands/biquads
http://imageevent.com/holl_ands/yagis
 

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Discussion Starter · #4 ·
Thank for the suggestions and for letting me know that the DB4e doesn't work on VHF.
I didn't know that the matching impedance that the A-D use filters the VHF signals!!!
The mclapp M4 Super-4-Bay (9.5x9.0) would be my first choice as a DIY antenna.
Right now all the welded mesh wire that I can find here are more than 50 feet long, which is too much, since I need only 40''. Maybe I have to figure out how to make a reflector by simple wires.
My second choice would be to combine two yagi antennas (UHF+VHF). I would maybe build a yagi VHF as described on http://imageevent.com/holl_ands/yagis/ch135elyagioptnikiml

MZ
 

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Discussion Starter · #7 ·
So according to the comparison given in http://www.hdtvprimer.com/antennas/comparing.html
It seems that the CM4228 is the best UHF antenna that can be used for HI-VHF. The new HD CM4228 seems to have a gain of 6bi on Hi-VHF-CH13.
In my case, I think that I would need an antenna with a gain > 4dbd on UHF and Hi-VHF. Since my tvfool report shows that the NM(db) =-3.
I am looking at two yagi combo UHF_VHF antennas:
One from winegard : http://www.winegarddirect.com/viewi...HDHD769-Series-TV-Antenna-(HD7694P)&p=HD7694P
The results for this antenna shows that it has a gain of 11.5 dbd at ch14 and 10.7dbd at ch50 which seems a bit weird since its peak gain is at ch14 and not at ch50!!!!
The second one is from Antenna craft: http://www.antennacraft.net/pdfs/HBU22_.pdf
I am wondering if anyone has experienced those antennas??
MZ
 

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Although it MIGHT be true (MUST model to determine the answer), I wouldn't like to generalize as to whether a contiguous full-width Reflector is NECESSARY to provide more or less "usable" Hi-VHF Band performance. A good counter-example would be two side-by-side CM4221HD 4-Bays using an RF Combiner:
http://imageevent.com/holl_ands/multibay/8bayrefl/horizstackcm4221hd
Note that although it uses two separate Reflector Rod structures, it is a FAIR-to-GOOD, but imperfect Hi-VHF Band antenna, with moderate Gain Loss in the Forward Raw Gain response, oftentimes with more Gain to the REAR....and Excessive SWR on some channels.

The 8-Bay CM4228HD, with contiguous, full-width Reflector Rods, isn't all that much better, with a Forward Raw Gain null on a different frequency, but at least it has more Gain FORWARD than Reverse....but Excessive SWR on some channels.

And the RF Combiner Mod version of the CM4228HD (and older CM4228) provided higher, more consistent Hi-VHF Raw Gain, except on Ch7, although with Excessive SWR (so the Horizontal Harness was NOT helping Hi-VHF performance as I has ASS-U-MEd):
http://imageevent.com/holl_ands/multibay/8bayrefl/cm4228hdmod
http://imageevent.com/holl_ands/multibay/8bayrefl/cm4228asbuiltrcm

Note that nearly ALL of the 8-Bay antennas designed for UHF provide imperfect performance in the Hi-VHF Band, despite their contiguous, full-width Reflectors. And note that M4 4-Bay with Double-Angle Reflector is equal or better than nearly all 4-Bay and 8-Bay antennas in both UHF and Hi-VHF Bands:
http://imageevent.com/holl_ands/multibay/4bayrefl
 

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The mclapp M4 Super-4-Bay (9.5x9.0) would be my first choice as a DIY antenna.
The M4 does a reasonable job on 13. I built the reflectorless model and pick up 13 at about 55km with it. Tried an AD CM5 and it was only marginally better. The M4 can be improved for VHF somewhat by adding some longer reflectors in the 28" to 36" inch range. (The length should be modeled for channel 12.) This was suggested by 300ohm in another thread but don't have the link handy.
 

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Each antenna is, of course, different so we shouldn't draw broad generalizations.
So FWIW, here are the 4nec2 simulation results for the Antennacraft U-8000 8-Bay Bowtie:
http://imageevent.com/holl_ands/multibay/8bayrefl/acu8000refl
Hi-VHF Raw Gain is minimal in the FORWARD direction but is very usable in the REVERSE.

If the 1/4-in Gap between Reflector Elements was eliminated, the Hi-VHF Raw Gain is directed in the FORWARD direction, but has significant Gain Loss on Ch 10, with Excessive SWR on Lower Channels. So the Hi-VHF performance was far from ideal. This mod also significantly reduced the UHF F/B & F/R Ratios, but UHF Raw Gain remained within +/- 1 dB:
http://imageevent.com/holl_ands/multibay/8bayrefl/acu8000fullwidthrefl

So whether Full-Width or Split Reflector we see the same sort of Hi-VHF problems in most 8-Bay Antennas.
 

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holl_ands:
in addition to the PCB balun, this link
http://www.hdtvprimer.com/antennas/comparing.html
says
>> Other 8-bays, like the 8800 and the DB-8, have a reflector that is not continuous across the right and left halves,
>>and thus they have no useful gain for VHF.

would that apply to the DB8e ?
I replaced my DB8 with a DB8e and my VHF HI channels (9 and 11) come in stronger
with the DB8e. You can see my results here:
http://www.digitalhome.ca/forum/showthread.php?t=41076&page=45
 

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just to add my 0.02cad:

i am using a db4 (the 'old' model) in my attic and am getting vhf in addition to uhf.
in fact, i am even getting channel 6 (global in ottawa) without any problems!

of course, it might have to do with the fact that vhf signals are quite strong in the area, making it possible for me and others to get vhf-low with what is supposed to be "just" an uhf antenna.

if you only want to get local signals, a db4e (or an 'old' db4) is perfectly adequate in most circumstances.

if you do not benefit from strong vhf signals in your area, maybe an accessory like the "ClearStream 2 VHF Reflector Assembly" that you could add to your db4e (you should find it on the antenna direct website and elsewhere) could do the trick for you?

cheers.
 

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Discussion Starter · #13 ·
Thank you for the advice.
Now, I get all the '10' Montreal local TV stations including TVA and CTV which are on ch10 and ch12 (VHF-Hi) at 100% by using a simple DIY antenna "2 bay bowtie" placed indoor near the window.
In July, when I move, I can use an outdoor antenna (the mast is already placed). Here is my tvfool report for my new location:
http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id=1dda6ed6ba096f
To summarize, my problem won't be the local TV stations as I can receive them with a small DIY indoor antenna, but the problem is the U.S TV stations and specially ABC on ch-13 and fox on ch-43 (weak signals).
Yes, that would be a great option of using the db4e for UHF which has almost 11dbd gain average on UHF and combine it with another Hi-VHF antenna.
Another option would be to simply use a compact combo UHF-VHF yagi or panel antenna.
My original question was regarding the db4e antenna gain on VHF-hi and its capability since the antenna direct website shows only its uhf performance.
Now I understand that this antenna is designed only for uhf and strong vhf signals and not for weak vhf signals.
I discovered also that the CM-4221HD has a gain of 3.5dbi==>1.35dbd on ch-13.

According to my understanding and my calculation.
For the ABC ch-13: the NM(db)=0.9db.
Let's say that the cable, connectors.... loss would be -2db.
I would use a pre-amp with less than 0.5db noise and 10db of gain
So in that case the gain of my antenna should be > 0.5-0.9 lets say 0.
Which mean that the gain of my antenna should be superior to 0dbd ==> 2.15 dbi.

I didn't considered the cable loss as my pre-amp gain is 10db, I only considered the pre-amp noise in my calculation.

Can any one tel me if that correct? or tell me what would be the minimum gain that I would need on VHF and UHF according to my tvfool report.
Any suggestions would be appreciated!!!

Cheers,
 

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First off, your TVFool report is for the default elevation of 10 feet. You should rerun the elevation at the intended height of the new antenna. This will make a big difference in the reception of the Mount Mansfield channels.

The bad news is that at your new location, the Mount mansfield channels are only 7 degrees off your local Mount Royal channels.
With 50-60 dB difference in levels for channels 12 and 13, you may find it hard or omposible to receive WVNY. Rerun the TVFool and we could discuss this more.
 

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We rarely suggest using any of our UHF designs for VHF reception since that is not what they are designed and characterized for. What VHF reception takes place is out of design band and is generally assumed to be coincidental to the intent of the design.

For most n-Bay antennas, one will usually find that VHF reception peaks and nulls are quite irregular and change tremendously with azimuth. Generally, they tend to receive VHF better off the back than the front, but it really depends on the specific design on the particular antenna under discussion.

Unless VHF channels are close by and strong, we assume it is better to recommend an antenna or accessory that has known VHF performance unless someone wants to give a UHF design antenna a try by itself first. They tend to work okay for "close in" situations or if at certain azimuths relative to the primary aiming direction.
 

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Discussion Starter · #17 ·
Hi all,
Here is my new tvfool report with the exact elevation :
http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id=1dda856879a397
I did a calculation based on the chart sent by Holl_ands :
I considered the coax loss (1.68), balun loos(1.5), pre-amp gain (10) and noise (0.5), the tuner noise (16db instead of 6 figured on the chart since my tv lock up when its SNR level indicate a value of 16db) and ended with -9.68dB let's say -10db.
PS: I experienced the the SNR threshold level (the minimum SNR to have a picture) for my tv tuner since I can't find it in the specs.

tvlurker: If I understand, the ch12 which has a strong signal will be noisy for the ch13!!!!So, Should I focus on UHF band only? and what would be my chance of getting the channel 43?
Holl_ands: how can I calculate the received signal level if I don't know the gain of my antenna?

Let's consider an antenna with a gain of 10 db ==> SNF=10-10=0db.
If I consider channel 43 with a power level of -87dbm==> my received signal level would be the same -87dbm. What this number can tell me? I don't know what is the minimum level of signal required by my TV.
PS: My TV is an LCD 46'' Samsung.
Thank you for your help and suggestions.

Cheers
 

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If you are using a preamp, the noise figure for the TV should not contribute too much to the System Noise Figure.

When doing all these calculations, you should end up with a System Noise Margin, As long as it is positive, you have a chance at WFFF.

I don't think you have much hope for WVNY, but you might be able to get WFFF.
Since your view of Mount Mansfield is blocked by terrain, you never know exactly how the signals will refract towards you. They may be better or worse than the model predicts, so just try it and see.
 

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Assuming 10 dBd (12 dBi) Gain for a 4-Bay Antenna will give you a reasonable "ballpark" number. DB-4E is close to that number on low-mid frequencies and is a couple dB better on high frequencies. It's also in the ballpark of CM4221HD, although high performance M4 and Kosmic-Quad 4-Bays are considerably better:
http://www.antennasdirect.com/cmss_files/attachmentlibrary/Technical Data PDF's/DB4E-TDS.pdf
http://imageevent.com/holl_ands/multibay/4bayrefl

As I remarked in the earlier cited post, the System NF Chart assumes an exceptional ATSC Tuner Noise Figure = 6dB. For presumed ATSC minimum SNR=15.2 dB (if no multipath) and Thermal Noise Floor = 106.2 dBm, this corresponds to Sensitivity = -85 dBm.

In 2008, a batch of Low-Rez CECB Converter Boxes were tested, finding a MEDIAN Sensitivity between -85 dBm and -86.6 dBm (variation was about +/-2 dB). These are the ONLY ATSC Tuners that had to pass an actual Sensitivity Specification Test derived from ATSC A/74 "Guidelines", which manufacturers complained was very difficult to meet, esp. when later required to also provide an Analog Pass-Thru feature. New (e.g. 2008 and later) HDTV's are "probably" also providing NF's in 5-8 dB ballpark, which varies across the TV Bands....and there is NO REASON to expect new Tuners to be significantly better than 2008-era CECB's.
http://www.nabfastroad.org/NABSTVDigitalConverterBoxEvaluation/DigitalConverter.asp

" The median on-channel RF sensitivity values, when considering each CECB unit across all the tested RF channels (low-VHF, high-VHF, and UHF) varied from -85.0 dBm (unit #1) to -86.8 dBm (unit #6), thus providing reasonable margin beyond the NTIA spec of
-83.0 dBm. Even analysis across all CECB units on the same channel showed that there is very little difference among RF channel frequencies across the three television bands: -85.2 dBm (CH 2) to -86.7 dBm (CH 6). Importantly, no sensitivity problems
existed in the low-VHF band where previous FCC lab testing showed problems on some of the early DTV receivers."


Older (2005-2006) HDTV's and HD-STB were found to have considerably higher Noise Figures:
http://transition.fcc.gov/oet/info/documents/reports/TR-05-1017-ATSC-reception-testing.pdf

"Median across all receivers (dB) 8.8 dB (Ch2), 7.6 dB (Ch10), 6.9 dB (Ch30)
Deviations of receivers from median
--Best performing receiver (dB) -2.5 dB, -1.3, dB, -1.3 dB
--Worst performing receiver (dB) 12.2 dB, 4.5 dB, 2.6 dB"


Note that NM "should" be positive by 10-20 dB to ensure year-round performance in the presence of
multipath, co-channel & adjacent interference, man-made interference (esp Lo-VHF), etc.
This is frequently called the "Fade Margin" in communication systems....

You also might need to guesstimate additional losses due to trees, surrounding buildings
blocking the signal (good luck!!!!), clutter loss if the signal grazes the rooftops and indoor loss
if located indoors (est 13 dB +/- 7 dB)....or more if Low-E glass & aluminized moisture barrier.
Yes, some people get intermittent reception with slightly negative NM...but troposcatter
propagation (esp across water) can't be relied on.

Also bear in mind that TVFool is based on the NTIA's Longley-Rice STATISTICAL Propagation Prediction model which calculates the NM that would apply for 50% of people in the presumed "Location" for 90% of the Time....hence the need to include 10-20 dB "Fade Margin" for 1-Edge and 2-Edge paths and perhaps 5 dB for LOS paths:
http://www.digitalhome.ca/forum/showthread.php?p=1480896
 
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