: Central/Eastern USA, Gulf Coast, Mexico, Caribbean
2012-01-18, 01:03 PM
Per DIY TV Antennas, Reflectors web page (http://m4antenna.eastmasonvilleweather.com/reflector/Reflectors.html)
The curved or angled oversize reflector along with swept forward whisker elements can help narrow the beam width of the antenna by squeezing the gain more in the forward direction and less on the sides and rear. This reflector also works well to enhance VHF-hi channel 7-13 reception. With this style reflector on a 4 bay UHF reception in the 60-80 mile range can be normal depending on antenna placement, surroundings and terrain.
Per M4 antenna 4-Bay Curved Reflector pdf (http://m4antenna.eastmasonvilleweather.com/Drawings/4%20bay%20curved%20reflector.pdf)
The reflector screen can be 36" high but 40" is slightly better.
Wider screens will give slightly better gain, any width from 30" to 48" works well.
Given the above information, what size curved reflector is recommend for our location?
Height: 36" or 40"?
Width: 36", 40", 44", or 48"?
2012-01-31, 12:20 AM
I've continued to research antenna information for our situation and found a very informative thread (http://digitalhome.ca/forum/showthread.php?t=115520):
Raw Gain Summary (Max is within NEW UHF Band) (http://digitalhome.ca/forum/showpost.php?p=1338393&postcount=125):
M8 (9.5"x9.0"): Ch14=16.2 dBi, Max=18.9 dBi, per mclapp 4nec2.
M4 (10"x9.5"): Ch14=13.8 dBi, Max=15.7 dBi, per holl_ands 4nec2.
M4 (9.5"x9.0"): Ch14=13.7 dBi, Max=15.5 dBi, per holl_ands 4nec2.
W-G HD-8800: Ch14=13.7 dBi, Max=15.5 dBi, per Ken Nist's HDTVPrimer.
Super-G-1483: Ch14=12.5 dBi, Max=16.0 dBi, per 300ohm 4nec2.
Old CM4221: Ch14=12.3 dBi, Max=14.5 dBi, per holl_ands 4nec2.
A-D 91XG: Ch14=11.5 dBi, Max=17.0 dBi, per holl_ands mod to Ken Nist's EZNEC.
CM4221HD: Ch14=11.2 dBi, Max=15.0 dBi, per holl_ands 4nec2.
CM4228HD: Ch14=10.5 dBi, Max=14.9 dBi, per holl_ands 4nec2.
M8 obviously has highest Gain on Ch14 and Max within NEW UHF Band,
but any of the other antennas could ALSO be stacked for a "nominal" +2.5 dB.
The two M4 models and W-G HD-8800 (aka PR-8800) were essentially the SAME.
Any of these would provide good performance on Ch14 and across the New UHF Band.
A-D 91XG, CM4221HD and CM4228HD had about 1 dB lower Gain on Ch14, which
would be difficult to observe in REAL OTA Tests......
And YES, the new CM4228HD (without mods) is WORSE than CM4221HD.
Even if the "Split" or "RF Combiner" mod were to be used with the CM4228HD,
I would expect the (not shown) insertion and phase matching loss in the combiner
would reduce the overall improvement to only 1 or 2 dB....no better than M4.
I really appreciate that comparison, excellent, thank you
It really shows the M4 is a VERY decent antenna, at least for across UHF, not bad for a DIY project. It seems like it comes down to a matter of where we need the gain. Obviously, though if we need good F/B, the 91XG is by far still the best.
Which of these two choices is best suited for our location?
M4 complete kit w/curved 1x2" welded-wire reflector (7-51 0ne-antenna solution)
AD 91XG + YA-1713 (7-69 stacked-antenna solution)
2012-01-31, 09:55 AM
Keep in mind that the M4 has 5 - 7 dBi gain for the DC VHF stations and 2 - 4 dBi gain for the Baltimore VHF stations. I lean towards the 91XG / YA-1713 combination for that reason.
2012-01-31, 10:18 AM
The VHF-hi gain figures you mentioned are for which version of the M4?
10" x 9.5"
9.5" x 9.0"
9.0" x 8.5"
And what width 40"-T curved-reflector?
2012-01-31, 12:18 PM
M4's on mclapp's website are MUCH HIGHER in both UHF and Hi-VHF Gain:
And it is important to note that the Hi-VHF Gain is directed FORWARD,
unlike many other smaller 4-Bay antennas with smaller Reflectors:
PS: Although mclapp doesn't post his EZNEC or 4nec2 files anymore, he did on his
previous website. The so-called "Curved" reflector was modeled as a Four-Angled
Reflector in his M4 and M8 antennas, whereas I modeled his Double-Angled Reflector.
I doubt there is much difference if you "smooth" out the angles into an actual curve,
esp for Hi-VHF where the WIDTH and Whisker Length are the primary parameters.
M4 (10x9.5) with 40"H x 36"W Double Angled Reflector: [Hi-VHF Gain = 9.5-9.0 dBi]
M4 (9.5x9) with 40"H x 40"W Curved Reflector: [Hi-VHF Gain = 8.6-8.9 dBi]
http://m4antenna.eastmasonvilleweather.com/Computer%20models/Computer%20models.html [See at BOTTOM.]
M4 (9.5x9) with 40"H x 36"W Double Angled Reflector: [Hi-VHF Gain = 8.6-8.8 dBi]
Incl. Effect of Forward Swept Bowties:
Kosmic Super-Quad (9.75x9.5) with 34"H x 28"W Single Angled Refl: [Hi-VHF Gain = 7.4-8.6 dBi]
2012-01-31, 12:41 PM
Thanks for the reply holl_ands.
Which version of the M4 would you recommend for our location (http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id%3d83877d4a4305a6) with which size and shape reflector?
2012-01-31, 12:59 PM
And the obvious winner is....drumroll.....M4 (10x9.5) with 40"H x 36"W Double Angled Reflector.
At least from the list of known 4nec2 & EZNEC models for 4-Bay Bowtie Antennas....
I started to build a set of Screen Reflectors with different Widths....but other distractions
are always....SQUIRREL!!!!....coming along to divert me away from that task.....and then I got
to thinking about how many different Bend angles and Lengths/Swept Angles/Tine Separations
and other parameters I would have to try to find the optimum configuration...so I thought
about building a variable, SYmbol driven, Screen Reflector model.....so I could use nikiml's
optimization scripts....which would take many DAYS to run each trial......so there it sits....
And then along came the huge KISS-Quad (Quasi-Parabolic) Reflector idea.....SQUIRREL!!!!
2012-01-31, 01:26 PM
Decision Chart for OTA Antennas in Canada v8.2 (http://beta.images.theglobeandmail.com/archive/01310/Digital_Home_anten_1310729a.pdf)
Small to Medium Combo 7-51
RCA ANT-751 - recommended* However, "Best diy may outperfom recommended"
With such respectable 7-51 performance, where would the M4 (10x9.5) with 40"H x 36"W rate for fringe performance?
Does the M4 (10x9.5) with 40"H x 36"W curved reflector have sufficient 7-51 fringe performance for our location?
How does the M4 (10x9.5) with 40"H x 36"W compare to the G-H w/NARODs that's listed as "Excellent" for Deepest Fringe?
2012-01-31, 01:50 PM
The "best" G-H with NARODs for Hi-VHF performance is found here:
http://www.digitalhome.ca/forum/showthread.php?t=121956 [Hi-VHF Gain = 8.3-9.3 dBi]
So G-H with NARODs is slightly lower Hi-VHF Gain and roughly same [UHF Gain = 13.6-15.5 dBi]
Looking at your TVFool report, you only "NEED" to receive stations as weak as
"The CW" (Real Ch40), with NM=16.5, although there MAY be different programming
on the weaker PBS stations (Ch29 NM=16.1 and Ch33 NM=11.8 and Ch27 NM=10.4).
If you are driving multiple TVs/DVRs/VCRs/HTPCs, you should use a mast-mounted
Preamp....although you should pick one of the lower Gain models to avoid possible
interference from FM stations.
I checked FMFool for your zipcode: there's a bunch of stations 12 miles away from the
(Post Office???), but they are all 1 & 2-edge so shouldn't be much of an interference
threat...BUT you should enter YOUR location into www.fmfool.com just to make sure.
If signal strengths are stronger than about -40 dBm, then you'll either need an
FM Band Full-Band Stop Filter (not just a narrow-band notch filter built into some
Preamps) OR buy a Preamp with ZERO VHF-Band Gain (Winegard calls it a VHF "Bypass"),
which will lose quite a bit of signal strength if you split to multiple coax drops.
I can't predict how much loss there is in your line of trees....but you'll need as much
Antenna Gain as is reasonably possible. Since the above DIY M4 has about as much
Hi-VHF Gain as the W-G YA-1713, it's certainly worth a shot....and if you find you
need more Hi-VHF Gain, you might need to add something significantly better than
the YA-1713 to make much of a difference...
OR start with mclapp's Vertical M8 for higher [UHF Gain=16.2-18.8 dBi] and [Hi-VHF Gain=10.0-10.8 dBi]:
Which will easily beat an A-D 91XG for UHF and is equal to W-G YA-1713 [~10 dBi] or AntennaCraft Y10-7-13.
PS: 4nec2 Results for AntennaCraft Y10-7-13 [much better than their specs imply]:
http://imageevent.com/holl_ands/logyagi/y10713 [Hi-VHF Gain=7.2-13.0 dBi]
You probably don't need the following, but in case anyone wanted to know:
One of our highest Gain for UHF is perhaps the KISS-Quad (Quasi-Parabolic) [UHF Gain=16.5-19.5 dBi]:
Other very high Gain (read "HUGE") antennas for UHF include the Curtain Quad and true Parabolas.
Hmmmm....what's our highest Gain Hi-VHF Antenna....4.7-ft high 2-Bay w Reflector [Hi-VHF Gain= 10.5-12.8 dBi]
the monster 9.5-ft high 4-Bay....I didn't model it, but add 3 dB for 4-Bay with Reflector: [Hi-VHF~13.8-15.3 dBi]:
2012-01-31, 02:10 PM
Thank you for your incisive analysis & recommendations. :)
WETA Ch27 NM=10.4 does have different programming than the MPT Maryland Public TV stations. But I don't know if this critical.
If the M4 isn't sufficient, we could always upgrade to an M8 with a 2nd M4. However, I'm hoping we don't have to go that tall.
How does the M4 one-antenna 7-51 solution compare to the not yet rescaled 91-XG for our location?
2012-01-31, 02:15 PM
otadtvman and holl_ands,
After getting a bit confused by diagrams showing tot-gain consistantly labelled "Raw Gain" and noting the relatively high VSWR for the high-VHF band plotted on his modeling (http://m4antenna.eastmasonvilleweather.com/Data/Data.html) page, I used information plotted on his field testing (http://m4antenna.eastmasonvilleweather.com/Data/Data.html) page. Note that the M4 design under test was a 9.75" x 9.5" with a curved reflector and 4.5' reflector spacing.
Note that the gain curve plotted in that comparison chart fits nicely with the combination of the tot-gain and VSWR plots.
2012-01-31, 02:31 PM
If you have a choice of PBS outlets and are worried about picture quality, note that, according to rabbitears.info, MPT stations devote an average of 12.55 Mbps to the main channel while WETA devotes only 9.15 Mbps. I know that I get irritated by macroblocking artifacts when watching WETA.
2012-01-31, 04:31 PM
otadtvman, uding mclapp's field test page, the antennas direct techical data, and this (http://clients.teksavvy.com/~nickm/gh_n3_uV.html) page that documents the best G-H designs for reference, I see a couple of scenarios similar to what holl_ands mentioned:
1) You cannot beat an M4 for performance vs. ease and low-cost of build for UHF. Based on the field tests, it should deliver very similar performance to an XG-91 (about a dB or so down over the band). Like holl_ands said, you may luck out and have enough VHF performance for the DC stations. If not, then you can easily add the VHF-hi antenna we've been recommending.
2) You cannont beat a Gray-Hoverman with top-hats for high performance in both VHF-hi and UHF in a compact space. The downside is the complexity of building such a beast. There are many posts in this forum that give tips on how to make the process easier. I would recommend searching for member unclesam's posts for his SNAP design. His albums are here (http://www.digitalhome.ca/forum/album.php?u=90934).
3) The XG-91 and YA-1713 have been the recommended fringe combination in many forums.
2012-02-01, 01:55 PM
NET GAIN vs RAW GAIN:
SWR (aka VSWR) causes Mismatch Loss, where Net Gain = Raw Gain - Mismatch Loss (ML):
I try to keep SWR below 2.7, which results in only 1 dB of ML. SWR=4.1 causes 2 dB of ML:
Note that it is also important to keep SWR low to minimize the ADDITIONAL loss due to
Error Vector Magnitude (EVM) degradation to the ATSC digital waveform (see Bendov articles).
As shown in the fol. simulation, SWR results in NULLS being formed every 1/2-wavelength along the coax:
The DEPTH of the "NULL" is the Mismatch Loss...which in most antennas should be fairly small,
so it's more like a GAIN DIP than a NULL. BUT, "NULLS" will ONLY be visible at the END of the Coax
when the electrical length is a multiple of 1/2-wavelength at a particular frequency. Hence
throughout each band, only ONE frequency will experience a (weak) "NULL", a few might experience
a partial "NULL" and the others will be unaffected. And perhaps NONE if high SWR is only experienced
over a narrow range of channels, as is typical for many antennas (e.g. commercial 4-Bays).
Bear in mind that 1-2 dB of Mismatch Loss will ONLY be "visible" on the WEAKEST channel positions.
Worst case, only one or two channels will have a NULL at the END of the Coax, which can be CURED
by inserting a short length of coax to hopefully move it to an unoccupied or strong channel position.
[Lots of luck determining whether you even HAVE a 1-2 dB NULL on a particular channel position!!!!]
When using a Mast-Mounted Preamp, the Coax length should be much less than a 1/2-wavelength
at the highest frequency (8.5-inches), so standing waves can't form and there will be NO NULLS
and hence NET GAIN = RAW GAIN. Since Preamps are inherently broadband devices, they also should
have much lower SWR than a typical tuner, with it's tuned input filter. So EVM degradation should
also be lower with a Mast-Mounted Preamp.....IF IT DOESN'T OVERLOAD & DEGRADE THE NOISE FLOOR.
I prefer to only report RAW GAIN and SWR...rather than copying multiple columns of data into Excel
to plot Net Gain....which as I've explained, is of minimal or NO consequence for most of our channels.
FYI: A-D 91XG plots for Raw Gain & SWR can be found here:
Rescaling would move the Gain curve to the left, reducing the BIG GAIN LOSS on Lower Channels.
PS: The mclapp "modeling" link in post#99 above was incorrect, use this one:
PPS: A reminder, don't forget to enter your location into www.fmfool.com to check for strong
FM stations to see whether Hi-VHF signals need to go through an FM Band Stop Filter prior to Preamp.
2012-02-01, 03:21 PM
Thank you for all the info and tips.
BUT you should enter YOUR location into www.fmfool.com just to make sure. If signal strengths are stronger than about -40 dBm, then you'll either need an FM Band Full-Band Stop Filter (not just a narrow-band notch filter built into some Preamps) OR buy a Preamp with ZERO VHF-Band Gain (Winegard calls it a VHF "Bypass"), which will lose quite a bit of signal strength if you split to multiple coax drops[.
There are 5 FM stations that are LOS and range from -44dBm to -22dBm between 3-5 miles away: 88.1, 88.9, 99.9, 103.1, 103.9.
2012-02-01, 05:29 PM
The strong ones can be a problem since their second harmonics (2xfreq) COULD desensitize some Hi-VHF
channels....do the math to see if they lie on top of your weak channels....
The strong ones will also increase the 3rd Order Intermod Noise Floor....which may or may not fall on
top of your weak channels....I provided a calculator:
http://imageevent.com/holl_ands/files/ota [Enter STRONG FM Freqs into DTV Interference Calculator]
M4 has FORWARD Gain~0 dBi and REVERSE Gain~2-6 dBi in the FM Band with a fairly broadbeam,
more or less Bi-Directional azimuthal pattern....so it's only suppressing FM signals if they happen
to be off to the SIDES when pointed in the desired direction for a particular DTV station.
If you don't care about Ch3, you could use a HLSJ Low/High-VHF Band Separator to provide 25+ dB
of suppression for Ch2-6+FM signals prior to the Preamp. Terminate unused Lo-VHF port with 75-ohm
coax terminator resistor. If you DO care about Ch3, you MIGHT need an FM Full-Band Stop Filter
or perhaps one to three narrow band notch filters....upper two and lower two fit in same notch...
you didn't say what each signal strength was....the one(s) at -44 dBm aren't much of a problem...
2012-02-01, 06:31 PM
If you don't care about Ch3, you could use a HLSJ Low/High-VHF Band Separator to provide 25+ dB of suppression for Ch2-6+FM signals prior to the Preamp. Terminate unused Lo-VHF port with 75-ohm coax terminator resistor.
Sounds like a plan! Any particular brand/model?
2nd harm. (MHz) VHF-hi
99.9 -21.9dBm 199.8 = 10
103.1 -31.0dBm 206.2 = 12
103.9 -33.5dBm 207.8 = 12
2012-02-01, 08:55 PM
Although I've see loss vs freq charts for UVSJ's, I haven't seen any for HLSJ.
Holland specs "look" better than Pico-Macom, but they're probably about equal...
PS: Probably not strong enough to cause any problems, but
2nd Harmonic of 88.1 is 176.2 (Ch7)
2nd Harmonic of 88.9 is 177.8 (Ch7)
2012-02-08, 09:08 PM
Been lurking for a while, and have been trying to figure out the answer to this question, but I'm not sure which of the conflicting answers that I've found should be the one I go with. So I think it's time that I ask for advice.
I have plans on constructing a SBGH antenna this weekend. Given my location (http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id%3d0b8614feab4017) does it make more sense to build two antennas, one pointed to the west and one pointed to the south and combine them. Or am I better off just going with one and aiming to the southwest?
I know that there's a minimum of 3db's lost when I combine antennas. But given how wide a view a single antenna would have to get, it strikes me that I might lose more db's from not being aimed correctly than from the combiner.
At the same time, I read a few posts from 300ohm who says that the GH antenna doesn't need to be aimed. But then I read others who talk about how that antenna does a fantastic job of blocking out stations when the signals are directly on the side. And then I look at the radiation plots (http://www.digitalhome.ca/ota/superantenna/performance.htm) and I think that it looks like aiming matters quite a bit.
So what do you think? Aim a single antenna to the southwest or build two and combine them?
Thanks in advance.
2012-02-08, 11:02 PM
my guess is you'll do just fine with one facing SW.
But build it give it a whirl, experiment and see how ya make out.
That's what it's all about, experimenting. And be sure to stop back
with your results and / or further questions once ya get a chance to try it out.