Central/Eastern USA, Gulf Coast, Mexico, Caribbean

[300ohm]

Since we at times have obvious multi-path interference (causing reception dropouts & signal meter on CM-7000 D-2-A converter to bounce wildly to zero despite strong signal) in our 2edge reception area is the curved reflector worth the more narrow beamwidth?

Did you used to have ghosts way back in analog days ?

[otadtvman]

In the NTSC era we used a CM-1162a in the attic aimed at DC and did not have a ghost issue. However, the neighbor's Norwary spruce windbreak is now much taller.

[300ohm]

It doesnt sound like multipath, but rather some sort of fading of the 2 edge signal, which for 2 edge signals is common. The spruce trees wouldnt cause multipath, but rather a straight forward signal blockage which increases when they are wet.
The flat or curved reflector wont make a difference either way.

[otadtvman]

It doesnt sound like multipath, but rather some sort of fading of the 2 edge signal, which for 2 edge signals is common.

2 edge signal fading would cause rapid signal fluctuations as displayed on the signal meter of a CM-7000 D-2-A converter between a very strong signal and zero along with reception dropouts?

[300ohm]

How long do these episodes last ? And when do they generally occur, ie morning, afternoon or night ?

Im skeptical that its multipath because of no reflected signals, ie ghosts, on analog. Of course something very large in the signal path could have been built since. Is the signal in the path of an airport ? Airplanes/helicopters produce those kinds of symptoms.

[otadtvman]

With the CM-7000, the signal meter is only displayed when one presses the "info" button on the remote. This function then displays a pop-up window over top of the video image. Thus, if one wants to see the whole video image, this function needs to be off. Consequently, the signal meter is not typically observed unless there is a reception issue.

Thus, it's typically during a storm, when there are audio and/or video dropouts, that I typically see these rapid signal fluctuations between a very strong signal and zero. I will need to double check what happens when there is rain w/o wind gusts.

About 2 miles from our house directly between us and the DC trnasmitters is a military base w/o an airport. However, there is occasional helicopter traffic. It also has an antenna farm that includes extremely large dish antennas. It's one of two emergency communications links between the Oval Office and the Kremlin.

In September 1998, an Army Signal Brigade communications facility was relocated to this base.

The brigade provides and defends global information capabilities to enable joint and combined Battle Command across the full spectrum of operations from the President of the United States to the warfighter and other Federal Agencies.

Growth in size and technical expertise at the battalion has been phenomenal. It is the gateway station for long haul communications worldwide serving 15 switching centers. It is a key element in the Washington Area Wideband System, which carries a variety of transmissions from the National Command Authority to worldwide users.

[300ohm]

Thus, it's typically during a storm, when there are audio and/or video dropouts, that I typically see these rapid signal fluctuations between a very strong signal and zero. I will need to double check what happens when there is rain w/o wind gusts.

Yeah, thats just additional signal blockage from the spruce trees when wet and shaking in the wind. The flat or curved reflector wont make much of a difference either way for that, except for the small bit of additional gain from the curved reflector. It may reduce the duration of the problem by 5%, but 95% of the problem will still be more than enough to annoy, heh.

I misspoke earlier, airplanes and helicopter do produce multipath along with signal blockage. But the solution for them is different than for traditional multipath/ghosting from the back or sides. For airplanes and helicopters, stacking two antennas vertically will reduce the effects. I dont think thats something you would want to do. Either way, the flat or curved reflector wont make a difference for the planes and chopters.

Basically as noted before, the larger reflector and tilting are going to do you the most good.

[majortom]

Originally Posted by otadtvman

2 edge signal fading would cause rapid signal fluctuations as displayed on the signal meter of a CM-7000 D-2-A converter between a very strong signal and zero along with reception dropouts?

otadtvman,
not familiar with the CM-7000, but does it normally have an indication someplace in between
when not receiving a good signal?
I know my LG TV will display ZERO signal when just below the threshold of reception, while at the same time the Zenith CECB will display a whisper of Signal when just below the lock threshold. All depends how the mfr designed it.

[otadtvman]

otadtvman,
not familiar with the CM-7000, but does it normally have an indication someplace in between when not receiving a good signal?

With the CM-7000, the signal meter is only displayed when one presses the "info" button on the remote. This function then displays a pop-up window over top of the video image.

The signal meter has a horizontal yellow bar - the stronger the signal - the longer the bar. Just to the right of the bar is a numerical readout from 0 to 100%

[coloradotrout]

Well.. I put a crude sbgh on the roof and the reception was no better -- maybe even worse -- then when it was sitting next to the tv. The roof raised it 20' and outside the 2x4 wall / window.

The sbgh was just a 12g. Cu wire bent to the old specs screwed to a 1x4 with a walmart balun. I've now made a pvc frame to hold up the same antenna and it's stitting next to the tv as well.

My old tv antenna had a permacolor preamp. It must have gone bad as the signal went from pretty good to lousy for all but 1 or 2 channels. I tried the preamp with my crude sbhg and it too was lousy. But w/o the preamp, was as I described above. So, my thinking is the 50' or so of coax is losing a lot of signal before it reaches my inline amp. I guess I need to haul a tv up to the roof and see if that's the case. Maybe my roof signal is just not much better than in the living room.

[otadtvman]

Per DIY TV Antennas, Reflectors web page

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

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"?

Thanks

[otadtvman]

I've continued to research antenna information for our situation and found a very informative thread:

Originally Posted by holl_ands

2011-10-17
Raw Gain Summary (Max is within NEW UHF Band):

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.

Originally Posted by balm

2011-10-17
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)

Thank you

[Dave Loudin]

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.

[otadtvman]

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?

Thanks

[holl_ands]

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:
http://m4antenna.eastmasonvilleweather.com/index.html
http://imageevent.com/holl_ands/multibay/4bayrefl

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]
http://photos.imageevent.com/holl_an...%20Max15-8.jpg
http://photos.imageevent.com/holl_an...Raw%20Gain.jpg

M4 (9.5x9) with 40"H x 40"W Curved Reflector: [Hi-VHF Gain = 8.6-8.9 dBi]
http://m4antenna.eastmasonvilleweath...%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]
http://photos.imageevent.com/holl_an...Raw%20Gain.jpg
http://photos.imageevent.com/holl_an...Raw%20Gain.jpg
Incl. Effect of Forward Swept Bowties:
http://photos.imageevent.com/holl_an...eep_2.0-in.jpg

Kosmic Super-Quad (9.75x9.5) with 34"H x 28"W Single Angled Refl: [Hi-VHF Gain = 7.4-8.6 dBi]
http://photos.imageevent.com/holl_an...in%20Chart.jpg
http://photos.imageevent.com/holl_an...in%20Chart.jpg