cm4228 ch 7-13 vhf performance

[Rick0725]

here's a guy who actually measured the net gain on the cm4228 for vhf ch 7-13

http://www.hdtvprimer.com/ANTENNAS/comparing.html

see net gain...cm4228 in dbd (up and down) - most antennas are measured in dbd...but look out in measurements in dbi=dbd +2.14

ch
7 0dbd
8 -4
*9 +3
*10 +6
*11+5
12-2
*13 +4

lets compare gain just on ch 9 (middle of band and a commom ch. measured by the manufacturers)

uhf only antenna examples from graph
cm4228 +3
pr8800 -3
cm4221 -14
db8 -19
sharpshooter -11
squareshooter -22

vhf/uhf combos - from mfg. specs.
winegard
hd 7080p +9.5
hd7082p +10.9
hd7084p +12.0
hd8200p +12.6

channel master - from mfg. specs
cm 3016 +8.7
cm3018 +9.0
cm3020 +9.9
cm3677+8.0
cm3679 +7.9
cm3678 +9.6
cm3671 +11.0

ch 7-13 vhf yagis - avg mfg. specs
6 element +7
13 element +10

for ch 9 ... on paper looking at a chart and a graph

cm4228 +3.

to put things into perspective...

-we are talking silver sensor/ square shooter uhf type performance for ch 10, 11, and 13 vhf with the cm4228... look at the net gain on the chart for these antennas (Just to give a reference some may be familiar with).

-ch 9,10,11, and 13 are in the positive...all others are kinda low and others negative.

-the dips on the graph are real deep and narrow...this means if the testing was off even a tadd, the dip could be moved to the left or right affecting performance.

-from the gain levels we are probably talking yellow, green, lt green as ok...going up to red , blue purple, the results success should lessen

-***the variables associated from user to user differ and affect performance...terrain, height above sea level, transmit powers, line of site, home construction materials (for attic installs), etc. , etc.

so yes, there are going to be reports of good reception...and there are many... and there are even some bad.

In general, antenna performance with dbd of less than 6 dbd can be considered marginal.

What does marginal mean?

-subtract coax losses
-subtract splitter losses
-subtract signal losses if installed in an attic
-subtract misc. factors that are not easily determined

The net result does not leave much gain.

The numbers above offer a comparison using a consistant form of measurement. And we never see it layed out in black and white...and it made more sense to me when I laid it out on paper.

This information is not intended to say that the cm4228 stinks. It is a great performer.

The variables mentioned above *** are giving us the variation in reception...and the pissing matches we read at the forums.

Please feel free to comment...

 

[dougruss]

Please feel free to comment...

I think I wasted my time reading this ??

 

[ralfyguy]

Rick, check out the values for my XG91!

 

[riffjim4069]

CM-4228 to receive upper band VHF in 2009?

Interesting read regarding CM-4228 operation in the VHF band...

I have two 4228 antennas w/matching CM-7775 UHF preamps: one pulls in DTV from DC (55+ miles) and Baltimore MD (90+ miles) and the other pulls in DTV from Richmond (51+ miles) and Charlottesville VA (53+ miles). I am extremely happy with the performance of the 4228, but need to make a decisions then local broadcaster turn off analog channels in early 2009 and, as in my case, a few of them revert back to their old VHF frequencies - my DTV heaven will turn into a DTV hell of sorts.

I've heard about some 4228s working well in the upper VHF range, but I had no desire to receive any VHF noise when I installed my 4228s - that's why I went with the CM-7775 UHF vice the CM-7777 UHF/VHF preamp. Needless to say, I'm in a weak signal area any VHF that's received doesn't even make it down the mast and 75-100ft. of RG-6.

Anyway, replacing my 4228 with two monstrously huge VHF/UHF antennas is not something I am going to do. The three local area broadcasters reverting back to VHF will be on 7, 9, and 12...I believe. Do you think it's possible for me to swap out my preamps and receive these channels with the 4228s? I don't have much faith in this solution...

 

[Rick0725]

the mfg claims 16.7 max gain between ch 50-69 but that is dbi...which is 2.14db above dipole (dbd)

dbd is the standard.

16.7-2.14=14.56. which aint too shabby

I have not seen mfg. specs for the 91xg anywhere.

 

[Rick0725]

Do you think it's possible for me to swap out my preamps and receive these channels with the 4228s? I don't have much faith in this solution...

You can try swapping the cm7775 with a cm7777 full band amp...and see how the cm4228 performs on the channels in question then.

If the stations currently transmit on those channels in analog ...there can be an indication how well the "potential" is for performance after the transition so to speak I would imagine...if you experimented now.

The variables I mention above are so difficult to determine (until you actually try).

 

[ralfyguy]

the mfg claims 16.7 max gain between ch 50-69 but that is dbi...which is 2.14db above dipole (dbd)

dbd is the standard.

16.7-2.14=14.56. which aint too shabby

I have not seen mfg. specs for the 91xg anywhere.

I think t still beats my old CM3020. What's the values on your 8200p?

 

[Rick0725]

I think t still beats my old CM3020. What's the values on your 8200p?

you got that right. the avg uhf gain of the cm3020 is 9.5 on the spreadsheet I received from cm a few years ago..

from what you are saying ...you have a hot antenna and I am really interested in trying one. Then I can honestly compare performance against my 8200P. I am hesitant because I am concerned about snow load especially on the elements close to the receiving element. We get alot of accumulated snow here...we are in the snow belt off lake ontario and it can come down hard wet heavy and fast. The antenna can come down from the load if not installed properly.

plus today I had a few minutes to play and I could not recieve a thing from the west and pictures were marginal to the east. kinda frustrates you sometimes and my antenna is 14' + feet long.

The avg uhf gain on the 8200P is 13.3 and max's out at 14.2...your high is 14.6

its back to the variable factors again.

 

[ralfyguy]

Rick I experienced days where the reception really sucked, no matter what you tried. I also think I made the mistake and tried to aim and tweak my antenna without the tropo forecast, and it usually was in the late afternoon/night hours, after I came home from work and tried. This is a HUGE mistake, because that's when the ducting most likely starts to take effect. I'll never do that again. I also will never try to aim and tweak my antenna for max results when it's overcast and rainy AND windy! In my case this showed, that reception was better in cloudy/overcast and rainy weather. The worst results I get on a clear, warm day with slight winds. But THAT's exactly the time for tweaking, because it won't get any lower than that. I bet your weak reception today took place in clear weather.
I am not sure about the XG91 any better than your 8200p, but it may depend on the case. The best thing about the XG91 is, I have NO problems with multipath whatsoever. This thing aims like a satellite dish. It's a real challenge to get the aim right. A couple degrees off decide between signal and NO signal. The beam width is only 25 degrees, but this is exactly what helps the multipath.

Anyways, the next time I go up there will be on a clear sunny day, and AFTER I checked the tropo weather under this link:

http://home.cogeco.ca/~dxinfo/tropo.html

Furthermore, it seems like I have to adjust the aim, depending of the time of the year, becasue of trees in my path. Right now I have to aim a little around the trees, because of foliage. In Fall/Winter I have to aim my antenna about 10-15 degrees over to the east and hit the towers straight. I know it sounds funny, but apparently this is what it takes at my location with the towers 75 miles away north. Don't forget that I am probably about 15 miles beyond the point where the curvature of the earth takes effect. This is probably an additional problem in my case besides the dang trees in the way, which by the way have REAL FAT foliage right now. After they started growing leaves, it went downhill rapidly here. The CM3020 worked well all winter, until the leaves came out. And then I bought the XG91, and my problems went away.

 

[Rick0725]

did you install a preamp like a cm7777 or cm7775 there with your install? that should help.

 

[ralfyguy]

I already had a 7775 with my 3020 before. I just left it there when I swapped it with XG91 and it works good together. Without a preamp, there ain't nothing going on around here. I had a RS preamp before, which is actuall not alot worse than the 7775. I compared both on the XG91. There's not a huge difference, but it makes a difference. And around here you gotta have the best stuff available, otherwise you're not getting anything to watch. The other day we had some bad storms, and my Dish Netwok programming was gone. I just switched the ViP622 to OTA and kept watching TV as there was no storm. The XG91 performs impressive in bad storms as there were no drops at all, and only a little pixelation every time a lightning flashed. But I bet that you get that with ANY antenna array out there, no matter what it is. It's a meajor electrical interfernce, no antenna can beat.

 

[Rick0725]

here are some interesting articles to read.

http://www.atechfabrication.com/reception_solutions.htm

What is the best antenna system?
Currently the best antenna system for fine tuning very weak signals is a pair of high gain JBX21WB antennas mounted to a horizontal boom and vertical tilter. Antennas should be placed 36" apart on horizontal boom measured between centers. This assembly is then mounted on top of a horizontal rotator attached to the end of a well supported mast. Mast recommendations are two 10 foot sections of mast (20' total) with guy wires terminated at the top of mast just below the rotator. Another set of guy wires at 10' will add extra rigidity to mast. Mast should be mounted to roof within 5' of highest point on roof. Minimum mast height is 15' above highest point on roof or 30' above ground with no obstructions. Antennas are connected to each other with a coax phasing harness. The down feed to set-top-box is RG-11 quad-shield coax for lowest signal loss. I do not recommend using a pre-amp with this system unless you plan to feed multiple STB's or have a coax run over 200'.

this guy used Light-weight, non-conductive fiberglass tube to cut down on the weight.

http://www.geocities.com/toddemslie/UHF-TV-DX.html

http://www.bobmerritt.com/dtv/dtv.htm

the blake's in these are similar in design to the 91xg you own. they both used rg11 quad shield instead of rg6. maybe you can give that a try to cut down on the losses.