... has anyone analized the db level of a 4228 hd stack with a simple splitter and a CH-7777 amp?

cudabob:

I assume that by "db level" you mean the computed raw or net gain of a specific stacking arrangement, with some specific spacing? I don't know of such a characterization. But at "The HDTV Primer (http://www.hdtvprimer.com)" there are extensive writtings on the pros and cons of stacking the (older) CM-4228. Look for the "Erecting a TV Antenna" link, then "Antenna Projects".

I'll attach one more comparison from my tree'd horizontal CM4228HD's for the low UHF channels 21, 23, and 26.
http://www.antennahacks.com/images/Hacks/Combined_vs_L&R_21-26.png

While these are barely useful signals given all the multipath, it is easy to discern the 2.5 to 3 dB projected increase in signal level. With some study an improvement in flatness (difference between max and min peaks) can be observed as well.

Together, I think these two captures provide somewhat of an "analysis", although I would more call it simply a field measurement. I think that numerous models and mathematical studies have already projected what can be observed in the above captures; that ganging produces about a 2.5 to 3 dB net gain. It also narrows the beam along the stacking axis; verical beamwidth if stacked vertically, horizontal beamwidth if stacked horizontally. (That can be good or bad, depending on your needs.)

As far as splitter and CM-7777 go... the choice of splitter will certianly affect the outcome, to varying degrees. There are dozens of designs floating around and no two designs and physical implentations yield precisely the same result. Phase and impedance imperfections on input ports can produce unpredictable results at unpredictable frequencies in the spectrum. Without test equipment it sometimes comes down to just buying several different models and trying them.

Two of the least loss models I've measured are the Perfect Vision 22-233, and lately a slightly better Ideal 85-132 that I found in Lowes. I've never characterized their port to port phase or impedance characteristics.

Adding an amplifier contributes nothing to the relative performance of ganged versus single antennas. It just adds gain, and a little noise, to whatever you get out of the antenna arrangement.

Best,
t

tballister,

I have seen definitive results with three different baluns over the stock harness lines. Now I realized I am do not analyzing the signal with as much precision as you are (I'm quite jealous by the way) but here is something that I have done different that you: when swapping baluns or phasing lines I never end up with the antenna gang pointed in exactly the same direction because I now rotor to re-peak signal since there are small discrepancies in the impedance of each balun / wire capacitance due to proximity which vary the the precise direction of the main lobe. I finally marked this on the pole because I first thought I was seeing synchronous pole slips on startup of the rotor which also do happen allot on my big heavy array.

Try it out, I thing you will be surprised: I learned about this effect while experimenting with loop baluns (delay lines) and watching a huge frequency dependent polar shift of my lobes.

I enjoy your testing results as I am sadly limited to 100 Meg.

Cheers!

Oh ya cudabob...

Forgot to straight out mention the 7777 (great amp) was a nightmare with this stack. Too much gain in our area. I also had problems with some lower power channels. I can get 11 with the 4228hd stack and a low gain distro amp (due to its superior overload capability) I even had problems with the AP8700 Winegard during tropo; it can accept a much higher input than the 7777 and it has less gain than the 7777 and for those reasons it worked better.

Funny: spell check came up with winograd for winegard... I see a new nick name here. :D (wino-grade)

The 7777 will need notch filters, we just need to borrow tballister's gear... hint.. hint... :)

tballister,
I have seen definitive results with three different baluns over the stock harness lines.

Ooooo..... lineloss: I don't quite understand what you're saying here. Do you mean definitively different? Definitively the same?

when swapping baluns or phasing lines I never end up with the antenna gang pointed in exactly the same direction ... Try it out, I thing you will be surprised.

Whew. Once again I'm really sorry but I don't understand what you're recommending I should try. :o

If you "... never wind up with the antenna pointed in exactly the same direction ..." the experiment has more than one variable. With more than one variable (in your case [a] change of balun plus [b] change of orientation), you don't know what result to attribute to what variable. That is a fundamental principle of such comparitive testing - only allow one variable at a time to be changed.

So, I'm really sorry; maybe I'm completely mis-interpreting...

t

Ooooo..... lineloss: I don't quite understand what you're saying here. Do you mean definitively different? Definitively the same

All slightly different, but the factory harness always lost in the high end of the spectrum in my testing.

.....So, I'm really sorry; maybe I'm completely mis-interpreting...

I think so. I'm saying just the opposite: I am suggesting you have to re-peak your antenna for each given channel to cut down on other variables.

Lets just say imperfect phase lines offset your main lobe -4 degrees from the physical center of your aligned array for a given frequency. Now you unknowingly rotor +4 degrees to attain a peak signal. Time to compare to baluns so you install them, but differences in baluns and wiring symmetry (300ohm side) shift the main lobe +2 degrees. You will compare two connection methods even though you are off 6 degrees from the peak signal of the second connection method. Above, you have perfectly captured the culprit but amplitude is only one part of the equation, and thus can only be compared at their peaks.

I think so. I'm saying just the opposite: I am suggesting you have to re-peak your antenna for each given channel to cut down on other variables.

Sorry, but I disagree, and stand on the methodology I cited: one variable at a time.

The principle question is, for a given fixed set of conditions, which component, A or B, produces the more desirable result. If you allow more than one variable to change, that comparison becomes invalidated.

Amidst the work done to test different antenna and OTA gear configurations something we must always consider is the audience of this forum. For pure testing we must obviously adhere to Occam's Razor and the scientific method, but at the end of the day let's make the results usable and replicable for our readers. In this case if a re-aim shows better results for the end user then let's say so even as we go about the continued testing. So be it with our advice. :)

I can accept that its a matter of what question you are attempting to answer...

Is it possible I would get better results if I bypass the pre-amp?

If your antenna has a good line of sight, your cable run is less that 100ft, and you are not running a couple splitters, then yes; your amp may not be helping your weakest signals. With the amp you may see most signal strength numbers go up, but you don’t really need those ones to go up. One channel or a combination of strong channels may cause your amp to clip; this created distortion is small in proportion to a strong signal so it’s no big deal, but this same distortion may be large enough when compared to a weak or marginal signal. Once you get too small of a signal to noise ratio you loose your channel. The simple way to see what you are really getting (if you can) is to connect your antenna directly to an ATSC tuner box with a very short cable: take a small TV up on the roof or feed your antenna coax with the output of the tuner (set to channel 3 or 4). Whatever you can get this way is about as good as it gets (without getting very technically intrusive). Now you will have a baseline to gauge over amplification. ;)

Cheers!

I am in St. Catharines. I am going to have 2 4221hd's mounted on a single
10 foot mast attached to the chimney. they will be pointed in opposite directions for t.o. and buffalo.

Sorry for the late response, but I highly recommend that you not combine two 4221hd's pointed in opposite directions. A much better option would be to remove the reflector on your 4221 (or on a 4228 if you need the extra gain) to make the antenna bi-directional (the forward gain you get from the reflector is less than the signal you would loose by trying to combine the antennas). Given that you are in St. Catharines, you may not need to remove the reflector as the signals from Buffalo may be strong enough to travel through it.

also: what is the way to combine these 2 antenna into a single feed and keep everything in phase.

It is almost impossible to phase match antennas pointed in different directions as they are in different planes, so I wouldn't even try. You might be able to do it for one specific channel, but it wouldn't work for any other channels. A better option is to use highly directional antennas so that they won't receive each other's channels, making phase matching irrelevant.

Lineloss, your post #494 sounds like what I need.

I have 2 CM4228HD's I am mounting them as a stack on a rotor on a 55 foot tower up in Pontypool. I was planning to mount the stack without any mods, just a splitter to join them. But would you recommend that I do the hack with changing out the Baluns first? Could I use 4 baluns and 3 - 2 way splitters to connect the 16 bays or is 1 - 4 way splitter like you suggest much better (less loss)? Is there a 4 way splitter you could suggest?
Thanks GBOTT

Have you done the simple hack of removing the black covers?

No I have not done anything as yet. I have been using a stock CM4228HD for the last 2 years and it has worked pretty good. But now since having to change my rotor I was going to stack 2 4228's. I was initially thinking of just stacking them with no mods at all. But now am starting to think I should do the Balun mods first.

Hi guys,

so i got a hd stacker from Dennys and a 91XG.
The bottom antenna from the HD stacker is a UHF and i was thinking of installing the 91XG right underneath.

The two antennas from the stacker are 18 inches appart so i was thinking of doing the same with the 91XG. I also got a Winegard cc-7870 combiner/coupler.

What do you guys think ?

Just simply remove the black cap covers that are on the centre of the bowties- much easier than the balun mod.

The two antennas from the stacker are 18 inches appart so i was thinking of doing the same with the 91XG.

The 18" difference has no bearing on where you'd stack another UHF antenna under the HD stacker, because the HD stacker is made up of a VHF and a UHF antenna. The other problem is you're trying to mix two different antennas.

Unless of course you're talking about aiming them in different directions?

I think your best bet would be to use *just* the 91XG for UHF, and get a separate VHF antenna for whatever stations you're trying to pick up. If you're intent on using the HD stacker, I'd try to source/build and identical UHF yagi section, and use the K7MEM calculator to calculate the correct stacking spacing...

Good luck!

Thanks poutanen so antennas need to be the same in order to stack them

xilbus please read Post #16 in the OTA FAQ (http://www.digitalhome.ca/forum/showpost.php?p=675713&postcount=16). It is important in order to understand the issues involved.

I just decided to join my old yagi with my new 4228hd and now I get nothing. Just with the 4228hd I got 24 stations. Can some one help me out?
It looks like something like this:

-|--|--|-- <- yagi facing north east
|
|
combiner ----- 4228hd mounting on the tower of the yagi facing south east
|
cm7777 preamp
|
line to power injector