Combine 2 antenna(1 uhf, 1vhf/uhf)

[GADGET71]

I am looking to add either a vhf only antenna or a vhf/uhf combo to my already existing CM 4228 UHF antenna.  What is the simplest and most effective way to do this?  The reason I want to do this is that Fox 47(DT 11) is VHF, and I have trouble picking it up most of the time with my 4228.
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[mhz40]

Combining antennas is a technical science and is not recommended without having a good background in RF and some test equipment.  If you want to pursue this, the easiest way is going backwards through a 2-way splitter.  Doing this cuts your receive power in half (3db loss) on both antennas.

[audiopile]

If Fox 47 is actually coming in at VHF 11 - a 4228 is going to work fine for that frequency. If it's not working well - describe exactly what's wrong?If it's at UHF 47 - again - a 4228 should work really well. Does your HDTV or STB give you some sort of semi-cryptic signal strength indication? On the channel you are having problems with - does this bounce around?

[GADGET71]

Audiopile-

I can not get 47 to come in as DT 11(VHF), I have a signal strength meter on my dish 811.  
I have my 4228 in the attic of a two story.  Don't want to put one on the roof otherwise this would probably help.  All my UHF channels out of Madison are high 80's to low 90's.   Once in a while fox will come in around 75, but usually around 50 which is not enough to display.  Anyways, any suggestions?
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[audiopile]

1.) I assume that you have been to antennaweb.org and gotten the location of the transmiting antennas you are trying to get?2.) Did you use a compass to align antenna?3.) Have you called the station to see if they are operating at full licensed power or as a STA at some ridiculously low power? Because I am rental scum - I am forced to put a 4228 under my landlord's roof - I have spent at least 5 times as much time aligning this mess under the roof ( with OK results) as I would have had to spend to align it on a rooftop mount ( with almost certain execellent results). When you put a antenna under the roof you create the RF equivalent of a WW-2 era swimming tank - a really ineffecient system.
Bluntly - if you are not roofmounting your 4228 because you don't like the way it looks - get over it - you're going to spend a lot more time looking at your TV than either you or your neighbors are going to spend looking at your rooftop antenna. If you absolutly MUST have it under the roof - be prepared to waltz the thing around your attic.High gain antennas basically trade off acceptance angle for gain. Basically the "window" a 4228 sees thru is narower (spl?) - but it has oodles of usable gain within that window. By using a antenna under a roof you are basically trying to look thru a RF venitian blind. BTW - solid -rigid - mounting of the antenna is still a base requirment for even attic mounts when you are dealing with a 4228 or any larger antenna. OK- rotate the antenna about 5Deg. at a time - check both your signal strength ( which really isn't) and what the actual picture looks like.TAKE NOTES. One of the dubious pleasures of under roof installs is that you will probably find you can't get all available channels all the time from any one angle/location/orientation. Once you have determined that any particular spot in your attic won't work - move the antenna and start over. Always start with your compass orientation and work around that . Since you are having trouble with only one local channel - you really must know if it is a "real" channel or a STA. If still a STA - don't even start on this project - wait untill they go to full power ( sometime next summer??) and your problems will probably go away. It's important that you achieve the proper emotional state ( complete frustration) - so that you can feel comfortable with rooftop mounting the 4228 and have complete confidence that you wasted a whole lot of time and energy screwing around under the roof.Good luck!

[bradsmainsite]

Audiophile this is a classic piece I'm lovin it to bad you can't post this in bright flashing neon lights or something for all those people who think they must conform because none of their neighbors have one on their roof!  

I still think this is a cable tv conspiracy!

Anyway great piece!

[Mark Strube]

Audiopile - paragraphs. Bradsmainsite - periods. If you two teamed up, I shiver at what the posts might look like.  :rofl:

(No offense, but I just couldn't resist making this observation. )

[Nels Harvey]

I'm not sure a 4228 antenna will do very good on a VHF frequency, even ch. 11.  Ch. 11's frequency is 198 to 204 MHz.  UHF frequencies just start at 470 MHz.  A fine antenna like the 4228 does a great job at UHF, and it has a good gain figure, but it just isn't possible for that same antenna to perform well on VHF.

You don't say just how far you are from the Candleabara antenna where most of the Madison TV transmitters are located.  Ch. 47, Ch. 21, Ch 27/26, Ch. 11 and Ch. 3 are all located on that tower, which is over 1700 feet high.  Analog Ch. 15, and 57, as well as their digital counterparts Ch. 19 and 32, are located on the new Ch. 15 tower just south of the Beltline.  Those antennas are about 1100 feet up, or less.

I would think you would be able to use a standard two way TV splitter to combine the two antennas.  These work two ways, and basically divide the signal in half, or a 3db loss.  It doesn't take much to lose that much signal in the coax, especially on UHF frequencies.  I'm an advocate of adding an antenna amp just after the splitter.  Be sure the amp is capable of amplifying the UHF frequencies, and doesn't cut off at around 450 MHz.  An amp at that location will help overcome cable loss, and bring the best signal to your receiver.

I have had good luck using Radio Shack amplifiers, in spite of the general opinion on this site!  The important thing is to never use an amplifier stronger than 10db.  The 20db amplifiers tend to produce oscillations on UHF frequencies, and produce a bad name for the RS amps.  Look for an inline amp that inserts near the splitter, but gets power from an adaptor that places DC on the coax, from the other end, near the receiver.  RS has a 10db gain amp just like that.

If you are able to receive Ch. 11 better with a second antenna, I'm sure you will receive Ch. 3 much better as well.  Be sure you only use a VHF antenna, so there isn't a phasing difference with the 4228 antenna.  That could cause interference and even ghosting.  If you can find a two way splitter that says UHF on one side, and VHF on the other, that would be desireable because you get a little attenuation from the opposite band, but a standard splitter ought to work.

Good luck!  Nels....

[jfelbab]

Actually the CM 4228 has a lot of gain at CH11,  5 to 6dB, in fact.    See graph below.  

My advice to you is to add a CM signal preamplifier.  This should give you the added gain that you need and still leave you with an indoor system. I'd suggest the CM TITAN 2  #7777.

Gain Chart VHF Frequencies

[GADGET71]

I see alot of antennas, what look to be dated?   They have a VHF antenna near the top of the mast and just below it they either have a small YAGI for UHF or I have seen a CM4221.  Does anyone here know how they are connected together or if it is just a splitter?
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DR750SE

[Nels Harvey]

Actually the CM 4228 has a lot of gain at CH11,  5 to 6dB, in fact.    See graph below.  

I don't see the CM 4228 as having a lt of gain on Ch. 11 at all!  In fact, if you study the chart, you can see while the lower part of the frequency indeed has about a 5db gain, as you go higher in the frequency, the signal is attenuated by as much as 6db.  This inbalance will cause the decoder of the digital signal to have fits, if the lower signal level is too low to decode properly.  Remember, the signal covers the whole 6 MHz. with high energy, not just a spot at where Ch. 11 starts.

A separate antenna can also be oriented separately from the 4228, and moved around for better results considering it's attic location.

As far as amplifiers go, I agree that there are several good amplifiers available.  I mentioned the RS amplifiers only because they are pretty readily available.  I do recommend staying with only a modest gain with any amp, of about 10db, or so.  I have seen several 20db amps oscillate on UHF frequencies, and think they do so internally.

Nels....

[jfelbab]

http://www.hdtvprimer.com/ANTENNAS/cm4228.html

This antenna is advertised solely as a UHF antenna.  But, as many people have discovered, it has strong gain for VHF-high, especially channel 9-13.  What gives it this ability is the continuous screen.  Other 8-bays have a reflector that is not continuous across the right and left halves.  Those antennas have little usefulness for VHF channels.

If you use a combiner to add another antenna, you will at the very least cut your signal strength in half for both antennas.  You may also incur problems with multipath which can, in many cases, be a much larger problem than raw gain.

I'd definitely try the CM7777 preamp as a first course of action.

Also note that securing the two screen segmants to the mast may change the RAW signal levels somewhat and is worth a couple of cable ties.

[Nels Harvey]

Actually the CM 4228 has a lot of gain at CH11,

If you use a combiner to add another antenna, you will at the very least cut your signal strength in half for both antennas. You may also incur problems with multipath which can, in many cases, be a much larger problem than raw gain.

I don't recall assembling a VHF/UHF antenna that didn't incorporate a splitter to combine the two separate antennas into a coax connector.  Isn't that the same as what GADGET71 wants to do?  It seems obvious that in spite of the capabilities of the CM4228 antenna, it isn't working in the current location.

I'd definitely try the CM7777 preamp as a first course of action.

The proper placement of a good preamp can certainly improve reception problems, but if the antenna is picking up multipath signals, or excessive 'twist'  (difference in gain) on the signal level across the 6 MHz. of the channel,  the digital decoder in the receiver can have a difficult time with the signal.

TV reception really narrows down to trial and error, unless sophisticated equipment, like a spectrum analyzer is employed.  Even a field strength meter (Jerrold, ETC.) can be very helpful.  The final result, of course, is what is seen on the TV.

Nels....

[bradsmainsite]

I have seen lots of reference to obtaining a CM 4228 at Marmax in Milwaukee for
around $40.00 isn't this a wholesale distributor and would you not need a sellers permit number or FEIN number to be able to purchase this or anything from them :confused: and who would you talk to there to get around this?

[waterhead]

Marmax will also do retail, over-the-counter sales, to walk in customers. Their main business is wholesale sales of cable, phone and TV supplies, and because of this don't advertise. I bought my 4228 from Dave Grebetz, but anyone there will sell to you. It helps if you know exactly what you want, like a tripod and mast  also.

Here's a link to their web site and the UHF antenna page:

Marmax Distribution Company