Hi all,

I'd like to feed the signal to the second TV and I am not sure what's the best way to amplify it. Please help.

I have cm4221 in my attic since April 08. I am in Maple, ON.
I have excellent reception on all channels except 29 and 2-2 (I think it's NBC).
The antenna is directly connected to the TV, but the cable is quite long - close to 100 ft, if I had to guess. Please see the pic for details. The red line from the attic to the main floor TV via the basement is the existing setup.
I now have second TV in the bedroom on the second floor. The green cable is also in place.

I am pretty sure if I just put a splitter in place the signal might be too weak.

I first thought to add pre-amp in the attic, but I read now that the pre-amp has to be on the antenna while the power supply has to be installed as close to the TV as possible and before any splits. That means the PS would be in the attic in my case, after that - the splitter and run to the TV on the 2 floor will be 10-15 feet, but to the TV on the main floor the run would be quite long again. Will it work..? What model? CM 7777 or 7778? ( I don't know the diff).

In case you wonder why I have that long cable from the attic to the main floor. It's new house and the builder ran tv cables from every bedroom on the second floor to the attic and from there they all go to the basement near the electrical panel. Once I had the antenna in the attic I had the cable hanging in my stairs for a while. Then I found one of the builders cables in the attic, cut it, connected it to the antenna and voila I got the signal in the basement w/o breaking any walls/fishing cable. From the basement it was easy to get the cable to the living room on the main floor via cold air return.


Any help will be much appreciated.

http://i134.photobucket.com/albums/q86/leonkaz/antenna.jpg

A preamp would be advised in your setup.

I would connect the power supply in the 2nd floor. This way it won't be too hard. Also the cable going back up to the attic won't be long and from there connect it to the basement feed.

So you will basically add the splitter on the 2nd floor.

The difference in the 2 preamp you listed is 3db more gain on the UHF side. This makes no real difference as the 7778 has more than enough gain for your needs. Even if you plan to split 4 ways.

Good luck.

I am pretty sure if I just put a splitter in place the signal might be too weak.
So.. just hook up a splitter and try it first. Everything may be fine.

I first thought to add pre-amp in the attic, but I read now that the pre-amp has to be on the antenna while the power supply has to be installed as close to the TV as possible and before any splits.
No, you can put the power supply anywhere in the chain before the splitter. Including right there in the attic with the pre-amp.

Cheers

Please post results for your location from TVFool so we can see whether you
have strong signals that could overload a Preamp and also so we can guesstimate
whether your signals are strong enough to work just fine without a Preamp.
[Trying to predict signal strength indoors and in attic is imprecise.]
[I assume indoor loss is 13 dB +/- 7 dB and perhaps less in attic.]

Simplest way to do this to enter your address (or LAT/LON) into www.tvfool.com
and then copy the results <url> into a post on this forum. TVFool will not display
full address (or LAT/LONG) to maintain privacy.

Choice of Preamp depends on strength of strongest Analog and Digital stations.
Preamp selection is described in "OTA Reception Files" within fol. folder:
http://imageevent.com/holl_ands/files

High gain Preamps, such as the CM7777 are only suitable when there are no
nearby TV transmitters and hence is best suited for rural locations.

Nearby FM transmitters can also cause overload, esp. if you disable the FM Trap
to receive Ch6. Use www.fmfool.com to calculate strong FM signal levels.

At the other end of the spectrum, the Winegard HDP-269 low gain Preamp
has the highest resistance to overload and hence is suitable for urban/suburban.

========================================
Most RF Splitters do NOT pass DC Power. Hence Power Insertion Module would
need to be between the Preamp and the RF Splitter.

However, most "Satellite Splitters" pass DC Power on ONE port, or BOTH ports,
such as ALL of these:
http://www.radioshack.com/product/index.jsp?productId=2103928
http://www.beachaudio.com/Philips/Sdw50100-17-p-98724.html
The Philips is also sold as the Zenith ZDS-5010.

Since it also covers the TV bands, a "Satellite" Splitter can be located in between
the Preamp and a Power Insertion Module conveniently located near either of
your TVs. Be sure to check the OTHER TV to make sure it does not have a
DC short on the coax or inside the TV (extremely rare..."DC Block" can fix).

I just took delivery of an HDP-269, and I'm a little disappointed in the results. My Toshiba 52XF550U has a built in signal meter with SNR & Power in dB. I'm seeing an average 9dB of power boost across all Toronto+Bufflo digital channels, but less than 1.5dB increase in SNR.

I was hoping it would boost some of my less reliable channels (e.g. CITY) and reduce the drop-outs on the Buffalo stations. (Although I had very few problems with NBC during the SuperBowl.)

It did boost MyTV enough for my TV to lock on to the signal, which it couldn't do before, but not enough for sound. Maybe after I built the wideband GH and mount it outside.

I just took delivery of an HDP-269 ...
... less than 1.5dB increase in SNR.
That sounds pretty much right on the money.

Figure your good TV had a 5-6dB NF (noise factor) on the internal pre-amp. The Winegard HDP-269 advertises an average NF of 3dB (probably more like 4dB at UHF frequencies). So, subtract the two, and that's the predicted improvement for SNR, minus any added connector losses from inserting the pre-amp.

Pre-amps are (almost) entirely about NF.

Cheers

Here are the results from tvfool.com as suggested
(this is further to my question upthread whether I need pre-amp)

http://i134.photobucket.com/albums/q86/leonkaz/Radar-All.png

Anyone has an opinion on those (http://www.advancedreceiver.com/page47.html).

They have specific frequency (http://www.advancedreceiver.com/page12.html)available for the same price.

470 - 722 (narrow tune) N.F 0.6 Gain 15 Application television

Anyone has an opinion on [these?] (http://www.advancedreceiver.com/page47.html)

They don't quote impedance, so it is probably a 50-ohm device.
Price does not include the power supply/injector.
Wrong connectors (again, indicates 50-ohm rather than the desired 75-ohm impedance).
Price is identical to the superior/proven 0.4dB pre-amps (75-ohm) from Research Communications.

Cheers

ericball: What sort of SNR numbers are you talking about????
You're never going to see SNR much above the high 20's and maybe low 30's due to
quantization noise in the receiver and numerous imperfections in the transmitted signal.
After all, ATSC doesn't "NEED" more than about 20 dB SNR to counter severe multipath.

leonkaz: You have two very strong VHF stations and at least six very strong UHF,
which would make it difficult to use a Preamp to receive those weak LOS stations.

I would recommend upgrading to CM4228 if you are not satisfied with simply
adding an RF Splitter. The original design had moderate Hi-VHF (CH7-13) gain
and, although worse than rabbit ears, it should be adequate to receive your CH5.
[The jury is still out wrt VHF gain for the new CM4228HD version....worst case,
you'll need to add a VHF antenna.]
For VHF gain curves, see www.hdtvprimer/ANTENNAS/comparing.html

Once you have tried just an RF Splitter (and CM4228???) and want to see
if a Preamp will improve reception, try using the very high overload Winegard
HDP-269 Preamp. The extra attic loss may provide enough attenuation
to prevent "overload"---or maybe not....

BTW: "Overload" is a mis-nomer. Each PAIR of strong signals cause (mostly)
third order intermodulation distortion (IMD), which acts as noise across other
channel positions, where the noise becomes up to three channels wide.
This noise prevents reception of weak channels....all across the UHF band.

I would insert a Variable RF Attenuator between Antenna and Preamp.
Each dB of attenuation reduces interfering IMD by 3 dB, so you'll only
need to dial in a small amount of attenuation.
http://www.solidsignal.com/prod_display.asp?prod=1296F

holl_ands, Thanks. what if I move my cm4221 to the roof - I presume that should improve the signal somewhat..?

I don't understand a lot of what you wrote, but thanks anyways :D

holl ands:


I have two 4221HDs coupled together, and would like to pre-amp the top antenna to get a couple more stations. If I put the pre-amp just below the top antenna, use a power pass coupler/splitter and then place the power injector just before the TV would this work? I have a few stations that are close by and don't want the pre-amp to overload the system as you discussed before. My question: is an attenuator in order, where would I place it, and is this an automatic device, or will I have to adjust it according to the channel I want to watch?

holl_ands, Thanks. what if I move my cm4221 to the roof - I presume that should improve the signal somewhat..?

I don't understand a lot of what you wrote, but thanks anyways :D
Roof mounted will help to receive weaker stations....but you still might have to insert a
Variable RF Attenuator to dial down the strongest stations in order to maximize the
overall dynamic range....you can't "hear" a conversation when cymbals are crashing.....

holl ands:


I have two 4221HDs coupled together, and would like to pre-amp the top antenna to get a couple more stations. If I put the pre-amp just below the top antenna, use a power pass coupler/splitter and then place the power injector just before the TV would this work? I have a few stations that are close by and don't want the pre-amp to overload the system as you discussed before. My question: is an attenuator in order, where would I place it, and is this an automatic device, or will I have to adjust it according to the channel I want to watch?
Are the two antennas pointed in same or different directions??? If same, the one without
the Preamp wouldn't contribute very much and the combiner will become a 4 dB attenuator.

Can you post the results <url> from www.tvfool.com???
And which are you trying to receive.....which can you live without....

holl ands:

My results are below. My preference is only the eastern (NE and SE) signals, which most I can get, the only additional ones I want to get are wutv and wnyo.

One 4221 is pointed to the NE and the other (top mounted) is pointed ESE.

http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id%3d39da9fb179

http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id%3d39da9fb179

holl_ands - my situation is very similar to leonkaz's, though most of my numbers are 5dB lower. Question though: is the HDP-269's gain of 12dB enough to reduce the overall system noise figure in a case where I have about 10dB (estimated) cable/splitter losses (1 in-line splitter, 1 splitter in my tuner card, aprox. 50 feet of cable)?

I'm actually surprised how many OTA'ers in the Toronto area are are using CM7777's when local stations are quite powerful. It seems like even a AP-8700 would overload quite easily, and this is assuming zero gain since the strong stations (local Canadian networks) in my case are approximately 30 degrees offset from the weak ones (the US major network, which is where I'd point the antenna [4228]).

In some areas of the city, the strong Canadian and weak US networks are almost in-line, meaning you might be getting 10+dB of gain off your antenna before you even hit the preamp -> in that case I don't see how any preamp, even the HDP-269, could possibly give good results..

For reference, here is the link to my tvfool plot. Thanks for your help.

http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id%3dad028defa4

When (on a CM Titan pre amp) it says "full lightning and surge protection", would there be any point to also install an arrestor in line ?
Thanks

I'm actually surprised how many OTA'ers in the Toronto area are are using CM7777's when local stations are quite powerful.
It's not about the gain, but rather the noise factor (NF). The CM7777s boast a near 2dB NF, and that's why they are popular. Most other amps generally have 3-6dB NF.

Remember, the whole point of a pre-amp is to improve the noise margin, so a very low NF is paramount. A good (aka. low NF value) pre-amp is effective anytime that the NF of the pre-amp is lower than the NF of the receiver (TV/pvr/tuner-card). Since most of the latter have a 5dB or worse NF, the CM7777 is just about always a win for weak stations. Even in the (very rare) cases where artificial attentuation is needed to tone things down again.

Cheers

mlord,

Although I agree with you that noise figure of the preamp is a very important concern, I have to add a few other points where I disagree with your assessment:

- According to the Friis equation (http://en.wikipedia.org/wiki/Friis_formulas_for_noise), the noise figure of the preamp is the first, and usually most significant, contributor to overall system noise. However, the second contributor is directly related to the gain of the preamp. The second term in the Friis formula is (Noise Figure of Receiver minus 1) divided by (gain of preamp). Therefore, the statement that it's not about the gain isn't entirely true. It's very much a combination of the NF and the gain of the preamp that lower the overall system NF. If your preamp's NF was 1.0 but the gain was also 1.0, you'd see little improvement, or you might even make things worse.

- I have a feeling that a LOT of people are overloading their CM7777's around the GTA because it's very easy to overload them. Consider my tvfool plot (link in previous post). If you enable the analog stations on the chart, we have NINE stations at -33dBm or higher. Using holl_ands's guidance for derating in the preamp chart, you're looking at about -25dBm input level ASSUMING NO ANTENNA GAIN into your preamp. The CM7777's maximum input level is only -36dBm, howeer, so therefore you're very very easily overdriving it. The result? The IMD (inter-modulation distortion) caused by this overload will effective increase the NF of the preamp to a very high value, nullifying most of the value of the preamp in the process. This would impact the weakest channels most, and things would get even worse once you add in antenna gain into the equation. Although the CM7777 seems to work for a lot of people, I suspect that a HDP-269 would work a lot better, thus the basis for my initial question.

Tom