Setup advice for my location in San Diego - Solved
 

I'm having a little trouble with my setup and I'm trying to figure out the best solution. I live central in San Diego but because of my location I'm having trouble with a couple of the channels.
XETV-DT (Real: 23, Virt: 6.1 CW) doesn't come in at all.
KNSD-DT (Real: 40, Virt: 39.1 NBC) very spotty reception.
KBNT-DT (Real: 51) doesn't come in at all.

Signal analysis:
http://www.tvfool.com/?option=com_wr...da326379d96ff6

My setup is as follows:
-- Antenna -->CM-4220HD mounted on the roof 15 ft from the ground
-- 25 ft cable goes into Channel Vision CVT-2/8PIA-III 8 way splitter. I'm only using 2 of these and I have terminated the rest of them. One side goes directly to another TV with a DTV PAL box. Channels 6 and 39 come in here at about 70% strength.
-- The other split goes into my computer via 20 ft cable. Here it gets split into 2 tunner cards (HDTV Fusion Gold RT 5). Here I can't see the 3 channels in question.
I am surrounded by hills which I think it is impacting my signal, but everything else comes in fine (everything else includes Virt: 10.1, 8.1, 69.1, 51.1 and 15.1 I don't really watch the rest)

Any suggestions on what I need to do to improve my signal.
Another antenna? a pre-amp? Any recommednation would be greatly appreciated.

Sorry for the long and confusing post but I'm trying to include any info that can help.
Thanks from San Diego

I would move up to a CM4221HD. A preamp could help significantly, since even with your splitter/amp you are only getting 70% strength on you good channels. Raising your antenna couldn't hurt either.

I'd say that your problem is caused by high losses.

The 8 way splitter has about 11 db loss, the two way splitter has another 3.5 db. The downlead has about 2 db and the interconnect cabling adds another 2 or so.

Total loss 11 + 3.5 + 2 + 2 = 18.5 db. The typical tuner has a noise figure of 10 db. The 4220 has roughly 6 db gain. The predicted NM in your installation is 22.5 db. KNSD has a NM of 25.4 db. There's about 3 db missing somewhere, but that doesn't really matter much.

I'd replace the 8 way splitter with 6 ports terminated with a two way splitter. You should gain about 7 db.

The next improvement to contemplate would be an antenna upgrade to an HD1080. That antenna is optimum for you because it has a VHF pattern that's backwards from the UHF pattern, which is exactly the direction of your VHF stations. The UHF gain is also a bit higher than your 4220.

Finally, consider a AP4700 preamp. That's a UHF only preamp that bypasses VHF. That's the only amplifier that is appropriate in your situation.

Thanks for the detailed response. Would this antenna also work for UHF channels? It says it is "VHF antenna".
Also, why would I need VHF only pre-amp? I though channels 2-18 were VHF. The channels I"m having trouble with are at 23 (CW), 40 (NBC) and 51 (KBNT)

Of the San Diego majors, only 8 & 10 are VHF, all the rest are UHF stations regardless of their original analog channel number.

Upgrading from a 2-bay to a 4-bay might help, but, as TG suggested, you have excessive distribution losses that need to addressed at the same time. Using an 8-way splitter when you should be using a 2-way splitter is a waste of 7-8 dB of signal power. Fixing that problem might be enough to solve the issues. being on the wrong side of the hills from the UHF towers doesn't make things any easier, either. A stronger (higher gain) UHF antenna might be called for.

I"m using a amplified splitter which provided 4 dB gain into each output. I thought that by using an amplified splitter, I was improving the signal?
Do i need to get a pre-amp for UHF?

Tv Antennas and Reception
 

Read and understand this about Real and Virtual tv channels. http://forum.tvfool.com/showthread.php?t=695

The 3 channels I'm having trouble with are all UHF. What in my understanding is wrong about that?

Sorry, I missed that the splitter that you had was amplified. The splitter is a very good one, but designed for CATV systems where all the signals are the same level.

Here's it's spec sheet; http://www.channelvision.com/index.p...product_id=254

The output level rating is +23 dbmv assuming 160 channels all with the same level and analog TV. With the 5.5 db typical gain the input rating would be +17.5 dbmv (+17.5 dbmv is equal to -31.25 dbm) Adjusting the spec to two channels yields an input capacity of roughly -7.25 dbm. At that level, the intermodulation products are 60 db below a single carrier. The VHF stations on your TVfool report are -23.3 and -24.1 dbm, but that's average power. The gross peak power on those two stations is about -11.5 dbm (ignoring antenna gain and line losses). The amplifier is very close to saturation.

In an off-air environment amplifiers must be selected very carefully. The distribution amplifier that you have is not optimum for your application. The suggestion of a AP4700 preamp removes the possibility of VHF overload. The distribution amplifier should be removed from the system.

Tower Guy , you are 0 for 1 so far. I substituted the amplified distributor with a passive two way splitter and the signal got worse. The tuner card software shows the signal strength so here are the comparison:
With the distributed amplifier, only two ports used and the rest are terminated:
Channel(real) ..Signal Power ... Signal Strength
6 .....................15 dB .......... 45% (can't watch)
8 .....................31 dB .......... 100%
10 .....................30 dB .......... 100%
30 .....................29 dB .......... 100%
40 .....................19 dB .......... 72% (stutters)
18 .....................25 dB .......... 97%
19 .....................31 dB .......... 100%

With a passive two port splitter:
Channel(real) ..Signal Power ... Signal Strength
6 .....................6.1 dB .......... 22% (can't watch)
8 .....................25 dB .......... 100%
10 .....................27 dB .......... 100%
30 .....................24 dB .......... 90%
40 .....................8.3 dB .......... 30% (can't watch)
18 .....................20 dB .......... 72%
19 .....................25 dB .......... 95%

Looking at the drop in signal, it corresponds to the 4 dB gain the amplified splitters claims it provides.
I ordered the pre-amp you recommended but I will try it with my current antenna. I let you know if it makes any difference.

Anyone else has any other suggestions?

Thanks from San Diego

How about Channel Master 4228HD, would this be a good option for me, or would it be an overkill?

I also missed that your 8-way splitter was actually a distribution amp. Your tests with the SNR readings indicate poor incoming signal strength of the UHF signals rather than insertion loss from your distribution system.

Your problem channels are all UHF and come from either San Miguel or Tijuana. Unfortunately, both signal paths are obstructed by 200' hills about 3/4 of a mile away. These obstacles will significantly attenuate and potentially scatter the incoming signals.

It appears that your tuner's software is displaying the SNR of the incoming signals. Bare minimum should be around 16 dB for a perfect signal, 18-25 for a poor quality (multi-path degraded).

Channels 8 & 10 transmit from La Jolla. You can probably see their towers at night. They will likely be easily receivable off the back of any UHF antenna without effort. We just need to make sure you don't accidentally turn them into a problem.

Several things to think about:

If your existing mount permits it, tilt the front of antenna upwards a bit (5-10°). This is easy to do with a J-mount, but won't be doable if you have a fixed vertical mast

The UHF-only pre-amp has good potential to help as long as the problem isn't multi-path. Amps won't fix multi-path.

Do consider the upgrade to the 4-bay if the UHF-only preamp doesn't solve the problem. It "flattens" the reception window in the vertical axis without affecting horizontal beam width. We'd like to keep our horizontal beam width (due to the spread between transmitter locations) unless we are suffering from multi-path. In that case we need a more directional antenna and will likely have to compromise.

The 8-bay antenna will be a much narrower beam-width than the 4-bay. It will be much more directional than the 2 or 4-bay, which will help in rejecting reflected signals (multi-path), but may have the undesirable side-effect of becoming too directional to pick up both Tijuana and San Miguel signals simultaneously.

Bottom line is you'll have to try a few things until you get it right.

If the pre-amp doesn't work, which antenna should I pick. So far I have 3 choices in mind:
Channel Master 4228HD
Winegard HD-1080
Winegard HD7694P

I'm having a slight preference toward Winegard HD7694P. Would it work for my situation?

Seriously, if you're not going to listen to advice from persons in the industry such as TG or myself, just let us know so we can use our time assisting others who do listen.

What do you mean? I am trying your suggestions.
Just using the splitter didn't work.
I ordered the pre-amp and it should get here next week. I'm trying to plan forward in case the pre-amp doesn't work (since my problem is 2Edge signal it sounds like pre-amp might not work).
I had gotten 2 different suggestions for antenna and there was Winegard HD7694P antenna I had found good reviews for. I was just trying to find out if it was appropriate for my situation.

The HD 7694P would be a mistake. The HD7694P is a wonderful antenna for someone else, but not you. Your VHF and UHF stations come from two different directions. Your choices are the HD1080 or a combination of two antennas, one VHF and one UHF.

The 4228 HD is a UHF only antenna, but you have VHF stations that you need to receive.

Also, like AD Tech, I find your combative troubleshooting style unpalatable.

I apologize to both you guys. I'm not sure why I'm coming across as combative, but I'm just trying to figure out what is going on and why.

I was trying to look at the specs for CM 4220 (which i currently use) and HD1080 to figure out why HD1080 is better. I can't figure out the difference. any help?

The reason I'm asking more questions for HD-1080 is that AntennaWeb recommends "Blue" type of antenna for me. WineGuard rates the HD1080 up to "Red". http://winegard.com/offair/index.php

Does it matter if I'm going to add a pre-amp anyways?

I don't know if you aimed the 4220 HD for best signal on UHF and the VHF just happened to fall in place, or a compromise position that picked up the most stations. With a UHF only preamp either antenna should work for you, but the 4220 would be best coupled with a Y5-7-13 VHF antenna and a UVSJ. The HD1080 may not be any better on UHF than the 4220HD, but it will be far better on VHF.

To aim the antenna I had my dad in the roof and me in front of the TV. I tried the antenna 360 deg in small increments and to find the best position for the UHF channels. The VHF channels seem to have no problem in all positions. I plan on trying tilting the antenna 8-10 degrees up to see if I can catch more of the scattering signal.

With that info it's still hard to determine if your problem is multipath caused by the 2 edge path or a combination of losses and overload in your distribution system.

Have you ever tried connecting the 4220 to a single TV set to see if you can pick up the troublesome stations?

No matter which problem is causing your reception difficulty, your distribution system needed work.