goforit,
How long is the run between the combiner and distro amp?
Could you not combine, and then feed into the pre-amp, or are you worried about overloading the pre-amp with strong signals from the one antenna that you are choosing not to amplify?
Amps are usually used to overcome line losses. They won't make a poor signal better.

cheers

Amps are usually used to overcome line losses. They won't make a poor signal better.
A good pre-amp will effectively make a poor signal better, if it has a noise-figure (NF) better than that of the TV/tuner it connects to. That's the primary use of pre-amps around here. Attenuate the signal again afterward if it's too strong for the set.

Cheers

goforit,
How long is the run between the combiner and distro amp?
Could you not combine, and then feed into the pre-amp, or are you worried about overloading the pre-amp with strong signals from the one antenna that you are choosing not to amplify?
Amps are usually used to overcome line losses. They won't make a poor signal better.

cheers
The run is not long, 5-10 feet.
To maximize the pre-amp, I am mounting up against the antenna.
Two separate lines, one amped, one not, then joined in the house, and then splitter or distribution amp for 2 TVs.

My biggest concern is signal loss on the one antenna (joiners, coax length, etc.), that's why it is amped and why I want to use a distribution amp instead of a normal splitter that has 3.5 db loss.

A good pre-amp will effectively make a poor signal better, if it has a noise-figure (NF) better than that of the TV/tuner it connects to. That's the primary use of pre-amp around here. Attenuate the signal again afterward if it's too strong for the set.

Cheers
I will be using the CM 7778 pre-amp, Winegard coupler CC7870, and then the CM 2 way distribution amp. I believe the CM 7778 and distribution amp both have very low noise levels, so that's good.

I'll try a regular splitter first, and if is poor, will try the distribution amp.

goforit,
Go for it! (sorry couldn't resist ;))
_____________________________

mlord,
A good pre-amp will effectively make a poor signal better, if it has a noise-figure (NF) better than that of the TV/tuner it connects to. That's the primary use of pre-amps around here.
In my post I was referring to poor signal coming out right at the antenna, not at the tv tuner. Amplifying nothing still gives nothing, right? :eek:.

BTW when you say "around here", do you mean here = digitalhome.ca, or here = Ottawa? I know in the Ottawa area you guys have to fight for some weak signals. Just curious.
_____________________________

Okay time for a power inserter question.

Is there any reason why I can't use a SW44PI instead of the supplied CM 0747 for powering a CM 7775? The SW44PI is a used for powering sat switches, but is a T-style inserter - that is, the power inserter is comprised of two units: the power adapter ---> coax carrying DC ---> inserter. The CM 0747 is a single unit, meaning that that the power adapter and inserter are in the same unit. The benefit of using a T-style power inserter, is that I am currently using diplexers that do not pass power on the ANT side. To use the CM 0747 without removing the diplexers I would have to add the CM0747 outside where it is exposed to the elements and I have no AC nearby to power it. I'm not sure that a diplexer exists that passes power on both legs - it is counter-intuitive I think. I would prefer to use an existing abandoned rg59 run to feed power remotely to a T-style inserter, rather than running a new RG6 feed solely for OTA.

SW44PI specs:
47-2300 MHz
+ 18 VDC
Inserter loss <= 1.0 dB
Return loss >= 12 dB

The CM 0747 is + 18 VDC, but I have no data for losses.

I'm concerned about the return loss figure of the SW44PI.

If I get time I'll sketch up and post my current and proposed schematics for other people's ideas.

_____________________________

cheers, and happy DXing

A good pre-amp will effectively make a poor signal better, if it has a noise-figure (NF) better than that of the TV/tuner it connects to. That's the primary use of pre-amps around here. Attenuate the signal again afterward if it's too strong for the set.

Cheers

This is true of course, but where in the world does one actually find the noise figure specs for your TV's built in ATSC Tuner??

I just scoured 3 product manuals with no such information given.

As I have been toying with the idea of adding a pre-amp for exactly this reason alone, it sure would be helpful to do a comparison.

My 7778 has 2.2dB noise, could a built in tuner be better than that?

Based in actual sensitivity (-86 dBm +/- 1 dB), most CECBs have NF = 5 +/- 1 dB:
http://www.digitalhome.ca/forum/showthread.php?p=935241
Note they tested a variety of different tuners.

Recent DTV/HDTVs may also have same (excellent) performance...and 2-4+ dB more for older tuners.

This is true of course, but where in the world does one actually find the noise figure specs for your TV's built in ATSC Tuner??
I don't actually use my TV's tuner for much, but the wonderful 6th generation tuner in the HVR-950Q USB stick I use for our very distant PBS station has a NF of about 5dB.

Without the pre-amp, it gets nothing when tuned to PBS. But with the 0.4dB NF pre-amp (yes, 0.4dB) it generally always has a good signal lock.

That's due to the +4.6dB NF boost, which saves me having to install a big parabolic dish to otherwise have any chance at the same reception.

And even the strong (analog) locals look much better through the pre-amp than not (using PVR-250 tuners for those).

Cheers

I'm considering getting a preamp, I'm thinking of either the CM7777 or Winegard 8275. On paper the Winegard seems the better unit as it has slightly higher gain on UHF, but are there any other limitations or undesirable features? The CM is $20 more expensive.

I know that the CM has power fed through the coax connection, eliminating the need for a separate power feed. I downloaded the manual for the Winegard unit and it shows a similar arrangement with a power injector.

I got my expected reception results from TVFool and some of the CN tower stations are around -30 dBm (CBLT for example). Do I understand correctly the literature on the preamp, that this is already higher than max input that the CM7777 can take? (which is -35.8 on the preamp chart) (of course, this is assuming outdoor installation, no other losses taken into consideration etc. in my case I am in attic but no splitters, cable is direct run to ATSC tuner. Even the wall plate where cable comes out of the wall is a pass-through type as this eliminate a connection)

I was wondering if that is the case, then if I were to get a pre-amp, should I aim it for the Buffalo and Niagara Falls area to improve reception of those channels, without overloading the tuner on the CN tower channels?

Hmmm... how would I know if I am overloading in any case?

I've been able to make progress on my cable routing over the week; I've got it routed from the attic to the basement and back up where the TV is. I haven't cut the cable to final length yet, once I do I will know the final length of my coax cable run, but I don't think it will be more than 50'.

Location is Richmond Hill Leslie and Elgin Mills

Legacy2009:

Pre-amp performance does not depend on their stated gain factors. As mlord has said before, it really comes down to their noise factor (in non-overload) with the lower NF the better. And on this measure, the CM7777 scores higher than the AP8275.

Judging by what you've said, I believe the CM7777 would work in your case. Three reasons I say this: 1) Your attic will decrease signal strength well below -35 dBm. 2) With a directional antenna, you can point towards Buffalo and your antenna will reject part of the TO signals, reducing their received signal levels. 3) I am using a CM7777 with ambient signal levels as high as -10 dBm and I don't suffer from overload.

You will know if you have overload when you start losing strong channels. Your reception overall will decrease under overload.

In the end, only testing will confirm a pre-amp's use!

STL

I don't think this was discussed before, but the in-line power injector usually has a ~1 dB insertion loss.

This isn't huge (or perhaps even material), but this source of loss could be added to tczernec's pre-amped system loss spreadsheet.

I think that most of us had assumed that the power injector had a neutral effect on signal levels because it is part of the amplifier system. But the gain and NF quoted for the pre-amp are gross of the power injector insertion loss downstream...

So the 10 dB gain and 6 dB VHF NF / 6.5 dB UHF NF GE pre-amp sees another 1 dB of system loss downstream. So there is very little useful amplification left with this amplifier...

STL

STL, thanks for the clarification. I knew there had to be a reason why the CM was a bit more money than the WG unit. Can anyone guess where I'll be going next weekend:D

In the meantime I will do the hardware modif to my 4228HD.

What if, down the road I end up moving the antenna to the roof? Would I have to be concerned about overload?

The posts at the beginning of this thread with Yaamon and stampeder seemed to indicate a sense of urgency when testing under possible overload conditions. These were from a few years ago, I wonder if this better handled by the newer tuners? I just got into OTA and got the "Centronics" from Save And Replay.

Also bear in mind that transmitter power levels are expected to INCREASE in the near future....

Many Canadian stations have much higher post-2011 power levels and many U.S. stations
have "maximization" requests either approved and are working on implementation or are
waiting for approval...this is over and above the "Authorized" levels assumed in TVFool.

Also bear in mind that transmitter power levels are expected to INCREASE in the near future....

Many Canadian stations have much higher post-2011 power levels and many U.S. stations
have "maximization" requests either approved and are working on implementation or are
waiting for approval...this is over and above the "Authorized" levels assumed in TVFool.

Do you have any more information on this? Any links to provide? How much more power and how many more miles are expected as a result?

This sounds very exciting, especially in fringe areas.

Larry

But with the 0.4dB NF pre-amp (yes, 0.4dB) it generally always has a good signal lock.What is the pre-amp you are using that has the 0.4dB NF?

Larry

I think it's a pre-amp from Research Communication- from the UK. I was checking it out on the web- looks expesive- twice the price of common pre-amps- W, CM; shipping will probably be pricey too. Maybe there is a North American distributor.

What is the pre-amp you are using that has the 0.4dB NF? ... Where did you buy it?
It's a Research Communications (http://www.researchcomms.com) type 9260 HDTV pre-amplifier. This is the UHF-only version; they also have a UHF/VHF model for the same price, as well as a version that has a sharp drop-off above 700Mhz for the new (smaller) USA 2009 DTV band.

The pre-amp, PSU, and shipping total is only UK104, which is rather good for a product that is many times better in every way than just about anything else out there.

Well, not *every* way -- you do have to attach your own 120V plug onto the end of the pre-wired power cable. :)

At current exchange rates, that's around CAD$186 or USA$166.

Cheers

I'm not sure what the advantage of the lowpass at 700 Mhz on the 9261 is over the 9260. Sure, some markets will see channels 52-69 disappear and there will be no need to amplify those frequencies. But would one stand to gain by using the 9261 over the 9260?

I haven't heard of any one overloading from old nearby 900 Mhz cordless phones or even analog cellphones running on AMPS... he he.

I'm not sure what the advantage of the lowpass at 700 Mhz on the 9261 is over the 9260. Sure, some markets will see channels 52-69 disappear and there will be no need to amplify those frequencies. But would one stand to gain by using the 9261 over the 9260?
Post-transition, those old channels will be recycled. It is quite possible that something on them might be strong enough to product adjacent channel interference for channels 50-51, especially if the stations one wants are very weak and distant.

That's the idea. But for now, in Canada, the 9260 is the better choice, since we still have channels up there.

Cheers

Qualcomm's MediaFlo has been aggressively taking over Ch55 for nation-wide video to cell phones.
Other Ch52-69 users are expected to follow big time after next week's Transition.

In San Diego, Qualcomm has six distributed 50 kW transmitters, several of which are
surrounded by neighborhoods who have never had to deal with strong local signals.
I'm two miles away from their torch...next closest is 14 miles. When the rest of the
channels fire up (if they haven't already), I'm going to have lots of intermods.
At least they're using moderate power levels...don't know about the other channels...

In Los Angeles nearly a dozen new areas are affected.

I recently read that 58 markets are already approved for CH55 operations, but I haven't
found an easy way to search for the transmitter locations, except fol. hints.
Here's 2007 list of MediaFlo approvals with license numbers (search for Qualcomm):
http://www.fcc.gov/Document_Indexes/Media/2007_index_MB_Order.html
Here's the Southern California license. Select each number and click on Attachments-> YES:
http://wireless2.fcc.gov/UlsApp/UlsSearch/license.jsp?licKey=2479928
Apparently a SINGLE NETWORK all the way from the border with Mexico to Reno, Nevada.

PS: Although MediaFlo is designed to operate with Cell Phones (reverse path is 3G/4G),
by the end of the year, U.S. customers may need their OTA antenna for some of these mostly
unannounced new services (movie download?).....not sure what (if) schedule is for Canada....