The power should be passed from injector to preamp, so clearly something is wrong if power is also going PAST the preamp, no?

If the amp is doing what it has always done, then it is definitely getting power. But, I think you are confusing the DC & AC/RF voltages...

Injector sends up the DC to the amp, and inside the Injector is a blocking capacitor that stops the DC from going to the TV set. They use DC to power these amps because the RF signal that you want to recieve is actually a very small (in most cases) AC signal and can pass easily within a DC potential.

With the DC side - between amp and injector, you should not feel anything when you touch the cables or connectors. Yes, something is creating a very small AC/RF voltage on the input side of the pre-amp, but it may be of no fault of the amp itself. As MajorTom said, a very high powered transmitter nearby... Ham, CB, etc... could also induce signals producing those stray RF/AC voltages.

With proper grounding you should have no problems whatsoever. Whatever caused the feeling you got when you touched the connector should disappear when the outer shield of the coax is grounded.

There is nothing to worry about.

What made me want to go back to my library was I remembered back at like 14, getting an RF burn when I was tuning a new style of CB antenna that had come out. It was a 1" x 1" box that mounted in the top-center rear window of the vehicle. The idiot I was working with and installing it for, actually keyed the transmitter while I was making an adjustment to one of the trim caps inside the box, and I got an RF burn. That made me want to check things out and when I was comming back to answer... "MajorTom" said it basically in his post...

Greg

I went back up twice today and once yesterday and I did not feel the tingling sensation anymore.

Truly bizzare. Anyways to prevent myself from going too far off-topic I will elaborate more about the grounding in the appropriate topic, feel free to continue the discussion there, I would appreciate it.
http://www.digitalhome.ca/forum/showthread.php?p=1105500#post1105500

SO to clarify, the amp does NOT send any DC voltage towards the antenna? That the injector sends DC voltage backwards against the AC RF current ONLY to the preamp? SO basically the section that is amplified is the 100 feet run between amp and injector, and NOT the downlead?

Anyhow, here is my tvfool by the way to illustrate the signal strengths. The strongest transmitter in my area is RF5 power -17.1 dBm, not too strong.

I think the 7778 and 7777 are too strong in amplification. I would like to know if there are better alternatives for me based on the tvfool report?

I went back up twice today and once yesterday and I did not feel the tingling sensation anymore.

Truly bizzare.

That's a good sign.. and also probably means that someone was just close by, enough that when they transmitted, you felt that tingling.

SO to clarify, the amp does NOT send any DC voltage towards the antenna? That the injector sends DC voltage backwards against the AC RF current ONLY to the preamp? SO basically the section that is amplified is the 100 feet run between amp and injector, and NOT the downlead?

That is correct. The only part of the cable run that should have any DC voltage present is between the injector and the pre-amp. It is considered as part of the downlead, but it's only a section of the whole.

Anyhow, here is my tvfool by the way to illustrate the signal strengths. The strongest transmitter in my area is RF5 power -17.1 dBm, not too strong.

We really need to see the entire report if you could post the link to it, that would be great...

Greg

SHOOT I forgot to link it. Sorry.

Really stupid me...
http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id%3d9fbe3a5ef62369

Wow.. that's one interesting area to be located.. Signal wise...

And your setup is Antenna at 28ft, 300 to 75 balun, 40 ft RG6 Cable, CM 7778 Pre-amp, another 100 ft Cable, to the Power Injector, and then small cable between the injector and the TV.

You're right.. It would be a little difficult to nail down the Buffalo stations without over powering the pre-amp input at your location. You're almost on that as they say, sweet spot of 15 or so miles. With all the signals comming off the CN Tower, they are all fairly strong (in the -17 to -30dbm range) depending on the stations output power.

With the CM amplifiers putting out 23 (7778) to 26db (7777) gain on UHF, You are easily putting a few of the local stations close or into the overload condition and then some. By adding the cable between the Antenna and the Pre-amp, you've actually dropped your signal level about a 3db loss assuming the balun with about 1.5 db loss and your 40' of cable adding another 1.6 to 1.8 db loss depending on the frequencies it is recieving. And then you have the Antenna gain on top of that as well... (not sure what you have there.. and if you have a rotor or not).

The problem is that that loss also drops those Buffalo stations as well. To be honest, if it's just a 1 TV house... I'd actually go to a very directional antenna with a rotor. Something with a narrow beamwidht. That way you focus on the station that you want, and any signals from the side and back are reletively redundant.

I wouldn't move the CM Pre-amp back up top near the antenna. Looking at the Pre-amp chart in post 1, you might want to go with a pre-amp with much less gain.. but you still may run into some problems with small overload. Something like the Winegard HDP-269 might be a better idea. It's only a 12db gain pre-amp, but it allows for stronger input signals, which is something you have at your site. It's input is a little more forgiving, and without the higher gain, it's a less likely to go into overload. You might even be able to mount it right at the antenna head without any problems which would mean a better ampflication of the buffalo stations.

But no matter the combination, grounding is always the best policy.. lol..

Greg

PS: Yes, there should be no problem with a female to female coax joiner inserted where the pre is now, if you want to move it back up the mast.. Those are generally a straight through, no loss connectors.

SO basically the section that is amplified is the 100 feet run between amp and injector, and NOT the downlead?

The amplified signal continues on past the power injector, but you are right and the down lead from the antenna to the pre-amp is not amplified. That is why you typically want the pre-amp as close to the antenna as possible.

That is why you typically want the pre-amp as close to the antenna as possible.

I know.
I've always understood that actually :)
It's just I can't, and I think BrotherTank explained it best.

Your directional antenna suggestion sounds logical, but the problem is I might lose those side signals entirely given that alot of antennas have large NEGATIVE gain on their side lobes. Increasing the directioanlity might make it worse. It might still be okay to get let's say, CBLT-DT or CFTO-DT, but the weaker stations from the side will definitely suffer. They already suffer quite a hit with my current antenna, the Channel Master 4221HD, which has quite a wide beam width. No rotor. I need the amp for the Toronto and Hamilton channels moreso than the Buffalo ones (except WGRZ).

The amp might be amplifying noise on top of that too, so perahps that is why some channels are eratic, and some are fine?

I did a simple calculation for a problematic channel.

WGRZ is at 13.6 dB NM. According to this (http://imageevent.com/holl_ands/multibay/4bay/kosmic?p=0&n=1&m=-1&c=4&l=0&w=1&s=0&z=4) my antenna has about 8-10 dB gain on that specific frequency. Let's say I lose around 1.5db from the balun, and another 1.8-2db of lineloss, plus the 2.2dB noise figure from the 7778. Discounting other losses (because of preamp)

I would still have a good positive NM for that channel well above the detection threshold and no dropouts. Yet this channel proves to continue to be a pain.
A similar channel at a lower frequency and lower NM on TVFOOL (WNYB on RF26) comes in just fine.

WGRZ is at 13.6 dB NM... ...I would still have a good positive NM for that channel well above the detection threshold and no dropouts. Yet this channel proves to continue to be a pain.As you can see in the following poll, WGRZ is known for causing problems for some people on the Canadian side of the lake, when it should not be doing that according to "the numbers":

Hardest Buffalo OTA Stations To Get In Golden Horseshoe? (http://www.digitalhome.ca/forum/showthread.php?t=120780)

When it comes to OTA reception the actual vs the theoretical can sometimes be wide apart. As valuable as they are, technical tools and calculations can sometimes stumble in situations like that of WGRZ. That is one of the primary reasons I started Reception Results threads for every part of Canada in a separate forum, so that people can see how others in their own area are doing for the actual signals out there as opposed to simply relying on what "should" be available.

This is a perfect case of how the technical numbers just don't jibe with the real world, so personally I would not use WGRZ as a yardstick in your situation unless you intended to build an antenna specifically to conquer the problems. ;)

As you can see in the following poll, WGRZ is known for causing problems for some people on the Canadian side of the lake ...
Weird. That cheapy $13 quad-bowtie antenna I put up gets it without any trouble (Yonge and Lawrence), as does its $20 identical twin (Bloor & Christie).

I guess it must be location location location. ;)

And the time of year too, according to quite a few people over the years. :rolleyes:

I've been reading many of the posts here... (that's why it's taken me this long to write my first post since I joined a few weeks ago), and I've noticed many people making statements that have no merrit. Your's isn't one of them, although my second quote below is, and I will get to some of them later that need correction... Please don't think badly of me because of this...

Err, well me too. I think some people are learning and others are too busy to help repeat the same stuff over again. Also, it seems that when it comes to pre-amps every manufacturer has their own spec metrics or don't provide any at all. Hopefully people try to correct anything that is in-accurate.


The main reason for the notch filter/channel block is to removed or reduce adjacent analog channel interference and to lower the recieved signal level from said station. When everything is digital, you will not need it for adjacent channel interference, but you will want it to control the recieved signal level.


This is not quite accurate.

See http://www.digitalhome.ca/forum/showthread.php?t=124224 and holl_ands "Third Order IMD Calculator - RevC_1.xls". You are correct that digital has smaller leakage outside the assigned channel. However, when ever RF is mixed you get cosine/sine products which cause RF signals to add/subtract. In the thread above, I think that the orignal poster says there are problems 10 channels above/below. I guess that there are tuners with a 60Mhz inter-mediate frequency. This mixing is going to happen whenever you have a non-linear (read powered) equipment.

So, an all digital world will have problems with both signal level (overloading tuner AGC) and high power stations stepping on lower power ones. It is just that it isn't so easy to find as just adjacent stations. This will be a problem with pre-amps post Aug 2011... Or is that what you meant and I just didn't get it?

Edit: Tuners have problems 14 or 15 channels apart (not 10 as I stated). That gives 80-90Mhz as the IF.
Edit: http://photos.imageevent.com/holl_ands/files/ota/Third%20Order%20IMD%20Calculator%20-%20RevC_1.xls

I just got this thing at a garage sale with no power injector. My solution was grab a decent 12VDC wall wart and open the metal case of the distro amp. I put the 12VDC at the "power" TV port 1 before the blocking capacitor (caution : place 12VDC at the centre pin of port 1 would send 12VDC straight to your brand new LCD TV - I didn't do this) and it works great on TV ports 2, 3, & 4. Connecting a TV onto port 1 causes a malfunction that I don't understand. Any advice would help.

"24db" of adjustable gain at 3 out of 4 ports and yes it is working. I have 2 TV's hooked up so far with no signal loss (better signal strengths too!).

Sounds like you have found the reason it was at a garage sale...port 1 is dead.

For five bucks. I can't complain. I only have 3 TV's in the house to connect to anyway. The 12V power supply "brick" is rated to 3A and is normally used in "TriplePlay "applications. Over kill but it worked and the LED shines bright!
:D

Does that power source have any overload protection ? If anything goes wrong it could destroy all of your tuners.

Does that power source have any overload protection ? If anything goes wrong it could destroy all of your tuners.
Ya, the 12VDC plastic "brick" is has OVP. Good point though ota_canuck. Thanks.

Back.. Sorry Little.. within 24 hours of posting that, I got hit with an HD going bad, and I lost everything on the drive... Including my XP operating system...

So, an all digital world will have problems with both signal level (overloading tuner AGC) and high power stations stepping on lower power ones. It is just that it isn't so easy to find as just adjacent stations. This will be a problem with pre-amps post Aug 2011... Or is that what you meant and I just didn't get it?

Correct... different ways of saying the same thing, but I was trying to make it less "tech". In our case (mine and Goforit's), we are sitting almost underneath the CHCH tower (Although, I think I'm a little closer to it than he is). Using a notch filter is almost a must for us to be able to really amplify those distant or Fringe-Deep Fringe signals without overpowering our sets AGC or overloading the Pre-amp input for that matter.

I built my own little pre-amp from scratch and built in 3db of drop on the three major channels comming off the CHCH tower, before it does any type of gain insertion into the signals. And it works quite well. It allows me to amplify those distant stations better than if I'd gone out and bought say the Wineguard 269.

So as Stampeder said after my post on Filters:

Yes, always keep attenuation to a minimum, but let's be clear that attenuation is an essential tool for CATV/OTA system engineering and tuning. There is a time and a place for attenuation, as there is amplification.

Greg

Hmmm I'm thinking this thread is the right one to ask about preamps if not I apologize and request a move.

I'm currrently using a Radio Shack 15-118x with 10dB (as listed on the bottom) and it does certainly make a difference but was wondering what people think about if , of course, the Channel Master 7777 would make a difference in incrreased or more reliable reception on the spottier channels.

I'm in a high fringe area reasonably far from towers with some/ a few trees and a mountain blocking some signals if that matters.

Thanks for any info.

nakedgord, you asked in the right spot.

The preamp can only help with signal losses that happen after your antenna. Any obstructions in the way (trees, buildings, mountains, etc...) will reduce the signal and you can never get it back. All you can do is make sure as much of the remaining signal as possible makes it down to your tv.

There are 2 numbers you need to look at in a preamp, the gain and the noise margin (NM). The noise margin tells you how much noise the preamp itself will inject into the signal, and the gain tells you how much down-stream losses the preamp can compensate for. The 7777 has a 2dB NM, which is quite good. The problem with cheap preamps is the NM can be very high, as much as 7 or 8dB (or possibly even more), which is really adding a huge amount of noise into the tv signals. Does your RS 15-118x have any NM on it? It may be in the original paperwork that came with it if you still have it. If they don't specify it, it's probably large.

The amount of gain you need is determined by how much cable you have after the preamp and how many splitters. As a rule of thumb, add up all of your cable losses (~1dB for every 18ft of RG6) and splitter losses (usually written on the splitter) and then add 10dB, and that's how much gain you want. You may find the 7777 too powerful, as it has a lot of gain. Your preamp you said had 10dB of gain, which would only be really effective for a short cable run with maybe a 2-way splitter. It will help, but a more powerful preamp may be required for optimum signal strength.

Hope that helps.

Thanks for the reply Dr.

There's no NM on the bottom and the orig paperwork is long gone. However my run is actually a 15ft cable since my antenna is in the corner of my apt propped up on a cpl of Ikea square tables so I'm wondering if there's even a chance it'd improve/increase reception.

The Source sells some Antennacraft models for $50 and $60 so perhaps that might be something I should consider since, unlike CM retailers, they do have a return policy if it doesn't work out.

Thanks again for the input.