Signal Amplifiers (Amps, Preamps, Distro Amps) - See Chart in Post #1

[icniagara]

Originally Posted by majortom

are you sure your not hooking it up wrong?
you aren't trying to power the pre-amp via the previous owner's
satellite system are ya? maybe take a picture of all the pieces u have in ur system, and draw a diagram an post em here where folks .
can take a look at ur setup, perhaps spot what's wrong.

CM 4 Bay mounted on my second floor chimney + 6" coax + cm 0068 + 30 ft coax run + ground that goes into my main electical box ground (where the satellite used to be grounded) + 2 ft line into my basement +cm 0068 power source pluged into a surge protected outlet + 12ft of coax into splitter+ split 1: 10ft run to my tv + split 2: 4 ft run to my pc tv card.

Currently the CM0068 is now sitting back in a the box that CM sent me when 1 returned my first Pre-amp and everything is rigged up with a coax extender where the pre-amp used to be and a radio-shakish GE "24 Db" In-line amp where the power source used to be. I have enough channels with the cheap amp that I think I can rule out wires and bad connections, though I did check all of them numerous times using our wireless phones as a walkie talkie with my poor patient wife at the other end monitoring our TV for signal. I have had many configurations since the cm 0068 went black one day, but I only get signal from channels other than the mysteriously strong local CW channel, when the cm 0068 is bypassed...so is the most likey hypothesis that my cm 0068 is fried, or did I miss something in my careful reading of the many posts from the fine contributors to Digital Home?

[majortom]

Sounds OK to me. Had to look back in one of ur old posts from 2009 to find where in Niagara Falls ur at. Looks like ur not very far from the Grand Island Transmitter sites. Here's an approximate TVfool for you, maybe u can plug in ur exact address and antenna height to zero in a little better, if I'm not guessing right...

http://www.tvfool.com/?option=com_wr...9fbea9da7751a9

Your closer to that site than I am here just outside of Buffalo, and your top two or three in ur TVfool says it.
The Mysteriously strong CW station is WNLO-DT UHF CH 32, which is on Grand Island, so explains that. Driving
by Grand Island along the River you should see the Transmitter Antennas all over the place.
One concern may be that with one at -22 dBm, and two more UHF at -30 and -35 dBm respectively ur already exceeding the max input for two strong signals, let alone 3, for a CM-0068 as in the Pre-Amp chart from Post #1 here. Grand Island also has some AM and FM Transmitters on it, so that would make it even worse. Thinkin maybe your seeing some Intermod produced by the Pre-amp due to the strong Grand Island signals at ur Pre-AMP input. In addition I don't think your downlead is very long compared to some. Mine's like 50' maybe more and my drops
coming off a four way splitter are at least 2 to 3 times longer than yours. Have you tried running your system without a pre-amp at all? Is it stable?
Do you have a Rotor system available? That might be more effective at pulling in the Toronto stations when ya wanna watch them, just move the antenna.

Doesn't explain any of the two CM-0068 failing on you, but maybe the 2nd one isn't really broke? Maybe ya just don't really need one at your location???

Heres a cheezy noise figure calculator I made a while ago, similar to that found in Post #1, presently it has my rough guess numbers for here plugged in to it, just change for ur downlead, and ur pre-amp specs...

https://docs.google.com/leaf?id=0B1k...ut=list&num=50

Be interesting to see how your Grand Island Stations compare to mine (Actual C/N samples from TSReader), since
ur basically behind the WUTV Grand Island Transmitter, while I'm in front of it and a little further away distance wise than you.
The other two GI stations aren't using a directional antenna which is why they are pretty strong for u.

Also, out of curiousity, are you seeing WNGS-DT on VHF CH 7 there in Niagara Falls?

[bpringlemeir]

Originally Posted by majortom

I dont think anyone is under the impression that ANYTHING could survive a direct strike.

Apparently a direct strike can be about one terawatt. That is 150dBm and I am pretty sure that it will overload most of the pre-amps. You should get a clear picture though. Hopefully it is not ducting.

Edit: If people are concerned about direct strikes, it is probably better to install a lighting rod at a higher point than the antenna with separate grounding. I don't know what the distance from the antenna would need to be without affecting reception.

[majortom]

You should get a clear picture though. Hopefully it is not ducting.

hehe...
No concern here, enough trees much higher than me to provide a decent halo of protection. Not to mention the Transmitter site down the road.

[icniagara]

Majortom, you are an asset to this board. I am looking into your advice and I forgot how fun TVfool can be... I get the wngs daystar channels np here in NF.

I was able to test my pre-amp on my home made 4-bay that I had swapped out for the CM 4bay and I think it works...I had read in a previous post that if your pre-amp is dead it will not only cease to amplify antenna signals, but it will also not pass any signal through it. For example i get 2 channels (PBS and the CW from the Island Antenna farm) without amplification, but when my pre-amp blew the first time i got zero channels, so again if my pre-amp is toast it would not pass the unamplified signal through, correct?

[majortom]

I had read in a previous post that if your pre-amp is dead it will not only cease to amplify antenna signals, but it will also not pass any signal through it.

Since I've personally never seen a pre-amp fail completely (knockin on wood) I may not be the best one for that question.

Having said that, when your testing it are you seeing any analog channels? Say CBLT5, CHCH11, CITS 36, TVO 19, CBLFT 25? If your not seeing those at all, or very weak, just snowy (snow = noise) without any herringbone (herringbone = fm interference from GI that may not be there if it's not actually amplifying anymore) on the VHF channels, I'd be inclined to say it's broke. Say that cause I'm thinkin ur close enough to GI, that if it was really working, u'd see classic signs of herringbone on ur VHF analog stations when facing GI.
Have you checked the Downlead cable, to be sure it's providing the DC voltage to operate the Pre-AMP?
A cable could fail such that it lets some signal thru, fooling you in to thinking it's OK without the Pre-AMP,
but isn't able to pass DC Voltage from the DC Insertor to the Pre-AMP.
(i.e - cruddy connectors, corrosion, kinks, torn insulation exposing or worse fraying the braid, etc.)
Rule that out...I'd use a DMM to measure the DC Voltage at the Pre-Amp end of the downlead, while the DC Injector
is plugged in to the other end of the downlead, downstairs or where ever it is normally.
If your still in doubt, try taking the pre-amp and a spare antenna to a friend or relative's house and see how it plays over there.

[icniagara]

I tested it on a NTSC only TV with great results on 19 25 35 41 47 52 55 56 (US shopping channel?) 57 and 69. 5, 9 and 11 were present but not as clear as the UHF analogue channels.

[majortom]

While watching the analog stations, compare the analog with the Pre-AMP Power Injector Plugged in Vs the Pre-Amp Power insertor Unplugged.
Major difference with it powered vs off -> ur preamp is amplifying.

[ota_canuck]

Just looking at icniagara's tvfool. Being so close to those broadcast towers and using a preamp could be knocking out the digital tuner due to major overload coming from 6 different sources.

[bentoronto]

Originally Posted by bentoronto

snip
3. Getting the balancing circuitry inside the pre-amp box would enlarge the range of opportunities for protection tricks (high-pass filters, resistances, diodes, little elves....) ahead of the first transistor.

How come an engineer like you is busy only asking questions of an amateur like me?

Here's a pre-amp design from the wonderful Brian Beezley. It illustrates two points.

1. Yes, you can put a tuned circuit and maybe other stuff ahead of the transistor. I suppose the general purpose antenna amps discussed in this thread can't have much early tuning since they are designed to handle an exceedingly large bandwidth. The early tuning wouldn't influence lighting much, but it might have a lot of influence on the big overload issue since it helps keep out bands other than the one it is designed to facilitate.

2. When he put the cover on his little project box, it changed the tuning. That means amateurs don't stand a chance of getting RF amps right if small moves like that change the alignment (and apropos the risk of doing mods inside the Sony XDR-F1HD tuner),

[bentoronto]

Originally Posted by Jase88

snip
Putting a preamp in the house won't help. You'll be losing the advantage of overcoming line-loss, which is what a preamp is primarily for.
snip

I guess you have to do the math. Seems to me that moving the antenna pre-amp downstream, say 15 feet and into the attic or even further, might represent a pretty minor dB cable loss and in exchange for major practical benefits.

Question: we are forever talking about RG6. Doesn't anybody sell a super colossal low-loss cable that isn't inconceivably expensive? Shielded 300-ohm twin-lead?

[iblackford]

Originally Posted by bentoronto

Here's a pre-amp design from the wonderful Brian Beezley. It illustrates two points.

1. Yes, you can put a tuned circuit and maybe other stuff ahead of the transistor. I suppose the general purpose antenna amps discussed in this thread can't have much early tuning since they are designed to handle an exceedingly large bandwidth. The early tuning wouldn't influence lighting much, but it might have a lot of influence on the big overload issue since it helps keep out bands other than the one it is designed to facilitate.

2. When he put the cover on his little project box, it changed the tuning. That means amateurs don't stand a chance of getting RF amps right if small moves like that change the alignment (and apropos the risk of doing mods inside the Sony XDR-F1HD tuner),

The tuned circuit in front of the preamp is actually essential to proper operation of the preamp. This is because at the frequencies we want to amplify, the FET's impedance isn't anywhere near 75 ohm. The tuned circuit performs input matching, and some filtering, depending on how it's designed. The same is true for the output matching circuitry, but filtering here is less beneficial, as overloading if it's a problem, would have already occurred.

Putting the cover on the box would have somewhat unpredictable effects if it's a metal cover. Some commercial preamps that I have seen have plastic boxes, which is also another option?

[majortom]

might represent a pretty minor dB cable loss and in exchange for major practical benefits.

15 feet from my antenna would mean penetrating the roof I just spent good $$$ and sweat tearing and replacing two years ago, in order to get to the attic. Not practical here. A helluva lot more $$ than a 30 dollar pre-amp, roughly a factor of a 100. I'd rather leave it where it's supposed to be and take my chances climbing the ladder once in a while. Not a big deal.

[icniagara]

Originally Posted by majortom

Have you checked the Downlead cable, to be sure it's providing the DC voltage to operate the Pre-AMP?

Faulty wire was the culprit, it was fun to play with a DMM. I am fascinated by the idea that tv signal could pass through a coax wire but that the charge from the power source could not. My faith in the CM0068 is restored and my confidence in the people who contribute to this board is fortified. Many thanks you's.

[goforit]

Choice A: use CM3412 amp– 2 ports feeding two TVs- each port rated at a gain of 11 db.

Choice B: use CM3410 amp – 1 port exit – small piece of coax – feed into simple 2-way splitter for 2 TVs- single port of CM3410 rated at a gain of 15 db (splitter rated at loss of 3.5 db).

Noise of both amps about 3?

A or B?