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

[alebowgm]

Originally Posted by goforit

I think of trying the CM 7778 again (now that the analogs have shut down); it is attractive for the separate UHF/VHF inputs and FM trap.

Note that the CM7777 and CM7778 as of Feb 2012 no longer have separate UHF/VHF inputs. It is now a combined input. The photos on 'The Source' website are misleading.

Which leads to my question for re_nelson, I am assuming the CM 7777 you tested with was the older model with separate inputs and not the V2 model with the combined input? I would be interested to see if they have any difference when compared against each other.

[re_nelson]

The CM-7777 model in use here is the classic, with the separate UHF/VHF inputs. I'm a tad skeptical of the new model but would like to see a shootout between the two units.

I suppose I'm a bit jaded on anything new from Channel Master, probably due to the more favorable reviews of the original CM-4228a UHF antenna as opposed to its successor.

[BOUVAL]

The CM-7777 model in use here is the classic

Re_Nelson,

That's one thing I thought of asking you when you wrote post #3134 yesterday.

I did buy the new generation CM7777 last week just to try it with its 30 dB gain to hopefully get channel 13.

Well, to make a story short, no channel showed. So I brought it back to the dealer and exchanged it. With the second one installed around eleven in the morning, it worked, but not any better than my old CM7778. I came back home around four in the afternoon and I was getting only half of the local channels. I brought back that second one , did not ask to be reimbursed yet. Being french speaking and them english , I told them that it would be easier for them to get in touch with Channel Master and find the prblem.

In my mind, the problem could be overloading, what else ?

My TV Fool: http://www.tvfool.com/?option=com_wr...267eee22a6d100

Thank You
.

[re_nelson]

BOUVAL - I'll defer to the real experts here to give you guidance. I'm still fairly new at OTA and don't have the experience of others who have been into this far longer.

My role is little more than a collector of data to measure the performance of the various preamps. I leave the analysis of the numbers to people like holl_ands. I'll also reiterate that I'm in a prime location (nearly perfect in every way) for OTA reception. Consequently, I've never been confronted with having to deal with signal challenges, either due to overload or too weak signals.

[ADTech]

Using a high-gain amp that close to the broadcast signals makes overload highly probable. The 7778 was a far better choice than a 7777.

There is rarely any advantage in selecting a high-gain amp over a medium gain amp except when there is an extensive amount of signal attenuation due to a lossy signal distribution system. For example, extremely long cable runs and or multiple splits in a weak signal area would be the suitable area for such an area.

With digital signals, all we need is a "Goldilocks" signal, not too weak and not too strong. Please note, the "Goldilocks" range is pretty large for power levels. Amplifying a signal more than it needs is not going to improve anything.

[re_nelson]

Amplifying a signal more than it needs is not going to improve anything.

Except for fanatics such as yours truly who don't actually watch television but look at power levels on measurement tools. I take a cue from Spinal Tap and want it to go to 11 on a 10-point scale!

Yes, I'm just joshing since I really know better...I think...

[majortom]

Bouval,
Agree a high gain preamp is probably not the right solution.
In addition to ur tvfool, take a look at ur fmfool and compare it to ur TVFOOL.

Maybe try the same test with a VHF HI High Pass filter to attenuate the FM Broadcast band by at least 30 dB, but passing VHF HI.
2nd harmonic of FM being VHF HI, a high gain preamp may pump up the trash even more in VHF Hi. Especially if ur TV antenna has to aim at very strong FM stations to aim at the desired TV station.

I designed mine around a 156 MHz cutoff frequency, not the prettiest thing, but it seems to work OK (I posted a schematic of what I built in the filters thread a long time ago).
In my situation I have an FM Broadcast tower right behind me within 1/2 mile, so it's always strong no matter the aim. But with the homemade VHF HI HPF between the antenna and preamp input, with my TV antenna aimed at the CN tower in Toronto (FM Tower behind it), I'm able to pull in CHCH RF 11 (NM 9.6) and CFTO RF 9 (NM 5.8) with a Winegard AP 8700 Preamp almost all the time from Buffalo. Also keep in mind in order to aim at the CN Tower, I also nearly have to aim at Grand Island where three strong local stations are.
No question, it's not an ideal situation here either, but it does work for me.

If that doesn't work, keep the VHF Hi High Pass filter, but try a lower / medium gain Preamp that won't overload and cause intermod so easily.

[El Gran Chico]

If anyone is wondering what the inside of a CM 7778 looks like (bought mine in 2007), I opened mine up yesterday for the first time.



At the upper right, you can see the combined/separate switch for VHF (in the default "combined" position). At the bottom, you can see the FM trap switch (in the default "in" position).

[ADTech]

At a glance, it looks just like a 7777.

[roderunner72]

Just cut the cable tv and hooking up my OTA.

I'm in Kent, WA, 15 miles south of Seattle.

I have
AntennaCraft 70 Boom HBU-22 Antenna
GE 4 Way distribution Amplifier from HomeDepot.

I'm not sure if the amp goes at the antenna, or the old Comcast cable TV demark on my home, which is easier of course.

My current setup.

Antenna on 1 story house on 10' mast
Connected to the old Comcast Demark on my house with 75 feet of Coax cable
This is where my Amp is, which then splits out and connects to my TV's.

Is the amp placement correct?

Before I got the Antenna, (yesterday) I hd a thin peice of copper wire fashioned into a round loop with a straight end like a Q and stuck that inside the input port on the amp and a metal coat hanger hanging off the outer threaded portion. I was able to pull 30 channels with that. Without that I got no channels. But now I'm hooking up the antenna and not sure where the amp goes.

Thank you

[ProjectSHO89]

Put the DA at the demark.

[morehp]

roderunner72 which amp did you get? you indicated its a distribution amp.
You may want to consider a preamp... and then you most likely will not need a distribution amp.
Its best to locate the preamp as close to the antenna as possible. This way you will capture the most amount of weak channels.. assuming you have weak channels you would like to receive.
Placing the preamp at the antenna will boost the signal strength of the weak channel(s) so the signal is not as degraded or gone by the time it gets to your tv tuner. This way your tv tuner will tune in more channels including weak signal strength channels that would be otherwise lost or too weak of a signal by the time the signal traveled through all the coax and connections to get to the tuner in your TV.
I have the Channel Master 7777 mast mounted directly behind the antenna and it made a night and day difference between the number of channels I can routinely receive compared to without the preamp.

[ProjectSHO89]

A 7777 is a poor choice for his suburban location. kent is less than 20 miles from his towers and, unless he's buried in a valley, he probably doesn't need an amp anyway. Besides, the old "classic" 7777 has been discontinued and has been replaced by a new version that I haven't seen any test results on.

Since he already has the DA, it was suggested to put it where it belongs. If he was starting from scratch, or the DA doesn't work out, then a different path would be needed.

[Jase88]

Anyone have an opinion on the new "combined" input design?

I for one don't like it. My thinking is that insertion loss will be greater using a UVSJ, rather than the separate inputs on the "classic" CM7777.

[BOUVAL]

My thinking is that insertion loss will be greater using a UVS

True, but the extra gain compensates.

I tried two of them and in my location it's overloading and I don't have time to fool around with attenuators.

Actually I use a CM7778 (not the new one) and it suits my needs.

Here's what's in the box of the new CM7777
.