Should we add a Scenario 5, to compare to scenario 2?:)

LOL MT. It was fox Rochester R28 V31 not Buffalo. Other channels were? I dunno we were racing at the time. I think Flavoie may be on to something. I will try again soon and dial back the power level. Wait till then and we will see. Panamark without the second amp the long runs from the split 50’ or more lose lots of channels. Definitely I need the second amp.

Hey everyone,

I'm looking for some opinions regarding preamps and distribution amps for my soon-to-be OTA setup.

We're cutting the cable and want to wire the entire house up to an attic-mounted antenna. It's a two story house (plus basement) with the main cable distribution point being in the basement (in the electrical closet). Unfortunately, that means a long cable run from the antenna and then multiple even longer runs to each TV.

- There will be 4 TVs connected to this (4-way split)
- With my current test setup using an Antennas Direct CS2, mounted indoors and connected directly to a single TV, my signal strength is fairly good (strongest channel is 91%)
- The final setup will likely be with an Antennas Direct CS4.
- Here's my TVFool results: http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id%3dc77a89e73108ca

My question: What would you recommend for this, a preamp or a distribution amp (or both)?

I've found a few posts regarding this in this thread, but answers seem to vary depending on individual situations.

A distribution amp installed where the coax cable enters the basement (about 40 feet of cable from antenna) boosted signal strength on all distant stations and I now get a strong signal on all four of my sets. I was also told that a pre-amp would be good since MyTV 49 is weak, but I'm not really into their programs anyway and am afraid that it might over-power my CN Tower stations signals, not to mention the relative increased strength of signals after Canadian transition August 2011.

For the very low one-time cost of these gadgets, get both and try them. Or as a minimum buy the distribution amp, then if needed try the pre-amp.

A preamp is a low noise amp which can be mast mounted (with power going through the coax instead of a power cable). Rule of thumb is the closer your preamp or amp is to your antenna, the better. Except for some situations which you mention when you're very close and aiming directly at a local transmitter. You should have the lowest noise figure preamp or amp possible for best reception, and consider what others have been successful with in your region.

Hm. Well, I'd like to minimize the amount of times I have to go in the attic, so I guess I'll try with the preamp first and then add the distribution amp after if needed :p (I also have the same problem with MyTV, but I am interested in receiving it)

Thanks. I'll let you know how it turns out!

You will have trouble with a preamp and lots 'o' local strong signals. No pre amp needed in GTA. Go with distribution only.

I apologize if this has been asked and answered...there were a lot of pages here to find this.

If you have a multi-port distribution amp (4 or 8) and are not using all the ports, should you load the unused ones? Or does the amps internal circuitry take care of this?

Thanks in advance.

It's always a good idea to terminate unused ports. F terminators are very cheap.

Yeah, that's what I thought. Thanks Jase

You will have trouble with a preamp and lots 'o' local strong signals. No pre amp needed in GTA. Go with distribution only.
The preamp won't be amping my signals much. The amp is only there to make up for the long runs of cable involved (It's at least 150ft of cable to the splitter alone, which is a passive 4-way).

I've just got everything set up in the attic and am wondering if there's any electrical/builder code I need to worry about for the coax cable, especially since there is power running through it for the pre-amp? Should I have the cable buried in the insulation (blown insulation) or is it OK to have it strung in the rafters?

The preamp won't be amping my signals much. The amp is only there to make up for the long runs of cable involved (It's at least 150ft of cable to the splitter alone, which is a passive 4-way).

You've got a problematic situation.

Long run after the antenna or not, you just can't blast the high-gain pre-amp if there are strong local signals. You need something like the low-gain 269 Winegard pre-amp or start right off with a 8 dB distribution amp. Then you might benefit from another distribution amp in place of the splitter.

You always have the choice to keep the preamp and use it as a distribution amp if, like others in your region seem to think, your preamp overloads at the input from too strong local signals.

EDIT: previous poster says it could still pose a problem.

I'm not sure I understand the difference between using a high-gain preamp with passive splitter, or a low-gain preamp with a distribution amp. How does the end result differ?

try reading this jack & jill explanation of intermodulation distortion in non-linear devices as it pertains to satellite communications. It's the same principle with OTA, just replace his use of multiple carriers within a satellite transponder with the multiple receive signals on the input to your OTA Preamp, and you got it.

http://www.32apsk.org/wordpress/

I'm not sure I understand the difference between using a high-gain preamp with passive splitter,
or a low-gain preamp with a distribution amp. How does the end result differ?
There are several variables at work, which is why you can find two Excel spread sheets in Post#1.
http://en.wikipedia.org/wiki/Noise_figure
One calculates the Overall SYSTEM Noise Figure when using a single Preamp or Distro Amp, and
the second calculates when using two Cascaded Preamp/Distro Amps. A splitter may be internal
to the Distro Amp and acts the same say as a separate splitter after a stand-alone Amp.

(a) When away from any strong signals (including FM), a Mast Mounted HIGH-GAIN Preamp and
Splitter is usually close to ideal, with very little loss between the antenna and the first amplifier stage.
Any loss after the Preamp, including the Noise Figure of the Tuner itself is REDUCED by the amount
of Gain in the Preamp. A Distro Amp should only be considered if splitting to more than say 4 drops.

(b) A Distribution Amplifier without a Mast Mounted Preamp will always be less sensitive than (a),
since the cable loss from the antenna to the Distro Amp directly degrades Noise Figure and they
are lower Gain. So they are only suitable when all of your signals are well above threshhold.

(c) A LOW-GAIN Mast Mounted Preamp followed by a Distro Amp can be difficult, since it is doubly
susceptible to desensitization when Intermodulation Noise falls on affected weak channels. The
cable loss between the amps may be enough to reduce this effect, or a small amount of additional
loss may need to be inserted. [IMD is reduced by 3 dB for every 1 dB of insertion loss.]

The Excel calculators found in Post#1 help with the System Noise Figure, but do NOT address the
desensitization (e.g. "overload") calculation due to Intermod Noise Distortion (IMD). For that,
some assistance is found in Overload and (recently updated) Interference calculators found here:
http://imageevent.com/holl_ands/files/ota
However, since no one knows the "overload" specs for any of the Distro Amps or DTV Tuners,
you're gonna have to guesstimate what happens in a Cascade Preamp/Distro Amp configuration.

More on IMD and striving to maximize the SFDR (Spurious Free Dynamic Range):
http://www.odyseus.nildram.co.uk/Systems_And_Devices_Files/Linearity.pdf
http://www.arl.army.mil/arlreports/2007/ARL-TR-4235.pdf
http://www.fiber-span.com/Application_Note_Spurious%20Free%20Dynamic%20Range.pdf

Hi Folks,
I have two antennas each with a CM7777 installed on top. They work great. I was wondering if there is a way to install an LED along the RG6 (with DC inserted) so that I can confirm that the DC is present at a glance?

Thanks,

Bobby

Winegard's power inserter has such an LED. I haven't seen any others on the market yet.

but it's probly not meant to be used with a channel master preamp, since the winegard insertor has an internal voltage regulator, it's designed to drive the winegard preamps. dunno what CM does.

Hi Folks,
I have two antennas each with a CM7777 installed on top. They work great. I was wondering if there is a way to install an LED along the RG6 (with DC inserted) so that I can confirm that the DC is present at a glance?

Thanks,

Bobby
Where do you want the LEDs, at the preamp, at the power supply, or somewhere in between?

If it's in the coax near the power supply, you would need to make something like a T adapter in a small metal box for F connectors (it would look like a large splitter or A/B switch) because none is available as far as I know. The coax run to the preamp would connect to each side of the top of the T; the voltage tap would be at the bottom of the T. You would connect a dropping resistor between the center conductor and the LED to give about 20 mA of current at 18 volts for an ordinary LED. The other side of the LED would be grounded. You might need a small RF choke between the center conductor and the resistor to keep the RF isolated from the LED circuit. The choke would be like the one in the power supply that isolates the RF from the DC so that they are able to coexist on the coax that goes to the preamp.

If you want it in the power supply, it is possible to mount in there, but you would need to open the power supply. I would advise against that unless you are experienced in working on AC powered equipment and don't mind voiding your warranty.

It is also possible to mount the LED in the preamp if you want a light to look at in the dark. That would also require a modification.

I favor the first approach because it is the safe way to do it and it doesn't void a warranty.

There is a solid state resetable fuse (more exacty self-resetting; it looks a lot like a ceramic capacitor) inside the 7777 power supply to protect it if there is a short from DC to ground. The 18 volts is under load; when the preamp isn't connected it's more like 22 volts.