A TV Amp?

[CalebATC]

Howdy,


I have a question, correct me if I am wrong please!

A TV amplifier. One you plug into the wall to get better signals. An input and output, and a 120v plug.

It says "50-900 MHz VHF/FM/UHF 10db gain".

So, does that mean I should be able to plug this into my scanner it do AM signals too? Will it hurt my scanner from the power?

I thought I'd ask, don't feel like breaking anything!

Thanks!
Caleb

 

[kpoe_28]

Howdy,


I have a question, correct me if I am wrong please!

A TV amplifier. One you plug into the wall to get better signals. An input and output, and a 120v plug.

It says "50-900 MHz VHF/FM/UHF 10db gain".

So, does that mean I should be able to plug this into my scanner it do AM signals too? Will it hurt my scanner from the power?

I thought I'd ask, don't feel like breaking anything!

Thanks!
Caleb

It will boost the signal but will also boost the noise that comes in through the coax. I tried it one time took it right back off. If your going to go with an amp, I'd go with a tower top, mount it right at the base of your antenna.

 

[reconrider8]

Finally someone brings this up i have been wondering if a tv amp would work on a scanner

 

[CalebATC]

Ok. I will try it. I do live on the outskirts of the city, so I shouldn't get too much interference. I will experiment and post the results! Thanks!

By the way, do you have a permit for the 100' tower? What is the maximum height above ground level to have an antenna without a permit? Thanks again

Caleb

 

[CalebATC]

Wow. I just did some experimenting!

So I am getting not the best ducting, but a little bit. Nothing spectacular.

I plugged it into the scanner. I went from RSW_ATIS from 2 bars to 5 bars on the pro-164.

Then over to MCF_ATIS, which is 90 miles from me. 3 bars. It was just barely breaking the squelch without the amp, and when the amp goes on, it gives it almost full clarity.

I did have to turn my squelch up quite a bit. I am running 100' of RG-6 to my ST-2. Mounted at 45' AGL

I guess I will go buy one!

73
Caleb

 

[jackj]

The TV amp will work within it's spec'd frequency range. You might not get the 10 db of gain they list, that figure might be it's best gain and may not cover the whole frequency range of the amp. It will amplify noise along with signal but all amps will do that regardless of where you mount them. Mounting the amp at the base of the antenna will help to reduce the effect of noise generated by the amp but not noise the antenna picks up.

As for needing a permit for a tower, a lot depends on how far you are from an airport and if you are in the normal flight path. This restriction is determined by the FAA. Anything over 200 foot has to be lighted, again according to the FAA. Your local zoning board may also have restrictions as well as any home-owner's association or deed covenants you might be subjected to.

And you thought you lived in a free country!

 

[N2JDS]

I have one running on my system, it feeds two scanners. Only thing I found was I had to use the Attenuation on quite a few channels, which was picking up the darn paging towers that seem to be a problem to many scanners. Once I set all that I had to, it was all good.

 

[CalebATC]

As for needing a permit for a tower, a lot depends on how far you are from an airport and if you are in the normal flight path. This restriction is determined by the FAA. Anything over 200 foot has to be lighted, again according to the FAA. Your local zoning board may also have restrictions as well as any home-owner's association or deed covenants you might be subjected to.

And you thought you lived in a free country!

Haha, well, where I am about to move, there is a VR military training route that some T-39's fly alot, for mountain training. Well, we don't even have a home owners accociasion lol! And my closest neighbor is about 1 mile away.

Anyway, it is working great. I went up to where my FM trap is, and put the amp up there, approximently 50' of wire before the antenna, and it did cut down a good portion of the noise. Im looking forward to moving, and getting my setup even more finely adjusted. I did expect it to not have as much gain in some bands.

I did pick up Tamp international ATIS, which I am about 95 miles away from. For aviation, that is really good. I am hearing a lot of aircraft doing touch and goes near Tampa, perfectly clear.

I wish I would have done this earlier! And I am getting 3 bars on the ARTCC sectors @ SRQ, which is 60 miles away.

How do one of these amps compare to a preamp? I am guessing a preamp would have less noise?

Hmm... I am thinking of getting another old amp off the other TV and see how much that will give me

Edit from the previous post: I did find the VHF channels had a whole lot more noise than the UHF, but the UHF didn't have as much gain. Hmm

Thanks for all the help

 

[W2NJS]

It actually IS a preamp, regardless of what the manufacturer calls it.

 

[CalebATC]

Oh, ok

 

[reconrider8]

which amp did you get?

 

[zz0468]

Those things sometimes work for people, but you can easily be fooled into thinking it's helping, when the reality is, it may not be. The most critical specification for a preamp is called 'noise figure'. Less important is the gain.

In order for a preamp to actually help with weak signal reception, a preamp MUST have a noise figure less than that of the receiver or scanner, and just enough gain to overcome the noise generated in the receiver itself. Typical scanner noise figures are going to be in the 4-6 db range (which is really not all that great). Typical TV receiver noise figures are much higher than that.

The end result is, many TV preamps may have a noise figure of 6 or 8 db, which HELPS a tv receiver, but in front of a scanner, it'll make strong signals stronger, marginal signals a bit less marginal, and weak signals disappear right into the noise, which is why you can be fooled.

I would avoid any preamp that does not specify it's noise figure, and if it does, anything higher than 2-3 db is a waste of time. And lower is better. And even a low noise preamp can destroy the noise figure of the entire system if it has too much gain and overdrives the rf amplifiers in the receivers. Attenuators are frequently put between an LNA and the receiver to prevent that from happening.

 

[radioman2001]

TV pre-amps will work, very well in some instances. Our shop has 4 monitoring radio's on a single antenna split and amped with a 10 db TV amp. The impedance mismatch has minimal impact on the gain.

 

[CalebATC]

Yes- It definately did take a large toll on the LVHF, on about 50 MHz it takes the squelch right out, making me have to put it about 1/2 way up. On the civil air band (108-137) it did do quite a bit of damage. Although it did provide a exceptional amount of gain. I am now hearing the Tampa ATIS, which I could never of heard without it, and is over 90 miles away.

Now on the UHF military band (240-380 around that area) it didn't do anything noise wise. But it did provide the most gain I belive. I am now hearing the same station from SRQ in VHF and UHF, UHF preformed a whole lot better.

And now, there are some F-16's up. Usually I get them around 3-4 bars, now I am getting them 4-5 bars. They are in the same MOA sector as always, just a better signal.

But, I think after I get my rigs all setup in the new house, I will probably leave it on.

I was going from hearing 2 ARTCC sectors on UHF and VHF, to hearing about 6 sectors. It really did the work. More than I expected. I am satisfied.

@ReconRider8 , it is just some amp I had connected to my tv. Just one from Home Depot.

 

[jackj]

As an experiment, try disconnecting the antenna and terminating the amp input to see what happens with your squelch setting on VHF-Lo. The noise might be environmental noise picked up by the antenna and not generated by the amp.

 

[WA1ATA]

It seems to me that the main advantage of a preamp is to overcome the coax loss in the situation where there is a very long run of coax between the antenna and the scanner.

For it to make an improvement, it should be located as close to the antenna as possible.

A preamp is also useful as lossless (actually, with gain) replacement of a splitter when feeding one antenna to multiple scanners ----- as 2001Radioman noted above.

One thing to watch out for when using a preamp is overload/intermodulation. That is when a powerful signal overpowers the preamplifier. That will generate spurious signals at all sorts of sum and difference frequencies. For example, if you have a nearby 100MHz FM station, and are trying to receive another signal at 440MHz, you will find spurious signals at 440-100, 440+100, 440+/-200, etc.

Charlie

 

[CalebATC]

It seems to me that the main advantage of a preamp is to overcome the coax loss in the situation where there is a very long run of coax between the antenna and the scanner.

For it to make an improvement, it should be located as close to the antenna as possible.

A preamp is also useful as lossless (actually, with gain) replacement of a splitter when feeding one antenna to multiple scanners ----- as 2001Radioman noted above.

One thing to watch out for when using a preamp is overload/intermodulation. That is when a powerful signal overpowers the preamplifier. That will generate spurious signals at all sorts of sum and difference frequencies. For example, if you have a nearby 100MHz FM station, and are trying to receive another signal at 440MHz, you will find spurious signals at 440-100, 440+100, 440+/-200, etc.

Charlie

Yes, I took it off yesterday. My dad was getting mad because the TV was all blurry haha

And will do Jack, I will post results.

I do have a FM trap, that takes out most of the stuff. I do have a 154.135 dispatch station really close to my house (Fire Station, and a Tower in the back), this seems to get some very crazy overload when they do a dispatch. It is so close and powerful I can put my scanner with the rubber ducky under a pillow and it still be full signal.

And I heard some data, sounded like RTTY on 273.3 and surrounding channels.... never there before the amp.

But other than that, everything worked out fine. I'll make sure to pick one up at RS or Home Depot here soon.

 

[zz0468]

Some comments [not corrections =) ]

It seems to me that the main advantage of a preamp is to overcome the coax loss in the situation where there is a very long run of coax between the antenna and the scanner.

For it to make an improvement, it should be located as close to the antenna as possible.

The purpose of a preamp is to set the noise figure of a receive system. The reason you want it as close to the antenna as possible is because any loss before the first active device directly adds to the system noise figure. If you start with a 1 db nf preamp, then put it behind 3 db of coax loss, your system nf is now 4 db, assuming you don't destroy the system nf with too much gain or loss downstream from the preamp. So, it isn't so much to overcome the loss of the cable, as it is to avoid the loss of the cable from destroying the system nf in the first place.

A preamp is also useful as lossless (actually, with gain) replacement of a splitter when feeding one antenna to multiple scanners ----- as 2001Radioman noted above.

A distribution amp can handle that task, if the whole thing is preceeded by a good preamp. But if the preamp has excessive gain, some of it can be 'wasted' in the splitter, with no detriment. Commercial multicouplers will often have a preamp, attenuators, a distribution amp, more attenuators, and then the splitter. And total gain of the whole thing is only a few db.

One thing to watch out for when using a preamp is overload/intermodulation. That is when a powerful signal overpowers the preamplifier. That will generate spurious signals at all sorts of sum and difference frequencies. For example, if you have a nearby 100MHz FM station, and are trying to receive another signal at 440MHz, you will find spurious signals at 440-100, 440+100, 440+/-200, etc.

The third order intercept or IP3 specification describes a preamplifier's resistance (or lack of) to overload conditions. There are some very good transistors out there that have really really low nf and really high IP3 that are ideal for preamplifiers. Unfortunately, TV preamps are seldom build using these devices, so performance can be pretty compromised, when compared with what's actually available. You get what you pay for.