800 Meg preamp

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firemantom26

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I have a Wilson Yagi Antenna for 700/850MHz, specialized high-gain - 301111 and would like to know what would be the best low noise preamp to help improve reception? I have a Homepatrol unit.

Thank You

Tom
 

davenlr

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If you can find a TV mast mounted preamp that still covers the older full 2-82 channel range, that will cover the 800Mhz band you are wanting. Since they just recently dropped down to 52 channels, I would think most of the TV amps designed a while ago, like the channel master and winegard amps would still handle them. You would just have to check the specs. These would be 75 ohm amps as well, so you would need one with coax input and not twin lead (300 ohm) inputs. There would be a little mismatch if your antenna is a 52 ohm feed, but if you are not transmitting, it would not be detrimental.

http://www.amazon.com/Antennas-direct-PA-18-Ultra-Pre-Amplifier/dp/B0018CDGEQ/ref=sr_1_3?ie=UTF8&qid=1394384527&sr=8-3&keywords=mast+mounted+antenna+amplifier
 

zz0468

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I wouldn't use a tv preamp if I were you. They are generally poor quality and more likely to induce intermod than a higher quality preamp. Just getting "more bars" is not the goal of a preamp.

The first thing you need to do is decide if you actually need one. What's happening that makes you think so?
 

firemantom26

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I wouldn't use a tv preamp if I were you. They are generally poor quality and more likely to induce intermod than a higher quality preamp. Just getting "more bars" is not the goal of a preamp.

The first thing you need to do is decide if you actually need one. What's happening that makes you think so?
I have a few locations that I want to receive that are coming in only when the conditions are right. I added a amp but it did not help and only increased the noise level not the signal.
 

zz0468

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I have a few locations that I want to receive that are coming in only when the conditions are right.
It's quite possible that a preamp won't help that. The best you can hope for is to make marginal reception not marginal. If there's no signal at all, a preamp won't fix it. How far away are the stations you want to hear, but can't?
I added a amp but it did not help and only increased the noise level not the signal.
That's not surprising. Scanners are already pretty sensitive. Adding gain frequently will overdrive the scanner with noise, and cause intermod. What type of preamp did you use? Most preamps have way too much gain, so need some attenuation between the preamp and the receiver.
Noise figure is also EXTREMELY important. In fact, it's 95% of what you should be looking for. If a preamp doesn't have it's NF listed in the specs, drive through, please. The noise figure MUST be lower than the receiver for it to actually do any good. If doesn't matter what the gain might be.
The typical scanner has a NF of 4-6 db, depending. Some TV preamps are about the same, or worse. The end result is, you get "more bars" on strong signals, and weak signals just go away. You may also just get more noise.

I wouldn't bother with a preamp who's noise figure is any more than about 3 db. The lower the NF, the better.

As for gain, anything more than about 8 to 10 db gain is too much. Plan on adding an attenuator between the receiver and the preamp. The value would depend on the gain of the amp.

Also look for a spec called IP3. Third order intercept, that's the preamp's ability to tolerate strong signals without overloading. The higher the number, the better.

As you can see, it can get pretty involved. I'm of the opinion that most people are better off without preamps. They can be more trouble than they're worth if you don't understand what they actually need to do.
 

n5ims

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A preamp should be one of the last things you do to "fix" your antenna system.

Start with the coax, especially at the higher frequencies like 800 MHz. A good low-loss coax is a must unless you have nothing but strong signals (and if so, why would you want a pre-amp). For short runs (up to 50' or so), RG-6 should be the minimum you should use. LMR-400 is a must for longer runs (say 50' - 150'). LDF4-50A should be used for anything much over 100' or so. Keep in mind that these are the minimum grade of coax you should use!

Next start with a good antenna that's designed for the frequency range(s) you're listening to (note the "listening to" part of that, I'm saying not to match your antenna's range to your scanner's range or you'll end up with a wide-bandwidth but minimal signal strength antenna). A good antenna designed specifically for 800 MHz and has good gain numbers on that band will give you much more signal for the same cost as a general coverage antenna.

If you have some special needs (simulcast issues, distant systems you want to cover, etc.) you may need a more specialized antenna. A directional yagi will give you much higher gain numbers and allow you to focus the energy from a single tower to help fix either of those issues.

Height is often your friend with scanning. Having your antenna up as high as you can will often provide you the best signal strength. The down side is your coax run will need to be longer (perhaps much longer) so you'll need to use a better grade coax.

If you have a great antenna, designed for the band you're listening to, feed with a high quality low-loss coax, on a tall tower and still need help pulling in that signal you may simply not be in an area where you can get a good signal on it. It may be worth trying a good preamp (located by the antenna) to see if it helps or hurts your reception.

You'll probably also need to add some filters to prevent nearby strong signals from overloading the preamp and/or receiver. What filter can't be guessed at from afar, but must be searched out at the location in question. It's very hard to guess what signals may be strong enough without actually looking around and doing some scanning for strong signals. The places to start looking are cell towers nearby (up to a couple of miles), FM or TV broadcast towers nearby (could be up to 10+ miles away), NOAA Weather Radio stations, paging stations, or even standard two way radio towers ("nearby" is very relative here based on their transmitter power levels).
 

prcguy

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Here is a very high level 800MHz preamp with probably too much gain but they are very cheap, see:
2 Lucent KS 21583 250mW 900MHz Amplifier 750 930 MHz G 45nu ll2 | eBay

If you could get this up near your antenna and place a bandpass filter in front of it you will have more 800MHz signal than you know what to do with. Here is a filter that may cover your frequencies of interest to place in front of the preamp:
Microwave RF UHF Bandpass 700 860 MHz Filter Tested | eBay

These particular amps are pulls from cell sites and have a very high IP1 or compression point of 250mw, so they will be less prone to overload compared to some cheaper amps. I'm not sure of the noise figure but they would have to be reasonably low. I have a couple of these and was really surprised at the performance although I have not placed one into service yet.

If you could get this at your antenna it would not really matter what coax you used since the amp will determine the noise figure of your antenna/front end and lots of coax downstream will have a negligible effect.
prcguy
 

firemantom26

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A preamp should be one of the last things you do to "fix" your antenna system.

Start with the coax, especially at the higher frequencies like 800 MHz. A good low-loss coax is a must unless you have nothing but strong signals (and if so, why would you want a pre-amp). For short runs (up to 50' or so), RG-6 should be the minimum you should use. LMR-400 is a must for longer runs (say 50' - 150'). LDF4-50A should be used for anything much over 100' or so. Keep in mind that these are the minimum grade of coax you should use!

Next start with a good antenna that's designed for the frequency range(s) you're listening to (note the "listening to" part of that, I'm saying not to match your antenna's range to your scanner's range or you'll end up with a wide-bandwidth but minimal signal strength antenna). A good antenna designed specifically for 800 MHz and has good gain numbers on that band will give you much more signal for the same cost as a general coverage antenna.

If you have some special needs (simulcast issues, distant systems you want to cover, etc.) you may need a more specialized antenna. A directional yagi will give you much higher gain numbers and allow you to focus the energy from a single tower to help fix either of those issues.

Height is often your friend with scanning. Having your antenna up as high as you can will often provide you the best signal strength. The down side is your coax run will need to be longer (perhaps much longer) so you'll need to use a better grade coax.

If you have a great antenna, designed for the band you're listening to, feed with a high quality low-loss coax, on a tall tower and still need help pulling in that signal you may simply not be in an area where you can get a good signal on it. It may be worth trying a good preamp (located by the antenna) to see if it helps or hurts your reception.

You'll probably also need to add some filters to prevent nearby strong signals from overloading the preamp and/or receiver. What filter can't be guessed at from afar, but must be searched out at the location in question. It's very hard to guess what signals may be strong enough without actually looking around and doing some scanning for strong signals. The places to start looking are cell towers nearby (up to a couple of miles), FM or TV broadcast towers nearby (could be up to 10+ miles away), NOAA Weather Radio stations, paging stations, or even standard two way radio towers ("nearby" is very relative here based on their transmitter power levels).

I am running the proper antenna. " Wilson Yagi" 35 feet in the air. RG6 100 foot run
 

rbm

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Good quality RG6 coax has a loss of around 6.8 dB per 100' in the 800-900 MHz range.
(It works reasonably well and I use lots of it. In fact I buy RG6 compression fittings by the thousand. ;)

The 'first' stage in the system 'sets' the overall system noise figure.
Once that is set, there's not much, if anything that you can do to improve it.
Any loss in the coax adds directly to the system noise figure.

For weak signals you must improve the noise figure as well as increase the signal at the scanner end of your coax.
I'll refer you to an old post of mine that may help.
http://forums.radioreference.com/splitters-filters-multicouplers/127403-splitter-amplifier-coupler-noise-figure.html#post946187

So, with that out of the way, if you don't have any very strong, nearby signals, you can improve your reception of the weakest signals.
Read that again. ;)

You'll need a relatively low noise preamp mounted right at the antenna. (I prefer a 2 dB NF or less)

The image below shows what happens when you move a preamp from the scanner end of the coax to the antenna end.

In BOTH cases shown, the components of the antenna system are identical, just in different order.

There's a dramatic improvement in noise figure with the preamp mounted right at the antenna.

Rich

 
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rbm

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I should have mentioned the amplifier I like to use in the 800-900 MHz range.

I use several Mini-Circuits ZQL-1900MLN amplifiers.

The specifications are higher than the 800-900 MHz range but if you look at the first image below, you'll see that they have good gain and low noise figure well below their specified range.

They're around $265 brand new, but ........................
you can find them on ebay for around $40-$50 or so. ;)

The specifications for the ZQL-1900MLN:
1.5 dB noise figure
25 dB gain
IP3 around 41 dBm

I mount them in a weather resistant enclosure like I show in this post:
http://forums.radioreference.com/scanner-receiver-antennas/115239-pre-amps-local-powering-versus-remote-powering.html#post860180

Rich

Mini Circuits ZQL-1900MLN
 

rbm

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I tried my model 9263 amp did nothing to improve and made it worse...........

Pricing and puchasing inforation for low noise 0.4 dB NF HDTV preamplifiers
Works great for my tv antenna
What frequencies are you interested in receiving?

The 9263 amp is for VHF (175 MHz - 700 MHz)

Without testing it above 700 MHz, it's unknown if it's useful above that range.
It may have some filtering that attenuates everything above 700 MHz or so.

Or, you could have strong signals nearby that desensitize your scanner when you add a preamp.

Rich
 

firemantom26

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What frequencies are you interested in receiving?

The 9263 amp is for VHF (175 MHz - 700 MHz)

Without testing it above 700 MHz, it's unknown if it's useful above that range.
It may have some filtering that attenuates everything above 700 MHz or so.

Or, you could have strong signals nearby that desensitize your scanner when you add a preamp.

Rich
I am intrested in the 800 MHz area I think the 9260A would be a better choice but I am not going to spend $175 US Dollars for the amp power supply and shipping and not work.

9260A
UHF
470MHz - 806 MHz
14 - 69 (USA/CAN). http://www.researchcomms.com/Purchasing.html
 
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davenlr

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I rather think its pretty close to useless, with consumer grade amps, to expect them to actually bring in signals that are not receivable at the antenna itself. My use of preamps, other than for satellite reception, is pretty much limited to amplifying the signal present at the antenna connection enough (but no more) to overcome the loss in the feedline between the antenna and the receiving device. If you add up all the losses of the coax and any other devices on the line (surge protectors, splitters, etc), then purchase an amp that covers the frequencies you want, and has a noise factor that is low, you should have good results, barring overload from very close by transmitters (FM and TV included).

If you cant get what you are wanting to listen to, with a scanner plugged into the antenna with a very short coax (less than 10 feet), then I seriously doubt an amp would improve that. Only a higher gain antenna will help.
 

firemantom26

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I should have mentioned the amplifier I like to use in the 800-900 MHz range.

I use several Mini-Circuits ZQL-1900MLN amplifiers.

The specifications are higher than the 800-900 MHz range but if you look at the first image below, you'll see that they have good gain and low noise figure well below their specified range.

They're around $265 brand new, but ........................
you can find them on ebay for around $40-$50 or so. ;)

The specifications for the ZQL-1900MLN:
1.5 dB noise figure
25 dB gain
IP3 around 41 dBm

I mount them in a weather resistant enclosure like I show in this post:
http://forums.radioreference.com/scanner-receiver-antennas/115239-pre-amps-local-powering-versus-remote-powering.html#post860180

Rich

Mini Circuits ZQL-1900MLN
found one on ebay for $39.00 plus small fee shipping...........
 

rbm

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found one on ebay for $39.00 plus small fee shipping...........
That's a good price for that preamp. If I didn't already have more than enough of them, I'd jump on it too. ;)

And with the antenna you have, if you're not troubled with strong signals near you, you should be able to hear anything in the air. ;)

Last summer I was showing someone locally what a preamp can do for you when it's mounted right at the antenna.
It's much easier to visually see the difference than try to describe it.

So ......

The three screen captures below are of reception of SatCom narrow band transponders around 250 MHz.
With and without a preamp mounted at the antenna (RF Bay, Inc LNA-580)

You can see the obvious effect the preamp has.

Rich

For this test I used an X-Wing antenna fed with 60' of RG6 coax.
The images were captured within minutes of each other. Just enough time to go outside and install and remove the preamp.

No Preamp installed:
You can barely even tell that there are any signals present.



No Preamp installed but the RF gain at the receive end increased by around 17 dB.
The signal comes up considerably but so does the noise. Notice the 'speckling' in the waterfall area.



Preamp installed at the antenna, and RF gain back to where it was originally.
Not only are all of the signals much stronger, but some that were completely lost in the noise before are now present.

 
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