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LNA 1500 Pre-Amp

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#1
I recently purchased this Pre-Amp from R.F.Bay,And installed it at the end of the coax before it went into a Stridsburg Multi-coupler.I have not noticed really any difference in reception,That being said,Should i have installed it at the antenna end? The unit itself is really small and dont know how it would be outdoors exposed to the elements,Any ideas? Anyone else using this?
 

JamesO

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#2
The Stridsburg Multi-couplers tend to be 0 dB loss or unity gain with an internal amplifier stage. These tend have a Noise Figure of about 3.5 dB which is a bit high. It would not be considered a LNA in my opinion.

The R.F. Bay LNA-1500 has a Noise Figure of 3.3 dB which is only slightly better than the Stridsburg Multi-coupler. So the LNA-1500 will not be much of an improvement mounted right at the Stridsburg Multi-coupler input and it could be over driving the Stridsburg Multi-coupler amplifier stage as well.

For any of a number of reasons it would far better to have the LNA-1500 right at the base of the antenna. You would probably want to put the LNA-1500 inside some sort of weather proof plastic box. Then you need to have a power feed to the amplifier. Often you can use Bias-T's to power the amplifier via the coax so you will not need an additional power feed. You technically only need 1 additional wire if you do not power the amplifier via the coax.

You need to be careful when cascading amplifiers because you can over drive or saturate the 2nd amplifier and put it into compression and elevate the noise floor. Often you may need to add attenuation between amplifiers, but if you mount the amplifier at the base of the antenna, the coax will likely have enough loss to help balance the amplifiers.

The other recommendation is to use a variable power supply to fine tune the LNA-1500 gain. Usually the Noise Figure will drop when the input power/gain is reduced with a lower power feed. This somewhat gives you an adjustable gain amplifier. Sometimes you could have negative side effects with reduced Voltage as the gain over frequency performance may change slightly, but you will need to experiment.

Personally I will not run any first stage amplifier/LNA/ULNA that has higher than a 1-1.5 dB Noise Figure. The very first amplifier stage in a receiver chain is what sets the overall performance of the system. The lower the Noise Figure, the better. You pay for the performance, but you can find wideband ULNA's with noise figures below 1 dB, some as low as 0.6 dB. The very low Noise Figure amplifiers is what is recommended for best performance.

Since you have the R.F. Bay LNA-1500, I would consider installing it directly at the base of the antenna if possible. If you can return the amplifier, I would consider returning the amplifier for a much lower Noise Figure wideband amplifier.

You should search my user name here on the forum, I have a number of comments about LNA's and some of the options I have used in the past.
 

rbm

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#5
I should have mentioned this.

If you already receive some transmissions well enough that they are 'full quieting', you will see absolutely NO difference whatsoever on them with a preamp.
You just can't get any better than full quieting. (on FM)

A good preamp will only help to improve noisy signals. And/or reduce some 'picket fencing'.

I've seen lots of comments that amplification will also amplify noise.
That is simply NOT true unless you have a nearby noise source, you overload your receiver, or create intermodulation.

And more db of gain is not always better. You only need enough gain to bring the desired signals to a usable level. (If possible)

Any loss in your feed line is directly added to the overall noise figure of your system.

If you have a receiver that has a 3 db noise figure and connect it to a feedline that has 6 db of loss, your overall system noise figure will be in the neighborhood of 9 db.

Connecting a low noise figure preamp right at the antenna negates that.
Then, the overall system noise figure is 'close to' the noise figure of your preamp.

In my case, with a good preamp, some signals that are almost lost in the noise, and barely receivable, are brought close to full quieting.

Rich
 
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rbm

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#7
Can this be powered by a Bias T?,,If so do i clip off the power leads off the Pre-Amp?
You would need two bias tees.

One to inject the power, and another prior to the pre-amp to block the DC and provide a connection point for the power leads.

You would then connect the pre-amp power leads to the DC port on that bias tee.

Rich

One example of that:



.
 

cpetraglia

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#8
You would need two bias tees.

One to inject the power, and another prior to the pre-amp to block the DC and provide a connection point for the power leads.

You would then connect the pre-amp power leads to the DC port on that bias tee.

Rich

One example of that:



.
I would just use a 16 gauge speaker wire and run the DC up to the amp along side the coax. Seems a whole lot easier and less expensive. Won't there be losses from the two bias tees? Will a DC power circuit running along the coax affect the signal?
 

rbm

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#11
I would just use a 16 gauge speaker wire and run the DC up to the amp along side the coax. Seems a whole lot easier and less expensive. Won't there be losses from the two bias tees? Will a DC power circuit running along the coax affect the signal?
That's why I use RG6 coax with a 'messenger wire'.

I now supply DC to six pre-amps, with one wire that way.
You just need to be aware of the current requirement of the pre-amps and the voltage drop of the supply line. Copper only!

The first time I ran the coax/messenger wire up to the antennas, I soldered 8 wire pigtails to the end of the wire.

Adhesive shrink tubing and silicone sealed them to make them weatherproof.

Then, each time I added another pre-amp, I made crimp connections on another one of the pigtails, added silicone sealer, and adhesive shrink tubing to make them weatherproof as well.

I've never had a problem that way.
My oldest connection is going on 24 years.

There will be some RF loss because of the bias tees. Which should be negligible compared to the gain of the pre-amp.

The DC power on the coax shouldn't be a problem.
UNLESS you are using a switching regulator.
Then, you may see a lot of RF hash and interference on specific bands.

If your DC is clean, no problem at all.

By the way, my last house was about one mile line of sight to a hilltop with MANY commercial, TV, and FM antennas. With proper gain adjustment, I still had excellent results using a pre-amp.

That was back when Grove Enterprises was still in business and sold a pre-amp that mounted at the antenna and had a power supply with a gain adjustment at the scanners.

All I had to do was turn the gain up until I had intermod problems.
Then I backed it off a little and it stayed clean for years.

There was enough RF in the air there that one time my cable TV feedline from the pole had a broken ground. I got herring bone interference on the TV's every time some agency keyed up their repeater.

A good part of my working career was with extremely weak RF signals. (as in Astro Electronics)
I was lucky enough to have worked with some well known (at that time) experts.

If someone tells you something cannot be done, or will not work, they probably didn't try it themselves, or didn't take the time to make it work.


Rich
 

JamesO

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#13
Thought I would add this as an option.

This Mini-Circuits LNA is about 1/2 the price (around $80 depending on Tax and Shipping) of the RF Bay LNA-1500 and has a significantly much lower noise figure which is the KEY to a good receive system, especially when having to use amplifiers.

Granted the gain is not as flat as the LNA-1500, BUT Noise Figure is KING directly mounted at the antenna!

Mini Circuits LNA has 0.4 dB Noise Figure @ 800 MHz vs the RF Bay LNA has 3.3 dB @ 800 MHz!!! Almost a 3 dB difference. This is NO small change, it WILL make a major difference.

The only thing I an unsure of it how the Mini-Circuit amplifier performs between 10-50 MHz, but for most scanner applications this is non issue.

NOTE: The Mini-Circuits LNA has a 5 Volt supply, so be very careful how and what you power the amplifier.

https://www.minicircuits.com/pdfs/ZX60-P103LN+.pdf
 
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#14
This particular MiniCircuits amp looks like a very reasonable preamp to put in front of a passive divider or at the antenna to make up for coax loss. I would not go any lower in IP1 than 20dBm when choosing a broad band front end amp and the noise figure is not bad.
prcguy

Thought I would add this as an option.

This Mini-Circuits LNA is about 1/2 the price (around $80 depending on Tax and Shipping) of the RF Bay LNA-1500 and has a significantly much lower noise figure which is the KEY to a good receive system, especially when having to use amplifiers.

Granted the gain is not as flat as the LNA-1500, BUT Noise Figure is KING directly mounted at the antenna!

Mini Circuits LNA has 0.4 dB Noise Figure @ 800 MHz vs the RF Bay LNA has 3.3 dB @ 800 MHz!!! Almost a 3 dB difference. This is NO small change, it WILL make a major difference.

The only thing I an unsure of it how the Mini-Circuit amplifier performs between 10-50 MHz, but for most scanner applications this is non issue.

NOTE: The Mini-Circuits LNA has a 5 Volt supply, so be very careful how and what you power the amplifier.

https://www.minicircuits.com/pdfs/ZX60-P103LN+.pdf
 

dlwtrunked

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#15
Thought I would add this as an option.

This Mini-Circuits LNA is about 1/2 the price (around $80 depending on Tax and Shipping) of the RF Bay LNA-1500 and has a significantly much lower noise figure which is the KEY to a good receive system, especially when having to use amplifiers.
Granted the gain is not as flat as the LNA-1500, BUT Noise Figure is KING directly mounted at the antenna!
Mini Circuits LNA has 0.4 dB Noise Figure @ 800 MHz vs the RF Bay LNA has 3.3 dB @ 800 MHz!!! Almost a 3 dB difference. This is NO small change, it WILL make a major difference.
...
I used RF Bay LNA-1400 here for years. Better noise figure than the LNA-1500, flatter gain, and better IP3 than the LNA-1500. Not sure why anyone would prefer the LNA-1500 over it unless one rally wants to go down to 50 MHz. Spec say NF of 0.8 dB for LNA-1400 but one needs to know more about the NF measurements to really compare those. An essential thing I have always found with pre-amps it to put an FM blocking filter ahead of them--even if you do not think you have a problem--even a cheap such filter as found at Radio Shack (if you still have one) or on eBay will do. And of course the usual caveat: if you are near VHF high band pagers, NOAA, etc., you may need filters or a pre-amp my even be unwise unless you can attenuate the gain.
 
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#16
Just recieved the Hartwig LNA Mast mounted Pre-Amp all the way from Germany,Also purchased a Bias-T from Stridsbeg .All i need is a few connectors to go from the N-Female connectors on the Pre-Amp to go the coax .This will be my first time using one,Hopefully it will do the job.
 

JamesO

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#17
One thing to keep in mind, you may need a FM Broadcast band notch filter if you are in Metro areas. The FM Broadcast band filter will need to be installed at the input of the amplifier. This can cause a small hit on the overall performance, however, often the FM Broadcast filter makes a bit difference in reduction of images and intermod.

I have a filter coming that I need to replace a cheaper Radio Shack FM filter with.

Between FM Broadcast and Paging transmitters you need to be careful with pre-amps.

Let us know how the Hartwig Mast Mount works out.
 
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dlwtrunked

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#19
I hooked up the Pre-Amp at the mast fed by a Bias-T, I have to say that im not really seeing any difference in reception,In fact some of the reception is worse,Any ideas?
A couple things:
1. Are you comparing on very weak signals--that is where you should.
2. What are you listening too and how far away is it?
3. If it seems worse, something is wrong. You are possibly being de-sensed by a nearby transmitter. Are you using an FM broadcast band notch filter--everyone should, even if they do not think they have a problem as a lot of those people do. Related to that, how far are your nearest broadcast FM, TV, and cell towers?
4. What is your receiver, antenna, and coax?
5. You may be overloading the receiver. If that is the case, experimenting with an adjustable attenuator after the pre-amp may help.

Optimizing reception is sometimes tricky to avoid overloading the receiver. Here I have a pre-amp with an FM broadcast band notch and a 152 MHz pager notch before the pre-amp. I still get overload/intermod when the FD VHF at 0.8 miles keys up or the 2-meter repeater 30 W on the same tower is keyed.
 
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#20
There are a couple of things I do when playing with preamps to see if they are suitable for use but it takes some test equipment. First I look at what's coming down the coax with a spectrum analyzer to see if there are any super strong signals and what frequency they are on and what the levels are.

Then I connect either a an HP power meter or RF milivolt meter to the coax to measure the total power of the spectrum seen by the preamp. This will tell you right away if you will be getting anywhere near compressing or overloading the preamp. In one case I measured an aggregate power of -10dBM into a preamp with 30dB gain and a 1dB compression of +10dBM. That explained why it was a mess, the preamp was a good 10dB into compression and creating lots of IMD.

IMD will be created in any preamp well below its 1dB compression point and with a wide band antenna and lots of signals you will see IMD created way below the advertised compression point of an amplifier.

Another thing I noticed is the quality of an AM aircraft signal seems to be affected when a preamp is getting in trouble. Tune in some distant or even local AM aircraft without the preamp and note the audio quality and lack of noise on strong signals. If your preamp has lots of headroom and is up to the task you should hear the weaker aircraft signals a little better and the stronger ones should not be affected.

If the preamp is in trouble due to overload, the clean sounding strong signals without the preamp will now have some extra noise and hiss riding on them. I've noticed this on most preamps I've tried and the AM reception problem is easier to detect than scanning all the bands looking for IMD or ghost signals created within the preamp.

Give your setup the AM aircraft test with and without the preamp and let us know what you hear.
prcguy
 
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