Wide Band Pre-Amp

[cmed325]

Am currently using a R.F. Bay LNA-1500 Pre-AMP, However its not working as good as I hoped. Its being powered by a Bias-Tee. I would like to replace it with a different one that will also be powered the same way,All fed by LMR 400 Coax,,Any suggestions of another one I can try?

 

[prcguy]

Overload? Creating IMD?

Am currently using a R.F. Bay LNA-1500 Pre-AMP, However its not working as good as I hoped. Its being powered by a Bias-Tee. I would like to replace it with a different one that will also be powered the same way,All fed by LMR 400 Coax,,Any suggestions of another one I can try?

 

[Ubbe]

That amplifier has a 3,3dB noise figure. Try one that have 1dB or less. You have to see to that the total gain from antenna to scanner are something like 5-10dB or even less in problematic areas or you will probably put the scanner into overload that de-sense it and probably also get interferencies. A variable 0-20dB attenuator between amplifier and scanner/receiver are excellent for tuning up and down in attenuation to find the exact value when you have the best reception without any other problems popping up.

Ultra LNA 2GHz Gain>20dB PGA103 ESD Gain Stabilization USB cable PGA-103 NF .5dB | eBay
You should be able to get something like this in US:
Cable F-Type TV Attenuator Variable 0-20dB Reduce Signal Level | eBay

In the picture of the amplifier they show a choke on the circuit board that let you power it from the coax but isn't included in the schematics. Ask them to install that choke for you prior to shipping.

/Ubbe

 

[prcguy]

Looking at the specs on the R.F. Bay LNA-1500, it would be a terrible choice for a wide band preamp even in a rural area. Way too much gain and the 1dB compression and IP3 specs are too low to survive with a wide band antenna connected. It will create lots of IMD. The noise figure is not terrible, but for an amp with low IP1, IP3 specs it should be lower.

For comparison I recently bought a MiniCircuits ZX60-P103LN with less gain, about 18-20dB in the 100 to 500MHz range, a 1dB compression point over 22dBm or 12dB higher than the LNA-1500 and an IP3 spec around 39dBm or 16dB higher than the LNA-1500. With all that I find the ZX60-P103LN to be a complete failure connected to a Discone antenna, it gives me an unbelievably high noise floor with lots of IMD and FM broadcast stations spread all over the place where they don't belong. And that is with an FM trap and 550MHz low pass filter in front of it. The only thing the ZX60-P103LN has going for it is the low noise figure around .5dB, but that is meaningless when it is otherwise useless.

What you and I need is much less gain, something more in the 10 to 15dB range maximum and an IP3 another 10dB or more above my ZX60-P103LN. The closest thing I can find and I will be trying soon is a MiniCircuits ZHL-1010. Its got about 11dB gain from 50 to 1,000MHz, a 1dB compression point about 30dBm or 1watt (!) and a reasonable IP3 of 46dBm. The noise figure is a little high at about 3.5dB but when placed at the antenna it will give a lower system noise figure than any antenna connected through some coax to any receiver. The fact it has a big heatsink and consumes 525ma @ 12V should say something about its high signal handling capability.

I'll probably order a ZHL-1010 tomorrow but due to some other projects and travel it might be a few weeks before I install it in my tower top preamp/filter project described in another thread.

 

[cmed325]

Thank you, I will wait for your comments on this unit.

 

[RFI-EMI-GUY]

When you use a wideband amp directly connected to the antenna you risk tremendous overload ,and IMD from FM and TV broadcast signals. Also NOAA stations nearby can wreak havoc across the VHF band.

I have a wideband amp on a discone and it works well, but I had to notch the entire FM broadcast band to make it work.

What are you trying to receive?

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[cmed325]

Im monitoring mostly VHF and UHF Public Safety,,What AMP are you using? PRC Guy is going to try a ZHL 1010 and see how that works.

 

[Ubbe]

Not many people will have such a difficult receive loacation as prcguy seems to have. He has some of the worse situations I ever heard of. I tested two RF Bay LNA-540 and one SSB LNA-2000 at RF hell with several commercial radio sites no more than 100 yards away that carry 10-15 different transmitters in VHF and UHF bands. Half of them almost continusly in TX as control channels or heavily used trunked systems.

The amplifiers where connected to a commercial 4-stacked dipole UHF antenna and one 2-stacked dipole VHF antenna and they had no problem with de-sense or overload IMD without using any type of prefiltering. No scanner I had at that time could handle the complex signal enviroment and I had to use attenuation to get a total gain of minus 5dB to plus 10dB depending of scanner used. A FM broadcast filter between amplifier and scanner helped the most compromised scanners and the total gain could then be increased. The professional 2-way radios I tried could take the full 20dB gain without any problem and got increased reception, as well as the Icom R2500 which seems to have excellent high signal performancies. The type of amplifiers that use the PGA103+ chip have better performance than the RF Bay or SSB amplifier.

/Ubbe

 

[dlwtrunked]

Am currently using a R.F. Bay LNA-1500 Pre-AMP, However its not working as good as I hoped. Its being powered by a Bias-Tee. I would like to replace it with a different one that will also be powered the same way,All fed by LMR 400 Coax,,Any suggestions of another one I can try?

I have used antenna pre-amps for years (several decades). These are some key points that apply to starting with any reasonably good receiver.
1. The goal is to increase signal-to-noise ratio--not gain.
2. To do that will require fairly high gain and a low noise pre-amp. (Reference: Frii's noise figure equation--see the Wikipedia noise figure entry.) As others have stated, the LNA-1500 is not a good choice but some of their other models are.
3. That will in many/most cases lead to receiver overload/overload with nearby strong stations (even a 40 W repeater at 1 mile). One should always start with a good FM broadcast band notch filter (I recommend Mini-Circuits) and get to know PAR Electronics to filter other specific frequency problems. A pre-amp without notch filters is an invitation for problems.
4. A pre-amp at the antenna is always best but it is true that one at the receiver will sometimes help if one pays attention to the above.
If it were easier, the manufacture of the receiver would have designed the receiver with such a pre-amp already in it.
5. Be prepared to spend money and experiment to find something that works well. Appraise how well by listening and looking for intermodulation and overload--this is far most easily/cheaply done with an SDR receiver rather than a scanner. And because your local problems will change, every so often, you will need to look for new problems.
6. Ignoring the above (most?) often leads to worse reception.

In most cases, the cheapest/easiest thing that might improve reception is to improve the antenna, coax, or add an FM broadcast band notch. To add a good pre-amp and necessary (in most/many cases) other notch filters may require several hundred dollars--I do with 3 notch filters and a >$100 LNA.

 

[dlwtrunked]

...
What you and I need is much less gain, something more in the 10 to 15dB range maximum and an IP3 another 10dB or more above my ZX60-P103LN. The closest thing I can find and I will be trying soon is a MiniCircuits ZHL-1010. Its got about 11dB gain from 50 to 1,000MHz, a 1dB compression point about 30dBm or 1watt (!) and a reasonable IP3 of 46dBm. The noise figure is a little high at about 3.5dB but when placed at the antenna it will give a lower system noise figure than any antenna connected through some coax to any receiver. The fact it has a big heatsink and consumes 525ma @ 12V should say something about its high signal handling capability.
...

What FM notch filter are you using? Sounds like it may not be very good--some models short-change the low end of the FM broadcast band. Actually I use two Mini-Circuit FM notch filter back to back--literally kills those and essentially just those. Dropping the gain too much will (Frii's formula) not improve S/N significantly in your reception even with a low noise LNA.

 

[lolbananalol2]

I’ve heard the Jim M75 is a good one.


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[prcguy]

I'm using a military surplus 88-108 notch from Bird Electronics, its not that great at band edges. I'm looking at the MiniCircuits ZX75BS-88108-S+ which is a nice size with the connectors I want but its got too much attenuation in the lower VHF air band. The ZBSF-95-N+ is much better with good rejection over 88-108 and maximum attenuation around 88MHz where my strongest station is and its down just a little over 1dB at 118Mhz. I'll probably order that one today even though its has N connectors.

Update, just ordered the filter. I've probably given MiniCircuits over $600 in the last few weeks.

What FM notch filter are you using? Sounds like it may not be very good--some models short-change the low end of the FM broadcast band. Actually I use two Mini-Circuit FM notch filter back to back--literally kills those and essentially just those. Dropping the gain too much will (Frii's formula) not improve S/N significantly in your reception even with a low noise LNA.

 

[cmed325]

Thnx, Ill be waiting to see which LNA I should use,,Again,Im looking for one i can power by a Bias-Tee,,Running 75ft LMR from a Discone into a 8 port Stridsberg multicuopler.

 

[prcguy]

I would avoid running an amplified multicoupler after a preamp, sounds like a juggling act in balancing gain and avoiding overload. I think its better to choose an amp that will survive your environment with just enough gain to make up for feedline loss and passive splitter loss.

Thnx, Ill be waiting to see which LNA I should use,,Again,Im looking for one i can power by a Bias-Tee,,Running 75ft LMR from a Discone into a 8 port Stridsberg multicuopler.